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Atomically distributed iron electrocatalyst is valid for oxygen reduction reaction (ORR). However, accurate regulation of the structure improving its intrinsic activity is a challenge. Herein, a dual-atom catalyst FeCu-NC with atomically distributed Fe and Cu co-anchored on porous N-doped carbon is obtained. The FeN 4 and CuN 3 couple sites bridged by two nitrogen atoms, exist as Fe(II,III)N 2 (µ 2 -N) 2 Cu(I,II)N moieties with the metal distance of ∼2.5 Å in the structure of FeCu-NC. The synergistic effect of Fe and Cu dual-atom reducing the dissociation energy of *OOH intermediate, allows an optimized 4e- ORR reaction pathway. The FeCu-NC exhibits high-efficiency ORR activity with the half-wave potential (E 1/2) of 0.889 V (vs RHE) and outstanding stability without obvious decay for the E 1/2 after 10,000 cycles. The FeCu-NC based Zn-air battery presents large specific capacity of 795 mAh g−1 and energy density of 998 Wh kg−1 as well as high charge-discharge cycling stability superior to the Pt/C. [Display omitted] • A dual-atom catalyst FeCu-NC with Fe(II,III)N 2 (µ 2 -N) 2 Cu(I,II)N moieties is prepared. • The synergistic effect of Fe and Cu clearly reduces the dissociation energy of *OOH. • The FeCu-NC has a high ORR activity in an optimized 4e- reaction pathway. • The FeCu-NC based Zn-air battery exhibits a large stable energy density. [ABSTRACT FROM AUTHOR]

Single atomic catalysts (SACs), especially the catalysts featured by well-developed M-N 4 moieties, show excellent catalytic activity and spark enormous attention. However, the highly symmetric active sites may result in some degenerate electronic states for the d orbitals of the center metal atom, which suffer from the unsatisfactory adsorption-desorption behaviors during reaction. Herein, we develop an asymmetric anchor site by two types of nitrogen (sp-N and pyridinic N) created in the inherent edge-rich carbon domain of hydrogen-substituted graphdiyne (HsGDY), where atomic catalyst like manganese atoms can be asymmetrically anchored on the one side of hexagon carbon rings. The abundant elegant hexagon carbon rings on HsGDY not only facilitate the creation of edge sites, but also provide available space for the coordination of terminal ligands (OH) with Mn atoms. The as-synthesized Mn-N-HsGDY exhibits excellent ORR activity and an impressive long-term cyclability for over 3800 cycles in a rechargeable Zn-air battery. [Display omitted] • A facile method for preparing asymmetric active sites is proposed. • The Mn atoms are anchored by sp-N and pyridinic N of HsGDY sideways. • The Mn SAC exhibits excellent ORR activity and can run over 3800 cycles in a zinc-air battery. [ABSTRACT FROM AUTHOR]

The metal-nitrogen-carbon (M-N-C) type oxygen reduction reaction (ORR) catalysts are promising for hydroxide exchange membrane fuel cells, but catalysts with further improved performance are challenging. Here, we report the efficient improvement of the ORR activity of M-N-C catalysts by employing highly polarizable metal cation Ag+. Ag, Fe single atomic sites embedded in concave nitrogen doped carbon (Ag 1 Fe 1 /CNC) is successfully synthesized and shows high performance towards ORR, indicating by both the ultra-high half-wave potential of 0.917 V and membrane electrolyte assembly performance of peak power density up to 1.26 W cm−2. The binding energy of the ORR intermediates on the highly polarizable Ag site in Ag 1 Fe 1 /CNC was significantly tuned by the adjacent Fe site by more than 0.2 eV, and thus leading to a low theoretical ORR overpotential of only 0.398 V. The employment of the highly polarizable metal cation brings a novel and efficient approach to construct highly active catalysts. [Display omitted] • High performance oxygen reduction reaction catalyst Ag 1 Fe 1 /CNC is synthesized. • The highly polarizable Ag site shows ultra-high catalytic activity. • The Ag sites are significantly affect by the adjacent metals. • High membrane electrolyte assembly performance is achieved by using Ag 1 Fe 1 /CNC. [ABSTRACT FROM AUTHOR]

A novel in situ strategy to embed Co 9 S 8 nanoparticles into nitrogen and sulfur codoped hollow porous carbon (Co 9 S 8 @N-S-HPC) is achieved. The Co 9 S 8 @N-S-HPC can be used an efficient catalyst for both ORR and HER. The unique nanostructure and synergistic interactions between Co 9 S 8 and N-S-HPC play a crucial role to improve the electrocatalytic performance. • Co 9 S 8 @N-S-HPC is fabricated using a novel in situ formation approach. • Co 9 S 8 @N-S-HPC shows excellent electrocatalytic performance toward ORR and HER. • Synergistic effect of Co 9 S 8 and N-S-HPC improves the electrocatalytic performance. The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are critical processes for many energy conversion technologies, where efficient catalyst plays a key role in these reactions. Here we report a novel in situ strategy to embed Co 9 S 8 nanoparticles (NPs) into nitrogen and sulfur codoped hollow porous carbon (Co 9 S 8 @N-S-HPC). In this strategy, the ZIF-8 surface is firstly decorated by cobalt thiourea, and then coated with a shell of polymeric resorcinol-formaldehyde, followed by a high temperature pyrolysis treatment. The resulting Co 9 S 8 @N-S-HPC shows comparable catalytic activity for ORR compared with commercial 20 wt% Pt/C catalyst and superior long-term stability under alkaline conditions. Simultaneously, Co 9 S 8 @N-S-HPC also exhibits an excellent HER activity with low onset overpotential of 68 mV, a small Tafel slope of 78 mV per decade and a long-term durability in alkaline medium. First-principles calculations reveal that Co 9 S 8 particle can anchor in N-S-HPC via a Co-S bond and enhance the binding of Co 9 S 8 and N-S-HPC. The N-S-HPC can affect the electronic structure of supported Co 9 S 8 strongly. The combined experimental and theoretical investigation show the outstanding ORR and HER performances of Co 9 S 8 @N-S-HPC are attributed to its unique nanostructure and synergistic interactions between Co 9 S 8 NPs and N-S-HPC. [ABSTRACT FROM AUTHOR]

