Decoration of NiFe-LDH Nanodots Endows Lower Fe-d Band Center of Fe1-N-C Hollow Nanorods as Bifunctional Oxygen Electrocatalysts with Small Overpotential Gap

Single-atom Fe-N-C (denoted as Fe-1-N-C) catalysts exhibit inadequate bifunctional activities to conquer the sluggish oxygen reduction and evolution reaction (ORR/OER), hindering their practical applications in rechargeable Zn-air batteries (ZABs). Here, by employing Fe-1-N-C hollow nanorods as ORR-active support, OER-active NiFe-layered double hydroxide (NiFe-LDH) nanodots are evenly decorated through a spatially confined process to form NiFe-LDH/Fe-1-N-C heterostructure hollow nanorods with abundant accessible catalytic sites. The NiFe-LDH/Fe-1-N-C heterostructure not only enhances the ORR activity of pristine Fe-1-N-C but also realizes efficient bifunctional ORR/OER activity in one monolithic catalyst. Theoretical calculations reveal that introducing NiFe-LDH nanodots results in donation of electrons to the Fe-1-N-C matrix and thus lowers the Fe-d band center of the Fe-N-4 sites, dramatically narrowing the energy barriers of the ORR rate-limiting steps. As a result, NiFe-LDH/Fe-1-N-C nanorods deliver remarkable ORR activity with a half-wave potential of 0.90 V versus reversible hydrogen electrode, surpassing bare Fe-1-N-C and commercial Pt/C. Impressively, the integrated NiFe-LDH/Fe-1-N-C catalysts show outstanding bifunctional performance with a small overpotential gap of only 0.65 V. The liquid-state ZABs with NiFe-LDH/Fe-1-N-C as an air-cathode catalyst deliver a peak power density of 205 mW cm(-2) and long-term cycling stability of up to 400 h.

Automated summary

By introducing NiFe-LDH nanodots on the single-atom Fe-N-C catalyst, NiFe-LDH/Fe-1-N-C heterostructure hollow nanorods were formed, which exhibit enhanced activity for oxygen reduction and evolution reactions (ORR/OER) and achieve efficient bifunctional ORR/OER activity. This catalyst not only shows excellent ORR activity but also demonstrates impressive bifunctional performance, indicating its potential as an alternative to precious metal catalysts and its significance for practical applications in rechargeable Zn-air batteries.