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• An ultrafast and one-step controllable deflagration strategy is reported. • Gram-scale synthesis of ORR catalyst in hundreds of milliseconds is realized. • Excellent ORR performance and high durability has been achieved. • The formation mechanism of Co 3 O 4 quantum dots is proposed. Transition metal quantum dots (QDs) are ideal electrocatalysts due to their short ion diffusion path, high atom utilization and effective electron transfer properties. However, a lack of facile and large-scale synthesis strategy limits their industrial production and commercial application. In this study, a triaminoguanidine salt-induced one-step deflagration method is first reported for the ultrafast (hundreds of milliseconds) and gram-scale synthesis of Co 3 O 4 QDs-C 3 N 4 /rGO as an efficient oxygen reduction reaction (ORR) catalyst with high durability. The deflagration reaction process is carefully studied and the formation mechanism is proposed to explain the controllable synthesis of Co 3 O 4 QDs. An optimized sample is capable of achieving an excellent ORR performance in terms of an onset potential of 0.97 V (vs. RHE, equivalent to Pt/C) and the limited current density of −5.33 mA·cm−2 at 0.35 V (vs. RHE, ~7% higher than that of Pt/C). It is believed that this simple and effective synthesis strategy will open up an exciting new avenue to the future design and facile synthesis of Co 3 O 4 or other QDs-based functional materials. [ABSTRACT FROM AUTHOR]

• Fe-Co dual-metal doped N-coordinated graphene (Fe-Co-N-C) are investigated. • The activity of Fe-Co-N-C with different active sites for ORR and OER is tunable. • Active sites FeCoN 7 and FeCoN 8 possess a better bifunctional activity. • The extremely low overpotential of 0.22 V for both ORR and OER can be obtained. • The d-band center of Co atom is directly relevant to the activity of Fe-Co-N-C. Identifying the atomic-scale structures of active sites is crucial to develop Fe-Co dual-metal doped N-coordinated graphene (Fe-Co-N-C) as a promising electrode material for fuel cell or metal-air batteries but remains debatable. Here the catalytic performance of Fe-Co-N-C with different active sites, including FeCoN 6 , FeCoN 7 , and FeCoN 8 , towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is systematically studied by density functional theory calculations. We show that the stability and catalytic activity of Fe-Co-N-C for ORR and OER would be affected by the atomic-structures of active sites, and Fe-Co-N-C with active sites of FeCoN 7 and FeCoN 8 possess a better catalytic performance compared with FeCoN 6. The top site of Co atom is the main active center responsible for ORR and OER in active sites of FeCoN 7 and FeCoN 8 , in which the extremely low overpotential of 0.22 V for both ORR and OER can be obtained by regulating the atomic-structure of the active site. Importantly, we plot the relationship curve between the d-band center of Co atoms and overpotentials of ORR and OER on Fe-Co-N-C, which can link the atomic-structure of active sites to catalytic performance. These findings are great significance for the scientific design of efficient bifunctional catalysts. [ABSTRACT FROM AUTHOR]

• Nitrogen atoms were in situ doped into carbon cloth. • The catalyst is flexible and self-standing. • The catalyst sheet can be directly as assembled in a zinc-air battery as ORR catalyst and current collector of cathode. • The catalyst is a good substrate for powder ORR catalyst. Nitrogen doped carbon materials have attracted tremendous attention as the promising candidates for platinum-based catalysts toward oxygen reduction reaction (ORR). Herein, we report a facile preparation of N-doped carbon cloth (Co-N-OCC) as a flexible and self-standing electrocatalyst toward ORR by calcining oxidized carbon cloth coated with cobalt ions in ammonia atmosphere. The pyridinic N, Co-N and pyrrolic N, related to ORR activity, are the dominant configurations of nitrogen with an atomic ratio of 42.27%, 25.36% and 20.29% in the catalyst. The resulting Co-N-OCC shows favorable ORR activity with an onset potential of 0.87 V vs. RHE, an electron transfer number of 3.57, and good methanol tolerance in alkaline electrolyte. Co-N-OCC catalyst sheets were directly assembled in zinc-air battery as catalyst and current collector of cathode. The ORR catalytic performance of Pt/C is further boosted in a zinc-air battery by using the Co-N-OCC sheet as an electrode substrate. [ABSTRACT FROM AUTHOR]