Graphical abstract N-, O- and P-tridoped hollow carbons (NOPHCs) were successfully synthesized via pyrolysis of Co 2 P-containing polypyrrole (Co 2 P@PPY) precursors, and the subsequent removal of Co 2 P templates. Thanks to the synergistic effect of the multi-heteroatoms doping in the carbon framework and the large density of electrochemically active sites on the surface of hollow carbon, these metal-free materials have been proven to show remarkable performance toward both hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in alkaline media with excellent stability. Highlights • N-, O- and P-doped hollow carbons (NOPHCs) were successfully synthesized. • The materials were synthesized with the assistance of Co 2 P nanoparticles templates. • NOPHCs served as metal-free bifunctional electrocatalysts for HER and ORR. • The hollow structures gave large density of catalytically active sites for electrocatalysis. • Multi-heteroatoms dopants provided beneficial synergistic effects for modulating the adsorption of H 2 O and O 2 on the sites. Abstract To realize clean and renewable energy conversion systems, such as fuel cells and water splitting devices, cost-effective and energy-efficient bifunctional metal-free electrocatalysts are highly needed. Herein, N-, O- and P-doped hollow carbons (NOPHCs) are successfully synthesized via pyrolysis of Co 2 P-containing polypyrrole (Co 2 P@PPY) precursors and removal of Co 2 P templates. The materials are proven to serve as efficient and stable metal-free bifunctional electrocatalysts toward hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) in basic media. Notably, NOPHC 10 -900, which is obtained using 0.10 g of Co 2 P as template and pyrolyzed at 900 °C, exhibits high electrocatalytic performance for HER with a small overpotential of 290 mV at −10 mA cm−2, a low Tafel slope of 102 mV dec-1, and a great long-term stability for 19 h. Moreover, it affords decent electrocatalytic performance for ORR, with positive onset potential, high electron-transfer number, good methanol crossover tolerance and outstanding durability. The excellent electrocatalytic performance is mainly due to the synergistic effect of the multi-heteroatoms dopants in it and the large density of active sites on the surface of the hollow carbons. [ABSTRACT FROM AUTHOR]

