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[Display omitted] • Pyrolysis of cyanamide molecules forms a coating layer. • Nitrogen induces defect generation and promotes ordered phase transitions. • PtFe ordered alloy maintain high mass activity after stability tests. Ordered Pt alloy electrocatalysts have a special geometric structure and exhibit excellent oxygen reduction reaction (ORR) catalytic performance. Herein, we successfully prepared PtFe/PtNi ordered alloy catalysts by thermal annealing method under the protection of the encapsulated shell formed by pyrolysis of cyanamide molecules as well as the effect of the N element entering into the alloy system to cause defects, and kept the average particle size below 4 nm. The ordered structure enhances the electronic interactions, keeps more Pt0 valence states present and improves the ORR catalytic activity. Under acidic conditions, the PtFe ordered alloy catalyst had a mass activity of 0.752 A mg Pt −1 and a specific activity of 1.138 mA cm Pt −2, both of which were superior to the commercial Pt/C and disordered PtFe alloy. Importantly, the strong interaction between ordered Pt and Fe prevents the leaching of Fe and maintains high mass activity after a long period of circulation. DFT calculations show that the ordered PtFe alloy has a low reaction energy barrier, which is favorable for ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fe, Co, and N co-doped graphene-coated alumina nanofiber catalysts were prepared. • These materials exhibit good oxygen reduction and evolution reaction reversibility. • Prepared catalysts were successfully employed at the zinc-air battery air electrode. • The maximum power density of 149 mW cm−2 was observed during the battery discharge. • The charge–discharge cycling of the battery revealed the long catalyst lifetime. Aqueous rechargeable zinc-air battery (RZAB) is an emerging environmentally friendly energy storage device for a wide variety of industrial applications such as electric vehicles, consumer electronics, and stationary power plants. For successful commercialization of RZABs, a cost-effective bifunctional catalyst is highly required to catalyze the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) at the air electrode. Dual transition-metal and nitrogen-doped nanocarbon materials have shown good potential as an affordable and scalable bifunctional oxygen electrocatalysts alternative to Pt-group metal-based catalysts for RZAB. To achieve this goal, we have developed electrocatalysts based on Fe, Co, and nitrogen co-doped graphene-augmented inorganic alumina nanofibers (Fe/Co-NGr). The Fe/Co-NGr catalysts demonstrate high oxygen reduction and evolution reaction reversibility (Δ E) of 0.85–0.88 V due to the graphene-covered nanofibrous structure doped with FeCo alloy nanoparticles and containing nitrogen, transition metal (TM) coordinated to nitrogen and TM oxide active sites. The primary zinc-air battery with Fe/Co-NGr air electrode exhibits a high maximum power density of 149 mW cm−2 and a specific capacity of 807 mAh g Zn -1. The RZAB assessment has shown a low charge–discharge voltage gap of 0.86 V and high energy utilization efficiency of 58 % up to 90 h of charge–discharge cycling at 5 mA cm−2. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fullerene-based materials, distinguished by their well-defined molecular structure, offer a unique advantage in providing a controllable active site structure. • By controlling the coordination environment of the Pt particles to modulate catalytic performance. • Density-functional theory calculations reveal that the introduction of heteroatoms alters the surface charge distribution of fullerenes. • Pt/N-C 60 /BP2000 exhibits demonstrates superior oxygen reduction activity and stability. The interaction between catalysts and supports is recognized as a crucial factor influencing catalytic activity and stability. However, the carbon materials, which have been widely employed as the support at present, encounter challenges including intricate composition and the difficulty of precise control. In this study, the fullerene-derived carbon materials serve as support to electrocatalysts with low platinum. Fullerene-based materials, as the only carbon material with a well-defined molecular structure, have a controllable active site structure, which can provide a reaction model for studying metal-support interactions. Four kinds of fullerene-derived catalysts such as Pt/fullerene, Pt/nitrogen-doped fullerene, Pt/sulfur-doped fullerene, and Pt/phosphorus-doped fullerene, were synthesized. Once the coordination environment of the Pt particles was controlled, thus their catalytic performance was modulated. Despite a platinum loading of only 4.2%, Pt/N-fullerene demonstrates superior oxygen reduction activity and stability compared to commercial Pt/C (20%). Density functional theory calculations show that the introduction of heteroatoms can change the surface charge distribution of fullerenes, in which N-fullerene has a more negative electrostatic potential and can effectively anchor Pt. This research establishes a foundation for understanding the catalysts-support interaction and further precise control of the coordination environment of Pt. This provides new insights for designing efficient ORR catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • M–N–C catalyst with Single-atoms (Fe, Co) and Co nanoparticles were synthesized. • Optimizing PPy concentration enhanced the active site for ORR in alkaline media. • The prepared catalyst showed excellent ORR performance, stability, and durability. • The prepared catalyst based-zinc-air batteries achieved high performance. Non-platinum electrocatalyst development for improving the oxygen reduction reaction (ORR) is critical in electrochemical energy conversion applications such as zinc-air batteries (ZABs). Herein, we developed dual Fe-Co single atoms and Co nanoparticles embedded N-doped hollow carbon (Fe-Co/N-HCS-x) catalysts via the carbonization of polypyrrole (PPy)@zeolitic imidazolate framework (ZIF) core–shell particles, with various PPy concentrations. PPy serves as a secondary nitrogen source that enhances nitrogen amount and promotes metal dispersion to increase active sites density. The Fe-Co/N-HCS-x catalysts with optimized PPy concentration control demonstrated improved ORR performance in alkaline media, with a half-wave potential (E 1/2) of 0.921 V and an onset potential (E onset) of 1.019 V. Fe-Co/N-HCS-x also exhibited high ZABs performance, with a power density of 244.6 mW cm−2 and an operating time of more than 100 h. Our research contributes to the development of optimized active sites for ORR, which can be applied to new electrochemical storage and conversion systems. [ABSTRACT FROM AUTHOR]

The PtCo alloy nanofoam catalyst with optimized surface composition prepared by morphology engineering possesses enhanced multifunctional electrocatalytic performance. [Display omitted] • Morphology engineering of PtCo alloy nanofoams efficiently improved the utilization of Pt. • Self-assembled porous bimetallic PtCo ANs possess multifunctional electrocatalytic properties. • The Pt 2 Co 1 -ANs sample with optimizing surface composition exhibits enhanced catalytic activity. The exploration of high properties of electrocatalysts is imperative for the commercialization application of fuel cells. Enhancing the catalytic activity and stability of Pt-based catalysts can be achieved by rationally designing their morphology and composition. Here, we synthesized self-assembled PtCo alloy nanofoams (ANs) catalysts with controllable surface composition and porous network. The experimental results show that prepared Pt x Co 1 -ANs catalysts display excellent electrochemical performance in oxygen reduction reaction (ORR), methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). Interestingly, the mass activities of Pt 2 Co 1 -ANs with optimized surface composition for ORR, MOR, and EOR are 6.41, 6.64, and 7.71-fold higher than commercial Pt/C catalysts, respectively. Meantime, it also maintains high electrocatalytic durability in ORR, MOR, and EOR. Such results ascribe to the modified surface composition, optimized electronic structure, and porous interconnected nanofoam structure. These findings provide valuable insights into the design of highly active and durable multifunctional electrocatalysts with controllable shapes and composition. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ionic liquid (IL)-adsorbed catalyst changes the morphology of the catalyst layer. • IL adsorption reduces the ORR charge transfer resistance in the electrode. • IL adsorption enhances the stability under the accelerated durability test. A majority of studies focus on developing oxygen reduction reaction (ORR) catalysts and cathode configurations to enhance the performance and durability of polymer electrolyte membrane fuel cells (PEMFCs). In this study, resistance analyses of the membrane electrode assembly (MEA) are conducted to elaborate on the performance and durability improvements induced by the adsorption of [MTBD][beti] ionic liquid (IL) on the commercial PtCo/C catalyst. The morphological changes caused by IL adsorption are observed on micro and macro scales via physicochemical methods. From the half-cell measurement, when the 4 wt% IL was adsorbed, a 15 mV improvement in ORR activity occurred, and as the adsorption amount increased, the activity decreased. The MEA using 8 wt% IL adsorbed catalyst outperforms 1.7 times higher current density at 0.8 V and 40 % lower charge transfer resistance. Distribution of relaxation time resistance analysis reveals that oxygen mass transfer resistance (R mass), ORR charge transfer resistance (R ORR), and proton charge transfer resistance (R proton) decrease due to IL adsorption. During accelerated durability tests, IL 8 % MEA showed a 58 % increase in durability, and a lower degradation of R ORR and R proton encouraged improved durability. The resistance analyses in this study contribute to identifying the factors responsible for the performance and durability enhancement of PEMFC. [ABSTRACT FROM AUTHOR]

[Display omitted] • Pd-introduced pyrochlore (Y 2 Ru 2-x Pd x O 7) was synthesized by sol–gel method. • RuPd nanoalloy anchored on YRPO pyrochlore was synthesized by in situ exsolution. • P dopant increased oxygen vacancy and tailored electronic structure of metal atoms. • OER/ORR performance was confirmed by RRDE and Zn-air battery application. Metal-air battery technology is the most promising green technology. However, the sluggish kinetics of the oxygen evolution/reduction reaction (OER and ORR), which are key reactions in air cathode, must be improved. In this study, Pd substitution was introduced into Y 2 Ru 2 O 7 pyrochlore oxides and the ratio of Pd was varied (YRPO-x). Then, P-doped RuPd nanoparticles were synthesized on Pd-substituted YRPO pyrochlore (YRPO/RuPd-P) by an in situ exsolution process to create bifunctional electrocatalysts facilitating both reactions. The uniquely designed YRPO/RuPd-P catalyst exhibited the OER overpotential and Tafel slope (E j10 = 232 mV; Tafel slope = 37.1 mV/dec). Furthermore, YRPO/RuPd-P shows an E 1/2 of 0.82 V, indicating superior ORR activity. This was further investigated by applying in a unit-cell battery system, which showed an outstanding power density (163 mW/cm2) and robust charge–discharge stability. This study proposes a novel design strategy for bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

