CuO/CuBi₂O₄ bilayered heterojunction as an efficient photocathode for photoelectrochemical hydrogen evolution reaction

The poor photostability and low photoactivity are two bottlenecks limiting the application of CuO and CuBi₂O₄ as competitive candidates for photoelectrochemical (PEC) hydrogen evolution reaction (HER). To overcome the bottlenecks, we constructed a novel CuO/CuBi₂O₄ bilayered structure for PEC HER. The underlying CuO layer functions as the main photoabsorber, while the outside CuBi₂O₄ layer acts as a protection shield. After further decorated with the NiO_x electrocatalysts, the CuO/CuBi₂O₄/NiO_x photocathode exhibits a high photoactivity and remarkable photostability. We ascribe this excellent performance to the following factors: (1) the bilayer structure improves light harvesting efficiency, (2) the outside CuBi₂O₄ enhances the photostability, (3) the favorable band alignment increases charge separation efficiency, and (4) the presence of NiO_x facilitates the charges transfer at the interface. Therefore, this work not only sets a new benchmark efficiency for the CuO and CuBi₂O₄ heterojunction, but also provides principles for designing layered heterojunction for PEC water splitting.