• N-doped graphene exhibited high H 2 O 2 yield, selectivity and low EEC as cathode catalyst. • Novel in-situ metal-free EAOPs was developed, and possible catalytic mechanism was explored. • Graphite N and pyridinic N was active sites for H 2 O 2 and OH formation, respectively. • Compared with EF, in situ catalysis was more efficient and less affected by pH 5–11. • It showed excellent stability, reusability and performance for organic pollutants degradation. Highly efficient electrochemical advanced oxidation processes (EAOPs) based on carbon catalysts are promising and green technologies for environmental remediation. Herein, for the purpose of cost-effectiveness, wide pH suitability and excellent reusability, graphite felt modified with regulatable N-doped graphene was developed as a cathode to electrochemically generate H 2 O 2 with high yield and selectivity, and efficiently catalyze H 2 O 2 to form OH for organic pollutants degradation by in-situ metal-free EAOPs. Particularly, the catalytic mechanism of N-doped graphene for enhanced performance was explored. Optimized N-doped graphene showed a very high H 2 O 2 generation rate of 8.6 mg/h/cm2, low electric energy consumption (9.8 kW h/kg) and high H 2 O 2 selectivity of 78.02% in neutral pH solution. Compared with electro-Fenton (EF), this in-situ metal-free EAOPs on N-doped graphene displayed significant improvement on the degradation performance of organic pollutants in neutral and alkaline solutions, and was certified to be less affected by initial pH. The pyridinic N and C C in N-doped graphene enhanced the onset potential while graphite N determined the disk current of oxygen reduction reaction (ORR) process. Most importantly, it proved that the introduction of graphite N could promote the 2e- ORR process for H 2 O 2 generation, and the presence of pyridinic N could catalyze H 2 O 2 to the production of OH. Taken phenol as target pollutant, OH generated by N-doped graphene accounted for 80.72% while O 2 − contributed 19.28% to its degradation, based on which a possible mechanism for phenol degradation was proposed. Moreover, in-situ metal-free EAOPs showed excellent stability, reusability and performance for various organic pollutants degradation. This work would shed light on the catalytic mechanism for metal-free EAOPs, and thus promote its application for organic pollutants degradation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Oxygen reduction reaction catalysts based on bimetallic-organic framework. • Building hierarchical pore structures using soft templates combined with Zn evaporation. • The optimal catalyst exhibits ORR performance comparable to Pt/C in acidic medium. • Efficient and low-cost cathode catalyst for polymer electrolyte fuel cells. Abstract The development of highly active and cost-efficient electrocatalysts toward oxygen reduction reaction (ORR) is essential for widespread application of polymer electrolyte fuel cell (PEFC). In the present work, hierarchically structured porous Co-Zn-N-C electrocatalyst is prepared by using soft templated bimetallic-organic framework precursors. The as-synthesized hierarchically porous catalyst presents outstanding ORR onset-potential (0.88 V vs. RHE), half-wave potential (0.78 V vs. RHE), and diffusion limiting current density (5.73 mA cm−2), that is similar to that at commercial Pt/C catalyst in acidic electrolyte. It is found that the hierarchical porous architecture is important for its excellent catalytic activity and further testifies that the hierarchically porous electrocatalyst also exhibits superior single PEFC performance with a power density of 412 mV cm−2. The present work provides not only a facile and low cost strategy toward the preparation of hierarchically porous materials, but also inspires an approach for enhancing the ORR electrocatalytic activity of MOF-derived materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Herein, we designed a strategy to successfully synthesize a novel bi-functional rambutan-like oxygen electrocatalysts comprising in situ -formed N-doped metal (metal: Fe, Co or Ni) encapsulated carbon nanotubes grown on hollow-mesoporous carbon sphere (denoted as Me@N-CNT/HMCS). Metal acetate can catalyze melamine to generate uniformly distributed N-CNTs nanotubes at the surface of hollow-mesoporous carbon sphere. The Me@N-CNT/HMCS oxygen electrocatalysts with very low metal content show unexpectedly high catalytic activities toward both ORR, which is superior to commercial Pt/C. Especially, the optimized performance of Fe@N-CNT/HMCS is achieved with more positive onset potential (E 0 = 1.012 V) and half-wave (E 1/2 = 0.833 V). Additionally, this result indicated that excellent performance is attributed to the synergistic effect involve chemical composition, good conductivity, high porosity and unique rambutan-like structure. Highlights • We firstly reported a simple strategy to successfully synthesize high-performance bi-functional electrocatalysts of the 1D-3D rambutan-like carbon materials. • The excellent electrocatalytic activity was assigned to the synergistic effect between N doping, metal loading and rambutan-like electrocatalyst morphology. • The theoretical calculation study suggests that metallic Fe cluster can promote the O 2 adsorption strength in such chemical environment. Abstract Electrocatalysis of oxygen reaction is a critical step in operation of fuel cells and metal-air batteries. For the practical applications, the inexpensive non-noble metals catalysts with highly activity and stable need to be explored and utilized. Herein, a strategy for the preparation of a bi-functional rambutan shaped oxygen electrocatalyst is presented. The novel electrocatalyst is formed in situ with N doped carbon nanotubes grown on metal encapsulated hollow-mesoporous carbon sphere (Me@N-CNT/HMCS). The Me@N-CNT/HMCS oxygen electrocatalysts show high catalytic activities towards ORR, comparable to commercial Pt/C catalyst. The optimized performance of Fe@N-CNT/HMCS was achieved with a positive onset potential of 1.012 V and half-wave potential of 0.833 V. It is emphasized that Me@N-CNT/HMCS shows high stability and enhanced tolerance against methanol in alkaline medium. The Fe@N-CNT/HMCS electrocatalyst possessed a high OER activity with a low overpotential of 0.35 V at 10 mA cm−2 current density. The excellent performance could be attributed to the synergistic effect involving chemical composition, high conductivity, good porosity and unique rambutan-like structure. In addition, the theoretical calculation study suggests that metallic Fe cluster can promote the O 2 adsorption strength in such chemical environment. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • S and N doped graphene quantum dots enhanced photocatalytic H 2 O 2 production on TiO 2. • SN-GQDs induced visible light absorption and promoted charge migration. • Much improved formation and mildly inhibited decomposition of H 2 O 2 were observed. • Highly selective two-electron reduction of oxygen was realized on SN-GQD/TiO 2. • SN-GQDs provides active sites for *OOH formation and proton relay. Abstract Photocatalytic production of hydrogen peroxide (H 2 O 2) using water and molecular oxygen as the sole material source is a promising and sustainable solar fuel approach. Herein, we developed an efficient photocatalyst (SN-GQD/TiO 2) for H 2 O 2 syntheses by tuning TiO 2 with sulfur and nitrogen co-doped graphene quantum dots (SN-GQDs). The high luminescent SN-GQDs homogeneously dispersed on TiO 2 surface, which induces the extended visible light absorption and enhanced electron migration. The SN-GQD/TiO 2 exhibited 3.2 times H 2 O 2 yield (451 μmol L−1) as that of bare TiO 2 under simulated sunlight irradiation, which was also significantly higher than that over GQD/TiO 2 and N-GQD/TiO 2. Kinetic evaluations suggested that the formation of H 2 O 2 on SN-GQD/TiO 2 was dramatically accelerated by 2.4 times compared with that on TiO 2 , while the decomposition of H 2 O 2 was moderately suppressed (only 25% reduction). The increased H 2 O 2 formation on SN-GQD/TiO 2 was attributed to the boosted two-electron reduction of oxygen, which was confirmed by the electron transfer numbers (n = 2.2) obtained from Koutecky-Levuch plots, the less sensitivity of H 2 O 2 production to pH, and the insignificant signals for DMPO–O 2 − in ESR measurements. According to theoretical calculations and free energy diagrams of the ORR pathway, a mechanism of proton-coupled electron transfer (PCET) to produce H 2 O 2 was proposed to understand the highly selective two-electron H 2 O 2 production on SN-GQD/TiO 2. This study brings an insight to modulate highly selective two-electron photocatalytic reduction of oxygen by introduction of dual doped GQDs that can provide active sites for *OOH formation and proton relays. [ABSTRACT FROM AUTHOR]

