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Graphene supported FeN5 active sites, exhibiting high activity and stability of oxygen reduction reaction, enable a H2-air fuel cell to decay little during the latter 20–100 h operation. [Display omitted] • Electrochemically-exfoliated graphene improves forming FeN 5 with NH 3. • Graphene benefits catalytic stability of oxygen reduction reaction. • Fuel cell keep stable with little decay in latter 80 h operation. • High half-wave potentials in alkaline medium (0.940 V). Metal-nitrogen-carbon catalytic material, generally thought as a promising low-cost electrocatalyst of oxygen reduction reaction (ORR), surfers from long-term catalytic durability for fuel cell and metal-air battery. Here, we describe an approach of synthesizing electrochemically exfoliated graphene supported penta-nitrogen coordinated iron exhibiting encouraging ORR catalytic activity and durability. The synthesized catalyst exhibits high half-wave potentials in alkaline medium (E 1/2 0.940 V) enabling high-performance zinc-air battery and in acidic condition for durable fuel cell with a high peak power density (630 mW cm−2). The current density of a proton exchange membrane fuel cell loading the catalyst as cathode tends to decay little after initial hours under H 2 -air measurement, remarkably inhibiting commonly decline tendency of iron–nitrogen-carbon catalysts. DFT calculation combined with extensive experimental investigations demonstrate that penta-nitrogen coordinated iron supported by graphene is thermodynamically stable, and thus benefits the catalytic stability of ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • HME was applied as an oxygen electrode of the AEM-URFCs. • Introducing 3 D CNT framework provided high ECSA of catalysts, electron transport, mass transport. • The HME_URFC exhibited superior round-trip efficiency of 55% at 20 mA cm−2 with enhanced durability and cyclability. Developing three-dimensional porous oxygen electrodes (OE) is crucial for enhancing round-trip efficiency (RTE) of anion-exchange membrane-based unitized regenerative fuel cells (AEM_URFCs). Herein, a novel OE design of AEM_URFCs is presented based on a hierarchical mesh electrode (HME) with a porous carbon nanotube (CNT) framework. The HME, featuring square-shaped macropores achieved by dispersing catalyst nanoparticles on the CNT framework enhances surface area, mass transport, and electron transport. Half-cell test demonstrated superior oxygen reduction reaction and oxygen evolution reaction activity compared to conventional electrodes. Moreover, the HME maintained stable ORR and OER activity during the stability test. In single-cell tests, the AEM_URFCs with the HME exhibited higher RTE (55% at 20 mA cm−2), surpassing the conventional electrode (52%). Furthermore, RTE was maintained at a remarkable 41% under ultrahigh current density (250 mA cm−2), which is unprecedented in the literature. The AEM_URFCs featuring the HME displayed superior cyclability over 5 cycles and durable performances under both fuel cell and water electrolysis modes. [ABSTRACT FROM AUTHOR]

• Resonance structure as substrate molecules are introduced to form highly ordered PtCo alloys. • Synthesis of PtM (Co, Fe, Ni) ordered alloys use the same low temperature heat treatment conditions. • The ordered PtCo shows efficient electrocatalytic performance. Platinum-based ordered alloys have excellent catalytic performance for the cathodic oxygen reduction reaction (ORR) in fuel cells. However, these alloys exhibit a lower degree of ordering and larger crystal grains after heat treatment. Herein, a series of cyanamide group molecules (cyanamide, dicyandiamide, melamine) was employed as substrates to modify Pt-based alloys by promoting the binding between metal ions, leading to the preparation of ∼ 4 nm PtM (M = Co, Fe, Ni) ordered alloys after heat treatment. Among them, the PtCo ordered alloy prepared using hydrolyzed cyanamide with a unique resonance structure exhibits a high degree of order (93.1 %), and its mass activity of 0.915 A mg Pt -1 at 0.9 V is superior to that of Pt/C. The theoretically calculated adsorption energies of these alloys demonstrate that the resonance structure of the cyanamide substrate is beneficial for alloy formation, thereby facilitating ordered alloy synthesis. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly curved and ultrathin P-doped PdMo bimetallene is engineered. • The catalyst has superior performance in electrooxidation of various alcohols. • The activity for ORR surpasses that of commercial Pt/C catalyst. • DFT reveals that P doping enhances both OH adsorption and CO desorption. The commercialization of direct alcohol fuel cells (DAFCs) relies on the development of high performance electrocatalysts for both the alcohol oxidation reaction and the oxygen reduction reaction (ORR). In this study, a novel phosphorus-doped palladium-molybdenum (P-PdMo) bimetallene with a partially amorphous structure is demonstrated. The ultrathin and curved morphology of the nanosheets, combined with electronic regulation by phosphorus atoms, facilitates OH adsorption and CO desorption. Consequently, the catalyst exhibits significantly enhanced activity and durability in the electrooxidation of alcohols, including methanol, ethanol, ethylene glycol, and glycerol. Particularly toward ethanol oxidation, the P-PdMo bimetallene displays exceptional mass and specific activities up to 4.95 A mg-1 Pd and 8.28 mA cm−2, respectively. Furthermore, the P-PdMo bimetallene demonstrates outstanding ORR performance, with an onset potential of 1.0 V and a half-wave potential of 0.88 V. Overall, this study opens new avenues in metallene electrocatalysts and advancing toward the practical implementation of DAFCs. [ABSTRACT FROM AUTHOR]