The Pt 7 Ni 3 /C catalyst with heat treatment increased the conductivity by reducing oxygen bonding as well as changing the structure into an ordered FCT structure with good activity in PEMFCs. [Display omitted] • The Pt 7 Ni 3 /C catalyst with heat treatment at 700 °C exhibited excellent catalytic activity and stability. • The crystalline properties and long term durability performance of PtNi catalysts exhibited good evidence to improve ORR. • Pt 7 Ni 3 /C catalyst with heat treatment changed into an ordered FCT structure with excellent electrochemical performance. Demand for replacing the Pt catalyst in proton exchange membrane fuel cells (PEMFCs) has increased because Pt metal is rare and high cost. The most reasonable way is synthesizing Pt-base alloy using transition metals such as Co, Ni, Fe, and Mo. The Pt-based alloy catalysts exhibit excellent catalytic activity by creating a synergistic effect through the interaction between Pt and the transition metals. Here we present the best PtNi alloy composition and maximize the performance of the oxygen reduction reaction (ORR) activity in fuel cells by annealing the alloy under a hydrogen atmosphere. The Pt 7 Ni 3 /C catalyst indicated a higher ORR activity than other compositions due to different structural changes, and the annealing catalysts at 700 °C under an H 2 atmosphere improved the electrochemical activity and stability. The heat treatment increased the conductivity by reducing oxygen bonding as well as changing the structure into an ordered face-centered tetragonal (FCT) structure with good activity. The result of these studies provides a new way to develop high-performance and low-cost catalyst materials for fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZrP 2 O 7 was found to enhance the 2e− ORR performance of PC in real seawater. • ZrP 2 O 7 modification enhances proton transport efficiency of catalysts. • ZrP 2 O 7 modification resists magnesium and calcium deposition during ORR process. Developing 2e− ORR catalysts that utilize seawater as an electrolyte is crucial for advancing energy storage technologies and controlling marine pollution. While non-metal-doped carbon materials demonstrate strong 2e− ORR performance in simulated seawater, enhancing their performance at high current densities and ensuring stability in actual seawater are major challenges. In this paper, a ZrP 2 O 7 /P-doped carbon (PC) composite catalyst was synthesized by a one-step sintering method, which exhibited a high FE% of 95.89 % in 0.5 M NaCl solution with an H 2 O 2 yield of 3.52 mol g−1h−1, and also maintained an FE% of 83.79 % in real seawater. It was significantly better than PC (87.14 %, 3.20 mol g−1h−1 in 0.5 M NaCl, 68.15 %, 2.50 mol g−1h−1 in seawater). Experiments and theoretical calculations revealed the crucial role of ZrP 2 O 7 in enhancing ORR performance. It facilitates proton transfer to the catalyst surface and impedes the accumulation of magnesium and calcium hydroxides on the electrode, enabling efficient H 2 O 2 synthesis by the catalyst in real seawater under high current density. [ABSTRACT FROM AUTHOR]

A new methanol-assisted ZABs (named ZMABs) was proposed based on the strategy of replacing OER with MOR. The charging voltage ZMABs with NiCo 2 O 4 as bifunctional electrocatalyst was greatly reduced about 0.25 V. Moreover, after increasing the mass loading from 2.0 to 4.0 mg cm−2, at the current density of 10 mA cm−2, the charging-discharging voltage gap decreased by 41 mV, and the charging-discharging voltage gap was almost constant after cycling for 200 h in ZMABs. [Display omitted] • A novel Zn-methanol-air battery is proposed. • Flower-like NiCo 2 O 4 was obtained via chemical bath deposition and heat treatment. • The reasons for Zn-air battery failure during cycle tests were discussed. • The reasons for long cycle life of Zn-methanol-air battery were discussed. Aiming at the inevitable high charging potential problem of conventional Zn-air batteries (ZABs), biomass-assisted ZABs were proposed, which the oxygen evolution reaction (OER) in charging was replaced by biomass oxidation reaction. In this work, flower-like NiCo 2 O 4 was synthesized by a simple chemical bath deposition method, which exhibited more outstanding performance for ORR and methanol oxidation reaction (MOR). Compared with Co 3 O 4 and NiO, the NiCo 2 O 4 air electrode with the mass loading of 2.0 mg cm−2 displayed the highest current for ORR (−256.50 mA cm−2) and MOR (189.30 mA cm−2). Based on NiCo 2 O 4 air electrode, the charging-discharging voltage gap of methanol-assisted ZABs was greatly reduced to 0.55 V from 0.80 V of ZABs. By analyzing the changes of air electrodes before and after the cycle, the main reasons for enhanced stability are maintained structure, avoided carbon oxidation, and maintained catalytic activity. Moreover, to further reduce the charging-discharging gap, the mass loading was increased to 4.0 mg cm−2, charging-discharging voltage gap was reduced by 41 mV, which remained basically unchanged after cycling for 200 h. [ABSTRACT FROM AUTHOR]

The ORR performances and mechanism of penta -M 2 N 4 have been systematically investigated by density functional theory calculations. [Display omitted] • The dynamical and thermal stabilities of ten novel penta -M 2 N 4 are confirmed by density functional theory. • For the 4e− ORR, p -Rh 2 N 4 (Rh site), p -NiRhN 4 (Ni site), and p -PdRhN 4 (Rh site) are identified as excellent candidates for ORR. • The p- NiPdN 4 (Ni site) and p- PdRhN 4 (Pd site) show outstanding catalytic activity for the 2e− ORR process. • The ORR performances of penta -M 2 N 4 originate from the proper d-band center, and the interaction between the metal active center and the O atom. The excellent oxygen reduction reaction (ORR) activity of the nitrogen-coordinated metal site (the "MN 4 " site) makes them promising candidates. Hence, extending a similar family is of great importance for the development of the ORR catalysts. In this work, we investigate ten penta -M 2 N 4 (M = Ni, Pd, Pt, or Rh) by considering their stability, activity, and selectivity for the ORR performance based on first-principles calculations. Our results show that all the penta -M 2 N 4 (p -M 2 N 4) are dynamically and thermally stable and are promising for synthesis and application in the ORR. The 2e− ORR process overpotentials of p- NiPdN 4 (Ni site) and p- PdRhN 4 (Pd site) are estimated to be 0.07 V and 0.14 V, respectively, showing comparable activities to the well-known CoN 4 -C. For the 4e− ORR, p -Rh 2 N 4 (Rh site), p -NiRhN 4 (Ni site), and p -PdRhN 4 (Rh site) are identified as candidates with excellent ORR performance. Moreover, a structure–activity relationship between the electronic properties and the catalytic performance is established, and the orbital hybridization induced by alloying plays a crucial role in modulating the selectivity in ORR. Our study provides valuable insights for the design of ORR catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lamellar structured Ce-S-NC was synthesized with the sheet thickness of 2–3 nm. • Ce-S-NC was applied as the cathode catalyst in alkaline DMFC and DBFC. • Ce-S-NC cathode catalyst shows excellent durability at high current density. • Ce-S-NC are beneficial to improve mass transfer at cathode. Passive direct liquid fuel cells are promising power generation devices with the advantages of convenient transportation, storage for liquid fuel and high power density. This paper focuses on improving the intrinsic electrocatalytic performance and durability of nitrogen-doped carbon (N-C) cathodic electrocatalysts. Then, lamellar structured Ce-S-NC heterogeneous electrocatalyst was synthesized and used as a highly durable cathode for two types of passive direct liquid fuel cells, i.e. , direct methanol fuel cells (DMFCs) and direct borohydride fuel cells (DBFCs). In this work, the effect of the S/C molar ratio on the microstructure and electrocatalytic performance of the Ce-S-NC electrocatalysts was investigated, and excellent intrinsic oxygen reduction reaction activity was obtained at an S/C molar ratio of 0.15. The peak power densities of Ce-S-NC based DMFCs reached up to 12.5, 23.6 and 41.9 mW·cm−2 at 20, 40 and 60 °C, respectively. The peak power densities of 59.3, 84.6 and 132.6 mW·cm−2 were obtained in Ce-S-NC based DBFCs at 20, 40 and 60 °C, respectively. In the durability tests, both the Ce-S-NC based air-breathing DBFCs and passive DBFCs showed the stable operation than that of N-C and Ce-NC. When the current density increased from 50 to 150 mA·cm−2, the Ce-S-NC based DBFC can be operated for 882 h, and only 34 and 91 h for that of N-C and Ce-NC. The electrochemical impedance spectroscopy tests proved Ce-S-NC based DBFC showed the faster mass transfer efficiency. The outstanding durability of Ce-S-NC is mainly attributed to the improved defect density and mass transfer. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co 3 O 4 was modified by Ni through thermal treatment of Ni(OH) 2 -containing ZIF-67. • The presence of Ni creates more oxygen vacancies to boost electrocatalytic activity. • The presence of Ni weakens the interaction between surface Co and OH*. • A ZAB cell with the Ni-modified Co 3 O 4 cathode displays competitive performance. The commercial viability of zinc-air batteries (ZABs) depends upon the availability of cost-effective and high-performance bifunctional electrocatalyst, which can simultaneously accelerate both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Noble metal catalysts suffer from poor cycling stability and cost ineffectiveness. Here we report on a Ni-modified spinel Co 3 O 4 catalyst, which exhibits competing electrochemical properties to Pt/C in ORR and to RuO 2 in OER. A ZAB cell fabricated with the catalyst as cathode and Zn as anode exhibits a specific capacity of 803 mAh/g and a cycling stability of 240 h at 5 mA cm−2, comparable to commercial noble metal catalysts. Computational calculations reveal that Ni partially substitutes tetrahedral Co sites in spinel Co 3 O 4 to induce the formation of oxygen vacancies, which play an important role in hindering peroxide formation and enhancing electron conductivity. The presence of Ni in Co 3 O 4 also weakens the interaction between surface Co and OH*, lowering the overpotentials of ORR and OER. [ABSTRACT FROM AUTHOR]