• Nb-TiO 2 nanotubes were prepared as catalyst support for ORR by a hydrothermal method. • Well-dispersed Pt nanoparticles on the support show high activity and stability. • 6.0 wt% Pt/Nb-TiO 2 nanotube exhibited more improved activity and durability for ORR. Platinum is the most effective catalyst for oxygen reduction in proton-exchange membrane fuel cells (PEMFCs). Nevertheless, significant problems must be addressed for the effective use of Pt, such as the extremely low Pt utilization in the electrocatalysts and low durability due to corrosion of the support. Here, we present a promising approach for addressing these challenges by the facile synthesis of Nb-TiO 2 nanotubes as efficient support for Pt-based electrocatalysts. The Pt/Nb-TiO 2 nanotubes led to a marked enhancement of the oxygen reduction reaction kinetics, attributed to the increased electronic conductivity and strong metal-support interaction of the Nb-TiO 2 support. Moreover, compared to the state-of-the-art conventional Pt/carbon catalyst, the Pt/Nb-TiO 2 nanotubes show high durability because of their structural stability and retention of the high surface area during post-processing. The mass activity of the conventional Pt/C decreased by 37% after the ADT (126.9 and 80.1 A g−1 Pt before and after ADT, respectively), whereas that of Pt/Nb-TiO 2 was merely reduced by 22% (285.1 and 222.6 A g−1 Pt before and after ADT, respectively). [ABSTRACT FROM AUTHOR]

• Electrocatalytic activity of the CoFe 2 O 4 /C for ORR was improved after sonication. • Ultrasonic process enriched the Co2+ and Fe3+ cations on surface of CoFe 2 O 4 /C. • The Ultrasonic treatment improved stability of CoFe 2 O 4 /C catalyst. • More cations occupied tetrahedral than octahedral sites after sonication. Since ultrasonication was reported to be used for exfoliation of layered materials in water (Science-ref. 31), the method has never been explored in non-layered materials, in particular, the effect of ultrasonication on the surface property of materials. In this work, CoFe 2 O 4 /C nanoparticles were synthesized and processed using ultrasonic treatment in water. Through the ultrasonic treatment, the electrocatalytic activity of the CoFe 2 O 4 /C nanoparticles towards ORR was improved significantly with a higher mass activity (5.05 mA mg−1) than the original CoFe 2 O 4 /C (2.75 mA mg−1) in O 2 -saturated 0.1 M KOH solution. The half-wave potential on the original CoFe 2 O 4 /C was also shifted to the positive side by 60 mV. Furthermore, the treated CoFe 2 O 4 /C catalyst exhibits a constant half-wave potential with better onset potential after 2000 cycles, and a 50 mV of half-wave potential on the original catalyst was moved to negative under same test condition. The analysis from characterizations reveals that the enhanced ORR performance of the treated CoFe 2 O 4 /C resulted from the Co2+ and Fe3+ enriched surface with more cations being occupied in the tetrahedral sites than the octahedral sites after ultrasonic treatment. In addition, compared to the original CoFe 2 O 4 /C catalyst, the specific surface area of the treated CoFe 2 O 4 /C was improved 1.8 times, mesoporous grown to microspores with 2.2 times increased volumes, which has provided higher active sites and accelerated transport between O 2 and electrolyte during the ORR process. The ORR via the 4-electron transfer pathway on the treated CoFe 2 O 4 /C catalyst, while the 2-electron transfer process is favoured on the original CoFe 2 O 4 /C catalyst. This further signifies that the ultrasonic process had significantly influence on the electrochemical properties of the CoFe 2 O 4 /C catalyst. [ABSTRACT FROM AUTHOR]

• Fe-N-C films are co-sputtered from iron and carbon targets in a reactive nitrogen on glassy carbon substrates. • Thin films deposited at high temperature are smoother than the films annealed at high temperature. • Oxygen reduction reaction activity is greater for high-temperature samples than for the room-temperature samples. • High temperatures lead to increased graphitization of the carbon and increased hydrogenation of nitrogen. Electrocatalysts for the oxygen reduction reaction (ORR) based on complexes of iron and nitrogen in a carbon matrix (Fe-N-C) are a promising alternative to platinum group metal (PGM) based catalysts in polymer electrolyte membrane (PEM) fuel cells. Further improvements of Fe-N-C catalysts would benefit from model thin film studies of activity and stability of catalytic sites, but synthesis of Fe-N-C model thin films is challenging. Here we report on synthesis and characterization of Fe-N-C thin films produced by co-sputtering iron and carbon in a reactive nitrogen atmosphere onto removable glassy carbon rotating disk electrode (RDE) tips. Scanning electron microscopy (SEM) measurements indicate that the Fe-N-C films deposited at high temperature are smoother than the films annealed at high temperature. Electrocatalytic activity measured on the thin Fe-N-C films is greater for both high-temperature samples than for the room-temperature sample. From the analysis of X-ray photoelectron spectroscopy (XPS) data, exposure of the films to high temperatures results in increased graphitization of the carbon within the Fe-N-C films, and increased relative amount of graphitic and hydrogenated nitrogen species. Overall, the results of this study demonstrate the feasibility of a thin film model system approach for studying active sites in PGM-free catalysts. [ABSTRACT FROM AUTHOR]