Pt-based nanomaterials are regarded as the most efficient electrocatalysts for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, widespread adoption of PEMFCs requires solutions to major challenges encountered with ORR catalysts, namely high cost, sluggish kinetics, and low durability. Herein, a new efficient method utilizing Co-based metal-organic frameworks is developed to produce PtCo bimetallic nanoparticles embedded in unique nitrogen-doped hollow porous carbon capsules. The obtained catalyst demonstrates an outstanding ORR performance, with a mass activity that is 5.5 and 13.5 times greater than that of commercial Pt/C and Pt black, respectively. Most importantly, the product exhibits dramatically improved durability in terms of both electrochemically active surface area (ECAS) and mass activity compared to commercial Pt/C and Pt black catalysts. The remarkable ORR performance demonstrated here can be attributed to the structural features of the catalyst (its alloy structure, high dispersion and fine particle size) and the carbon support (its nitrogen dopant, large surface area and hollow porous structure). [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon materials with hierarchically mesoporous structure are synthesized in the present work via the pyrolysis of an interpenetrated non-porous metal-organic framework (MOF), viz . [Zn 2 (TPT)(BDC) 2 ]·H 2 O (SCUT-11, TPT = tris(4-pyridyl)triazine, BDC = 1,4-benzenedicarboxylate), as the precursor. X-ray diffraction reveals that the synthesized metal-organic framework (MOF) is of high purity of the crystalline phase, and its structure follows our previously reported SCUT-11. This triply-interpenetrated MOF features high density of Zn cations in their interwoven packing structure, which act as effective pore-forming agent to generate mesopores in final carbon. Physicochemical characterizations reveal that the resultant carbon has high specific surface area and bimodal mesopore size distribution, which originate from the removal of metal oxide and/or metal zinc. These textual features favour both oxygen mass transfer and accessibility of catalytically active sites. Electrochemical results confirm that the resultant carbon, synthesized by pyrolysis at 900 °C, shows a superior oxygen reduction reaction (ORR) activity, which is associated with high onset and half-wave potential up to 1.0 and 0.88 V, respectively. Further investigation suggests that the as-synthesized carbon catalyst exhibits a remarkable insensitivity towards anions, like sulphate and phosphate, compared with the Pt counterpart. The above features make this carbon catalyst promising to be widely used in different fuel cell types. [ABSTRACT FROM AUTHOR]

An ultrathin (thickness 1.0 nm) 2D nitrogen-doped hierarchically porous carbon (2DNHPC) film is developed by the nanocasting method; for comparison, a 3D nitrogen-doped ordered mesoporous carbon (3DNOMC) is also synthesized. Characterizations reveal that 2DNHPC is featured by an extremely high aspect ratio (several hundred) and a bimodal pore distribution. Such a 2D hierarchically porous structure is found to facilitate both the mass transfer of the reactive species and the utilization of active site in the electrode. First, 2DNHPC yields a larger limiting current than does 3DNOMC for the oxygen reduction reaction (ORR), revealing the key role of the low dimensional structure to facilitate the mass transfer. Second, at the loading of 500 μg cm −2 , 2DNHPC shows the same kinetic current with 3DNOMC, indicating that the two catalysts have the same active site and turnover frequency. In comparison, at a lower loading of 250 μg cm −2 , the kinetic current of 2DNHPC remains unchanged, which however seriously deteriorates for 3DNOMC. This result strongly highlights the effect of the carbon dimension on the utilization efficiency of the active site. Finally, it is noted that 2DNHPC yields a comparable ORR electrocatalytic activity and long-term stability with commercial Pt catalyst in both alkaline and acid media. [ABSTRACT FROM AUTHOR]

It is a crucial and challengeable task to develop non-precious metal catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in energy storage and conversion systems. Herein, a facile and cost-effective strategy was employed to prepare the mesoporous nitrogen doped NiFe layered double hydroxide/reduced graphene oxide (NiFe-LDH/NrGO) nanospheres via an one-pot solvothermal reaction by using GO, protonated g-C 3 N 4 nanosheets (p-CNNS), mixed metal salts and alkali as precursors in presence of surfactant. The doping of p-CNNS resulted in the superior ORR activity compared to pristine NiFe-LDH and NiFe-LDH/rGO. The ORR results demonstrated that the NiFe-LDH/NrGO hybrid involved a perfect 4e mechanism with better durability and methanol tolerance ability than commercial 20% Pt/C catalyst in 0.1 M KOH. NiFe-LDH/NrGO also displayed the excellent OER activity with a close onset overpotential to NiFe-LDH/rGO, but a more negative overpotential and a higher current density at η > 300 mV in the same alkaline medium. Overall, the outstanding catalytic performance toward both ORR and OER suggested that the NiFe-LDH/NrGO composite can be a new non-precious metal bifunctional catalyst in the related renewable energy fields. [ABSTRACT FROM AUTHOR]

Many alternatives to typical Pt-based catalysts have been developed to enhance oxygen reduction reaction (ORR) performance in acid medium due to their scarcity and high activation loss during the ORR. We synthesized mesoporous carbon nanostructures with multi-dopants such as iron, nitrogen, and sulfur as a cathode catalyst using the ordered silica templates and porphyrinic iron. The co-doped mesoporous carbon cathode catalysts exhibited a high ORR performance in an acid medium, i.e. complete ORR process and improved durability. The enhanced ORR properties of the catalysts might be ascribed to iron-containing catalytic active sites surrounded by nitrogen/sulfur species and a well-defined mesoporous carbon nanostructure. [ABSTRACT FROM AUTHOR]