[Display omitted] • Development of a highly efficient electrocatalyst (MnO 2 -Ru/rGO) for ORR in an alkaline medium. • Reduction in noble metal usage while maintaining superior catalytic activity compared to traditional platinum-based catalysts. • Insightful characterization, including electrochemical analysis and Tafel studies, demonstrating the catalyst's excellent performance. • Enhanced methanol tolerance under crossover effect conditions, expanding its potential applications. Oxygen Reduction Reaction (ORR) for clean energy is hindered by expensive Pt-based electrocatalysts, prompting efforts to replace it with alternative electrocatalysts. Thus, we started by synthesizing MnO 2 nanowires through a hydrothermal approach, followed by the growth of ruthenium nanoparticles (Ru NPs) without surface modification, using just 2.0 wt% of the noble metal (MnO 2 -Ru). However, to further enhance the electrocatalyst's performance and reduce costs, we combined different ratios of reduced graphene oxide (rGO) with the electrocatalyst. X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and energy dispersive X-ray spectroscopy were employed to characterize the chemical composition and morphological properties of MnO 2 -Ru. These analyses identified the presence of the compounds during synthesis and confirmed the deposition of Ru NPs on the surface of MnO 2 nanowires. The optimized MnO 2 -Ru/rGO demonstrated superior ORR activity than rGO, MnO 2 , and MnO 2 -Ru individually, with more positive onset potential (−0.054 V) and half-wave potential of −0.173 V. Notably, MnO 2 -Ru/rGO reduced oxygen via the four-electron transfer pathway. Furthermore, the higher stability and excellent methanol tolerance of MnO 2 -Ru/rGO compared to the commercial 20 wt% Pt/C indicates its suitability for fuel cells, maintaining approximately 70 % of its initial current after 8000 s. [ABSTRACT FROM AUTHOR]

[Display omitted] • A porous Zn-Se-N-C nanomaterial with a large specific surface area and significant defect density through the metal–organic frameworks (MOFs). • Surface topography characteristics are tuned by controlling the annealing temperature. • Zn-Se-N-C 1000 °C catalyst with comparable or even superior 4e- ORR performance to Pt/C catalysts. • ORR electrocatalytic activity can be enhanced by the synergistic effect between Zn and Se with DFT calculations. • Zn-Se-N-C-modified carbon cloth as an ideal substrate for cultivating electrogenic bacteria derived from anaerobic sludge. Microbial fuel cells (MFCs), a promising green energy source, have faced limitations in performance. To address this, we synthesized a porous Zn-Se-N-C nanomaterial with a large specific surface area and significant defect density through the utilization of metal–organic frameworks (MOFs). Surface unique topography characteristics are tuned by controlling the annealing temperature. Density functional theory (DFT) calculations confirmed that the synergistic effect of Zn and Se in ZnSe nanoparticles can significantly improve oxygen reduction reaction (ORR) electrocatalytic activity. Experimental results demonstrated that the ORR performance of Zn-Se-N-C 1000 °C catalyst is comparable to that Pt/C catalyst in both alkaline and neutral conditions, especially in alkaline media. When employed as the cathode catalyst in asymmetrical MFCs with a neutral anode and an alkaline cathode, the Zn-Se-N-C 1000 °C (cathode) -MFC system achieved an impressive output current density of 8 ± 0.2 A/m−2 and a remarkable power density of 2000 ± 30 mW m−2. Additionally, the unique pore structure of Zn-Se-N-C1000°C made it highly suitable as an anode in MFCs. The Zn-Se-N-C 1000 °C (anode) -MFC demonstrated an output current density of 7.1 ± 0.9 A/m−2 and a power density of 3000 ± 111 mW m−2. [ABSTRACT FROM AUTHOR]

Figuratively speaking, (C 6 H 5) 4 P+ and(C 6 H 5) 4 B- are assembled together like picture puzzles, achieving tight binding of P and B sources at the molecular level. After pyrolysis, the P/B co-doped carbon nanosheets obtained by bottom-up strategy exhibits superb ORR electrocatalytic performances due to the controllable nanosheet structure and abundant heteroatomic active sites. [Display omitted] • A bottom-up puzzle strategy is proposed to fabricate P/B co-doped nanocarbon. • Diverse nanosheets are achieved by using different P onium salts. • Self-assembly mechanism of P/B sources and further evolution are elucidated. • 4P-BC with ample P/B-induced active sites exhibits superb ORR activities. • This strategy provides a novel avenue for the design of metal-free electrocatalysts. Preparing metal-free and non-N-doped carbon-based electrocatalysts via pyrolysis encounters a significant challenge of low controllability for microstructure modulation and limited electrocatalytic activity. Herein, a bottom-up puzzle strategy is proposed to fabricate a series of phosphorus and boron co-doped carbon (P-BC) nanosheets. These P-BC nanosheets manifest diverse morphologies and distinct heteroatom doping levels, achieved through the innovative utilization of four similar P onium salts featuring varying benzene ring arrangements, coupled with a fixed B onium salt. Among them, the flat 4P-BC nanosheets with abundant P/B heteroatoms exhibit the optimal oxygen reduction reaction (ORR) performance (E 1/2 = 0.79 V, j L = 5.77 mA cm−2), and the assembled zinc-air battery displays a large power density (163 mW cm−2) and excellent long-term durability (450 cycles), which is attributed to the high specific surface area, enhanced defects or disorder, and ample P/B-doping induced active sites for electrochemical reaction. The assembly mechanism of functional units in solution and their intricate evolution at high temperature are elucidated for various P-BC nanosheets. This work elaborates the influence of precursors functional units on the resulting microstructure attributes and active sites properties, providing a novel avenue for the rational design and optimization of metal-free and heteroatom-doped carbon electrocatalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • High-entropy graphene quantum dots (GQDs) were used as metal-free electrocatalyst. • High-entropy GQDs are prepared via a solid-state microwave route at 180 °C. • The pyrolysis of six C and N precursors is carried out under microwave irradiation. • High-entropy GQDs provide highly catalytic activity toward oxygen reduction. • The catalytic activity is significantly enhanced via the heavy heteroatom doping. In this study, high-entropy graphene quantum dots (GQDs) are synthesized and utilized as metal-free electrocatalysts for the oxygen reduction reaction (ORR) in alkaline electrolyte. An efficient solid-state microwave route was used to synthesize the GQD catalysts. This synthesis method involves the pyrolysis of two carbon precursors and four dopant precursors under a pulse microwave irradiation at 180 °C. The synthesized efficient catalyst possesses an average particle size of about 5 nm. The synthesized GQDs catalyst contains six elements in the graphite-like lattices with numerous surface functionalities and dopants. Synthesized high-entropy GQD catalytic electrodes displayed ultra-high electrochemically active surface area and endurance for the ORR measurements. The GQD electrode shows a well-defined reduction peak at ca. −0.5 V and an onset potential at ca. −0.1 V vs. saturated calomel electrode in the diluted potassium hydroxide solution. The heteroatom doping into the GQD nanostructure greatly increased the ORR catalytic activity. The above synthesized non-metallic and inexpensive catalyst showed remarkable properties such as enhanced catalytic activity, selectivity, and superior durability. Therefore, synthesized GQD electrodes have great potential for energy applications, especially for fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti 3 C 2 T x porous nanosheets and nanowires are controllably synthesized through alkaline etching. • The etching mechanism and influencing factors in alkaline solution are revealed. • The increased edge active sites are beneficial to the performance improvement of Ti 3 C 2 T x nanowires. • Ti 3 C 2 T x nanowires exhibit higher ORR performance than Ti 3 C 2 T x nanosheets. • Ti 3 C 2 T x nanowires show high selectivity in reducing oxygen to hydrogen peroxide. Transition metal carbides, especially Ti 3 C 2 T x , display appealing prospects in the field of energy conversion and storage due to the unique combination of good conductivity and abundant functional groups. The physical structure as well as surface terminations of Ti 3 C 2 T x have significant impact on its properties when scaling down from 3D bulk to 2D sheets. However, moving toward 1D nanowire remains a great challenge because of the absence of anisotropic skeleton in Ti 3 C 2 T x. Herein, we demonstrate a facile strategy to convert Ti 3 C 2 T x nanosheets into crosslinked Ti 3 C 2 T x nanowires in hybrid alkaline solutions. The experimental results and theoretical calculation reveal that both OH− and O 2 play important roles in the controllable cutting of Ti 3 C 2 T x nanosheets into nanowires. Compared to Ti 3 C 2 T x nanosheets, crosslinked Ti 3 C 2 T x nanowires expose much higher density of active sites at edges and surfaces, making them ideal catalysts for oxygen reduction reaction (ORR). Unexpectedly, Ti 3 C 2 T x nanowires can selectively reduce oxygen through a 2e− pathway to hydrogen peroxide. The structural modulation of MXene opens a new avenue toward improved performance in emerging application fields. [ABSTRACT FROM AUTHOR]