• Hierarchical C-N/Co/Ti composite derived from MOF/TBOT precursor is obtained. • Structure consists of dodecahedron-like particles covered with twisted nanotubes. • Ti and Co are effectively separated in the upper and lower ends of nanotubes. • C-N/Co/Ti eletrocatalyst exhibits superior ORR properties than that of Pt/C. • Novel mechanism is ascribed from the phase composition and microstructure. C-N/Co/Ti composites derived from ZIF-67@TiO 2 precursors have been fabricated by a facile thermal treatment process. The morphology and composition are highly dependent on the available parameters inferring of exact hydrolysis of tetrabutyl titanate and sintering temperature. The obtained hierarchical microstructure is composed of numerous dodecahedron-like hollow boxes decorated with in-situ growth of size-tunable and twisting nanotubes on surfaces. The effective elemental separation of Ti and Co on the upper and lower ends of nanotubes can be realized by regulating the ionic migration and crystalline phase formation process at a high temperature. The as-prepared C-N/Co/Ti composites exhibit the enhanced electrocatalytic activities to oxygen reduction reaction (ORR) via a favorable four-electron pathway and the desired reaction kinetics with the low Tafel slope (67.8 mV dec−1), as well as the excellent methanol tolerance in comparison with the Pt/C electrocatalysts. The superior ORR electrocatalytic performance would be mainly contributed to the combination of the designed multi-phase composition, the enhanced surface adsorption/desorption, the modified surface/interface electron transfer mechanism, and the constructed Co/Ti double-active sites on different locations of microstructure. The present work presents a new insight for the synthesis of C-N-based inorganic composite with outstanding electrocatalytic behavior for ORR process. [ABSTRACT FROM AUTHOR]

• FeCo-OMPC is exploited as catalyst for both electrodes in EBC. • FeCo-OMPC is used for ORR, while GOx/[FeCo-OMPC/CNT] is prepared for GOR and HPOR. • FeCo-OMPC/CNT shows high activity to HPOR A. • The membraneless shows the MPD of 21.3 μW cm−2 with OCV of 0.17 V. • FeCo-OMPC based catalyst can be used for the implantable bioelectronics. Iron and cobalt co-doped ordered mesoporous porphyrinic carbon (FeCo-OMPC) is employed as the catalyst for both electrodes in membraneless enzymatic biofuel cells (EBCs). FeCo-OMPC is used for catalyzing oxygen redox reaction (ORR), while GOx/[FeCo-OMPC/CNT] is utilized as a catalyst for a series of glucose oxidation reaction (GOR) and hydrogen peroxide oxidation reaction (HPOR). The onset potential of the ORR by FeCo-OMPC is 0.31 V vs. Ag/AgCl, while that of HPOR by FeCo-OMPC/CNT and GOR-HPOR by GOx/[FeCo-OMPC/CNT] are both 0.12 V. The activity of this catalyst is better than previously reported similar catalysts due to the presence of Co species and high metal contents. As a result, the concentration of H 2 O 2 generated by GOR is 1.02–1.56 mM when the same glucose concentration as human blood is used. In addition, the EBC using GOx/[FeCo-OMPC/CNT] and FeCO-OMPC shows the maximum power density of 21.3 ± 2.97 μW cm−2 with open circuit voltage (OCV) of 0.17 ± 0.016 V. These values are significantly higher than those of EBC using the competitive Fe–N/CNT catalyst (0.11 V and 9.6 μW cm−2). Moreover, the OCV is close to the expected value by CV (0.19 V), confirming that the FeCo-OMPC catalyst can be used for implantable bioelectronics, such as biosensors and electroceuticals. [ABSTRACT FROM AUTHOR]

• The doped graphene with sp3 hybridization is more energetically profitable. • O 2 molecule can be directly dissociation on the G-PN 2 C 1 and G-PN 3. • The intensely adsorption is due to hybridize of p states of P and O atoms. • It is react more favorable for the ER mechanism of OH* to convert into H 2 O. • The G-PN 3 system is investigated to have lower overpotential. The density functional theory (DFT) calculations in this study were applied to investigate the oxygen reduction reaction (ORR) mechanism of non-equivalent P, N co-doped graphene. The simulation results showed that the formation of sp3 hybridization was energetically more profitable than that of the sp3d hybridized doped form. O 2 molecules directly dissociated on G-PN 2 C 1 and G-PN 3 by following the Eley-Rideal (ER) mechanism, which involves H 2 O formation by reaction with H+ from the electrolyte. Furthermore, G-PN 3 was found to perform better as ORR catalysts in an acidic medium due to their low overpotentials of 0.419 V. In contrast, G-PN 3 C 1 and G-PN 4 tended to follow the OOH* formation pathway, which showed a higher overpotential for the ORR. X-ray photoelectron spectroscopy (XPS) analysis and electrochemical experiments were performed to verify the calculation results, which indicated that the appropriate proportions of G-PN 3 led to greatly improved ORR performance in the following order: G-N < G-P 1 N 1.5 < G-P 1 N 2.1 < G-P 1 N 2.9. Therefore, enhanced catalytic performance for the ORR in an acidic medium can be achieved by controlling the proportions of N and P in the P, N co-doped graphene, so that we can design an efficient non-metallic catalyst for the cathode of proton-exchange membrane fuel cells. [ABSTRACT FROM AUTHOR]