A kind of 3D Fe-embedded N doped carbon framework catalyst is successfully developed and tested in the present work as a robust cathode catalyst for microbial fuel cells (MFCs). Due to the well-arranged mesopores, the high surface area, the interconnected conductive networks as well as the finely dispersed Fe-N active species, the as-prepared 3D Fe-N-C catalyst exhibits significantly enhanced ORR activity compared to commercial Pt/C. More precisely, the 3D Fe-N-C yields a more-positive half-wave potential of −0.08 V (vs . SCE) and remarkably stable limiting current of ∼6.2 mA cm −2 . The 3D Fe-N-C shows also an excellent tolerance to methanol as well as remarkably long-term stability with more than 82.4% retention of its initial activity after 55.5 h operation. Based on the as-prepared 3D Fe-N-C as the air cathode catalyst, a stable microbial fuel cell (MFC) device is fabricated and tested, performing a maximum power density of 3118.9 mW m −2 at a high current density of 9980.8 mA m −2 . More importantly, it is found that the Fe-N-C MAFC device could steadily operate for more than 250 h in a feed period, which is substantially longer than the Pt/C-MFC device. [ABSTRACT FROM AUTHOR]

Despite that nitrogen (N) and sulfur (S) co-doped ordered mesoporous carbon (OMC) as Pt-free catalyst for oxygen reduction reaction (ORR) shows a desirable performance, the synthesis method is always complicated and expensive, which greatly hinders its development and application. In the present work, a highly ordered mesoporous N and S co-doped carbon material is developed. The material is obtained by combining hard template and high-temperature pyrolysis method using cheap saccharin as a single-source molecular precursor, SBA-15 as the hard template and FeCl 3 as the catalyst to promote the carbonization process. It is found that the as-prepared SN-OMC catalyst, compared with the commonly used commercial Pt/C (20 wt.%), exhibits comparable ORR electrocatalytic activity with mainly four-electron (4e − ) process, superior stability and inertness to methanol in alkaline media, which could mainly benefit from the highly ordered mesoporous structure and the synergistic effect caused by the dual N and S doping. These advantages render SN-OMC a promising ORR electrocatalyst and a cheap alternative to Pt/C for practical fuel cell applications. [ABSTRACT FROM AUTHOR]

In the present work, graphene nanoflakes (GNFs) were grown at both low and high levels of nitrogen functionalization and subsequently put through a wet-chemical method to add iron functionalities to the surface and create active catalyst centers. No mechanical treatments are used in order to minimize the formation of defects on the GNFs and evaluate if iron-nitrogen-GNF edges or surface sites can generate catalytic activity rather than the macropore structures holding these functionalities on porous carbon black. The catalysts produced under various synthesis routes were characterized and screened for their performance as an oxygen reduction reaction (ORR) catalyst. Characterization included an electrochemical study, an examination of the carbon and nitrogen content and bonding structure, in addition to Raman analysis and the calculation of the BET surface areas. It was found that samples that were both treated with iron acetate and put through pyrolysis produced the most active samples. These samples were composed of graphitic carbon and contained a large amount of pyridinic nitrogen. Additionally, when working with GNFs generated with high levels of nitrogen, no extra nitrogen source was needed during the iron incorporation step. This study further develops the GNF-based catalyst already seen to be a suitable ORR catalyst for the polymer electrolyte membrane fuel cell. [ABSTRACT FROM AUTHOR]

Despite nitrogen doped carbon (N C) materials as metal-free electrocatalysts for oxygen reduction reaction (ORR) have shown desirable performance, the state-of-the-art of N C materials is still far from satisfaction for practical fuel cell applications. In the present work, sulfur (S) and nitrogen (N) dual doped ordered mesoporous carbon (SN-OMC) materials are for the first time successfully obtained by the aid of a convenient method under the same conditions, using polythiophene (PTh) and polypyrrole (PPy) as the precursors, ordered mesoporous silica (SBA-15) as the hard template, and FeCl 3 as the catalyst. The preparation conditions of the adopted method are gentle and easy to control and regulate. The experimental results have demonstrated that the obtained materials possess high ordering degree, large specific surface area and adjustable sulfur and nitrogen contents. It is found that the S 1 N 5 -OMC (the PTh/PPy feeding volume ratio is 0.5:2.5) exhibits excellent ORR electrocatalytic activity in alkaline media with desirable current density, methanol tolerance and long-term stability. Such excellent performance could be attributed to the synergistic effect between S and N, the high density of catalytic sites for ORR provided by high S-N heteroatoms loading, and the excellent mass transfer benefiting from ordered mesoporous pore structure. The present investigation provides a new approach to prepare S and N dual doped mesoporous carbons, which show great potential to be applied as fuel cell cathode electrocatalysts. [ABSTRACT FROM AUTHOR]

A new, two-step nanocasting method was developed to prepare N-doped ordered mesoporous carbon (NOMC) electrocatalysts for the reduction of O 2 to H 2 O 2 . Our strategy involves the sequential pyrolysis of two inexpensive and readily available N and C precursors, i.e. aniline and dihydroxynaphthalene (DHN), inside the pores of a SBA-15 hard silica template to obtain N-doped graphitic carbon materials with well-ordered pores and high surface areas (764 and 877 m 2 g −1 ). By tuning the ratio of carbon sources to silica template, it was possible to achieve an optimal filling of the pores of the SBA-15 silica and to minimise carbon species outside the pores. These NOMC materials displayed outstanding electrocatalytic activity in the oxygen reduction reaction, achieving a remarkably enhanced kinetic current density compared to state-of-the-art N-doped carbon materials (−16.7 mA cm −2 at −0.35 V vs. Ag/AgCl in a 0.1 M KOH solution as electrolyte). The NOMC electrocatalysts showed high selectivity toward the two-electron reduction of oxygen to hydrogen peroxide and excellent long-term stability. [ABSTRACT FROM AUTHOR]

