Interface‐Engineered InAlN/Cu₂O Photocathode with Accelerated Charge Separation for Boosting Photoelectrochemical Water Splitting

Cu 2 O has emerged as a promising material for sustainable hydrogen production through photoelectrochemical (PEC) water splitting, while inefficient charge separation remains one of the main challenges hindering its development. In this work, a new architecture of InAlN/Cu 2 O heterojunction photocathode is demonstrated by combining n‐type InAlN and p‐type Cu 2 O to improve the charge separation efficiency, thus enhancing PEC water‐splitting performance. The Pt/InAlN/Cu 2 O photoelectrode exhibits a photocurrent density of 2.54 mA cm −2 at 0 V versus reversible hydrogen electrode ( V RHE ), which is 3.21 times higher than that of Cu 2 O (0.79 mA cm −2 at V RHE ). The enhanced PEC performance is explained by the larger built‐in potential V b i of 1.43 V formed at the InAlN/Cu 2 O p–n junction than that in the single Cu 2 O photocathode ( V b i < 0.77 V), which improves the separation of the photogenerated carriers and thus relieves the bottlenecks of charge‐transfer kinetics at the electrode bulk and electrode/electrolyte interface. In this work, an avenue is opened for designing III‐nitrides/Cu 2 O heterojunction toward solar energy conversion.