Systematic Construction of Type-II BiVO₄/CoWO₄ p-n Heterojunction Photoanodes for Efficient Photoelectrochemical...

Photoelectrochemical (PEC) water splitting is widely regarded as a sustainable route for hydrogen generation, in which efficient water oxidation requires highly active photoanodes. Although bismuth vanadate (BiVO₄) is a promising visible-light-responsive photoanode because of its suitable bandgap, its PEC performance is still largely constrained by severe bulk/surface charge recombination and sluggish oxygen-evolution kinetics. In this work, p-type CoWO₄ nanoparticles were introduced onto n-type BiVO₄ to build a type-II p-n heterojunction. Intimate interfacial contact generates a built-in electric field that, together with the staggered band alignment, drives the directional separation and migration of photogenerated carriers. Meanwhile, CoWO₄ offers abundant catalytic sites and lowers the interfacial reaction resistance, thereby accelerating surface water oxidation. The optimized BiVO₄/CoWO₄ photoanode reaches a photocurrent density of 4.58 mA cm^-2 at 1.23 V versus reversible hydrogen electrode (RHE), representing a 3.6-fold improvement over pristine BiVO₄. A series of analyses and characterizations further confirm that the heterojunction effectively suppresses charge recombination, extends carrier lifetime, and promotes charge injection as well as interfacial water-oxidation kinetics, leading to improved PEC performance. Overall, this study demonstrates an effective heterojunction-engineering strategy for improving the PEC performance of BiVO₄-based photoanodes.