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 (≈6.6 × 5.6 cm²) 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.