Delafossite-embedded Z-scheme heterojunction photocathode with abundant heterointerfaces for boosted photoelectrochemical performance.

Layered delafossite, an inherently p-type semiconductor, has emerged as a highly promising photocathode material for photoelectrochemical (PEC) water splitting. However, its PEC performance and scalability are significantly limited by the shortcomings of conventional photoelectrode fabrication techniques, which often involve inferior physical adhesion or require harsh processing conditions. In this study, a CuO layer is introduced via in-situ oxidation of a copper foam (CF) substrate to achieve embedded anchoring of delafossite CuFeO (CFO), thereby developing a robust embedded CF/(CFO@CuO) photocathode. This configuration features extensive and strong 3D semiconductor/semiconductor heterointerfaces. The embedded structure significantly reduces the carrier diffusion length to the CF, thereby enhancing photocarrier collection efficiency. Additionally, this unique geometric design provides abundant heterointerfaces with all-round contact, promoting efficient carrier separation while strengthening interfacial binding. Theoretical calculations further reveal the formation of a strong built-in electric field and a Z-scheme heterostructure, which facilitate effective photocarrier separation and transfer while maintaining robust redox activity. Remarkably, the photocurrent density of the embedded CF/(CFO@CuO) photocathode at zero bias is 2.73-fold higher than that of the traditional sandwich-stacked CF/CuO/CFO photocathode and 21.55-fold higher than that of the original CF/CFO photocathode. Furthermore, the scalability of this approach is demonstrated through the fabrication of a 100 cm embedded photocathode. This work presents a scalable and cost-effective nanofabrication technique for robust photoactive films, enabling efficient and stable PEC water splitting.