• The preparation of nanofibrous cellulose and waste PVB composites via electrospinning method. • The fabrication of highly porous nanofibers by facile carbonization and KOH activation process. • The large surface area and defective graphitic layers by volatiles of waste polyvinyl butyral. Waste polyvinyl(butyral) (W-PVB) collected from the windshields of end-of-life vehicles has drawn considerable interest as a complementary and abundant resource. However, large amounts of W-PVB are still being buried in landfills every year owing to a lack of recycling techniques. As an alternative, we report the fabrication of carbon nanofibers from natural cellulose and W-PVB composites using a facile electrospinning, carbonization, and KOH activation approach. Interestingly, volatiles and residual carbon from a W-PVB matrix through carbonization produce highly porous carbon nanofibers and a defective graphitic surface layer, respectively. As a result of the large surface area (698.1 m2 g−1) and pore volume (0.2919 cm3 g−1) from abundant micropores, as well as the high density of active sites from defects, resulting carbon nanofiber shows a superior performance in environmental applications. It serves as a metal-free and un-doped carbon catalyst with a half-wave potential of 0.76 V vs RHE for the oxygen reduction reaction and a 99.6% removal of rhodamine B from water as an adsorbent for water remediation. This simple strategy can open a new approach to the design and synthesis of various classes of W-PVB-based composites, which will broaden the reuse of W-PVB in renewable and sustainable applications. [ABSTRACT FROM AUTHOR]

• Electrodeposited PtNiCu catalysts were prepared for the oxygen reduction reaction. • The alloy composition strongly affected the morphology and crystalline structure. • PtNiCu exhibited high activity and resistance to H 3 PO 4 poisoning. • Good stability was achieved with the optimal binder. One of the main issues hindering the commercialization of high-temperature polymer electrolyte membrane fuel cells (HT-PEMFCs) is their poor activity and stability in the presence of H 3 PO 4. In this study, PtNiCu ternary catalysts with various compositions for oxygen reduction reaction (ORR) were prepared by a simple electrodeposition technique. The morphologies and crystalline structures were found to depend on the alloy composition. Furthermore, electrochemical characterization in the presence of poisoning phosphate anions, clearly showed that the PtNiCu catalyst exhibited 5.5-fold higher specific activity than Pt 100. The half-wave potential of the PtNiCu catalyst was also approximately 160 mV higher than that of Pt 100. From the stability test, it was confirmed that Pt 100 was severely deteriorated, where the amount of performance loss was dependent on the binders and H 3 PO 4. However, the performances of the PtNiCu during the potential cycling in the presence of H 3 PO 4 were substantially higher than that of Pt 100 regardless of the binders, suggesting the high resistance of the PtNiCu to phosphate adsorption as well as its superior ORR activity. Among the competing binders, the PtNiCu–PVDF catalyst has good stability over 4000 potential cycles, suggesting its use as a highly promising ORR catalyst for HT-PEMFCs. [ABSTRACT FROM AUTHOR]

• ZnS decorated N, S co-doped porous carbon polyhedron are synthesized. • A small fraction of ZnS can greatly improve the ORR activity of the catalyst. • The ZnS@NC-3 shows comparable ORR activity with 20 wt% Pt/C catalyst. • The Zn-air battery using ZnS@NC-3 shows an open circuit voltage of 1.524 V. • The Zn-air battery exhibit a power density of 176 mW cm−2 and a specific capacity of 736 mA h g−1. Developing low cost, environmentally friendly and high efficiency oxygen reduction reaction (ORR) electrocatalysts is critical for clean energy conversion and storage devices including fuel cells and metal-air batteries. Herein, we developed a facile method to doping N, S and ZnS into carbon framework simultaneously. The N, S co-doping and extra ZnS active sites could prominently enhance the ORR performance of the carbon. The optimized sample ZnS@NC-3 exhibit an onset potential of 0.94 V and a half-wave potential of 0.84 V, which is comparable to 20 wt% Pt/C. In addition, the methanol tolerance and cycle ability are obvious superior than that of Pt/C. Moreover, when used as electrocatalysts for Zn-air battery, the battery exhibits an open circuit voltage of 1.524 V, a high specific capacity of 736 mA h g−1 and a max power density of 176 mW cm−2, demonstrating its great potential for clean energy conversion. [ABSTRACT FROM AUTHOR]