• A catalyst consisting of Pt 2 Ni 4 clusters adjacent to Pd nanoparticles on Ni-hydroxide is developed. • It surpasses the commercial J.M.-Pt/C catalyst by ∼75 times in alkaline ORR. • It shows progressively increasing mass activity up to 15 K stability test cycles. The oxygen reduction reaction (ORR) is a key "showstopper" for the commercial viability of alkaline fuel cells (AFCs). In this study, we developed a ternary nanocatalyst (NC) coloaded with Pt 2 Ni 4 atomic clusters and palladium (Pd) nanoparticles (NPs) on oxygen vacancies (OVs) enriched nickel hydroxide-support (henceforth denoted as NiPP). This material outperforms the commercial J.M.-Pt/C (20 wt%) catalyst by ∼75 and ∼38 times with exceptionally high mass activities (MA)s of 5050.3 mAmg Pt -1 and 952.3 mAmg Pt -1 at 0.85 V and 0.90 V vs RHE, respectively, in alkaline ORR (0.1 M KOH). The high structural reliability of the Pt 2 Ni 4 endows the NiPP NC with outstanding durability, where it achieves an optimum MA of 5755.9 mAmg Pt -1 after 10 K cycles in an accelerated durability test (ADT) and retains the original performance up to 15 K cycles. Moreover, NiPP delivers an outstanding power density (339.1.4 mW cm−2) and short circuit current density (910.8 mA cm−2), which exceeds the commercial J.M.-Pt/C (174.9 mW cm−2 and 720.4 mA cm−2) when serving as the cathodic catalyst in an AFC. The results of physical characterizations, electrochemical analysis and in-situ XAS analysis suggest that the exceptional performance is originated from the potential synergism between the neighbouring reaction sites of Pt 2 Ni 4 (OV in Ni(OH) x and Pd NPs). During ORR, the Pt 2 Ni 4 atomic clusters and OVs boost the O 2 splitting, while the adjacent Pd NPs promote the subsequent relocation of OH– ions. The obtained results provide the potential design strategies for the atomic-scale surface engineering of advanced ORR NCs in alkaline fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interfacial electronic structure of metal-support is regulated by heteratom doping. • N/S doping promotes the oxidation of Pt-Lewis acid center to a higher valence state. • S atom re-doping causes the d-band center of Pt to shift upward towards Fermi level. • High content of Ptx+ sites enhance the binding of Pt-Lewis acid to *OOH intermediate. • PtNi@N,S-HMCS with more Pt-Lewis acid shows high ORR activity and 4e- selectivity. Elucidating the mechanism of metal-support interface domain regulation is crucial for designing efficient fuel cell electrocatalysts. Herein, we propose an emerging strategy to enhance oxygen reduction reaction (ORR) activity and selectivity by regulating the Lewis alkalinity of carbon support to adjust the Lewis acidity of metal sites. The experimental results and density functional theory (DFT) simulations show that the introduction of N/S atoms into the carbon support structure will break the charge balance of the carbon skeleton and effectively regulate the charge distribution in the Pt-carbon interface domain, thus promoting the oxidation of the Lewis acid Pt atoms to a higher valence state Ptx+, so as to optimize the adsorption energy of oxygen-containing intermediates. Moreover, Bader charge analysis also verifies that N,S-HMCS, as a Lewis base, can receive more electrons from the Pt sites of Lewis acid, and the electron loss at Pt sites caused by N,S-HMCS strengthens interfacial electron effect. Meanwhile the strong electron adsorption ability of N/S atoms causes the d-band center of Pt atom orbital to shift upward to the Fermi level, which strengthens the binding of metal Lewis acid Pt sites with *OOH intermediates, and improves the 4-electron transfer mechanism. This research reveals the direct role of Lewis acid sites in ORR of fuel cell cathode, and provides a feasible way to guide the design of electrocatalysts with Lewis acid/base double centers. [ABSTRACT FROM AUTHOR]

In this work, we report the high-temperature confinement synthesis of N-doped graphitic carbon shells encapsulated PtCo nanoparticles embedded into porous Ketjenblack (KB) carbon architectures (PtCo@NGCS/KB) for fuel cells by a facile ligand carbonization strategy. [Display omitted] • The confinement synthesis of PtCo@NGCS/KB-800 is achieved by ligand carbonization. • Carbon shell reconstruction effectively improves the accessibility of surface sites. • PtCo@NGCS/KB-800 exhibits more outstanding ORR performance than commercial Pt/C. • PtCo and NGCS synergically account for the enhanced ORR performance. High-temperature reduction technology significantly improves the alloying process but inevitably causes the sintering of metal. Herein, we report the high-temperature confinement synthesis of PtCo nanoparticles encapsulated with N-doped graphitic carbon shells (NGCS) in porous Ketjenblack (KB) carbon architectures (PtCo@NGCS/KB) for fuel cells via ligand carbonization strategy. The optimal PtCo@NGCS/KB-800 exhibits outstanding mass and specific activities (840.2 mA/mg Pt and 0.94 mA/cm2, respectively) for oxygen reduction reaction (ORR), and possesses excellent stability with a smaller peak power density loss rate of 7.1 % than commercial benchmark Pt/C (23.7 %) after the accelerated durability test (ADT) in practical H 2 /air fuel cells. Experimental and theoretical investigations reveal that carbon shell reconstruction improves the accessibility of surface sites, and PtCo and NGCS synergically promote the enhancement of ORR performance. The NGCS encapsulation significantly reduces the energy level of the d-band center of Pt, promotes the desorption of intermediates, and lowers the reaction barrier for efficient ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • MOF-PPy composites were synthesized in a one-pot reaction. • The CoFe-NC-PPy with single-atom of Fe and Co was successfully synthesized. • PPy served as secondary nitrogen sources for enhanced ORR activity. • The CoFe-NC-PPy showed excellent ORR activity and durability in alkaline media. • The AEMFC performance with CoFe-NC-PPy exhibited remarkable efficiency. Metal-nitrogen-doped carbon (M−N−C) catalysts have emerged as highly active noble-metal-free catalysts for oxygen reduction reactions (ORR) in anion-exchange membrane fuel cells (AEMFCs). However, the performance of existing M−N−C catalysts is limited by the inaccessibility of internal M−N x active sites and loss of nitrogen doping after the carbonization process. Here, a single-atom Co, Fe and N-doped porous carbon catalyst (CoFe-NC-PPy) were constructed using a complex of metal–organic frameworks (MOFs) and polypyrrole (PPy). As a new approach, we synthesized MOF and PPy composites by combining in situ MOF synthesis and pyrrole polymerization in a one-pot reaction. Through pyrolysis, the PPy and MOF composites demonstrated an enhanced specific surface area, a high active-site density, and a high concentration of nitrogen species in the M−N−C catalyst. These contributed to a superior ORR performance (E 1/2 of 0.915 V) and high durability in alkaline media. Additionally, the CoFe-NC-PPy material studied in an AEMFC enabled high performance with a current density of 550 mA cm−2 at 0.6 V and a peak power density of 352 mW cm−2. This study suggests potential in combining polymers and MOFs in the synthesis of ORR catalysts for fuel cells. [ABSTRACT FROM AUTHOR]