Nitrogen coordinated Fe single atoms (Fe-N x SAs) anchored in carbon support is one of the most efficient electrocatalysts for oxygen reduction reaction (ORR). Engineering the microenvironment of Fe-N x sites to achieve enhanced activity is still challenging. Herein, we theoretically demonstrate that nitrogen dopants in carbon skeletons can optimize the adsorption of ORR intermediates on Fe-N 4 sites. Then, we introduce a rational strategy to anchor Fe-N 4 sites in nitrogen-rich carbon support with abundant tubular channels (Fe-SAs@NCTCs). Fe-SAs@NCTCs exhibits encouraging ORR performance with a half-wave potential of 0.91 V in 0.1 M KOH and 0.80 V in 0.1 M HClO 4. The assembled rechargeable Zn–air battery presents high power density and operates steadily with a narrow voltage gap of 0.76 V for 650 h. The results verify that the outstanding ORR activity can be attributed to the abundant nitrogen dopant, hierarchical porous structure, and abundant tubular channels. [Display omitted] • DFT reveals that Fe-(N-C 2) 4 -2N achieves optimal adsorptions of ORR intermediates. • Fe-SAs@NCTCs possesses abundant Fe SAs in nitrogen-rich carbon support. • Hierarchical porous structure with tubular channels renders rapid mass transport. • Fe-SAs@NCTCs exhibits remarkable ORR performances in alkaline and acidic media. • Zn–air battery assembled using Fe-SAs@NCTCs shows excellent performance. [ABSTRACT FROM AUTHOR]

Dual-atomic-site catalysts (DASCs), as an extension of single-atom catalysts (SACs), have attracted increasing attention owing to the synergistic effect. However, the study of DASCs is still at the early stages and mainly based on metal atom pairs. More experimental and theoretical exploration needed for further guiding the reasonable design of diatomic active sites. Herein, remarkable activity for oxygen reduction reaction (ORR) of Se 1 -NC single-atom catalyst was discovered, and then Fe/Se dual-atom catalysts were constructed to demonstrate the dual-atom sites synergistic effect. Encouraging, the Fe 1 Se 1 -NC catalyst displays significant enhancement for ORR towards Fe 1 -NC and Se 1 -NC in both alkaline and acid electrolytes. Spectroscopic characterizations and theoretical calculations reveal that there are multiple effects for the introduction of Se, especially for supplying new active sites, and effectively tuning charge redistribution and the spin-state of Fe active sites, which presenting a new strategy to improve the electrochemical performance based on the metal-nonmetal dual-atomic-site catalysts. Atomically dispersed metal(Fe) and non-metal (Se) dual atoms anchored on nitrogen-doped carbon for the first time. The co-exist of Fe-N 5 moiety and SeC 2 dual active sites displays significant synergetic enhancement for ORR towards Fe 1 -NC and Se 1 -NC. This work provides a unique insights of atomical introducing of non-metal active sites for rational design of more effective catalysts. [Display omitted] • Metal(Fe) and nonmetal(Se) dual-atom sites are prepared for the first time, which displays significant enhancement for ORR. • DFT calculations indicate that the co-exist of Fe and Se dual-atomic-site is more beneficial to *OH desorption process. • Se atom has several functions: (1) adjust the electronic state of the Fe-N X. (2) Serve as ORR site. (3) Create rich pores. [ABSTRACT FROM AUTHOR]

Highlights: [•] Ionic liquids are promising precursors for nitrogen-doped carbon catalyst for ORR. [•] Use of transition metal in the pyrolysis of IL is important for high ORR activity. [•] The graphitic-N content in the sp2-carbon network is key factor for high ORR. [•] Co is an effective metal compared to Ni for nitrogen-doped carbon catalyst. [Copyright &y& Elsevier]

Highlights: [•] Few-walled carbon nanotubes (FWCNTs) are synthesized by a CVD method. [•] N-FWCNTs are obtained by treatment with polyaniline and pyrolysis at high temperature. [•] N-FWCNTs with only ∼0.5at.% show high activity for oxygen reduction reaction (ORR). [•] ORR activity comparable to Pt-C is observed both in electrochemical cell and alkaline fuel cell. [Copyright &y& Elsevier]

Highlights: [•] We propose an alternative method for doping nitrogen in carbon materials. [•] Nitrogen is successfully doped in carbon black and ketjen black confirmed with Raman and XPS. [•] Nitrogen doped carbons exhibit better electrocatalytic activity with high mass activity. [•] Nitrogen doped KB shows better physical and electrocatalytic characteristics of all samples. [Copyright &y& Elsevier]

