Electronic structure tuning of FeCo nanoparticles embedded in multi-dimensional carbon matrix for enhanced bifunctional oxygen electrocatalysis

It is highly desirable to develop efficient, affordable and durable electrocatalysts to accelerate sluggish kinetics of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) for expanding the applications of Zn-air batteries (ZABs). Here, Fe1Co2 alloy nanoparticles (NPs) embedded in N-doped carbon nanotubes/carbon nanosheets (CNTs/CNSs) (denoted as Fe1Co2-NC) were synthesized in situ by pyrolyzing Fe-chitosan, Co-chitosan chelates and urea. It is demonstrated that the interaction of Fe and Co can effectively modulate electronic structure of Fe and Co, in which ionic state cobalt and iron were partially oxidized, contributing to the enhanced intrinsic catalytic activity. Meanwhile, CNTs/CNSs multi-dimensional porous carbon frameworks facilitated adequate exposure of active sites and mass/electron smooth transport. Accordingly, the resulting Fe1Co2-NC catalyst exhibited a high half-wave potential of 0.88 V (vs. RHE) for ORR and a small over potential (0.356 V) for OER, rendering it with an ultralow potential difference (0.706 V) that can rival that of Pt/C + RuO2 (0.69 V). Impressively, the assembled ZABs with Fe1Co2-NC as a cathode catalyst achieved a high open circuit voltage (1.501 V), maximum power density (203.4 mW cm−2), energy density (820.30 W h kg−1) and robust durability with a slightly increased voltage gap (0.058 V) after 209 h charge-discharge test, shedding light on the great application potential.