[Display omitted] • The oxygen storage process in Pd/CeO 2 -ZrO 2 (CZ) three-way catalyst is visualized. • The isotope labeling technique shows higher oxygen distribution around the Pd/CZ interface. • The enhanced oxygen distribution at the interface is elucidated by DFT calculation. • Zr enhances oxygen mobility in the bulk CZ by weakening the bond strength of metal–oxygen. Three-way catalysts (TWCs) are widely used to convert the exhaust gases produced by internal combustion engines, including hydrocarbons, CO, and NO x , into harmless gases such as CO 2 , N 2 , and H 2 O. TWCs mainly consist of a metal catalyst, catalyst support, and ceramic substrate, and their performance is known to be closely related to the oxygen storage capacity (OSC) of the ceramic substrates. However, oxygen storage is a complex multi-step process that is not yet fully understood. In this study, we visualized oxygen storage at the Pd/CeO 2 –ZrO 2 (CZ) interface in the practical operating temperature range of TWCs using oxygen isotope quench techniques and elucidated the detailed reaction mechanism using density functional theory calculations. Pd supported on CZ promotes the incorporation of oxygen into the CZ surface. In addition, our investigation of the transport behavior of the incorporated oxygen in the bulk regime reveals that the bond strength between oxygen and surrounding atoms is weakened by Zr doping, resulting in more facile oxygen vacancy formation and oxygen migration. Our results provide useful insights that will guide the future design of highly active TWCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The co-doping of graphitic-N and pyridinic-N in graphene is beneficial to improve the stability of the material, and the stability of the large triangular co-doped structure is the best. • Highly stable NDG has the following features: (i) presence of angular Corner-Meta-graphitic-N or H-Meta-graphitic-N near pyridinic-N; (ii) absence of graphitic-N pairs on the meta site; and (iii) multiple pores shared graphitic-N. • Graphitic- and pyridinic-N co-doped structures have higher ORR activity than the single-doped structures due to their lower overpotential and higher charge density at the active site. • The concentration of N doping has a significant impact on the ORR of NDG, and co doped structures with moderate N concentration have the best ORR activity. Nitrogen-doped graphene (NDG) has been widely used in electronic devices, optoelectronic devices, catalysts and other fields, due to its high stability, easy synthesis process and other excellent properties. Currently, the synthesized NDG often has extremely complex structures, such as various nitrogen types and different pore structures. Synthesizing NDG with specific structures to realize their applications in specific fields remains challenging. In this paper, the co-doping effect of graphitic-N and pyridinic-N on the structural stability of NDG is investigated from the perspective of theoretical calculations. By studying the co-doping of graphitic-N and pyridinic-N in different porous structures, it is found that co-doping is beneficial to improve the stability of the material. The co-doping of graphitic-N and pyridinic-N in triangular pore is the most stable structure among all co-doped structures. Further, we investigated the oxygen reduction reaction (ORR) activities of graphitic-N, pyridinic-N, and co-doped structures, respectively. The co-doped structure is found to have higher ORR activity than the graphitic-N or pyridinic-N doped structure. Our study provides important theoretical guidance for the synthesis of NDG structures with high ORR activity. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nitrogen doped carbon nanotubes encapsulated metallic Co nanoparticles are synthesized via various Co precursors. • Co@NCNT-Cl exhibits a 4-fold higher kinetic current density than Pt/C. • More Co–N pyridinic+pyrrolic -C structures are formed with CoCl 2 precursor. • Co–N pyridinic+pyrrolic -C structure hydrogenates O 2 to *OOH, further reduced to H 2 O by metallic Co. In this work, we report the diverse cobalt precursors for the synthesis of nitrogen doped carbon nanotubes encapsulated Co nanoparticles (Co@NCNT) as oxygen reduction reaction (ORR) electrocatalyst to verify the anion effect. The X-ray photoelectron spectroscopy (XPS) test indicates that more pyridinic and pyrrolic N species coordinate with Co atoms for cobalt chloride (CoCl 2) due to more defective sites on NCNT etched by chlorine compared to the counterparts of cobalt nitrate (Co(NO 3) 2), cobalt acetate (Co(Ac) 2) and cobalt triacetoacetate (Co(acac) 2). With higher content of Co–N pyridinic+pyrrolic structures, Co@NCNT-Cl exhibits a robust ORR performance highlighted by half-wave potential of 880 mV vs. RHE, corresponding to a 4-fold better kinetic current density than commercial Pt/C. The superior catalytic activity toward ORR originates from more Co–N pyridinic+pyrrolic structures efficiently hydrogenated the adsorbed O 2 to *OOH intermediate; additionally, its low binding strength with *OOH allows the mobility to metallic Co for splitting to generate O* species. Thus, a relay ORR catalysis is noticed for Co@NCNT-Cl. The assembled rechargeable zinc-air battery (ZAB) reaches a power density of 152 mW cm−2 sustained for 500 h, superior to Pt/C-IrO 2. Moreover, the all-solid-state ZAB delivers a maximum power density of 54 mW cm−2 and maintains for 30 h. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two types of Pd–Te nanoparticles with different surface compositions were prepared. • Pd–Te nanoparticles showed high H 2 O 2 electrosynthesis activity in acidic solution. • Structure–activity–selectivity correlations were established with respect to surface Te/Pd ratio. The selective 2-electron oxygen reduction reaction (2e− ORR) has emerged as a promising alternative for H 2 O 2 production to the traditional anthraquinone process, which has energy and environmental issues. H 2 O 2 electrosynthesis in acidic electrolytes is more relevant to practical conditions but requires a much higher overpotential, where precious metal-based electrocatalysts have exhibited high efficiency for the 2e− ORR. The electrocatalytic activity and selectivity are critically affected by the surface composition of the constituent elements. However, such effects in acidic electrolytes have been rarely investigated for precious metal compounds. In this work, palladium–tellurium binary compounds with two different surface compositions were prepared, and their electrocatalytic properties were compared to reveal the structure–activity–selectivity correlations. It was found that the compound with a higher surface Te/Pd ratio exhibited higher H 2 O 2 selectivity but lower activity due to the decreased numbers of Pd ensemble sites as well as surface Pd binding sites, respectively. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new "NH 3 -free" synthesis of thin carbon-shelled CrN nanoparticle is designed. • 1,2,4-1H-triazole is used as a metal-chelating agent and nitrogen/carbon source. • The hybrid structure is applicable to Cobalt-doped CrN. • The d band of CrN can be manipulated by metal doping. • The Co-CrN@C delivers a greater power density and cyclability than Pt/C in AEMFC. Hydrogen fuel cells are expected to be widely used in transportation and portable power generation. Unfortunately, sluggish cathodic oxygen reduction reaction (ORR) kinetics hamper the commercial application of the fuel cells. The quest for cost effective and highly efficient ORR catalysts is of great importance. Transition metal nitride (TMN) has received widespread attention mainly for its Pt-like characteristics. Here, we propose a new one-step "NH 3 -free" synthesis of thin-carbon-shell-encapsulated binary cobalt chromium nitrides (Co-CrN@C) using 1,2,4-1H-triazole as the nitrogen/carbon source. The Co-CrN@C exhibits almost ideal four-electron reduction of oxygen and achieves remarkable long-term durability and better methanol tolerance due to high-degree graphitization of the carbon shell. The X-ray photoelectron spectra and the density functional theory calculations unveil the origin of the intrinsic activity of the catalyst and the reaction mechanism. Furthermore, Co-CrN@C exhibits an impressive peak power density (PPD) of 488 mW cm−2, surpassing the 423 mW cm−2 for the Pt/C-driven anion exchange membrane fuel cells. These findings offer an indispensable strategy for rational design of high-efficient and durable non-noble catalysts. [ABSTRACT FROM AUTHOR]

S-doped Co on N-doped porous carbon (S-CoNPC) prepared using zeolitic imidazole frameworks exhibits a significantly improved electrochemical oxygen reduction reaction performance and durability compared to commercial Pt/C owing to the improved reactivity with sulfur and enlarged surface areas. [Display omitted] • S-doped porous CoNC (S-CoNPC) as an ORR catalyst was designed from bimetallic ZIF. • S-CoNPC showed the improved reactivity potential and enlarged surface areas. • S-CoNPC exhibited a significantly improved ORR performance and durability. The oxygen reduction reaction (ORR) is the most sluggish half-reaction in fuel cells; therefore, Pt-group metal (PGM)-based electrocatalysts have been employed to circumvent this limitation. However, the use of Pt, which is a precious metal, significantly limits the commercialization of proton-exchange membrane fuel cell (PEMFC) systems because of the high cost and low durability of Pt-based materials. Herein, we introduce advanced S-doped Co–N–C (CoNC) porous electrocatalysts (S-CoNPCs) derived from zeolitic imidazole frameworks as substitutes for PGM-based electrocatalysts. To improve the electrocatalytic activity of CoNC, sulfur doping, and acid etching treatment methods, which are innovative procedures, are employed to obtain high catalytic activity and a large surface area. S-CoNPC demonstrates an extremely improved electrochemical performance for ORR in both alkaline and acidic mediums compared with commercial Pt/C, exhibiting E onset , E 1/2 , and limiting current density of approximately 0.91 V, 0.85 V, and −6.7 mA cm−2 (at 0.40 V vs. RHE), respectively, which are in the suitable range for commercializing the PEMFCs system. Furthermore, S-CoNPC, which exhibits high selectivity, stability, and methanol tolerance, is a promising, novel, and advanced non-PGM electrocatalyst for diverse applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A cubic fluorite/perovskite Pr 6 O 11 -Pr 1.2 Sr 0.8 NiO 4+δ (PO-PSNO) heterostructure cathode is prepared by impregnation method. • The ORR reactive sites at the heterointerface are increased, thus enhancing the electrochemical performance of the heterostructure cathode. • About 10% PO impregnation can make the heterointerface have the best ORR reactive site. Pr 2 NiO 4+δ -based (Ruddlesden-Popper) perovskite-structured oxide materials are promising candidates for low and intermediate temperature solid oxide fuel cells (SOFCs) systems. In this study, we prepared a high-performance cubic-fluorite/perovskite heterostructure Pr 6 O 11 -Pr 1.2 Sr 0.8 NiO 4+δ (PO-PSNO) cathode for intermediate temperature SOFCs by solution impregnation method. By changing the impregnation amount of Pr 6 O 11 , the micro-morphology of the heterostructure was regulated, so that the heterostructure interface had the best reactive site. The oxygen reduction reaction (ORR) performance of Pr 1.2 Sr 0.8 NiO 4+δ is improved, and the content of surface Sr in the heterostructure electrode material is reduced. Our results indicate that the synergistic effect of PO particles and PSNO skeleton makes the heterostructure exhibit a high oxygen surface exchange properties and catalytic performance. When the impregnation amount of PO particles reaches about 10% of the PSNO skeleton, the heterostructure has the best ORR activity. The oxygen surface exchange coefficient (K chem) of 2-PO-PSNO is 5.8 × 10-4 cm·s−1, being 1.45 times as that of PSNO at 750 °C. Meanwhile, the polarization impedance (R p) of 2-PO-PSNO is reduced by 66% to only 0.114 Ω cm2. Our study provides a new approach for developing high-performance RP structured perovskite cathodes and demonstrates practical applications in the field of SOFCs. [ABSTRACT FROM AUTHOR]

