Nonprecious Metal Catalysts for Oxygen Reduction in Heterogeneous Aqueous Systems

Fe3O4-Encapsulating N-doped porous carbon materials as efficient oxygen reduction reaction electrocatalysts for Zn–air batteries

Fe₃O₄-Encapsulating N-doped porous carbon was synthesized for Zn–air batteries with higher energy density and better stability than Pt/C equipped devices.

Anion exchange of a cationic Cd(ii)-based metal–organic framework with potassium ferricyanide towards highly active Fe3C-containing Fe/N/C catalysts for oxygen reduction

An efficient Fe₃C-containing Fe/N/C catalyst towards oxygen reduction was pyrolyzed from a cationic Cd(ii)-based metal–organic framework modified by anion-exchange with potassium ferricyanide.

High-level nitrogen-doped, micro/mesoporous carbon as an efficient metal-free electrocatalyst for the oxygen reduction reaction: optimizing the reaction surface area by a solvent-free mechanochemical method

Acting as an efficient metal-free ORR electrocatalyst, nitrogen-doped porous carbon derived from coconut mesocarp was prepared by a solvent-free ball-milling process.

N-doped hierarchical porous metal-free catalysts derived from covalent triazine frameworks for the efficient oxygen reduction reaction

The hierarchical structure enhances oxygen diffusion, improves electron transfer, and exposes more catalytic active sites for the ORR.

Direct fabrication of bimetallic AuPt nanobrick spherical nanoarchitectonics for the oxygen reduction reaction

Bimetallic AuPt nanobrick spherical nanoarchitectonics synthesized via a one-step method show excellent ORR performance.

A cobalt metal–organic framework (Co-MOF): a bi-functional electro active material for the oxygen evolution and reduction reaction

Co-MOF catalyzes the ORR efficiently with a lower onset potential (0.85 V vs. RHE) by a four electron reduction path with better durability. It needs only 280 mV overpotential to deliver the state-of-art current density of 10 mA cm⁻².

Oxygen reduction reaction mechanism on a phosporus-doped pyrolyzed graphitic Fe/N/C catalyst

The interaction between neighbouring FeN₄ and P_subs sites of a P-doped pyrolyzed Fe/N/C catalyst promotes four-electron reduction through associative and dissociative mechanisms.

Bio-inspired chitosan-heme-vitamin B12-derived Fe–Co bimetallic-doped mesoporous carbons for efficiently electro-activating oxygen

Biomass-derived chitosan-heme-vitamin B₁₂ with definitive molecular structures was converted to bimetallic Fe–Co-doped mesoporous carbon for efficient oxygen electroreduction.

Defect engineering on electrocatalysts for gas-evolving reactions

The hydrogen evolution reaction (HER) and oxygen redox reaction, including the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are the core processes used for water splitting and in metal-air batteries. Thus, the design of electro-catalysts for use in the oxygen redox reaction and HER have received a lot attention around the world. Many strategies have been developed to improve these catalysts, including increasing the surface area, creating unique facet structures, enhancing the conductivities and so on. Among these improvements defect engineering on catalysts has been proven to be an effective and feasible way to accelerate the reaction rate. Herein, a short overview of the recent advances in defect engineering on electro-catalysts for ORR, OER and HER is presented, and the outlook for the defect engineering field is also summarized.

Solvent-Free Mechanochemical Preparation of Hierarchically Porous Carbon for Supercapacitor and Oxygen Reduction Reaction

Hierarchically porous carbon (HPC) derived from fallen flowers was prepared by a green method of combining solvent-free ball milling with the safe activating agent potassium bicarbonate. By regulating the mass ratio of KHCO₃ to biochar, the as-prepared HPC materials possess high specific surface areas of up to 2147.9 m²  g^-1 and abundant hierarchical pores comprised of micro-, meso-, and macropores. The specific capacitances of the HPC materials are able to reach 302.7 F g^-1 at a current density of 0.5 A g^-1 in 6 m KOH, and the symmetric supercapacitor composed of two identical HPC electrodes shows good stability because 100 % of the specific capacitance is retained after 5000 charge/discharge cycles and 90.5 % of the specific capacitance remains after 12 000 cycles. Nitrogen self-doped HPC materials also show higher electrocatalytic activity and stronger methanol tolerance for the oxygen reduction reaction than that of the commercial Pt/C catalyst. This preparation method can be extended to the green conversion of other varieties of biomass waste into useful carbon materials.

