Bulk-Heterojunction Electrocatalysts in Confined Geometry Boosting Stable, Acid/Alkaline-Universal Water Electrolysis

Alkaline water splitting electrocatalysts have been studied for decades; however, many difficulties remain for commercialization, such as sluggish hydrogen evolution reaction (HER) kinetics and poor catalytic stability. Herein, by mimicking the bulk-heterojunction morphology of conventional organic solar cells, a uniform 10 nm scale nanocube is reported that consists of subnanometer-scale heterointerfaces between transition metal phosphides and oxides, which serves as an alkaline water splitting electrocatalyst; showing great performance and stability toward HER and oxygen evolution reaction (OER). Interestingly, the nanocube electrocatalyst reveals acid/alkaline independency from the synergistic effect of electrochemical HER (cobalt phosphide) and thermochemical water dissociation (cobalt oxide). From the spray coating process, nanocube electrocatalyst spreads uniformly on large scale (approximate to 6.6 x 5.6 cm(2)) and is applied to alkaline water electrolyzers, stably delivering 600 mA cm(-2) current for >100 h. The photovoltaic-electrochemical (PV-EC) system, including silicon PV cells, achieves 11.5% solar-to-hydrogen (STH) efficiency stably for >100 h.