Active site switching on high entropy phosphides as bifunctional oxygen electrocatalysts for rechargeable/robust Zn–air battery

Abstract

High-entropy materials (HEMs) offer a quasi-continuous spectrum of active sites and have generated great expectations in fields such as electrocatalysis and energy storage. Despite their potential, the complex composition and associated surface phenomena of HEMs pose challenges to their rational design and development. In this context, we have synthesized FeCoNiPdWP high entropy phosphide (HEP) nanoparticles using a low-temperature colloidal method, and explored their application as bifunctional electrocatalysts for the oxygen evolution and reduction reactions (OER/ORR). Our analysis provides a detailed understanding of the individual roles and transformations of each element during OER/ORR operation. Notably, the HEPs exhibit an exceptionally low OER overpotential of 227 mV at 10 mA cm−2, attributed to the reconstructed HEP surface into a FeCoNiPdW high entropy oxyhydroxide with high oxidation states of Fe, Co, and Ni serving as the active sites. Additionally, Pd and W play crucial roles in modulating the electronic structure to optimize the adsorption energy of oxygen intermediates. For the ORR, Pd emerges as the most active component. In the reconstructed catalyst, the strong d–d orbital coupling of especially Pd, Co, and W fine-tunes ORR electron transfer pathways, delivering an ORR half-wave potential of 0.81 V with a pure four-electron reduction mechanism. The practicality of these HEPs catalysts is showcased through the assembly of aqueous zinc–air batteries. These batteries demonstrate a superior specific capacity of 886 mA h gZn−1 and maintain excellent stability over more than 700 hours of continuous operation. Overall, this study not only elucidates the role of each element in HEMs but also establishes a foundational framework for the design and development of next-generation bifunctional oxygen catalysts, broadening the potential applications of these complex materials in advanced energy systems.