Co‐optimization of CuBi ₂ O ₄ photocathode by heterojunction and hole‐selective layer for efficient photoelectrochemical water splitting

Abstract CuBi 2 O 4 is identified as a promising photocathode in photoelectrochemical (PEC) water splitting systems. However, the PEC performance of CuBi 2 O 4 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:NiO X /CuBi 2 O 4 /CuO composite photocathode was designed. Firstly, a thin Cu:NiO X film was inserted between CuBi 2 O 4 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 CuBi 2 O 4 electrode not only increases the absorption of sunlight and generates more photogenerated carriers, but also constitutes a heterojunction with CuBi 2 O 4 , 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:NiO X /CuBi 2 O 4 /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 CuBi 2 O 4 photocathode. The improved PEC performance is attributed to the synergy effect of the Cu:NiO X hole‐selective layer and the CuBi 2 O 4 /CuO heterojunction. Moreover, the combination with the BiVO 4 /CoS, an unbiased overall water splitting was achieved, which has a photocurrent of 0.193 mA·cm −2 .