Abstract: Pt nanoparticles supported on nitrogen-doped reduced graphene oxide (NRGO) were investigated for use as proton exchange membrane fuel cell catalysts. Artfully, NRGO was synthesized using a lyophilisation-assisted N-doping method, and simultaneous reduction of graphene oxide (GO) was achieved. A nitrogen content as high as 5.06% was obtained with pyridinic-N as the dominant nitrogen species. Pt nanoparticles with an average diameter of 2.5nm were uniformly loaded on NRGO using impregnation methods. Both cyclic voltammetry and oxygen reduction reaction (ORR) measurements revealed a higher catalytic activity and lower losses of the electrochemically active surface area of this novel Pt/NRGO catalyst in comparison to those of the Pt/GO and conventional Pt/C catalysts. Significantly, the catalytic activity of the Pt/NRGO in ORR showed almost no degradation even after 1000 potential cycles, indicating that our new catalysts have excellent stability. A mechanism for improving the ORR activity and the stability of the Pt/NRGO was tentatively proposed and discussed. [Copyright &y& Elsevier]

Abstract: The development of non-noble metal catalysts is of great interest due to their significant potential application in both fuel cell systems and metal–air batteries, particularly when considering long term commercial deployment. In this regard, novel Co-N-S/C non-noble metal catalysts supported on carbon, are synthesized in this study using a solvent-milling method followed by heat-treatment at elevated temperatures. Pyridine is used as the nitrogen-rich ligand for Co-N x precursor complex formation. The morphology and composition of the catalyst are characterized by X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, transmission electron microscopy (TEM) as well as X-ray photoelectron spectroscopy (XPS). Several catalysts containing different amounts of Co are also synthesized. The optimal Co content is found to be in the range of 10–15wt% nominal, in terms of catalytic oxygen reduction reaction (ORR) activity. This catalyst shows high electroactivity for the ORR with a high stability in alkaline media. Using rotating disk electrode measurements, and Koutechy–Levich analysis, the overall electron transfer number in the catalyzed ORR is found to be 3.8–4.0, suggesting the catalyzed ORR is a four-electron transfer process from O2 to H2O. [Copyright &y& Elsevier]

Abstract: N-doped carbon was prepared from dicyandiamide as the source for both carbon and nitrogen. Dicyandiamide was pyrolyzed at 900°C on various metal chlorides (MeCl2·xH2O, Me=Co, Fe, and Ni) to clarify the effects of metal type on the properties of the N-doped carbon. The results showed that electrochemical and physical characteristics of the N-doped carbon were altered by the type of metal seed. The N-doped carbon from Co showed the best performance in oxygen reduction reactions (ORRs) and the order of ORR activity was N-doped carbon from Co>Fe>Ni. Raman and XPS studies revealed that the metal type during pyrolysis step determined degree of sp 2-carbon network, and ORR activity of N-doped carbon was improved as the degree of sp 2-carbon network increased. The effects of the amount of metal precursor on activity of ORRs and rate of H2O2 formation were faint but the carbonization yield of dicyandiamide increased as the amount of metal precursor increased. The catalysts optimized by altering the type and amount of metal seed showed a 0.60V (vs. Ag/AgCl) onset potential and a 42% oxygen reduction reactivity at 0.40V (vs. Ag/AgCl) compared to that of a commercial Pt/C catalyst. [Copyright &y& Elsevier]

Abstract: Non-noble electro-catalysts were synthesized by pyrolyzing dicyandiamide (DCDA) on carbon supported iron oxide at 700°C, 800°C and 900°C. The effects of pyrolysis temperature on electrochemical properties towards oxygen reduction reaction (ORR) were investigated. After pyrolysis, newly generated carbon arising from DCDA was observed in all the catalysts. Especially at 900°C, carbon nanotubes (CNTs) were grown catalyzed by Fe2O3/C. Pyrolysis of DCDA at higher temperatures increased ORR activity significantly. The catalyst exhibiting the best performance towards ORR was Fe2O3/C pyrolyzed with DCDA at 900°C. EDX and XPS experiments revealed that nitrogen atoms from DCDA were doped into carbon and the amount of doped nitrogen increased with increasing temperature. The reason for high reactivity towards oxygen reduction reaction is due to nitrogen doped CNTs grown on Vulcan carbon support. The reactivity increased as the amount of doped nitrogen increased. [Copyright &y& Elsevier]

[Display omitted] • Novel nitrogen-doped aluminum-carbon composite (Al-Gr-N) was fabricated. • Over 2000 mg/L H 2 O 2 could be obtained in Al-Gr-N/O 2 system. • High porous volume and abound doped nitrogen species favored H 2 O 2 formation. • Al-Gr-N/O 2 system was effective to treat the landfill leachate. Herein we prepared a novel nitrogen-doping aluminum-graphite (Al-Gr-N) composite and applied for generating and activating H 2 O 2 to treat the landfill leachate. The results showed that Al-Gr-N composite could significantly enhance H 2 O 2 yield by oxygen reduction reaction (ORR), about 3 times higher than that of aluminum-graphite (Al-Gr) composite, due to its abundant N species, higher content of defects carbon atoms, higher surface area and porous volume, which enhanced the activity and selectivity toward two-electron pathway of ORR by increasing electron density, and promoting the mass transfer of reaction intermediates. The H 2 O 2 concentration achieved 2049 mg/L. The H+ from the hydrolysis of in-situ generated Al3+ could improve the ORR process, leading to high efficient production of H 2 O 2 at wide pH range. The in-situ generated Al3+ could act as the coagulant to enhance the pollutant removal. This composite could effectively treat landfill leachate due to its high H 2 O 2 and nascent aluminum. [ABSTRACT FROM AUTHOR]