3D HPN-GCNS/Co@CoO x as catalysts for ORR: The hybrids were fabricated by a controllable grading-pyrolysis strategy. The hybrids show 3D fluffy and hierarchically porous nanostructure in and out-of-plane, resulting in large accessible specific activity area, allowing the species to efficiently participate in ORR and facilitating the fast mass transfer; the graphene-like C nanosheets with N-rich dopant promote O 2 adsorption and assure fast electron transport; large numbers of Co@CoO x -based nanoparticles uniformly embedded on the C nanosheets and mesoporous active edge introduce more ORR active sites. The remarkable features synergistically enhance the ORR catalytic efficiency, making it a promising low-cost, highly efficient ORR catalyst. • The hybrids were successfully fabricated by a controllable grading pyrolysis strategy. • Graphene-like C nanosheets with N-rich dopant show in and out-of-plane nanostructure. • Co-based nanoparticles uniformly embedded on fluffy and hierarchically C nanosheets. • The remarkable features synergistically enhance the ORR catalytic efficiency. Here, Co@CoO x -based three-dimensional nitrogen-doped graphene-like carbon nanosheets (denoted as 3D HPN-GCNS/Co@CoO x) are fabricated by controllable grading-pyrolysis strategy, in which they show 3D fluffy and hierarchically porous nanostructure in and out-of-plane; large numbers of Co@CoO x -based nanoparticles uniformly embedded on graphene-like C nanosheets and mesoporous active edge introduce more ORR active sites. When applied for ORR, hybrids exhibit a half-wave potential (E 1/2) of 0.87 V and an onset potential (E onset) of 0.92 V in 0.1 M KOH, comparable to that of commercial 20% Pt/C. The hybrids display better methanol tolerance and stability, with almost no change of ORR performance before and after 5000 cycles. H 2 O 2 yield in ORR process is less than 5% and number of electron transfer is higher than 3.9. The remarkable features are mainly ascribed to synergistic enhancement effect, in which 3D fluffy and hierarchically porous nanostructure in and out-of-plane supplies large accessible specific activity area, allows species to efficiently participate in ORR and facilitates fast mass transfer; graphene-like C nanosheets with N-rich dopant promote O 2 adsorption and assure fast electron transport; large numbers of Co@CoO x -based nanoparticles introduce more ORR active sites. All the advantages synergistically enhance the ORR efficiency and make it a highly efficient ORR catalyst. [ABSTRACT FROM AUTHOR]

• Pt-Au/GNs with variable ratio of Pt:Au were obtained by a microwave assisted method. • Heterostructure of Pt (0) and Au (0) in Pt-Au/GNs was formed with Pt:Au of 1:0.1. • Pt-Au/GNs behave as bifunctional catalysts for catalyzing both MOR & ORR. • Pt-Au/GNs with lower Au content show superior electro-catalytic activity. • Pt-Au/GNs with higher Au content exhibit better electro-photo catalysis due to Au SPR. A facile microwave assisted strategy was used to synthesize a series of Pt–Au/graphene (simplified as Pt–Au/GNs) catalysts with controllable Pt:Au ratios, in which K 2 PtCl 4 , HAuCl 4 and graphite oxide were synchronously reduced using ethanol as a reducing agent. When a lower amount of Au is added, Pt and Au species form the heterostructure in Pt-Au/GNs composites, while as Au content increases further, excess Au particles are easy to agglomerate. Electrochemical experiments show that Pt–Au/GNs composites with lower Au content exhibit advantageous electrocatalytic performances and stability simultaneously towards methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). What's interesting is that, under simulated sunlight irradiation, Pt-Au/GNs composites with higher Au content behave superior electro-photo catalytic activities towards MOR and ORR, which is proportional to the size and content of Au. Comprehensive consideration of catalytic performance and cost, Pt–Au/GNs with the optimal Pt: Au ratio of 1:0.1 can serve as an efficient bifunctional electro-photo catalyst for catalyzing MOR and ORR. [ABSTRACT FROM AUTHOR]

A moderate content of MgO is highly required to optimize active species and thus bifunctional OER/ ORR activity. • Inactive MgO are applied to develop MgO-Co/N-doped carbon (NC) for OER/ORR. • MgO with moderate content can optimize active species for OER/ORR. • The optimal MgO-Co/NC shows highly bifunctional OER/ORR activity and durability. MgO-Co/N-doped carbon (NC) as highly efficient bifunctional electrocatalyst toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) was developed by a facile two-step pyrolysis method. The resulting electrocatalysts have a hybrid nanostructure of MgO-Co hybrid nanoparticles coated with NC shells. Although MgO itself is inactive for both OER and ORR, it still plays important roles in enhancing OER and ORR activity of MgO-Co/NC electrocatalysts. Of importance, a moderate content of MgO is highly required. Specifically speaking, MgO with moderate content is favorable for the resulting MgO-Co/NC electrocatalysts to achieve high ratios of O vacancy/total O (~0.46), graphitic-N/total N (~0.30) and Co3+/Co0 (~10.33), thus benefitting OER activity. Moreover, a moderate content of MgO also facilitates the formation of the abundant active Co2+ species and a high Co2+/Co0 ratio (~9.56) is obtained in the resulting MgO-Co/NC, which is in favor of ORR activity. The optimized electrocatalyst shows a low E j=10 (~1.56 V) for OER and a high value of E 1/2 (~0.85 V) for ORR. Its overall bifunctional activity of Δ E (Δ E = E j=10 − E 1/2) is as low as ~0.71 V. Its outstanding OER/ORR activity and bifunctional activity are comparable or even superior to precious metal electrocatalysts and recently reported Co-based bifunctional electrocatalysts. [ABSTRACT FROM AUTHOR]

