Gradient Mo Engineering in [100]‐Oriented CuWO ₄ Films for Boosted Photoelectrochemical Water Splitting

ABSTRACT Copper tungstate (CuWO ₄ ) is a promising candidate for photoelectrochemical (PEC) water splitting, yet its practical performance is severely limited by inefficient charge transfer. Herein, a gradient Mo‐doped CuWO ₄ film (CuW _x Mo _{1‐ x} O ₄ ) with preferential [100] crystal orientation was constructed via a facile hydrothermal route. Owing to the distinct crystallization behaviors of isopolytungstate and isopolymolybdate species, a continuous W/Mo compositional gradient is established along the direction perpendicular to the conductive substrate, giving rise to a stepwise band profile across the film thickness. Such stepwise band engineering, synergistically coupled with crystallographic orientation control, effectively accelerates the separation and transport of photogenerated carriers. As a result, the CuW _x Mo _{1‐ x} O ₄ film delivers a high photocurrent density of 1.53 mA cm ⁻² , and presenting limited decay in 50 h. This work highlights gradient band engineering as an effective doping paradigm to overcome charge‐transfer limitations in CuWO ₄ and provides a general composition gradient strategy for high‐performance photoelectrodes by integrating stepwise energy bands with tailored crystal orientation.