The rational design of non-noble-metal electrocatalysts for oxygen reduction reaction (ORR) with both excellent activity and robust stability still remains a key challenge nowadays. Herein, N-doped carbon wrapped Co nanoparticles core-shell nanostructures grafted on carbon nanotubes (Co@NC@CNTs) were achieved by a simple pyrolysis process using ZIF-67 and CNTs as precursors. Most importantly, this unique structure of Co@NC@CNTs is beneficial to increase the contact area of N-doped carbon and Co, inhibit the aggregation of Co@NC core-shell nanoparticles and protect the Co from dissolution, thus improving the electrocatalytic performance and stability for ORR. As a result, the well-defined Co@NC@CNTs electrocatalyst exhibits excellent ORR activity with a high onset potential, half-wave potential and limited current density, comparable to the commercial Pt/C in alkaline electrolyte. Furthermore, the Co@NC@CNTs electrocatalyst presents outstanding electrochemical durability and methanol tolerance in comparison with Pt/C. This strategy will open a new avenue toward the development of nonprecious high-performance ORR catalysts. Unlabelled Image • N-doped carbon wrapped Co nanoparticles core-shell nanostructures were achieved. • The Co@NC@CNTs presents outstanding electrocatalytic performance and methanol tolerance for ORR. • The improved performance was ascribed to the synergetic interaction between Co, carbon and CNTs. • The applicability of this strategy can be demonstrated to other non-noble metal electrocatalysts. [ABSTRACT FROM AUTHOR]

Herein, we introduce a facile strategy for the structure-controlled synthesis of one-dimensional PdCu nanocrystals via a seed-mediated approach. This developed strategy involves the synthesis of Cu nanowires with penta-twinned structure, and subsequent growth of Pd metal on Cu nanowires. The obtained one-dimensional PdCu nanocrystals are of rough surfaces and core-shell like architecture. Upon the tuning reactivity of (111) and (100) crystal faces on Cu nanowires in absence or presence of capping agent, one-dimensional PdCu nanocrystals with solid or hollow interiors (nanowires or nanotubes) can be controllably synthesized through galvanic displacement reaction, respectively. It is found that both PdCu nanowires and PdCu nanotubes exhibit better performance for oxygen reduction reaction compared with self-synthesized PdCu nanoparticles and commercial Pd/C in 0.1 M KOH electrolyte. Particularly, PdCu nanotubes show Pt-like performance, and achieve an onset potential of 0.941 V (vs. RHE) and a half potential of 0.825 V. The electron transfer number during oxygen reduction is close to 4 on PdCu nanotubes. Moreover, the catalytic stability of the obtained one-dimensional PdCu nanocrystals is much superior to that of commercial Pd/C and Pt/C catalysts. Unlabelled Image • A facile strategy for the structure-controlled synthesis of 1D PdCu nanocrystals via a seed-mediated approach is developed. • Capping agent is crucial for the structure-controlled synthesis of 1D PdCu nanocrystals with solid or hollow structures. • The obtained 1D PdCu nanocrystals exhibit excellent catalytic performance for oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Rational design of highly effective and low-cost oxygen reduction reaction (ORR) electrocatalysts to replace Pt-based catalysts is still a significant challenge for rechargeable zinc-air batteries. Hence, Fe, N co-doped one-dimensional carbon nanofibers with Fe 4 N species (Fe/N-CNFs) are synthesized through the electrospun technique combining with the "rapid calcination under vacuum" method. Benefitting from the one-dimensional structure obtained by the electrospun technique, the as-synthesized Fe/N-CNFs electrocatalyst with mesoporous exhibits a relatively large specific surface area of 624.12 m2 g−1. Notably, the intrinsic activity of Fe 4 N species as well as the large specific surface area can endow the resulting Fe/N-CNFs with a positive half-wave potential of 0.88 V compared with 20 wt% Pt/C (0.86 V) for ORR. The Fe/N-CNFs also exhibits better long-term stability than 20 wt% Pt/C. Furthermore, the rechargeable zinc-air battery constructed with Fe/N-CNFs as the cathode shows a high open-circuit voltage of 1.51 V, a peak power density of 135 mW cm−2 and an excellent cycle life for 55 h. The as-synthesized electrocatalyst is promising to replace the precious metal catalysts for rechargeable zinc-air batteries. Unlabelled Image • Fe, N co-doped carbon nanofibers (Fe/N-CNFs) with Fe 4 N species were synthesized. • The "rapid calcination under vacuum" was reported for the preparation of Fe/N-CNFs. • The one-dimensional structure of Fe/N-CNFs provides a large specific surface area. • The Fe/N-CNFs exhibits more excellent ORR activity than commercial 20 wt% Pt/C. • The Fe/N-CNFs endows zinc-air batteries with comparable performances to 20 wt% Pt/C. [ABSTRACT FROM AUTHOR]

[Display omitted] • Simple low-temperature etching of ZIF-67 generate crystalline-amorphous Co/Co 3 O 4. • ZIF@RGO-400 maintains a cubic structure with a high surface area of 900 m2/g. • ZIF@RGO-400 exhibits promising bifunctional catalytic activity for the ORR and OER. • Stability of ZIF@RGO-400 is greater than those of Pt/C and IrO 2 in zinc-air cells. Development of a simple method for synthesizing transition metal-based bifunctional catalysts is of great importance in the context of oxygen-involved electrochemical energy conversion and storage devices. In this effort, electrochemical catalysts consisting of amorphous cobalt and cobalt oxides on graphene oxide (GO) were fabricated using a solvothermal process followed by etching ZIF-67 with oxygen-rich functional groups on GO (≈ 29 at. %) in a weak reduction atmosphere at 400 ℃. During the calcination process forming the ZIF-67@GO-based materials, exposed cobalt metal centers are created by partial vaporization and oxidation of ZIF-67. Also, metal ions are reduced to form Co and partially combine with oxygen from GO to generate amorphous Co 3 O 4. Moreover, the porous framework structure of ZIF is retained under the mild calcination temperatures used. Benefiting from their porous framework and heteroatoms-doped composition, the ZIF-67@GO-based materials have low overpotentials of 319 mV at 10 mA cm−2 and high catalytic activities toward the oxygen evolution and oxygen reduction reactions in an alkaline electrolyte. In addition, the liquid zinc-air battery assembled with the ZIF-67@GO composite produced at a calcination temperature of 400 ℃ displays a high performance. Overall, the results demonstrate that the ZIF-67@GO composites have the potential to be high-performing catalysts in energy conversion devices. The readily controllable and high-yielding calcination method in this study is expected to serve as a model for new strategies to synthesize low-cost and efficient bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

The Ba2+ substituted perovskite La 0.7 Ba 0.3 Ni 0.5 Mn 0.5 O 3 empowers high discharge plateau voltage of Mg-air battery, which mainly results from the change in electronic structure of manganese ions and formation of oxygen vacancies. [Display omitted] • ORR catalyst La 0.7 Ba 0.3 Ni 0.5 Mn 0.5 O 3 was synthesized by a simple sol-gel method. • Mg-air battery displays 1.37 V discharge voltage and 65.224 mW·cm-2 power density. • High BET surface area provides large adsorption capacity for O 2 during ORR. • Proper oxygen vacancies and electronic structures promote ORR catalytic activity. • DFT reveals Mn d-band center upshifts and RDS energy barrier for ORR decreases. The air cathodes impact the electrochemical performance of primary Mg-air batteries greatly, in which the activity of catalysts plays a decisive role. Perovskites attract significant attention for their high oxygen reduction reaction (ORR) catalytic activity, unique structure, simple synthesis, and low cost. Herein, a series of La 1-x Ba x Ni 0.5 Mn 0.5 O 3 (x = 0.1, 0.2, 0.3, 0.4, 0.5) catalysts fabricated by substituting Ba2+ for La3+ at the A-sites of LaNi 0.5 Mn 0.5 O 3 are reported. As a result, the catalytic performance toward ORR exhibits a volcano curve with the increase of doping amount and the highest catalytic activity was achieved at 30 % of Ba2+ content. Importantly, the experimental and computational results explain the enhancement by the large O 2 adsorption capacity, the formation of oxygen vacancies, the increase in the content of Mn3+ as an adsorption active site, and the upshift of the Mn-3d band center toward the Fermi level, thereby facilitating the O 2 adsorption and reducing the energy barrier of the rate determining step of ORR. The Mg-air battery with the La 0.7 Ba 0.3 Ni 0.5 Mn 0.5 O 3 catalyst displays a high discharge voltage of 1.37 V and a maximum power density of 65.224 mW · cm-2. Therefore, this new ORR catalyst presents great potential in practical Mg-air batteries. [ABSTRACT FROM AUTHOR]