• Hierarchical CNT hollow microspheres with tunable size are successfully synthesized. • CNT HMS show superior electrochemical activity for ORR than solid carbon particles. • Optimized CNT HMS deliver a mass-loading independent high performance for ZAB. • CNT HMS endow the highly efficient utilization of active materials. Although carbon materials have shown large potential as efficient electrocatalysts for oxygen reduction reaction (ORR), their practical performance with high energy density and power density is difficult to maintain under high mass-loading due to the compact restacking that seriously hinders mass/charge diffusion. To overcome this issue, we demonstrate the design and synthesis of hierarchical Co-N-codoped carbon nanotube hollow microspheres (CNT HMSs) with high disperse, large surface area and uniform mesopores, which effectively guarantees the high electrochemical activity and stability towards ORR even under high mass-loading. As a result, the power density of Zn-air battery based on CNT HMS gradually enhances from 52.8 to 183.8 mW cm−2 with a good linear relationship when the mass-loading increases from 1.5 (traditional used for most reported works) to 6.0 mg cm−2, indicating a well-preserved catalytic activity with high mass-loading. In addition, the long-term stability (10 h) test illustrates that monodisperse morphology and uniform size distribution of CNT HMS have been well maintained, while the referent carbon particles show serious agglomeration and obvious increased particle size. This suggests a much enhanced stability of CNT HMS compared with traditional particles, which offers large opportunity for the practical applications in metal-air batteries or fuel cells. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mn-N-C catalysts were developed by a newly designed bis(imino)-pyridine precursor. • The structures of Mn-N-C are dependent on the growth of the precursor with NaCl. • The Mn-N-C nanosheets with short Mn-N length shows excellent ORR performance. • This work provides new understanding for the rational design of M−N−C. Revealing the correlation between the micro–macro structures and active sites of transition metal-nitrogen-carbon (M−N−C) for electrochemical oxygen reduction reaction (ORR) is essential to develop non-precious metal catalyzed fuel cells and metal-air batteries. Herein, Mn-N-C catalysts with various morphologies and microstructures were prepared using Mn2+ coordinated bis(imino)-pyridine-based polymer with N-rich content as a new platform of precursor, which was synthesized via a condensation reaction of 1H-1, 2, 4-Triazole-3, 5-Diamine and 2, 6-Diacetylpyridine. Results demonstrate that morphologies and fine structures (pore structure, N dopants, surface area, and atomic Mn-N bond length, etc.) of Mn-N-C catalysts are strongly dependent on the growth of the specific precursor with and without NaCl as a template and the secondary calcination temperature can further optimize the bond length of Mn-Nx moieties, resulting in significant activity differences between correspondingly derived Mn-N-C catalysts for ORR. Compared to Mn-N-C derived from the synthesized precursor without NaCl, Mn-N-C obtained by the precursor grown directly on NaCl features an ultra-thin nanosheet-like structure with a hierarchical pore distribution and a shorter Mn-N bond, presenting high ORR performance with a half-wave potential of 0.88 V in 0.1 M KOH and a tiny potential loss of 11 mV after 30 K cycles, which is also proved by high-performance practical single Zn-Air battery (139 mW·cm−2) and proton exchange membrane fuel cell (400 mW·cm−2). This work provides a new understanding of the critical role of morphology and Mn-N bonding length of M−N−C for enhancing ORR and a new route of developing non-Fe/Co-based M−N−C catalysts for electrocatalysis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Different preparation schemes of PBAs are systematically summarized. • Strategy developing high-performance PBAs-based electrocatalyst is proposed. • An insight into the future research direction of PBAs-based electrocatalyst is highlighted. Electrolytic water, metal-air cells and fuel cells are the key fields in the application of new energy. However, these fields are subject to the high overpotential of ORR (oxygen reduction reaction), OER (oxygen evolution reaction) and HER (hydrogen evolution reaction), and these reactions are limited by the efficiency of electrocatalysts. Therefore, developing highly active electrocatalysts becomes a key step to solve the above problems. Prussian blue analogues (PBAs) are ancient synthetic cyanide coordination polymer materials, which are widely used in ORR, OER and HER. The unique three-dimensional open metal frame structure and large specific surface area of PBAs greatly increase the contact area between catalyst and electrolyte, and improve the number of active sites. The easy adjustment of components is beneficial to enhance the inherent activity of each active site in the catalyst. In this paper, the recent progress of PBAs derived materials in electrocatalysis is reviewed. Firstly, different preparation methods of PBAs were summarized, and then the regulatory strategies to improve the electrocatalytic activity of ORR, OER and HER when PBAs derived materials were used as electrocatalysts were discussed in detail, including the chemical composition regulation of doping, as well as the structure and morphology regulation of core–shell structure, open nanoccages structure and composite with other materials. Finally, the major challenges and possible future research orientations in this field were discussed, providing a new vision for further application of PBAs derived materials in electrocatalysis. [ABSTRACT FROM AUTHOR]

Microbial fuel cells (MFCs) as renewable electricity-generation devices are often confronted with the poor long-term durability and high cost of cathodic catalysts. In this study, iron (III) metaphosphate/iron phosphide/partly-graphitized carbon ((Fe(PO 3 ) 3 )/FeP/PGC) catalysts obtained at 750–950 °C are used as air–cathode catalysts for oxygen reduction reaction (ORR) in single-chamber MFCs. As temperature increases, graphitization degree of carbon skeleton in (Fe(PO 3 ) 3 )/FeP/PGCs gradually increases to obtain a higher electrical conductivity. At 900 and 950 °C, monoclinic structured Fe(PO 3 ) 3 is formed in PGC structure to constitute the Fe(PO 3 ) 3 /FeP heterojunctions, which should originate from the partial oxidation of FeP. The maximum power density (1.162 ± 0.022 W m −2 ) of MFCs is obtained by Fe(PO 3 ) 3 /FeP/PGC (900 °C) cathode, which is higher than that of commercial Pt/C (1.052 ± 0.015 W m −2 ) and only has a decline of 4.56% after 1900 h operation (excellent durability). Well-dispersed Fe(PO 3 ) 3 /FeP heterojunctions and abundant oxygen-containing groups (C–O–C, C–O–H and C–OH) play the important roles in achieving the high charge transfer efficiency (8.7 ± 0.2 Ω) and long-term durability in bio-electricity generation. Fe(PO 3 ) 3 /FeP/PGC (900 °C) primarily proceeds the efficient four-electron ORR pathway by exploiting the synergistic effects between the active components (Fe(PO 3 ) 3 /FeP) and porous structure (533.77 m 2  g –1 ). This study provides the promising non-precious-metal ORR electro-catalysts for replacing Pt/C in renewable energy-generation systems. [ABSTRACT FROM AUTHOR]

Cost-effective cobalt oxides were synthesized at mild condition as alternatives to platinum catalyst for oxygen reduction in microbial fuel cells (MFCs). The catalysts were prepared by heating Co(NO 3 ) 2 above its decomposition temperature together with carbon black (CB). At a catalyst loading of 5 mg/cm 2 , cobalt oxide cathodes with a Co(NO 3 ) 2 to CB ratio of 0.732:1 produced a maximum power density of 1220 mW/m 2 , which was slightly lower than that of Pt/C cathodes (1360 mW/m 2 ). Further increase in the loading of cobalt oxides resulted in an increase in performance. The maximum power densities produced by cobalt oxide cathodes increased to 1400 mW/m 2 at a catalyst loading of 20 mg/cm 2 and 1540 mW/m 2 at 30 mg/cm 2 , which outperformed the Pt/C control. The durability of cobalt oxide catalysts was comparable to that of Pt/C in single-chamber MFCs with biological contamination. The costs of cobalt oxide catalysts were much lower than that of Pt/C catalyst, even when the loading of cobalt oxides was several times higher than Pt/C catalyst. These findings show that the facilely synthesized cobalt oxides were cost-effective catalysts for oxygen reduction in air-cathode MFCs. [ABSTRACT FROM AUTHOR]