Thermal Conversion of MOF@MOF: Synthesis of an N-Doped Carbon Material with Excellent ORR Performance

Here we propose a new strategy in which two isomorphic metal-organic frameworks (MOFs) [FJU-40-H (a) and FJU-40-NH₂ (b)] are used to construct the core-shell material MOF@MOF. This strategy based on nitrogen doping and specific surface has resulted in an N-doped porous carbon (NPC) material in a one-step thermal treatment in N₂ atmosphere; this material displays high catalytic activity for the oxygen reduction reaction (ORR). The materials were analyzed by SEM, XPS, Raman, specific surface area, pore size distribution and electrochemical measurements. It was found that NPC derived from the core-shell MOF@MOF can provide excellent catalytic ORR performance exceeding that of the single MOF. The onset potential is NPC-b@a-4h (-0.068 V)>NPC-a@b-4h (-0.075 V)>NPC-a-4h (-0.109 V)>NPC-b-4h (-0.113 V). Moreover, the results also show that the performance of NPC-b@a (n=4.15) is better than that of NPC-a@b (n=3.32), which means the different nitrogen content of ligands inside and outside of the core affects the ORR properties.

Atomic Fe-Nx Coupled Open-Mesoporous Carbon Nanofibers for Efficient and Bioadaptable Oxygen Electrode in Mg-Air Batteries

The recently emerging metal-air batteries equipped with advanced oxygen electrodes have provided enormous opportunities to develop the next generation of wearable and bio-adaptable power sources. Theoretically, neutral electrolyte-based Mg-air batteries possess potential advantages in electronics and biomedical applications over the other metal-air counterparts, especially the alkaline-based Zn-air batteries. However, the rational design of advanced oxygen electrode for Mg-air batteries with high discharge voltage and capacity under neutral conditions still remains a major challenge. Inspired by fibrous string structures of bufo-spawn, it is reported here that the scalable synthesis of atomic Fe-Nx coupled open-mesoporous N-doped-carbon nanofibers (OM-NCNF-FeNx ) as advanced oxygen electrode for Mg-air batteries. The fabricated OM-NCNF-FeNx electrodes present manifold advantages, including open-mesoporous and interconnected structures, 3D hierarchically porous networks, good bio-adaptability, homogeneously coupled atomic Fe-Nx sites, and high oxygen electrocatalytic performances. Most importantly, the assembled Mg-air batteries with neutral electrolytes reveal high open-circuit voltage, stable discharge voltage plateaus, high capacity, long operating life, and good flexibility. Overall, the discovery on fabricating atomic OM-NCNF-FeNx electrode will not only create new pathways for achieving flexible, wearable, and bio-adaptable power sources, but also take a step towards the scale-up production of advanced nanofibrous carbon electrodes for a broad range of applications.

Mesoporous S doped Fe–N–C materials as highly active oxygen reduction reaction catalyst

Highly active mesoporous S doped Fe–N–C ORR catalysts have been synthesized by pyrolysis of APS and FeCl₃ co-initiated poly(o-phenylenediamine).

Cobalt nanoparticles incorporated into hollow doped porous carbon capsules as a highly efficient oxygen reduction electrocatalyst

MOF nanocrystals are employed for the design and synthesis of cobalt nanoparticles embedded into hollow doped porous carbon electrocatalyst.

Simple preparation of carbon–bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts

Carbon–bimetal oxide nanospinels synthesized by a single step of autocombustion show high activity for oxygen evolution and reduction.