Anchoring Bimetal Single Atoms and Alloys on N-Doping-Carbon Nanofiber Networks for an Efficient Oxygen Reduction Reaction and Zinc-Air Batteries.

Electrocatalysts for the oxygen reduction reaction (ORR) play a central role in fuel cells and zinc-air batteries. Bimetal single atoms and nanoparticle hybrids are emerging ORR electrocatalysts, superior to the most exploited unary metal single-atom catalysts (SACs). Here, we report bimetal SAC-based nanofiber networks of CoFe@Co/Fe-SAC for efficient ORR electrocatalysis and zinc-air batteries. A facile and easy-to-scale-up process is developed, and the versatility is validated in three hybrids. Strong electronic interaction is revealed between bimetal single atoms and alloy nanoparticles, leading to improved catalytic performances for ORR. Specifically, the CoFe@Co/Fe-SAC hybrids exhibit a half-wave potential of 0.841 V in a basic electrolyte, comparable to the Pt/C electrocatalyst. Assembled in a zinc-air battery, a CoFe@Co/Fe-SAC hybrid-based cell demonstrates a power density 1.8 times higher than the benchmark Pt/C-IrO-based one, and it is stable for 150 cycles galvanostatic charge/discharge. The superior device performance is attributed to the appealing intrinsic activity, the carbon shielding effect for anti-leaching, and the hierarchical porous networks for large accessibility of active sites and favorable mass transport. Theoretical calculations suggest that alloy nanoparticles significantly improved the intrinsic catalytic activity of Fe single-atom sites at the expense of slightly lowering the activity of Co single-atom sites. This work presents a versatile process for the mass production of efficient composite electrocatalysts and highlights the power of bimetal single-atom-based hybrids and hierarchically porous structures for ORR device performances.