• The strong Au-Fe bond suppresses the leaching of Fe atoms in acidic media. • The Au atoms regulates the Pt atomic electronic structure and increases resistance to Pt atomic oxidation. • The L1 0 -PtAuFe catalyst exhibits outstanding ORR activity and stability. The intrinsic reactivity of PtM alloys during the catalysis of oxygen reduction reactions (ORRs) under acidic conditions is deactivated by the unavoidable leaching of cocatalyst M. Herein, we propose an unprecedented "Au-stabilized strategy" to stabilize the Fe atoms in L1 0 -PtAuFe via a strong Au-Fe bond. Simultaneously, the introduction of Au atoms regulates the Pt atomic electronic structure and increases resistance to Pt atomic oxidation, which is beneficial to further boost ORR activity and stability. As a result, the as-obtained L1 0 -PtAuFe exhibits minimal loss of mass activity after accelerated durability tests and is far superior to L1 0 -PtFe and commercial Pt/C. In addition, L1 0 -PtAuFe shows fantastic ORR activity, with a 7.3-fold improvement in mass activity and a 4.5-fold increase in specific activity compared to that of commercial Pt/C. This novel Au-stabilized strategy provides a new avenue to stabilize the M atoms in L1 0 -PtM alloys and further enhance their ORR activity and stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • A highly flexible and conductive 1D nanofiber-based cathode catalyst is synthesized. • The electrode presents a hollow beaded nanocage structure with exposed Co-N x sites. • Co-N x sites modified samples show superior ORR activity and methanol tolerance. • High power density of PAN-Co/ZIF-8-C-A based fuel cells are demonstrated. The rational control of Co-N x active sites dispersion in nanomaterials is significant to construct efficient oxygen reduction reaction (ORR) electrocatalysts in fuel cells. Herein, a novel strategy for the scalable synthesis of carbon nanofiber supported hollow beaded nanocage with accessible Co-N x sites in cavity wall (PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A) originated from zeolitic imidazolate frameworks (ZIFs) and polyacrylonitrile (PAN) is reported. Remarkably, the formed samples modified with Co-N x sites exhibit superior ORR activity, which makes it promising ORR catalysts for microbial fuel cell (MFC) and direct methanol fuel cell (DMFC). Accordingly, the maximum power densities of MFC decorated with PAN-Co-ZIF-8-C-A and PAN-Co/ZIF-8-C-A achieve 869.6 and 888.3 mW cm−2, which are 1.17 and 1.19 times higher than that of Pt/C. In addition, the PAN-Co/ZIF-8-C-A modified DMFC exhibits comparable power density of 23.27 mW cm−2 close to Pt/C electrode (25.63 mW cm−2). Such commendable catalytic performances can be primarily attributed to the synergistic effect of hierarchical porosity for fast mass transport, high conductivity for electron migration, and well-tuned Co-N x sites for oxygen reduction. This facile-effective optimization strategy may open a new avenue for exposing the catalytic centers of one-dimensional (1D) nanofiber and ZIFs-derived oxygen catalyst in fuel cells. [ABSTRACT FROM AUTHOR]

To effectively solve the electrochemical degradation problem of commercial Pt/C catalyst in fuel cell, nitrogen doped titania oxynitride (N-TiO 2) decorated Pt low-coordinated sites on a commercial Pt/C catalyst is achieved by coupling single-cycle selective atomic layer deposition of TiO 2 and following nitriding process that exhibits outstanding durability enhancement without changing the size distribution and wasting the electrochemical active area of Pt. [Display omitted] • TiO 2 was selectively decorated on Pt nanoparticles by atomic layer deposition. • The nitridation of TiO 2 stabilized the defect sites on Pt nanoparticles. • N-doped TiO 2 kept the exposure of Pt nanoparticles active sites. • N-doped TiO 2 decorated Pt/C showed durability promotion in fuel cell. The electrochemical dissolution of platinum (Pt) based nanoparticles and the consequent Pt active sites losses and particle aggregation have become a critical stability issue for the commercial proton exchange membrane fuel cell. Herein, nitrogen doped titania (N-TiO 2) stabilized Pt low-coordinated sites on a commercial Pt/C catalyst is achieved by simply coupling selective atomic layer deposition of TiO 2 and following nitrogen doping process. Selectively deposited N-TiO 2 on Pt nanoparticles keeps the exposure of Pt sites on (111) facets and increases the reduction states of Pt, which results in 1.7 times improvement of mass activity than commercial Pt/C. Besides, N-TiO 2 stabilized commercial Pt/C catalyst exhibits outstanding durability enhancement, showing only a 14.0% loss of mass activity after 30,000 potential cycles of rotating disk electrode tests and 91.7% retention after durability tests in humid fuel cell condition. The shielding role of N-TiO 2 could effectively inhibit the degradation of low-coordinated sites on Pt nanoparticles and maintain Pt size distribution, which is a promising strategy to prolong the lifetime of commercial Pt/C catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • N, S, and SN-doped graphene materials were synthetized. • Supporting Co 3 O 4 on GMs can increase electrocatalytic activity towards ORR. • ORR mechanism was studied by Tafel plots. • DEFC tests show better results for Co/SN-rGO compared to commercial Pt/C. Oxygen reduction reaction (ORR) is one of the key features for the efficient functioning of several energy conversion devices such as fuel cells, appearing the necessity of development of new low-cost catalyst materials. Heteroatom-doped carbon materials have attracted attention in this field due to its physicochemical and electronic properties. In this work, a nitrogen and sulfur doped material with anchored Co 3 O 4 nanoparticles (Co/SN-rGO) is proposed as cathode catalyst for direct ethanol fuel cells (DEFCs) and results are compared with different doped graphene nanomaterials (GMs). The effect of the heteroatoms and cobalt oxide nanoparticles in the final efficiency was studied. Synthesized materials were characterized and the activity of Co/SN-rGO and GMs for the ORR was studied. Co/SN-rGO presents high ORR performance in terms of onset potential (E onset), 0.86 V (vs RHE) and half-wave potential (E 1/2) 0.72 V (vs RHE). Tafel analysis shows 60 mV dec-1 at low overpotential for potential dependent ORR mechanism. Besides, when Co/SN-rGO performance is evaluated in a DEFC using a fuel cell test station, main results indicate higher catalytic activity, stability, and ethanol tolerance of Co/SN-rGO in comparison to a carbon-supported Pt catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of melamine-phloroglucinol-formaldehyde (MPF) for N -doped porous carbon. • Catalyst materials possess hierarchical porous structure, high specific surface area. • MPF/M = Fe, Co catalysts show high ORR activity in 0.1 M KOH (E 1/2 up to 0.81 V) • M N C catalysts show excellent electrochemical stability for 10,000 potential cycles. • Excellent AEMFC performance (P max = 347, 324 mW cm−2) with MPF/Fe and MPF/Co catalysts. Delving into highly active and cost-efficient electrocatalysts for oxygen reduction reaction (ORR) is crucial for the large-scale application of polymer electrolyte fuel cells. Anion exchange membrane fuel cells (AEMFCs) are promising clean energy devices owing to their mild reaction conditions and the high probability of employing Pt-free catalysts for ORR. Developing the promising non-Pt ORR catalysts for AEMFC is still of great importance. Herein, we report the transition metal (Fe, Co, Mn, and Cu) impregnated melamine-phloroglucinol-formaldehyde (MPF) polymeric networks to derive metal-nitrogen-carbon (M N C) electrocatalysts via a robust synthesis route. The catalysts are screened through variable metal contents and different pyrolysis temperature optimizations by virtue of their ORR activity. The controlled synthesis method resulted to the prominent textural properties of the catalysts with efficient active centers to enhance the ORR performance. Amongst, iron-doped (MPF/Fe), and cobalt-doped (MPF/Co) catalysts are performing better in terms of half-wave potential (E 1/2) values of 0.81 and 0.80 V vs RHE which is attributed to the highly active M−N x sites and hierarchical porous structure of catalysts. Outstanding electrochemical stability in half-cell and high-power density in an AEMFC (up to 347 mW cm−2) made the present work drive to the development of highly efficient M N C catalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]