• The structure of isolated Pt and Fe single atoms anchored on nitrogen-doped carbon is firstly prepared. • The PtFeNC delivers a high half-wave potential of 0.895 V for ORR. • The primary ZAB based on PtFeNC exhibits a high energy density of 807 mA h/g at 10 mA/cm2. Fabrication of Pt-based electrocatalysts with high activity and excellent durability is critical for the practical applications into zinc-air battery (ZAB). In this work. A novel strategy for the encapsulation of Pt species into the cavities of Fe-doped zeolite imidazolate framework is proposed to increase the density of active metal atoms and improve the activity effectively, where both isolated Pt and Fe single atoms anchored on nitrogen-doped carbon (PtFeNC) are obtained by a simple pyrolysis. Impressively, PtFeNC delivers a half-wave potential of 0.895 V (vs. RHE), Moreover, PtFeNC exhibits a lower yield of peroxide species than FeNC. Importantly, the ZAB battery shows a specific capacity of as high as 807 mA h/g at a discharge current density of 10 mA/cm2. Our findings show that dual- and multi- metallic single atom catalysts with abundant active sites can be achieved to boost electrocatalytic activity for their practical applications in energy storage though the new tactic. [ABSTRACT FROM AUTHOR]

• Novel core-shell FeCoMoS@NG was fabricated by simple and cost-effective method. • FeCoMoS@NG catalyst exhibits an excellent ORR activity with E 1/2 of 0.83 V vs. RHE. • FeCoMoS@NG shows better performances of OER (Eη 10 = 238 mV) and HER (Eη 10 = 137 mV). • FeCoMoS@NG based zinc-air battery shows a peak power density of 118 mW cm−2. • High efficient water splitting driven by FeCoMoS@NG based zinc–air battery devices. Emerging demands for the highly active, durable, and cost-effective trifunctional catalysts for overall water splitting and metal–air batteries in the scientific community. Herein, a novel strategy is demonstrated for the rational design of hierarchical iron cobalt molybdenum sulfide nanoflower encapsulated in nitrogen doped graphene (FeCoMoS@NG) through a facile, cost-effective, and single-step in-situ hydrothermal process. Owing to its hierarchical nanostructures, larger specific surface area, and exclusive porous networks, the optimal FeCoMoS@NG shows excellent catalytic activities for OER ƞ10 = 238 mV, HER ƞ10 = 137 mV, and ORR (0.83 V vs RHE). Most significantly, FeCoMoS@NG||FeCoMoS@NG water splitting device achieves a cell voltage of 1.58 V at 10 mA cm−2. Furthermore, FeCoMoS@NG based zinc–air battery endows a high power density of 118 mW cm−2, and overall water splitting was successfully driven by FeCoMoS@NG based zinc–air battery. This work provides new pathway for designing highly active and durable multifunctional catalysts for energy conversion and storage applications. [ABSTRACT FROM AUTHOR]

• A new Fe x N (x = 2, 3, or 4) has high catalytic activity towards ORR. • The Fe x N/NC shows an excellent methanol/CO tolerance. • The Fe x N/NC is promising candidate to replace the Pt based cathodic catalyst in Zn-air batteries. In this work, we have found that a new Fe-N module, Fe x N (x = 2, 3, or 4), in which the N atoms insert the lattice of Fe matrix, also has high catalytic activity towards ORR. We synthesized the Fe x N module embedded N-doped carbon material (Fe x N/NC) via a facile metal-organic framework (MOF)-templated approach. The as-synthesized Fe x N/NC shows a superb catalytic ORR activity as well as high methanol tolerance. The highly efficient catalytic active sites (Fe x N module and well-doped N species) were mainly responsible for the superb ORR activity. The synergistic mechanisms of the N-doped carbon support and Fe x N moieties for ORR at molecular level were elucidated by density functional theory calculations. The excellent catalytic ORR performance make the Fe x N/NC catalyst be a promising candidate to replace the expensive Pt based cathodic catalyst in Zn-air batteries. [ABSTRACT FROM AUTHOR]

An exclusively pyridinic nitrogen doped carbon material is rationally designed and precisely synthesized with a bottom-up method, which exhibits excellent performance for oxygen reduction reaction and superior stability for Zn-air battery. • A pyridinic N exclusively doped carbon material, named as PyN-GDY, is prepared by an ingenious cross-coupling reaction. • The PyN-GDY exhibits higher activity than commercial Pt/C for oxygen reduction reaction in alkaline medium. • The Zn-air battery with PyN-GDY as cathode exhibits superior stability and a higher activity than Pt/C-based battery. Rational design a metal-free catalyst with well-defined structure as alternative of noble metal is highly desirable but challenging to catalyze oxygen reaction for metal–air batteries. In this report, nitrogen with a specific configuration is selectively doped into the carbon skeleton to prepare a graphdiyne-like carbon material, in which one carbon atom in every benzene ring of graphdiyne (GDY) is substituted by pyridinc N (PyN-GDY). Composed by pyridine ring and acetylenic linkers, the PyN-GDY is prepared through a bottom-up strategy using pentaethynylpyridine as the monomer. The as-synthesized PyN-GDY with "defined" molecular structure is an ideal model for addressing the intrinsic activity of active sites at molecular level. It exhibits excellent performance in both alkaline and acidic media as electrochemical catalyst for oxygen reduction reaction (ORR). The PyN-GDY-based Zn-air battery is demonstrated more active and stable than commercial Pt/C-based battery. Density functional theory calculations are used to analyze and determine the possible active sites of PyN-GDY in ORR. The precise construction of specific nitrogen doped carbon material is an effective method to produce efficient catalysts for electrocatalysis. [ABSTRACT FROM AUTHOR]