Design and In Situ Growth of Cu₂O‐Blended Heterojunction Directed by Energy‐Band Engineering: Toward High Photoelectrochemical Performance

Abstract In the field of photoelectrochemical (PEC) water splitting, cuprous oxide (Cu₂O) is one of the most promising photocathode materials, but its performance is restricted by poor carrier separation ability and low photovoltage. In order to overcome these limitations, a new kind of Cu₂O‐ZnO blended heterojunction photocathode is designed and prepared by novel one‐step thermal oxidation method. ZnO granules are uniformly distributed in Cu₂O film matrix, forming a granular structure, which enhances the band bending of Cu₂O in the electrolyte and improves the photovoltage. In addition, the formed ladder type band alignment of Cu₂O‐ZnO facilitates the spatial separation of photoexcited carriers. Different from the conventional layered heterojunction, the granular structured heterojunction proposed in this work extends the built‐in electric field region and further promotes the transmission of photoexcited carriers from the photoelectrode to the electrolyte. At 0 V vs reversible hydrogen electrode (RHE), the photocurrent density of Cu₂O‐ZnO film is as high as −8.7 mA cm⁻², which is over 6 times that of bare Cu₂O (−1.3 mA cm⁻²). The onset potential positively shifts from 0.57 V vs RHE to 0.78 V vs RHE. This work provides an effective strategy for improving the PEC performance from the perspective of band alignment and material structure.