• A N,B,F-tridoped 3D carbon network is prepared through a NH 4 BF 4 triggered self-assembly of chitosan chain. • The as prepared catalyst demonstrate impressive ORR catalytic performance. • The as constructed zinc-air battery demonstrates high power density and good cycling stability. Nanoarchitecture design and electronic structure engineering are critically important for efficient electrocatalysis. Designing a multi-heteroatoms doped carbon with three dimensional nanoarchitectures can efficiently modulate the electronic structure, create more defective sites and offer a 3D electric conductive circuit, which however has been encountering difficulties in preparation. This work demonstrates the construction of a N,B,F-tridoped 3D carbon network through a novel NH 4 BF 4 triggered self-assembly of chitosan chain. Such a unique structure presents abundant surface active edge defects and in-plane nanopore defects. Density functional theory calculations reveal the significant coupling effect of N,B,F-tridoping down to the atomic scale, whereby the strong electronegativity of F (χ = 4.0) can positively charge the carbon matrix and contribute more adjacent carbon active sites. This endows the catalyst with impressive Pt like oxygen reduction reaction (ORR) catalytic performance, with a high onset potential of 0.95 V, half-wave potential of 0.818 V (vs RHE), and limiting current density of 6.0 mA cm−2. The as constructed zinc-air battery demonstrates a maximum power density of 175 mW cm−2, along with almost unchanged voltage after 25 h galvanostatic discharge. [ABSTRACT FROM AUTHOR]

• Highly Efficient electrocatalyst was constructed by using template-assisted approach. • Fe nanocrystals, high content of active sites and porous structure contributed to the remarkable ORR performance. • It opens up a general way to design of TM, N-decorated 3D porous electrocatalysts. Rational engineering of simple, economical and durable nonprecious metal electrocatalyst with excellent oxygen reduction reaction (ORR) activity is crucial for the electrochemical energy conversion devices, such as metal-air batteries and fuel cells. Here, we developed a highly efficient ORR electrocatalyst with rich and well-dispersed Fe-N x active sites and iron nanocrystals decorated three dimension (3D) porous carbonaceous matrix by a rational designed carbonaceous spheres templated strategy. The fabricated electrocatalyst exhibits outstanding ORR activity with onset potential of 1.0 V and half-wave potential of 0.90 V versus reversible hydrogen electrode in alkaline media, which is much better than benchmark Pt/C. In addition, it presents particularly better performance in terms of superior stability and excellent methanol tolerance capacity. Experimental studies display that the remarkable ORR activity primarily originates from the synergetic effect of rich Fe-N x active sites, sufficient carbon encapsulated metallic iron nanocrystals and desired meso/microporous structure. What worth to point out is that the facile synthetic technique can be extended to fabricate other low cost highly active transition metal-N-carbon scaffolds ORR electrocatalysts. [ABSTRACT FROM AUTHOR]

• A N-doped porous carbon electrocatalyst embedded with cobalt nanoparticles is synthesized. • The maximum power density of Co/N-C-800 is 1738 ± 40 mW m−2, 44.5% higher than that of Pt/C. • Pyrolysis promotes the reduction of cobalt and expansion of surface area. • Graphitic-N, Co(0) and cobalt oxide synergistically promote exposure of active sites and speed 4-electron transfer process. High-performance porous carbon embedded cobalt nanoparticles derived from chitosan, which is applied to microbial fuel cell as cathode catalyst, is prepared using one-step high-temperature calcining method. The nitrogenous porous carbon embedded cobalt nanoparticles treated at 800 °C (Co/N-C-800) is a high-efficiency electrocatalytic material due to its low electron transfer resistance and high exchange current density. The maximum power density of Co/N-C-800 is 1738 ± 40 mW·m−2, which is 44.5% higher than that of Pt/C (1203 ± 18 mW·m−2). In fact, the high specific surface area of 335.08 m2·g−1 for the porous carbon can provide an adequate amount of oxygen and exposed active sites that contribute to the oxygen reduction reaction. Moreover, the graphitized carbon, graphitic nitrogen and cobalt nanoparticles are all involved in the improvement of oxygen reduction reaction performance. In brief, porous carbon with external cobalt nanoparticles is a promising catalytic cathode due to its low cost, facile synthesis and excellent performance. [ABSTRACT FROM AUTHOR]

Repulsion of step-edge Pt atom to the adsorbed hydrogen, which boosts the oxygen reduction reaction. • Pt 1.2 Cu octahedron with different step densities are fabricated. • ORR catalytic activity is in positive correlation to the number of steps. • E ads (O) values show a contradictory trend, where the near-step site is detrimental. • A novel "hydrogen activation" pathway is put forward. • The rate-determining oxygen hydrogenation process is boosted via this pathway. Identifying the influence of the step defects is crucial for the development of high-performance Pt-based catalysts towards oxygen reduction reaction (ORR). To this end, intense research based on the oxygen adsorption energy (E ads (O)) criterion has been carried out for Pt single crystals, yet hardly can these studies be applied to the alloy system, considering the strain and ligand effects. Here we demonstrated that for a typical alloy (that is Pt 1.2 Cu octahedron), the activity is in positive correlation with the number of steps which, however, are detrimental to ORR as determined by the E ads (O) results. Using a combination of kinetics and electron density differences calculations, a novel "hydrogen activation" pathway is put forward. It is shown that the step-edge atoms can apply a repulsive force on the adsorbed hydrogen atoms, which reduces the energy barrier of the rate-determining oxygen hydrogenation process by 0.1 eV compared with the corresponding smooth surface and eventually accelerates the ORR kinetics. [ABSTRACT FROM AUTHOR]

