An activity–selectivity–stability-balanced bifunctional high-entropy phosphide for overall seawater splitting at industrial-level current density

Abstract

Seawater electrolysis is considered as a promising pathway to substitute freshwater electrolysis for large-scale sustainable and clean hydrogen production. However, conventional electrocatalyst materials often suffer from severe corrosion and performance degradation in high-salinity environments mainly due to the presence of aggressive chloride ions. Besides, the chloride ion-induced competitive anodic chlorine evolution reaction also needs to be avoided since it can lead to low electrolysis efficiency. The application of high-entropy materials (HEMs) offers a potential solution to these challenges. The unique compositional complexity endows HEMs with remarkable properties including significantly enhanced resistance to corrosion and improved catalytic activity, allowing them to exhibit excellent stability and efficiency in the seawater electrolysis process. Herein, a metal–organic framework-derived high-entropy NiCoFeMnCu phosphide/carbon ((NiCoFeMnCu)₂P/C) composite with a three-dimensional structure was in situ prepared on a nickel foam (NF) substrate for achieving highly active and stable seawater splitting. As a result, the ultralow overpotentials of 88/195 mV (hydrogen evolution reaction (HER)/oxygen evolution reaction (OER)) in alkaline freshwater and 100/223 mV (HER/OER) in alkaline seawater at 10 mA cm⁻² were obtained, revealing its exceptional bifunctional performances. Furthermore, a two-electrode electrolyzer assembled by using (NiCoFeMnCu)₂P/C/NF demonstrated continuous stable operation for 480 h at an industrial-level current density (1 A cm⁻²) without obvious activity decay, and almost no hypochlorite species were detected in the alkaline seawater electrolyte, confirming its robust chloride resistance and high selectivity. Therefore, this (NiCoFeMnCu)₂P/C electrocatalyst should be a promising bifunctional electrocatalyst for overall seawater splitting.