Prussian Blue Analogue-Derived NiFe Sulfide Enabling Synergistic ORR/OER via Tuned Electronic Structures for Zn-Air...

Bimetallic sulfides have emerged as promising four-electron oxygen electrocatalysts for Zn-air batteries (ZABs). Herein, we report a Prussian blue analogue-derived NiFe sulfide embedded in carbon nanocages (NiFeS/CNCs) with a polydopamine-derived carbon coating. The heterostructure and conductive carbon framework endow the catalyst with enhanced charge transfer and mass transport properties. Importantly, the strong electronic coupling between Ni and Fe sulfides, together with the abundant NiS₂/FeS₂ phase interfaces, creates a high density of accessible active sites and optimizes the oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) kinetics. As a result, NiFeS/CNCs exhibits excellent bifunctional ORR/OER activity, delivering a low OER overpotential of 167 mV at 10 mA cm^-2 (superior to commercial IrO₂) and an ORR half-wave potential better than Pt/C. During OER, surface reconstruction occurs, where NiS₂ transforms into catalytically active NiOOH species, accompanied by the oxidation of Fe to higher valence states, revealing the dynamic nature of the active phase. As a result, NiFeS/CNCs exhibits excellent bifunctional activity toward ORR and OER. The assembled rechargeable Zn-air battery delivers a peak power density of 105.9 mW cm^-2 and demonstrates long-term cycling stability over 1000 h at 5 mA cm^-2, highlighting its potential for practical energy applications.