The oxygen vacancies on the multi-dimensional cross-linked Fe-N-C catalyst surface adjust the electronic band structure to enhance the oxygen reduction reaction electrocatalytic activity and apply to Al-air batteries. [Display omitted] • ● Satisfactory ORR electrochemical performance was achieved by the multidimensional cross-linked structure co-working with oxygen vacancies. • ● The multidimensional cross-linked structure builds high-speed conductive channels, and oxygen vacancies provide abundant active catalyst centers. • ● Fe-N-CNTs-900 rich in oxygen vacancies has a higher conductive band potential. • ● The origin and formation mechanism of activity were explored. Surface oxygen vacancy increases active site numbers, and multidimensional cross-linked structure improves the exposure of active sites. Thereby, they can enhance the oxygen reduction reaction (ORR) performance of Fe-N-C catalysts effectively. Herein, Fe(NO 3) 3 ·9H 2 O and carbon nanotubes (CNTs) were introduced into zeolitic imidazolate framework nano leaves (ZIF-L) to prepare multidimensional cross-linked Fe-N-CNTs with surface oxygen vacancies through co-pyrolysis at the high-temperature. As expected, the synthesized multidimensional cross-linked Fe-N-CNTs-900-0.2 composite rich in oxygen vacancies increased the conduction band potential and improved the reducing capacity. Thus, Fe-N-CNTs-900-0.2 possessed a better ORR electrochemical performance (half-wave potential = 0.892 V vs. RHE) that surpass the Pt/C catalysts. Moreover, the Al-air batteries containing Fe-N-CNTs-900-0.2 displayed a higher maximum power density than those of Pt/C catalysts. The electronic band structure shows that Fe-N-CNTs-900-0.2 rich in oxygen vacancy concentration has higher conduction band potential and effectively improves the activity of ORR catalysts. This work innovatively proposes that the joint work of multidimensional cross-linked structure and oxygen defects is an effective method to enhance the ORR performance and clarifies its internal reaction mechanism, which provides a new idea to design and preparer Fe-N-C catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Galvanic replacement was employed for Ag nanoparticles with varying amount of Pd. • Galvanic exchange on AgNWs resulted in growth of Pd particles on the hollowed NWs. • Increasing Pd content above 10% in AgPd yielded hollowed or half-moon shape structure. • High oxygen reduction activity was observed on AgPd nanostructures in alkaline media. In this work galvanic exchange was employed as bimetallic catalyst preparation method to obtain AgPd nanocatalysts. Ag nanoparticles synthesized by the citrate method and commercial silver nanowires (AgNWs) were used for Pd spontaneous deposition. From transmission electron microscopy images, the particle sizes were determined between 10 and 20 nm and AgPd particles with the Ag/Pd molar ratio of 18:82 obtained using MP-AES were larger compared to those of 89:11 ratio. The galvanic exchange process resulted in porous and half-moon shaped particles. Pd distribution for AgPd/C_1 (18:82) and AgPd/C_2 (56:44) catalysts was rather uniform. Decreasing the amount of Pd salt in the galvanic exchange bath led to only surface decoration of Ag particles as can be seen in the case of AgPd/C_3 (79:21) and AgPd/C_4 (89:11). AgPd120NW and AgPd80NW samples showed the Ag/Pd ratio of 82:18 and 94:6, respectively. The electrocatalysts were studied for oxygen reduction reaction (ORR) in alkaline media using the rotating disk electrode technique. Higher specific activity values for ORR were obtained on larger particles, however galvanic exchange process was not limited to surface layers, thus increasing Pd content resulted in lower mass activities. For all the AgPd catalysts a typical Tafel slope value of ∼−60 mV was observed. [ABSTRACT FROM AUTHOR]

In order to inhibit the corrosion of carbon support and agglomeration of Pt nanoparticles in conventional Pt/XC-72 catalyst, the conventional Pt/C catalyst was modified by in-situ deposition of amorphous tungsten carbide (WC) at the catalyst/support interface. The results show that proper amount of WC can improve the performance and durability of catalyst, and excessive addition of W element will combine with oxygen and transform into WO 3 , thus covering Pt nanoparticles and reducing the active site of catalyst. When W content is controlled at 20 wt%, the half-wave potential (E 1/2) of oxygen reduction reaction (ORR) polarization curve of Pt-WC (20 wt% W, PWC20) catalyst is positively shifted by 31 mV compared with that of conventional Pt/XC-72 catalyst, and the mass activity and specific activity of catalyst are increased by about 2.0 times at 0.85 V. After 10,000 cycles of accelerated durability test (ADT), the electrochemical active area (ECSA) of PWC20 catalyst decreased by 21.7% and the E 1/2 was negatively shifted by 22 mV, while the ECSA of conventional Pt/XC-72 catalyst decreased by 49.49% and E 1/2 shifted by 42 mV negatively. The peak current density of methanol oxidation reaction (MOR) is 1.41 times higher than that of conventional Pt/XC-72, and the forward scanning potential of methanol oxidation shifts 36 mV negatively. After 1000 cycles of ADT, the forward peak current density decreased by 15.23%, while the conventional Pt/XC-72 decreased by 26.62%. The results of CO stripping voltammetry and X-ray photoelectron spectroscopy (XPS) analysis show that the modification of catalyst/support interface by WC significantly improves the anti-CO toxicity ability of conventional Pt/C. The synergistic effect between WC and Pt enhances the metal-support interaction. The durability of catalyst toward ORR and MOR was improved by the modification of catalyst/support interface, and the performance and durability of proton exchange membrane fuel cell (PEMFC) cathode catalyst layer were also improved. Unlabelled Image • The interface stability of Pt and XC-72 was improved by amorphous WC anchoring. • The synergistic effect of Pt and WC could enhance electrochemical activity of ORR and MOR. • The maximum power density decreased by 24.38% while it was 51.64% for the commercial Pt/XC-72 after accelerated cycle test. [ABSTRACT FROM AUTHOR]

Herein we investigated how Fe-coordinated, N-doped carbon nanotubes (CNT) enhance oxygen reduction reaction (ORR) activity by comparatively studying CNT with different pyridinic and graphitic nitrogen ratios, "Fe-CNT-PA" and "Fe-CNT-Py" in reported experimental results. Density functional theory (DFT) calculations revealed that the catalytic activity of Fe or N-doped CNT sponge for ORR was affected by nature of N dopant (pyridinic N (N P) or graphitic N (N G)) and Fe doping states (adatom or substituent). The N components in the carbon network of CNT changed the catalytic properties of metal-free CNT to that of a semi-metal-like CNT by reducing the band-gap energy. Further incorporation of Fe reduced the band-gap energy to zero, producing metal-like conductor properties. When Fe is coordinated with N components on the CNT structure, coordination of Fe as an adatom than as a substituent causes the coordination sites to exhibit higher spin density distribution and stronger hybridization, enhancing the ORR catalytic properties of CNT. This catalytic activity is more substantial when the Fe adatom is combined with a pyridinic N (N P) site by lowering the adsorption energies of ORR intermediates rather than that of O 2. Based on these results, we investigated the structural and electronic properties of "Fe-CNT-PA" and found that a "Fe-CNT-PA" structure with Fe adatom adjacent to an N P site had zero band-gap energy, higher binding energy, lower working function, and magnetic moment, and thus exhibited more improved ORR activity than "Fe-CNT-Py". Unlabelled Image • Change from metal-free CNT to metal-like CNT by pyridinic N and graphitic N-incorporated CNT. • More enhanced ORR on the Fe adatom site than Fe substituent in the CNT. • More enhanced ORR on Fe adatom-pyridinic N coordination site than Fe adatom-graphitic N coordination site. [ABSTRACT FROM AUTHOR]

Exploring biomass-derived non-precious metal carbon-based electrocatalysts have attracted intensive interest in the field of energy conversion due to their low-cost, ecofriendly and sustainable. Herein, we report a novel strategy for preparation of Co/N doped hierarchical porous carbon microspheres (Co/NHPCMS), via pyrolysis ZIF-67@SA/NaHCO 3 microspheres prepared by in-situ growth of ZIF-67 on electrospray Co-SA/NaHCO 3 microspheres. ZIF-67 nanocrystals were well distributed on the ions cross-linked alginate/NaHCO 3 microspheres. The pyrolysis of ZIF-67@SA/NaHCO 3 microspheres could provide abundant active sites and rich porous structure. More importantly, NaHCO 3 plays an essential role in obtaining large mesopores and high pore volume, which is benefit to facilitate the diffusion of reactants. With these merits, Co/NHPCMS-600 exhibits an outstanding ORR electrocatalytic performance with a half-wave potential of 0.827 V. Besides, Co/NHPCMS-600 catalyst exhibits superior catalytic stability and tolerance to methanol in the ORR. This work provides a promising route based on sustainable biomass toward high performance electrocatalyst in the field of energy conversion. SA/NaHCO 3 aqueous solution was spraied into the solution of Co(NO 3) 2 via electrospray, and Co-SA/NaHCO 3 hydrogel microspheres were formed instantaneously. In this stage, Co2+ can bond with the G blocks of alginate molecular chains via the ion exchange with Na+ to form the cross-linked structure. Furthermore, Co2+ was confined in the "egg-box" structure and act as the metal source of ZIF-67. ZIF-67@SA/NaHCO 3 microspheres were prepared through the subsequently in-situ ZIF-67 nanocrystallines growth in 2-methylimidazole methanol solution. After carbonization in N 2 atmosphere with different pyrolysis temperature, Co/N doped hierarchical porous carbon microspheres (Co/NHPCMS) were obtained. Unlabelled Image • Alginate was adopted as precursor to constructed 3D conductive carbon frameworks. • ZIF-67 nanocrystals act as in-situ doped nitrogen source to promote catalytic performance. • The integration between alginate and ZIFs may pave a way for production of non-precious metal carbon-based electrocatalyst. [ABSTRACT FROM AUTHOR]

Replacing the commercial Pt/C with non-precious metal-based electrocatalysts in the proton exchange membrane fuel cells and metal-air batteries is still challenging. Herein, an electrocatalyst (described as Fe-N-C/Fe 100- x-y-z P x O y N z /NPC, NPC is N, P co-doped carbon) composed of multiple active components, such as NPC, iron-based porous hollow spheres and Fe-N-C, is reported, which exhibits an excellent activity that is comparable to state-of-the-art Pt/C for half-cell and full zinc-air battery in alkaline media. This catalyst exhibits an excellent activity with a half-wave potential of 0.86 V for the ORR in alkaline media, which is 10 mV more positive than to that of Pt/C (0.85 V), and a gravimetric energy density for zinc-air battery is up to 675 Wh Kg zn −1. The excellent activity is attributed to the synergetic effect of active NPC, iron-based porous hollow spheres (Fe 100- x-y-z P x O y N z) and Fe-N-C in its structure. In addition, phosphoric acid groups are partially remained in the structure for our catalyst that make the catalyst excellent hydrophilicity. This work adds a new member into family of non-precious metal-based ORR electrocatalysts. Unlabelled Image • N, P co-doped carbon, iron-based porous hollow spheres and Fe-N-C, is reported. • The electrocatalyst exhibits an excellent activity that is comparable to Pt/C in alkaline media. • Phosphoric acid groups are partially remained in the structure that make the catalyst excellent hydrophilicity. [ABSTRACT FROM AUTHOR]