• A highly efficient Pd 3 Cu aerogel alloy for oxygen reduction reaction is firstly developed. • The aerogel alloy displays much enhanced ORR activity as compared with the noble metals. • The aerogel alloy also delivers excellent and multifunctional HER and EOR performance. • The density functional theory calculations are carried out for revealing the ORR mechanism. Pd has been considered as a potential substitution of the Pt-based electrocatalyst for oxygen reduction reaction (ORR) in the fields of fuel cells, however, the binding strength between the bare surface and the intermediates is much stronger than that on Pt, leading to its inferior ORR activity. Alloying noble metals with nonprecious metals provides a cost-effective strategy for electrocatalyst design. In this work, we have demonstrated a novel Pd 3 Cu aerogel electrocatalyst derived from a mild reduction agent via the self-assembly and freeze-drying technique. The resulting catalyst shows a typical three-dimensional and "pearl-like" aerogel structure. Combining the structural features and optimized chemical compositions, the Pd 3 Cu aerogel exhibits remarkable pH-independent performance over the commercial Pt/C electrocatalyst. Notably, the optimized Pd 3 Cu aerogel displays excellent ORR activity with a half-wave potential of 0.90 V vs RHE, with a limiting current density of 5.8 mA/cm2 under the alkaline conditions, which is among the best of the reported noble metal-based ORR electrocatalysts. In addition, the resulting Pd 3 Cu aerogel delivers excellent hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR) performance. Furthermore, the density functional theory (DFT) calculations reveal that the unique partially oxidized Pd 3 Cu aerogel has led to a shift‐down of the d-band center of the active sites, which energetically optimizes the binding strength of the adsorbed O intermediate during the ORR process, therefore accelerating the ORR activity. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of metal alloys to improve their electrocatalytic property. [ABSTRACT FROM AUTHOR]

ORR pathways on the surface of (a) Co@Pd and (b) CPCo-3 NCs at an open-circuit voltage (OCV) and under potential driven conditions from 1.0 to 0.7 V. In Co@Pd NC, the O 2 splitting to 2Oads occurs in the Pd surface the Oads is relocated to the neighbouring oxygen vacancies for conducting the reduction reaction with H 2 O in CoO X V sites. In CPCo-03, the hydration reaction removes the amorphous CoO X and thus expose the CoPdO X V to the electrolyte from OCV to 1.0V. The PdCoO X V sites are reaction centre for the O 2 splitting to 2Oads and collaborate with the neighbouring Pd atoms for completing the ORR. [Display omitted] • A novel catalyst of oxygen vacancies enriched atomic CoPdO x clusters is developed. • It delivers a mass activity of 426 mAmg Co −1 at 0.90 V vs RHE in alkaline ORR. • It increases the mass activity by 40 % at 20 k potential cycles in degradation test. Considering the technological importance of fuel cells, developing highly efficacious, durable, and Platinum (Pt)-free catalysts are crucial. In this work, we propose a novel nanocatalyst (NC) comprising oxygen vacancies (OV) enriched atomic CoPdO x clusters (CoPdO x V) anchored Pd nanoparticles (NP)s on cobalt-oxide support (denoted as CPCo). As-prepared CPCo NC with an additional 3 wt% of Co decoration (denoted as CPCo-3) delivers an exceptionally high mass activity (MA) of 4394 mAmg Co −1 at 0.85 V vs RHE and 426 mAmg Co −1 at 0.90 V vs RHE in alkaline oxygen reduction reaction (ORR) (0.1 M KOH), which surpasses the commercial J.M.-Pt/C (20 wt%) catalyst by 65-times. More importantly, the CPCo-3 NC exhibits outstanding durability in an accelerated durability test (ADT) with a progressively increased MA by 40 % (6,140 mAmg Co −1) as that of the initial condition after 20 k cycles. Through in-depth physical characterization, electrochemical analysis, and in-situ X-ray absorption spectroscopy (XAS), we demonstrated the conceptual framework of potential synergism between the CoPdO x V and neighbouring metallic Pd-sites. In this event, the surface-anchored CoPdO x V species coupling with OV promotes the O 2 splitting, while the neighbouring Pd-sites simultaneously trigger the Oads relocation (i.e. OH− desorption) step. In addition, the cobalt oxide support underneath assists the electron injection to surface Pd-sites. This work not only marks a step ahead for designing high-performance transition metal oxide catalysts for fuel cells but also uncovers the material's aspects of cobalt that shall spark motivation for the other catalytic applications. [ABSTRACT FROM AUTHOR]

• Simple, cost-effective one-step synthesis of novel Fe-Mo double atom catalyst. • Fe-Mo double atom catalyst is shown to exhibit overall oxygen electrochemistry. • Mechanistic understanding of the bifunctional oxygen electrochemistry. Exploration of cost effective and high performance electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is becoming the paramount interest towards the emerging renewable energy technologies such as fuel cells, metal air-batteries and water electrolysers, etc. One of such catalysts is single atom catalyst that exhibits well defined active sites with very high atom utilization efficiency but selective mainly towards ORR. We demonstrate one-step synthesis of carbon–nitrogen (CN)-coordinated Fe-Mo double atom catalyst with high atom utilization efficiency towards both ORR and OER. The catalyst exhibits enhanced activity with lower overpotential associated with ORR and OER (ΔE = E j=10(OER) - E 1/2(ORR)) and better mass activity in comparison to that of Mo-N-C and Fe-N-C, even better than the state-of-the-art Pt/C and RuO 2 catalysts for ORR and OER, respectively. This place the double atom catalysts in the series of non-precious metal based bifunctional catalysts for overall oxygen electrochemistry and is due to the electronic structure modification around the metal atoms induced by other neighbouring metal atom. The double atom Fe-Mo-N-C exhibits a remarkable and highly durable ORR performance with suppressed peroxide generation due to the muted outer sphere electron transfer mechanism in comparison with the commercially available state-of-the-art Pt/C electrocatalyst. Moreover, Fe-Mo-N-C shows remarkable enhanced overall oxygen electrochemistry at higher temperature (323 K - a temperature 25 K above the room temperature), widening its applicability. Overall, this work paves the way to design multi-atom catalysts towards multi-functional electrocatalytic activities. [ABSTRACT FROM AUTHOR]

