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

Abstract

Abstract 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.