Abstract Due to the large surface area, unique atomic configurations and dispersed metal sites, metal-organic porous monolayers provide a promising strategy for catalysis. Among them, the transition metal dimer phthalocyanine (TM 2 Pc) monolayer is one of the interesting members. Herein, we studied the oxygen reduction reaction (ORR) of TM 2 Pc with a series of transition metal dimers (M = Mn-Cu and Ru-Pd) by using the density functional theory. Volcano plot suggests that Fe 2 Pc has the best ORR activity. This is also confirmed by thermodynamic and kinetic study. Among the studied TM 2 Pc, Fe 2 Pc has the highest working potential of 0.98 V (smallest overpotential of 0.25 V), larger than 0.78 V for pure Pt. The energy barrier calculations show that for Fe 2 Pc, the rate-determining step is the *OOH hydrogenation to form *OH + *OH with an energy barrier of 0.25 eV, much smaller than 0.80 eV for pure Pt. Therefore, Fe 2 Pc has good ORR activity compared with pure Pt. These results also indicate that the introduction of transition metal dimer on phthalocyanine monolayer would provide a novel strategy for the design of high efficient ORR catalysts. Graphical abstract Fe 2 Pc monolayer exhibits the highest catalytic activity for ORR and is promising catalyst for ORR. Unlabelled Image Highlights • The oxygen reduction reaction (ORR) of TM 2 Pc with a series of transition metal dimers (M = Mn-Cu and Ru-Pd) has been studied by using DFT calculation. • Volcano plot suggests that TM 2 Pc (M = Fe, Co and Ru) exhibits high ORR activity. • Among the studied TM 2 Pc, Fe 2 Pc has the highest activity for ORR both in thermodynamics and kinetics, with a small overpotential of 0.25 V and energy barrier of 0.25 eV, which is smaller than that of pure Pt. [ABSTRACT FROM AUTHOR]

Abstract Searching for an efficient non‑platinum electrocatalyst for oxygen reduction reaction (ORR) is of great significance for some energy conversion devices. In this work, Pd‒Ni‒P hybrid nanocatalysts loaded on nitrogen-doped carbon supports (defined as Pd‒Ni‒P@NC) are prepared by simply reacting Pd(II)/Ni(II)-dimethylglyoxime with NaH 2 PO 2 at 500 °C. Compared with Pd‒P@NC and Ni‒P@NC counterparts, the Pd‒Ni‒P@NC exhibits a more positive onset potential and higher specific/mass activity towards ORR due to the interfacial coupling interaction between Pd 3 P 0.8 and Ni 2 P. Moreover, it has a higher catalytic durability and better methanol tolerance than commercial Pt/C catalyst. The surface valence state analysis and electrochemistry characterization reveals that the enhanced electrocatalytic performance of Pd‒Ni‒P@NC is attributed to the modified Pd 3d electronic structure and improved charge transfer character, originating from the incorporation of Ni 2 P component. Our study provides an alternative non‑platinum electrocatalyst for ORR in fuel cell and metal-air battery. Graphical abstract Pd‒Ni‒P@NC hybrid nanocatalysts are prepared by reacting Pd(II)/Ni(II)-dimethylglyoxime with NaH 2 PO 2. The Ni 2 P component in Pd‒Ni‒P@NC not only tunes Pd 3d electronic structure but also improves the charge transfer character, which endows Pd‒Ni‒P@NC a high electrocatalytic performance towards ORR. Unlabelled Image Highlights • Pd‒Ni‒P@NC hybrid nanocatalysts are prepared by reacting Pd(II)/Ni(II)-dimethylglyoxime with NaH 2 PO 2. • Surface Pd 3d electronic structure can be modified by interfacial coupling interaction. • The Ni 2 P component can improves the charge transfer character. • Pd‒Ni‒P@NC shows a high electrocatalytic performance towards ORR. [ABSTRACT FROM AUTHOR]

Abstract The design of new cathode materials is vital to develop the high performance proton exchange membrane fuel cell (PEMFC). The adsorption properties of the species involved in the oxygen reduction reaction (ORR) and several ORR mechanisms on phosphorene were presented with using the first-principle calculations. Results show that the H adsorption is more preferable than O 2 , and the OOH spontaneously form from the adsorbed H and O 2. The HOOH from the hydrogenation of the OOH species could be further hydrogenated into OH and H 2 O, and the OH would be finally hydrogenated into the (second) H 2 O. The reaction barrier of rate-determining step is 1.02 eV. Moreover, the presented kinetic processes are confirmed by the thermodynamic simulation from Gibbs free energy calculations and molecular dynamics simulations. These results indicate that phosphorene as one of new 2D materials could be a promising metal free cathode material for PEMFC. Highlights • Phosphorene could be a promising metal free cathode material for proton exchange membrane fuel cell. • The reaction properties of the possible ORR elementary steps on phosphorene are revealed in details. • Kinetic ORR processes are confirmed by the thermodynamic simulation from Gibbs free energy calculations. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The novel in-situ foaming technology from Gemini surfactant interfacial coupling. • The N, P dual-doped carbon nanosheets with multi-wrinkled surface was prepared. • As metal-free carbon catalyst for ORR, the limiting current density reached 6.7 mA/cm2 at 1600 rpm. • After about 9 h continuous test, the current density of this catalyst remained above 91%. • Wrinkles induced p z -orbital of C stretched out to bond with single electron on π 2p * orbit of O 2. Abstract N, P dual-doped carbon nanosheets was prepared by an in-situ foaming technology. The crude lecithin extracted from egg yolk was explored to prepare this novel carbon material. In the synthesis process, the crude lecithin molecular is as the Gemini surfactant and the graphitic carbon nitride (g-C 3 N 4) plays the role of self-sacrificing template. At the high temperature, the sandwich-mixture "lecithin/C 3 N 4 /lecithin" expanded and carbonized with the decomposition of g-C 3 N 4. This induces the formation of many multi-wrinkled nanosheets and synchronously constitute a multi-doped carbon foam. This unique carbon material exhibits a super-efficient catalytic activity towards oxygen reduction reaction, with the limited current density of 6.7 mA cm−2 tested at 1600 rpm in 0.1 M KOH solution, which is far larger than that of Pt/C (20%) catalyst (5.5 mA cm−2). It was demonstrated that this novel catalyst also possesses great catalytic stability. After about 9 h continuous test, the current density of this catalyst remained above 91%. These results demonstrate that the N, P dual-doped multi-wrinkled carbon nanosheets can be used as the high-efficient metal-free electrocatalyst towards oxygen reduction reaction. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Co 2 N-x-T@NC electrocatalyst was prepared via in situ polymerization and pyrolysis under NH 3 atmosphere. • Co 2 N-2-700@NC exhibited excellent electrocatalytic activity towards ORR. • Co 2 N-2-700@NC showed better long-term stability and tolerance to methanol than Pt/C catalyst. Abstract Co-N-C electrocatalysts have attracted great attention in electrocatalytic ORR (oxygen reduction reaction) field. In this work, we propose to prepare Co 2 N nanoparticles embedded N-doped mesoporous carbon by a facile method including in situ copolymerization and pyrolysis under NH 3 atmosphere. The results show that more N atoms can be doped in carbon framework by NH 3 pyrolysis, it is also found that pyrolysis temperature and Co content can influence the ORR performance of samples. The sample prepared by adding Co precursor and pyrolysis at 700 °C has high N content (11.86 at.%) and relative large specific surface area (362 m2 g−1), and it also exhibited superior electrocatalytic ORR performance in terms of E onset (−0.038 V vs. SCE), E 1/2 (−0.126 V vs. SCE) and large current density (5.22 mA cm−2). Additionally, the sample also shows better stability and resistance to methanol poisoning than Pt/C catalyst. The synergistic effect of Co-N active centers and hierarchical porous structures contribute the excellent electrocatalytic activity, which are considering as alternative catalysts for ORR in full cells. [ABSTRACT FROM AUTHOR]

Highlights • Successful synthesis of unprotected PtPd NCs supported on OMC. • Low PtPd loading (10 wt%) of PtPd NCs/OMC. • Much higher ORR activity than that of commercial Pt/C (Pt loading: 20 wt%). • The excellent stability and methanol tolerance of Pt 3 Pd 1 NCs/OMC in HClO 4. Abstract Bimetallic PtPd alloys are regarded as promising high performance oxygen reduction reaction (ORR) catalysts. However, the application of a subnanometer scale PtPd bimetallic nanoclusters (NCs) is rarely studied. In this work, ordered mesoporous carbon (OMC) supported PtPd NCs with the constant metal loading of 10 wt% and various Pt:Pd atomic ratios were synthesized by a modified polyol reduction route. The PtPd NCs show a maximum activity at Pt:Pd molar ratio close to 3:1 with a mean size of ∼2.35 nm. The specific activity (SA) and mass activity (MA) of Pt 3 Pd 1 NCs/OMC (PtPd loading: 10 wt%) is 2.5 and 4.1 times higher than those of the commercial Pt/C (Pt loading: 20 wt%) in 0.1 M HClO 4. Meanwhile, the Pt 3 Pd 1 NCs/OMC exhibits improved methanol tolerance and durability for ORR. Therefore, the Pt 3 Pd 1 NCs/OMC is excellent candidate that may become a practical cathode catalyst for fuel cells. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The screened X 3 (HITP) 2 catalysts possess different active sites compared with the well-known Ni 3 (HITP) 2. • Ir 3 (HITP) 2 and Rh 3 (HITP) 2 show the most excellent ORR catalytic activities among all the X 3 (HITP) 2. • Ir 3 (HITP) 2 and Rh 3 (HITP) 2 also have excellent tolerance to CO, NO, SO 2 , and CH 3 OH. Abstract The search for cheap, stable, and more active oxygen reduction reaction (ORR) catalysts is of great significance to proton exchange membrane fuel cells, and two-dimensional metal–organic frameworks with metal–nitrogen active sites are attracting increasing attention. The ORR mechanisms on X 3 (HITP) 2 (X = Cr, Mn, Fe, Co, Rh, Os, Ir) catalysts are studied by density functional theory. All possible adsorption sites are explored, and the central metals rather than hydrogen or carbon atoms are demonstrated as the most favorable catalytic sites, completely different from the case of the well-known Ni 3 (HITP) 2. The predicted ORR activities of X 3 (HITP) 2 follow the order of Ir 3 (HITP) 2 , Rh 3 (HITP) 2 , Co 3 (HITP) 2 , Fe 3 (HITP) 2 , Os 3 (HITP) 2 , Cr 3 (HITP) 2 , and Mn 3 (HITP) 2 , during which the first two have the highest onset potential of 0.92 and 0.86 V, respectively. This result uncovers that the ORR behavior of X 3 (HITP) 2 can be engineered by substituting the central metals. The linear relationships between the adsorption energies of O 2 , OOH, O and that of OH species illustrate that the adsorption strength of OH can be used as the activity descriptor for the current X 3 (HITP) 2. Ir 3 (HITP) 2 and Rh 3 (HITP) 2 not only have good ORR activities and stabilities, but also have high anti-poison abilities to some impurity gases, as well as CH 3 OH molecule. [ABSTRACT FROM AUTHOR]