Atomically dispersed FeCu-NC catalyst containing FeN 4 and CuN 4 dual active sites is synthesized, and the assembled hydrogen fuel cell of using FeCu-NC as cathode presents a ultrahigh peak power density. DFT calculations reveal that the strain effect from the CuN 4 species efficiently tailors the electronic structure of FeN 4 species and therefore boost its catalytic activity. [Display omitted] • Atomically dispersed FeCu-NC catalyst containing FeN 4 and CuN 4 dual active sites is synthesized. • The FeCu-NC exhibits better ORR performance than commercial Pt/C and Fe-N-C single-atom catalyst in alkaline medium. • Using FeCu-NC as cathode, the assembled hydroxide exchange membrane fuel cell presents a ultrahigh peak power density. • DFT calculations reveal that the synergistical effect of FeN 4 and CuN 4 species efficiently boosts the ORR. Compared to most popular single-atom catalysts (SACs), the dual-atom catalysts may possess better catalytic performance due to the synergistic effect of dual-atom sites. However, revealing the synergistic mechanism of dual-atom sites to improve catalytic activity is still insufficient. Here, atomically dispersed FeCu-NC catalyst containing FeN 4 and CuN 4 dual active sites is synthesized, and has been identified by high angle annular dark-field STEM and X-ray absorption spectroscopy. The as-synthesized FeCu-NC exhibits a half-wave potential of 0.882 V, which is nearly 40 mV superior to Pt/C catalyst and 24 mV better than Fe-NC SAC in alkaline medium. Using FeCu-NC as a cathode catalyst, the assembled hydroxide exchange membrane fuel cell presents a peak power density of 0.91 W·cm−2, which is ∼ 21% higher than of Fe-NC based one (0.76 W·cm−2). DFT calculations reveal that the strain effect caused by the CuN 4 species replacing the neighbor carbon environment of the FeN 4 species, can efficiently tailor the electronic structure and reduce the OH* adsorption on FeN 4 species and therefore improves the catalytic activity and kinetic process of ORR. This work provides a new insight into the synergistic catalysis of dual-atom sites for ORR. [ABSTRACT FROM AUTHOR]

[Display omitted] • A synchronous complexation-polymerization strategy of synthesizing M−N−C electrocatalysts was developed. • As-synthesized Fe-N-C exhibits excellent ORR performance in Zn-air battery and fuel cell. • This strategy provides a flexible platform to advance molecular-level design and synthesis M−N−C catalysts. Developing atomic transition metal coordinated by nitrogen doped carbon (M−N−C) eletrocatalysts for oxygen reduction reaction (ORR) is critical to achieve low cost metal-air batteries and fuel cells. Herein, a general method of synthesizing M−N−C was developed via a synchronous complexation-polymerization strategy, in which nitrogen-containing ligand was coordinated with specific transition metal ions and diamino aromatic compound was simultaneously polymerized by the metal ion as initiator; by the following pyrolysis in a molten NaCl bath, M−N−C was finally synthesized. Fe-N-C was synthesized by this strategy using 2, 4, 6-Tri (2-pyridyl)-1, 3, 5-triazine (TPTZ) as ligand for FeCl 2 , and 1, 8-Diaminonaphthalene (DAN) as monomer of polymerization. Results demonstrate that introducing DAN into TPTZ-Fe2+ significantly affect the derived carbon structure and electrochemical performance of corresponding Fe-N-C. The Fe-N-C prepared by TPTZ and DAN with the molar ratio of 1:1 shows excellent ORR activity and durability, whose initial half-wave potential is 0.90 V in 0.1 M KOH and 0.80 V in 0.5 M H 2 SO 4 respectively, after 10 K cycles, the potential is only 14 mV loss in 0.1 M KOH and 20 mV decay in 0.5 M H 2 SO 4. And the ORR performance as cathode is further proved by a single practical Zn-air battery with a maximum power density of 192 mW cm−2 and a specific capacity of 800 mAh g Zn -1, much higher than 137 mW cm−2 and 735 mAh g Zn -1 of the same loading of commercial Pt/C catalyst and proton exchange membrane fuel cell with a high power output of 640 mW cm−2. Attributed to the vast kinds of ligands, metal ions and polymerizing monomers, this strategy provides a flexible platform of synthesizing advanced M−N−C catalysts, compared with other reported methods. [ABSTRACT FROM AUTHOR]

[Display omitted] • A newly developed hollow structural Fe-N-C catalyst is synthesized by a template-free method. • Fe-N sites are embedded in an ultrasmall, ultrathin, and interconnected porous carbon structure. • The exposure and utilization of Fe-N sites was maximized by twice acid treatment. • The optimal catalyst (HNP-16) exhibited higher E 1/2 and faster ORR kinetics than Pt/C. • HNP-16 delivered a P max of 37.6 mW cm−2 in a membraneless DFFC, 140% higher than Pt/C. Fe-N-C oxygen reduction reaction (ORR) catalysts are still limited in poor ORR activity due to low Fe-N exposure and utilization. Here, we report a newly developed Fe-N-C catalyst with Fe-N sites embedded in a micro/mesopore-interconnected, ultrasmall (5–45 nm), ultrathin (1.3 nm), and hollow nanocarbon structure, which is synthesized by a facile, scalable, and template-free method by using cheap and safe reagents. Moreover, the exposure of Fe-N is maximized through twice acid treatment to tune the surface composition of the catalysts. The mass sites density of the optimal catalyst HNP-16 reached 45.0 μmol g−1, much higher than that of untreated HNP-0 (7.4 μmol g−1) and common treated HNP-1 (12.2 μmol g−1). Benefiting from a collective contribution of abundant surface Fe-N active sites and structural advantages, HNP-16 exhibits higher half-wave potential and faster ORR kinetics than commercial Pt/C. Detailed electrochemical analysis revealed the relationships between coordination and ORR activity. The higher content of Fe-N results in faster ORR kinetics while O-related species lead to an undesired 2-electron ORR pathway. When HNP-16 was employed as the cathode catalyst in a membraneless direct formate fuel cell, it delivered an accelerated ORR current response and achieved an unprecedented maximum power density of 37.6 mW cm−2, which was 1.4 times higher than that of Pt/C. The superior performance of HNP-16 is attributed not only to the highly exposed Fe-N sites but also to the rapid mass transfer provided by the favorable hollow structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • Carbon supported hybrid electrocatalyst (Ag/Co/C) is facilely synthesized via flash Joule heating. • Ag/Co/C exhibits excellent activity as a low-cost ORR catalyst, thanks to the synergy between Ag and Co. • Ag/Co/C displays superior tolerance to methanol and ethanol in ORR as compared to commercial Pt/C. The commercial catalysts for oxygen reduction reaction (ORR) are highly dependent on the scarce and expensive Pt to achieve high activity and reasonable durability, especially for the fuel cells used in automobiles. Ag alloys have been proposed as promising candidates for non-Pt ORR catalysts in alkaline media, with reasonably high activity at significantly lower cost. Herein we demonstrate the synthesis of Ag/Co/C hybrid electrocatalyst for ORR via radiative flash Joule heating. Unlike the previously reported solid-solution structure of the quenched immiscible alloys by flash Joule heating, the large immiscibility gap in the liquid state of the Ag-Co alloy prevents the formation of solid solution. The hybrid catalyst exhibits a specific activity 40 times and a mass activity 52 times higher than that of the pristine Ag/C at 0.8 V vs. RHE in alkaline media, and its tolerance to methanol and ethanol is superior to that of commercial Pt/C. The enhanced activity and good stability are attributed to the enhanced oxygen adsorption energy on silver due to the strong interaction between silver and cobalt. [ABSTRACT FROM AUTHOR]

