Co-optimization of CuBi2O4 photocathode by heterojunction and hole-selective layer for efficient photoelectrochemical water splitting

CuBi2O4 is identified as a promising photocathode in photoelectrochemical (PEC) water splitting systems. However, the PEC performance of CuBi2O4 is far from expected due to the limited separation and transport efficiency of photogenerated carriers. To address the above issues, a cost-effective ternary Cu:NiOX/CuBi2O4/CuO composite photocathode was designed. Firstly, a thin Cu:NiOX film was inserted between CuBi2O4 and FTO conducting substrate as a hole-selective layer, which promotes the transmission of photogenerated holes to the FTO substrate effectively. Furthermore, the modification of CuO film on the CuBi2O4 electrode not only increases the absorption of sunlight and generates more photogenerated carriers, but also constitutes a heterojunction with CuBi2O4, creating a built-in electric field, which facilitates the separation of electrons and holes, and accelerates the electrons transfer to electrode-electrolyte interface. The fabricated Cu:NiOX/CuBi2O4/CuO composite photocathode exhibits a surprisingly high photocurrent density of - 1.51 mA.cm(-2) at 0.4 V versus RHE, which is 2.6 times that of the pristine CuBi2O4 photocathode. The improved PEC performance is attributed to the synergy effect of the Cu:NiOX hole-selective layer and the CuBi2O4/CuO heterojunction. Moreover, the combination with the BiVO4/CoS, an unbiased overall water splitting was achieved, which has a photocurrent of 0.193 mA.cm(-2).