CoN x -based helically coiled nitrogen-doped carbon nanotubes (CoN x /HCN-CNTs) for electrochemical oxygen reduction: The hybrids were fabricated by two-step pyrolysis strategy, in which the helically coiled nitrogen-doped carbon nanotubes (HCN-CNTs) show a uniform diameter of approximately 50 nm and CoN x -based nanoparticles are not only distributed either at the tip or inside of HCN-CNTs, but excitingly, they are uniformly dispersed on the surface of HCN-CNTs. The remarkable features have greatly assured higher ORR catalytic efficiency, better methanol tolerance and stability than commercial 20% Pt/C, making it a promising low-cost, highly efficient ORR catalyst. • Hybrid electrocatalysts are successfully fabricated by two-step pyrolysis strategy. • N-CNTs show uniform diameter of about 50 nm and helically coiled nanostructure. • CoN x -based nanoparticles can be uniformly dispersed on the surface of HCN-CNTs. • The hybrids possess higher ORR activity, stability and better methanol tolerance. Here, CoN x -based helically coiled nitrogen-doped carbon nanotubes (CoN x /HCN-CNTs) are reported based on two-step pyrolysis strategy, in which the helically coiled nitrogen-doped carbon nanotubes (HCN-CNTs) show uniform diameter of approximately 50 nm and CoN x -based nanoparticles are not only distributed either at the tip or inside of HCN-CNTs, but excitingly, they are uniformly dispersed on the surface of HCN-CNTs. When applied for ORR, CoN x /HCN-CNTs show excellent ORR activity, with good onset potential and higher current density, comparable to that of the commercial 20% Pt/C. The half-wave potential is 0.92 V (vs reversible hydrogen electrode, RHE) in 0.1 M KOH, 20 mV higher than that of 20% Pt/C. Most importantly, CoN x /HCN-CNTs display better methanol tolerance and higher stability. After 28,800 s, the current density only decreased by 1.4%. The high ORR performance maybe related with synergistic enhancement effect, in which CoN x -based nanoparticles can induce a host-guest electronic interaction and according improve the local work function of the HCN-CNTs, making carbon layer have higher ORR activity; meanwhile, the ORR activity of embedded CoN x -based nanoparticles can be greatly improved, mainly attributing to the protection of HCN-CNTs and weakness of the Ostwald-ripening-like effect in ORR progress. The features make it one of the best non-noble-metal catalysts for ORR. [ABSTRACT FROM AUTHOR]

• g-C 3 N 4 /GN, with significantly reduced band gap, exhibits enhanced charge transfer. • Pyridinic N in pure g-C 3 N 4 is the binding sites for O, OH, and functional for ORR. • Single-atom Fe in modified g-C 3 N 4 by graphene is predicted to be effective for ORR. The intrinsic electronic and catalytic properties of two-dimensional (2D) graphitic carbon nitride (g-C 3 N 4) and its heterostructures were investigated as a potential oxygen reduction reaction (ORR) electrocatalyst. g-C 3 N 4 is rich in native pyridinic N and shows favorably interactions toward ORR intermediates, but lacks the ability for efficient charge transfer for practical electrochemical processes. The electronic structures of freestanding g-C 3 N 4 and hetero-bilayers paired with graphene (GN) and hexagonal boron nitride (hBN) monolayers were evaluated using Density Functional Theory (DFT). The energy band gap for the g-C 3 N 4 /GN bilayer, calculated from the HSE06 hybrid functional, is found to be significantly narrowed.. Moreover, a four-coordinated Fe atom, with Fe anchored by the pyridinic N (Fe-N-C) exists, resembling the GN-based FeN 4 motif. The bindings of ORR intermediates at these single Fe atom sites were also found to be tunable, suggesting that there are opportunities to fine-tune g-C 3 N 4 -based materials to achieve superior performance as Pt-free electrocatalysts. [ABSTRACT FROM AUTHOR]