• Freestanding metal–organic framework assembly is firstly fabricated. • Producing a series of hierarchically ordered porous carbon nanomaterials. • Achieving an extremely low ORR potential in both alkaline and acidic media. • Catalysts are applied in Zinc-air batteries and fuel cells, showing a higher power density than the noble metal catalysts for Zinc-air batteries. Efficient electrocatalysts for oxygen reduction reaction (ORR) are desirable but challenge in harsh conditions, which seriously limits the widespread application of many clean energy devices. Herein, a series of zeolitic imidazolate framework-8 (ZIF-8) assemblies are fabricated using a freestanding template and further used as pyrolytic precursors for synthesizing metal-free ORR catalysts. Impressively, the optimized 3D porous nitrogen-doped carbon (PNC-30) exhibits a half-wave potential of 0.90 and 0.76 V in alkaline and acidic electrolytes, respectively. Furthermore, when used as the cathode in zinc-air batteries, PNC-30 reaches a power density of 150 mW cm−2, 1.6 times higher than the commercial Pt/C. And, the PEMFCs equipped with PNC-30 cathode deliver a high power density of 562 W g−1. Experimental results and computational analysis indicate that the outstanding ORR performance is ascribed to the unique trimodal-porous structure, where micropores give abundant active sites/defects and meso-/macropores provide rapid mass transfer capabilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Au@PdPt porous nanowires were prepared via a two-step approach. • The catalysts possess core-shell structure and trimetallic composition effect. • The catalysts exhibit excellent performance for oxygen reduction reaction. • The strategy provides a simple route for preparing porous core-shell nanowires. The design of porous one-dimensional (1D) Pt-based nanoarchitectures is significant for fuel cells. The incorporation of Au into Pt-based electrocatalysts is an efficient strategy to enhance its electrocatalytic performance. In this work, we propose a facile strategy to synthesize Au@PdPt porous nanowire architecture with an Au nanowire (Au NW) as the core and a porous PdPt surface as the shell (Au@PdPt pNWs). 1D core-shell nanoarchitectures with porous surface provide sufficient active sites and rich reactant transfer channels for O 2 adsorption and activation. Compared with PdPt mesoporous nanoparticles and commercial Pt/C catalyst, the Au@PdPt pNWs show superior catalytic performance for electrocatalytic oxygen reduction reaction. The present synthetic strategy can be widely used for the preparation of porous core-shell structured metallic nanowires for various electrocatalytic applications. [ABSTRACT FROM AUTHOR]

C 4 N was firstly synthesized from DAP via one-step hydrothermal method and composited with single-atom Pt or Ru to form high-performance electrocatalysts. [Display omitted] • A novel one-step hydrothermal method was used to synthesize C 4 N. • Pt or Ru single-atom is composited with C 4 N to obtain electrocatalyst. • The electrocatalysts show high-performance ORR activity and good stability. • The DFT calculations reveal the reaction mechanism of the electrocatalysts. Pt/C is a practical electrocatalyst for oxygen reduction reaction (ORR) in metal-air batteries and fuel cells, however, also suffers the drawbacks of high cost and instability, which have propelled people to search for new substitutes, such as single-atom metal electrocatalysts. Herein, C 4 N was firstly synthesized from 2,3-diyldiamine phenazine via one-step hydrothermal method rather than the traditional way that two monomers react in organic solvent, and then loaded with single-atom metal (Pt or Ru) to form new electrocatalysts. The so-formed M@C 4 N (M = Pt or Ru) electrocatalysts show more excellent ORR performances with higher half-wave potential and better stability and methanol tolerance as compared with the commercial Pt/C. Specifically, the half-wave potential of 1%Pt@C 4 N and 0.5%Ru@C 4 N is 0.861 V and 0.828 V, respectively. Density functional theory calculations reveal that 1%Pt@C 4 N has stronger adsorption of reactant species and faster kinetics than 0.5%Ru@C 4 N in ORR pathway. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biomass-derived porous carbon nanosheets reviewed for sustainable energy applications. • N-doping, by chemical-free self-doped approach, modulates electrocatalytic properties. • Use of same biomass as C and N precursor leads to green and scalable production. • High surface area, porosity, defects and heteroatom-doping improves electrocatalytic activity. • N-doped PCNs used in energy conversion (fuel cells) and storage (supercapacitor) devices. Ultrathin porous carbon nanosheets (PCNs) with large aspect ratio and hierarchical porous layered structure provide numerous catalytic active sites along with chemical stability, large surface area and high electrical conductivity that is ideal for energy conversion and storage devices. The doping of PCNs with nitrogen and other heteroatoms improves the electrocatalytic properties needed for energy applications. However, routine synthesis methods based on molecular assembly or templates yield only small samples that restricts the use of PCNs in flexible electronics and energy devices and moreover, the use of toxic etching agents to remove templates is not environment-friendly. Therefore, the scalable and low-cost production of highly active and robust biomass-derived PCNs is of paramount importance and it can be achieved by the use of low-cost, abundantly available, sustainable biomass. In the present article, biomass-derived PCNs and their N-doping has been reviewed for energy applications, primarily as oxygen reduction reaction catalysts in fuel cells and as electrodes in supercapacitors. The synthesis of PCNs from twenty biomasses, ten for each application, and their N-doping by conventional (using ammonia or urea) and self-doped green (using biomass) approach has been discussed. In the green approach, same biomass is used as C as well as N (or heteroatom) precursor for N or heteroatom-doping of PCNs and it has recently emerged as a very promising green strategy for the scalable synthesis of N-doped PCNs from biomass. It can be further tuned to develop advanced carbon nanomaterials from diverse biomass materials for various sustainable energy related applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • BCFZY and Ni doped BCFZY cathodes are synthetized. • Ni doped BCFZY improves the oxygen ion and proton conductivity of the cathode. • BCFZYN has a good thermal stability and a reduced thermal expansion coefficient. • Ni doping enhances the ORR activity in both O-SOFCs and PCFCs. • BCFZYN exhibits a prominent stability in both symmetrical cell and single cell test. To develop a cathode with excellent oxygen reduction reaction (ORR) activity and durability at intermediate-to-low temperatures is significant to boost the advancement of solid oxide fuel cells (SOFCs), a fascinating energy conversion technology with low emissions and high efficiency. Perovskite oxides have been extensively developed as cathodes, and doping is an important strategy to alter the lattice diffusion and surface exchange properties of perovskites, to tailor catalytic performances for various redox reactions, including ORR for SOFCs. The reported BaCo 0.4 Fe 0.4 Zr 0.1 Y 0.1 O 3-δ (BCFZY) is a promising cathode for SOFCs. Herein, to further improve the performance of BCFZY at reduced temperatures, we systematically investigate the partial doping of B-sites with different metal elements, including Mn, Ni, Cu and Zn at a fixed content of 5%. Among them, it is found that Ba(Co 0.4 Fe 0.4 Zr 0.1 Y 0.1) 0.95 Ni 0.05 O 3-δ (BCFZYN) exhibits the lowest polarization impedance in both oxygen ion and proton conducting fuel cells. Based on conductivity relaxation experiments and oxygen and hydrogen permeation tests, it is found that nickel doping improves oxygen mobility, surface exchange kinetics, and bulk oxygen ion and proton conductivity. Thereby, a high ORR activity on oxygen ion and proton conducting electrolytes is achieved, reaching 0.038 and 0.607 Ω cm2 at 550 °C, respectively. The cells with the BCFZYN electrode show outstanding operational stability (200 h of operation in a symmetrical cell and 1000 h of operation in a single cell). This suggests that the BCFZYN is a promising cathode of next-generation SOFCs. [ABSTRACT FROM AUTHOR]

