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 a large-scale sustainable and clean hydrogen production. However, conventional electrocatalysis materials often face severe corrosion and performance degradation in the high-salinity environment mainly due to the presence of aggressive chloride ions. Besides, the chloride ions 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 bestows 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) 2 P/C) composite with a three-dimensional structure was in-situ fabricated 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 fresh water and 100/223 mV (HER/OER) in alkaline seawater at 10 mA cm -2 were obtained, revealing its exceptional bifunctional performances. Furthermore, the two-electrode eletrolyzer assembled by using (NiCoFeMnCu) 2 P/C/NF demonstrated a continuous 480-h stable operation at an industriallevel current density (1 A cm -2 ) without obvious activity decay and almost no hypochlorite species was detected in the alkaline seawater electrolyte, confirming its robust chloride resistance and high selectivity. Therefore, this (NiCoFeMnCu) 2 P/C electrocatalyst should be a promising bifunctional electrocatalyst for overall seawater splitting.