Graphical abstract Nitrogen-doped carbon nanotubes with well-defined tubular morphology and controllable shell thickness as efficient nonprecious oxygen reduction reaction electrocatalysts have been reported. Highlights • Halloysite nanotubes were used as the template for the synthesis of uniform N-CNTs. • The shell thickness of N-CNTs can be well-controlled. • N-CNTs showed excellent catalytic activity toward the oxygen reduction reaction. • N-CNTs with the pyridinic N content of 21.6% showed the best oxygen reduction reaction performance. Abstract Halloysites were applied as the template to form halloysite/polyaniline core/shell hybrids through an oxidative polymerization route, where the amount of aniline monomer could be adjusted to precisely control the shell thickness of polyaniline. The pyrolysis process was then applied to ensure the carbonization of the polyaniline to form halloysite/nitrogen-doped carbon core/shell hybrids. Finally, halloysites were removed, resulting in the formation of nitrogen-doped carbon nanotube with a uniform morphology and a controlled shell thickness. The shell thickness and pyrolysis temperature of nitrogen-doped carbon nanotubes were optimized to improve the electrocatalytic performance involved in oxygen reduction reaction. The nitrogen-doped carbon nanotubes showed good electrocatalytic activities toward oxygen reduction reaction in 0.1 mol L−1 KOH aqueous solution, making them a promising cathode catalyst for alkaline fuel cell applications. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Laser-generated ligand-free Pt nanoparticles as benchmarking catalyst. • Homogeneous particle distribution on almost defect-free gas phase synthesized graphene. • Graphene supported Pt nanoparticles show enhanced stability during ORR. • Improved stability is tentatively attributed to better corrosion resistance. Abstract Ligand-free platinum nanoparticles were prepared by pulsed laser ablation in liquids (PLAL) and employed as a benchmarking catalyst to evaluate the durability of a new gas-phase synthesized graphene support in oxygen reduction conditions. Raman measurements showed that the graphene, as compared to Vulcan, was almost defect free. Transmission electron microscopy and initial electrochemically active surface area measurements confirmed good dispersion of the catalysts on both supports. During durability tests, graphene supported Pt nanoparticles showed much better ECSA retention (75% on graphene as compared to 38% on Vulcan), ultimately retaining a higher ECSA than a commercial sample subjected to the same procedure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Tungsten nitride decorated with N-carbon dot are developed using a facile route. • Excellent activity and better stability was observed compare to commercial Pt/C. • Synergistic effects caused by hybrids facilitate the conductivity and mass transfer. Abstract Developing efficient and cost-effective oxygen reduction reaction (ORR) catalysts for fuel cells is quite necessary but still full of challenges. In this study, tungsten nitride nanosheets (WN NSs) decorated with nitrogen-containing carbon dots hybrid materials are developed using a facile two-step route. Specifically, a sandwich-like porous electrode, which contains a N-doped carbon layer encapsulated with uniform carbon dots (N-CDs) and a sheet-like WN for both-side formation of N-CDs, is obtained and designed as a novel type of ORR catalysts (denoted as N-CDs@WN). The N-CDs@WN hybrid shows superior catalytic activity via a four-electron pathway and demonstrates excellent stability over long periods of time and resistance to methanol. The excellent electrocatalytic properties of N-CDs@WN hybrids benefited from a hierarchical structure with large specific area, numerous active sites, and synergistic effect between CDs and WN that can facilitate the conductivity and mass transfer during the ORR process. Compared to other carbon dots-based nanocomposites, our facile synthetic route for N-CDs@WN not only presents the advantages of being relatively green, simple, and cost-effective but also is an attractive alternative for the electrocatalyst in the non-precious ORR. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel ORR electrocatalyst derives from an organic complex. • The complex provides metal active species and heteroatoms. • The optimized CENC-1000 exhibits superior ORR activity and stability. Abstract The search for non-precious-metal catalysts with low cost, high activity and stability to substitute Pt in oxygen reduction reaction (ORR) attracts tremendous attention. Herein, novel ORR electrocatalysts of cerium species embedded N-doped carbon (CENC) materials are prepared by the chemical oxidative polymerization and pyrolysis methods, using polyaniline-coated cerium organic complex (Ce(TTA) 3 Phen) as the precursor. The experimental results have revealed that the electrocatalytic activity of the obtained electrocatalysts for ORR is affected by the pyrolysis temperature. Remarkably, the as-prepared CENC-1000 exhibits a good catalytic activity in terms of limiting current density, onset potential and half wave potential, as well as superior tolerance to methanol crossover for ORR as comparable to commercial Pt/C in alkaline media. The high performance is attributed to the introduction of nitrogen active sites and Ce active species (generated from the pyrolysis of CENC precursor), which endow CENC-1000 with enhanced electrocatalytic activity. This approach makes CENC-1000 a promising candidate as cathode catalyst in renewable energy conversion devices. [ABSTRACT FROM AUTHOR]

Highlights • CoOx@N-doped graphene structure with tunable Co oxidation state was prepared. • Co d-band center can be manipulated by altering Co oxidation state, facilitating ORR. • Electron structure of graphene shell was tuned by inner CoOx. • Core-shell structure prevent CoOx core from etching out, enhancing ORR stability. Abstract Metal@nitrogen-doped carbon core-shell structure, processing both the stability of inner metal species and manipulated electron structure of outer carbons, is regarded as a promising catalysts for oxygen reduction reaction. In the traditional fabrication of such materials, metal ions are reduced into metallic particles, which make it hard to control oxidation state of metals. In this work, we report tunable oxidation state of Co in CoOx@N-doped graphene simply by changing the pyrolysis temperature of Co 3 O 4 /polyaniline. Under high temperature, polyaniline decompose and release various organic gases, which can partially reduce Co 3 O 4 and serve as gaseous precursors for the in-situ growth of graphene in the meantime. The balance of these two reactions is crucial to control the oxidation state of Co. Thus, its catalytic activity towards oxygen reduction reaction can be easily tuned by inner CoOx core with different electron structure. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Taro stem are used to prepare bifunctional carbon materials. • The 3D N-doped carbon has abundant macropores, micropores and mesopores. • The 3D N-doped carbon presents excellent long-term stability for ORR. • The solid-state symmetrical SC achieves the outstanding power density. Abstract Biomass-derived carbon materials have garnered intensive consideration in energy fields, such as fuel cells and supercapacitors, due to their inexpensive precursors, abundant resources and facile synthesis. Herein, we report a facile strategy based on taro stem precursor to synthesize a 3D nitrogen-doped porous carbon (3DNPC) with micropores, mesopores, macropores, large specific surface area (1012 m2 g−1) and nitrogen content (4.8 at%), which displays high catalytic activity and stability for oxygen reduction reaction and good electrochemical properties for supercapacitors. Compared with the commercial Pt/C catalysts, the 3DNPC-800 with 3D porous structure, proper total doped N and high graphitic N content, presents brilliant long-term stability (96.5% retention after 20,000 s) and resistance to methanol crossover for oxygen reduction reaction. With respect to electrode material of supercapacitor, the 3DNPC-800 possesses high specific capacitance (236.4F g−1 at 0.1 A g−1) and outstanding long cycle durability (89.3% retention after 10,000 cycles at 20 A g−1). Moreover, the prepared symmetric solid-state supercapacitor devices achieve outstanding power density (5 kW kg−1 at 5.56 Wh kg−1). Consequently, economically and sustainably utilization nature of materials to fabricate heteroatom-doped carbon materials, having great potential in electrochemical applications, is presented. [ABSTRACT FROM AUTHOR]

Highlights • Cu promoted nitrogen-doped carbon was prepared. • The Cu-N/C electrocatalyst exhibited satisfactory ORR activity. • The Cu-N/C showed great methanol tolerance and long-term stability. Abstract Rational design of oxygen reduction reaction (ORR) electrocatalysts based on earth-abundant elements is critical important towards sustainable energy applications. Among various reported ORR electrocatalysts, transition metal-nitrogen doped carbon (TM-N/C) materials such as Fe-N x /C and Co-N x /C exhibit excellent catalytic activity. Nevertheless, comprehensive understanding of these TM-N/C electrocatalytic systems is still lacking, which demands extension of investigation to other TM-N/C systems (Cu, and Mn, etc.). Herein, we developed a Cu promoted nitrogen-doped carbon (Cu-N/C) via high temperature pyrolysis of Cu-adsorbed zeolite imidazole frameworks (Cu@ZIF-8). The Cu-N/C electrocatalyst exhibited satisfactory ORR activity with half-wave potential of 0.813 V in 0.1 M KOH electrolyte. Moreover, it also showed excellent methanol tolerance and long-term stability. The enhanced ORR electrocatalytic performance is attributed to the strong synergetic effect between Cu(II)-N ligands and Cu0 NPs, sufficient active sites, and fast mass transfer. [ABSTRACT FROM AUTHOR]