• The PtNi/C NWs shows significantly improved ORR activity after treating in NH 3. • Different atmospheres can realize different surface composition of PtNi/C NWs. • The high catalytic performance can be attributed to optimal ΔE O of PtNi/C NWs. The oxygen reduction reaction (ORR) takes place on the surface of catalyst, and the precise control of surface component at atomic scale has been an important factor to effectively improve the performance of catalysts. Herein, a highly active and stable catalyst is designed by constructing Pt skin and controllable near-surface atomic distribution of PtNi alloy nanowires (NWs). It is found that the d-band center of Pt-skin down-shifts with Pt ratio in the surface/near-surface of PtNi alloy decreasing, and correspondingly the adsorption energy of atomic oxygen (ΔE O) on PtNi alloys weakens, confirmed by experimental results and theoretical calculations. The optimum PtNi/C-NH 3 NWs exhibit the enhanced mass activity (1.02 A mg Pt −1) and specific activity (3.86 mA cm−2) for ORR, which are 5.7-fold and 11.4-fold higher than those of commercial Pt/C, respectively. Moreover, the H 2 /air fuel cell of PtNi/C-NH 3 NWs exhibits a current density of 308 mA cm−2 at 0.8 V, which is superior to that of the 2020 target of the U.S. Department of Energy (DOE). Our study provides a new perspective and approach in promoting the electrocatalysis on alloy nanomaterials for ORR. [ABSTRACT FROM AUTHOR]

• Non-precious novel bimetallic oxide of Fe 2 O 3 -MoO 3 /NG core-shell catalyst prepared first-time. • Uniformly nano-sized core Fe 2 O 3 -MoO 3 NPs homogeneously dispersed and wrapped by shell NG sheet. • Incorporation of MoO 3 with Fe 2 O 3 could modify the electronic structure of entire bimetallic oxide. • Synergistic surface-strain capabilities are engineered by segregation of atomic arrangements. • Fe 2 O 3 -MoO 3 /NG deliver superior catalytic activity along with remarkable durability/ stability. In-expensive transition metal catalysts are the most favorable substitutes to the noble metal catalysts for oxygen reduction reaction (ORR) in fuel cells energy technology. Herein, the article focused on the synthesis of uniformly distributed nano-sized bimetallic Fe 2 O 3 -MoO 3 oxide encapsulated nitrogen-doped graphene (NG) (Fe 2 O 3 -MoO 3 /NG core-shell structure) catalyst through well-controlling reaction parameters and its prospective applications towards ORR for the first time. Thus, these unique synergistic interactions of bimetallic Fe 2 O 3 -MoO 3 and NG support could modify the surface-strain effects, which led to enriching catalytic activity. Thus, Fe 2 O 3 -MoO 3 /NG core-shell structure demonstrated excellent catalytic activity, and far exceeding in long-term durability, better methanol tolerance compared to commercial Pt/C catalyst. Furthermore, the monometallic oxide (Fe 2 O 3 or MoO 3) or NG individually have poor activity for ORR, but their hybrid materials (Fe 2 O 3 -MoO 3 /NG) influenced strongly due to their structural properties, such as crystal structure, exclusive porosity, particle size and multiple active interfaces, display unexpected and remarkably high ORR activities similar to Pt/C in alkaline medium, This makes Fe 2 O 3 -MoO 3 /NG core-shell structure a suitable and efficient non-precious electrocatalysts with high catalytic ability, that could open up a new promising approach to advanced catalysts for electrochemical energy conversion and storage. [ABSTRACT FROM AUTHOR]

• Synthetic strategies for single-atom catalysts are summarized. • Operando characterizations for their structural identification are discussed. • Advances in catalytic mechanisms and practical applications are provided. • Key challenges and future opportunities in the emerging field are highlighted. Electrochemical oxygen reduction reaction (ORR) is at the heart in many sustainable energy conversion technologies such as rechargeable fuel cells and metal-air batteries. Currently, various noble/transition metal-based materials have been developed as catalysts for boosting their catalytic performances. Among them, single-atom catalysts (SACs) have received increasing interest as promising electrocatalysts owing to their maximum utilization of active species, low-coordination environment, quantum size effect and tunable metal-support interaction. Over the past few years, tremendous SACs have been fabricated by using various approaches and are further used for the advanced energy conversion process. In this review, we offer a critical overview on the state-of-the-art design of SACs under the framework of bottom-up and top-down strategies and in-situ/operando characterizations. We also comprehensively present recent advances in the development of SACs for ORR electrocatalysis, fuel cells and zinc-air batteries, and describe key challenges and future opportunities in this emerging field. [ABSTRACT FROM AUTHOR]

• Facile synthesis of cobalt oxides incorporated covalent organic frameworks. • High catalytic activity, poison tolerance and good durability of Co/N-C-COPs. • Co/N-C-COPs prepared at 800 °C exhibited the best ORR catalytic activity. • Power output of Co/N-C-COPs cathode is similar to Pt/C cathode in MFC and DFFC. Synthesizing high efficient oxygen reduction reaction catalyst is crucial for electrochemical technologies such as fuel cells. Herein, we proposed a covalent organic polymers derived carbon with cobalt oxides incorporation (Co/N-C-COPs) as ORR electrocatalysts for fuel cells. The Co/N-C-COPs was demonstrated to possess sufficient active sites and uniformly dispersed cobalt and nitrogen elements. The as-prepared Co/N-C-COPs at 800 °C showed the best ORR catalytic activity with a half-wave potential (−0.16 V vs. Ag/AgCl) and limiting current density (3.99 mA cm−2) similar to that of Pt/C (−0.15 V vs. Ag/AgCl and 4.05 mA cm−2) in alkaline media. When using the Co/N-C-COPs as cathode electrocatalyst, two types of home-made fuel cells (microbial fuel cell and direct formate fuel cell) delivered a comparable or even higher power output than that using Pt/C, due to its intriguing features including high catalytic activity, high poison tolerance and good durability. These results suggested that the as-proposed Co/N-C-COPs catalyst probably provide an alternative avenue for developing the cathode electrocatalysts for fuel cell applications. [ABSTRACT FROM AUTHOR]