Electrocatalytic Oxygen Reduction Reaction by the Pd/Fe-N-C Catalyst and Application in a Zn–Air Battery

Developing a non-platinum catalyst that effectively catalyzes the oxygen reduction reaction (ORR) is highly significant for metal–air batteries. Metal and nitrogen co-doped carbons (M-N-Cs) have emerged as alternative candidates to platinum. In this work, dual-metal Pd/Fe-N-C electrocatalysts were synthesized by the one-step pyrolysis of phytic acid, melamine, and Pd/Fe-based salts. The Pd/Fe-N-C catalyst exhibited a good catalytic ability during the ORR process and outperformed the commercial Pt/C catalyst as regards mass activity, catalytic stability, and methanol tolerance. It was found that Pd-Nx is the active center, and the synergistic effect from the Fe component introduction endowed the Pd/Fe-N-C with an excellent catalytic performance towards the ORR. When assembled into a Zn–air battery, its specific capacity was ~775 mAh gZn−1. Meanwhile, the peak power density could reach 3.85 W mgPd−1, i.e., 3.4 times that of the commercial Pt/C catalyst (1.13 W mgPt−1). This implies that the Pd/Fe-N-C catalyst has potential applications in metal–air batteries.

Transformation of CoFe2O4 spinel structure into active and robust CoFe alloy/N-doped carbon electrocatalyst for oxygen evolution reaction

Electrochemical water splitting is an environmentally benign technology employed for H₂ production; however, it is critically hampered by the sluggish kinetics of the oxygen evolution reaction (OER) at the positive electrode. In this work, nitrogen-doped carbon-coated CoFe electrocatalysts were synthesized via a three-step route comprising (1) hydrothermal reaction, (2) in-situ polymerization of dopamine and (3) carbonization. The effect of carbonized polydopamine on the overall physicochemical properties and electrochemical activity of CoFe catalysts was systematically studied. By controlling and optimizing the ratio of CoFe₂O₄ and dopamine contents, a transformation of the CoFe₂O₄ structure to CoFe alloy was observed. It was found that CoFe/NC_30% (prepared with 30% dopamine) exhibits an excellent catalytic activity towards OER. A small overpotential of 340 mV was required to generate a current density of 10 mA cm^-2 in a 1.0 M KOH electrolyte. More importantly, the CoFe/NC_30% catalyst reflected exceptional durability for at least 24 h. This research sheds light on the development of affordable, highly efficient, and durable electrocatalysts for OER.

Electronic interplay: synergism of binary transition metals and role of M-N-S site towards oxygen electrocatalysis

Towards rational catalyst development, a binary Fe-Co centre has been coordinated with S and N in a nanocarbon matrix. An electronic drift between Fe-Co and an extended +R effect from the S dopants towards the metals through the p_z orbital of N are beneficial for oxygen electrocatalysis and a zinc-air battery.

Highly Accessible Atomically Dispersed Fe-N x Sites Electrocatalyst for Proton-Exchange Membrane Fuel Cell

Atomically dispersed transition metal-N x sites have emerged as a frontier for electrocatalysis because of the maximized atom utilization. However, there is still the problem that the reactant is difficult to reach active sites inside the catalytic layer in the practical proton exchange membrane fuel cell (PEMFC) testing, resulting in the ineffective utilization of the deeply hided active sites. In the device manner, the favorite structure of electrocatalysts for good mass transfer is vital for PEMFC. Herein, a facile one-step approach to synthesize atomically dispersed Fe-N x species on hierarchically porous carbon nanostructures as a high-efficient and stable atomically dispersed catalyst for oxygen reduction in acidic media is reported, which is achieved by a predesigned hierarchical covalent organic polymer (COP) with iron anchored. COP materials with well-defined building blocks can stabilize the dopants and provide efficient mass transport. The appropriate hierarchical pore structure is proved to facilitate the mass transport of reactants to the active sites, ensuring the utilization of active sites in devices. Particularly, the structurally optimized HSAC/Fe-3 displays a maximum power density of up to 824 mW cm-2, higher than other samples with fewer mesopores. Accordingly, this work will offer inspirations for designing efficient atomically dispersed electrocatalyst in PEMFC device.

Recent advances of noble-metal-free bifunctional oxygen reduction and evolution electrocatalysts

Bifunctional oxygen reduction and evolution constitute the core processes for sustainable energy storage. The advances on noble-metal-free bifunctional oxygen electrocatalysts are reviewed.