Controlled doping of specific N species is considered to be an effective yet a challenging strategy to boost the ORR performance of the N-doped carbon. Herein, we report a facile synthesis of tailored active-N-dominated doped defective carbon nanotube (CNT) catalysts by in-situ pyrolysis of defective CNT (OCNT) coated with cobalt(II) ions in ammonia atmosphere. With the guidance of defects and cobalt(II) ions, more active N species (pyridinic-N, graphitic-N and Co-N x) related to ORR activity are inductively doped into the OCNT forming the active-N-dominated doped OCNT-N catalyst. The resulting OCNT-N shows more favorable ORR activity with an onset potential of 0.94 V vs. RHE, half-wave potential of 0.82 V vs. RHE and better selectivity toward four electron path of ORR due to the synergistic effect of these active nitrogen species and structural defects. Most encouragingly, the according Zn-air batteries using OCNT-N as cathode catalysts can achieve a peak power density of 170.2 mW cm−2 and show a slight voltage loss of only 0.86% after continuous discharge for 12 h at 10 mA cm−2. Our findings demonstrate that the resulting synergy of active N species induced by defects and cobalt(II) ions and defect sites considerably may contribute to boost ORR catalytic activity. Unlabelled Image • Pre-oxidization renders carbon nanotubes more structural defects liable to N doping. • More oxygen functional groups related to defects induce the doping of active nitrogen species. • A tailored active-N-dominated doped CNT prepared by pyrolysis of OCNT coated with Co2+ in ammonia atmosphere. • Defects tailored N-doped CNT shows enhanced activity toward ORR. [ABSTRACT FROM AUTHOR]

The urea-formaldehyde resins carbon (UFC) and Fe-containing UFC (Fe-UFC) have been prepared by direct carbonization of urea-formaldehyde resins (UF resins) without any surfactants. On this basis, N-doped materials of UFC/MnO 2 and Fe-UFC/MnO 2 composites were successfully synthesized by the situ redox method. UF resins played both roles of carbon source and nitrogen source. The specific surface areas are 265.7 m2·g−1 and 229.4 m2·g−1 for UFC/MnO 2 and Fe-UFC/MnO 2 , respectively. Direct methanol fuel cells (DMFCs) were assembled with the prepared catalyst as cathode catalyst, polymer fiber membrane (PFM) as electrolyte film and PtRu/C as anode catalyst. DMFCs and cyclic voltammetry (CV) performance tests indicate that Fe-UFC/MnO 2 -based DMFC displays superior oxygen reduction reaction (ORR) catalytic activity than UFC/MnO 2 owing to Fe-N x existing and a large number of pyridine-N in Fe-UFC/MnO 2. The lone pair electrons of pyridine-N can coordinate with transition metal elements and form Fe-N x groups on Fe-UFC/MnO 2 , which can be used as the electrocatalytic active sites for ORR. On the other hand, the presence of iron on the prepared catalyst can reduce the band gap, facilitate the transfer from MnIII to MnIV, and provide free electrons for adsorbed O 2 or active oxygen species, thus accelerating the conductivity and ORR catalytic efficiency. • UF resins can be used as not only carbon source, but also nitrogen source. • UFC/MnO 2 and Fe-UFC/MnO 2 have large BET surface areas of 265.7 and 229.4 m2·g−1, respectively. • Fe-N x groups on Fe-UFC/MnO 2 surface can act as the electrocatalytic active sites for ORR. • The presence of iron on catalyst can reduce the band gap thus accelerating the ORR catalytic efficiency. [ABSTRACT FROM AUTHOR]

A facile one-pot hydrothermal method was proposed to fabricate nitrogen-doped carbon quantum dots (N-doped CQDs) on the surface of nitrogen-doped carbon nanotube (N-doped CNTs). The microstructure of the N-doped CQDs/N-doped CNTs hybrid was investigated by using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Furthermore, their electrocatalytic activity of the N-doped CQDs/N-doped CNTs hybrid in oxygen reduction reaction (ORR) was systematically evaluated and it was found that the N-doped CQDs/N CNTs hybrid deposited as such exhibits a high performance for ORR in terms of a low onset potential of −0.03 V vs. Ag/AgCl, a high limiting diffusion current density of ~5.5 mA cm−2, and a one-step 4e ORR process, holding great potential for future metal-free catalysts. • A N C QDs/ N-doped CNTs composite catalyst was prepared by a simple wet chemical method. • The modification of the N-doped CNTs with N C QDs resulted in a higher activity for ORR. • The synergy in integrating N-C QDs with N-doped CNTs lead to the good ORR performance. [ABSTRACT FROM AUTHOR]

Despite significant methodical improvements in the synthesis of N-doped graphene, there are still unsolved questions regarding the control of content and the configuration of nitrogen species in graphene honeycomb network. A cross-examination of X-ray photoelectron spectroscopy and Raman spectroscopy findings indicates that the nitrogen dopant amount is graphene thicknesses dependent, but the various nitrogen dopant coordination can be obtained on both double- and few-layer graphene. Characteristic defect features (D′) appearing in Raman spectra upon N-doping is sensitive to nitrogen dopant coordination, graphitic-pyridinic/nitrilic species and therefore the doping level can be identified. Pyridinic and nitrilic nitrogen as primary species turn graphene to p-type semiconductor after a mild thermal treatment. • Graphene thickness controls the types of the N-dopants. • Thermal treatment makes graphene pyridinic nitrogen rich, crucial in electrochemical oxygen reduction. • Raman spectroscopy identifies the not only the doping level but also the type of the dopant. [ABSTRACT FROM AUTHOR]