Cu2O/CuO heterojunction formed by thermal oxidation and decorated with Pt co-catalyst as an efficient photocathode for photoelectrochemical water splitting

Cuprous oxide (Cu2O) is a highly efficient p-type semiconductor, which has an appropriate band gap and favorable energy band positions, making it ideal to be considered as a photocathode material for photoelectrochemical (PEC) water splitting. However, the theoretical efficiency of Cu2O is still unachievable in practical situations due to the low separation rate of photogenerated electron–hole pairs. In this work, the surface of the Cu2O film was directly converted to CuO by thermal oxidation to form a Cu2O/CuO heterojunction with fewer defects at the interface. The PEC tests suggest that the Cu2O/CuO photocathode exhibits a photocurrent density of − 1.99 mA/cm2 at 0 V vs. RHE benefit by the heterojunction with a good interface for efficient charge separation and transfer, which is 3.3 times higher than Cu2O (− 0.6 mA/cm2). Furthermore, the performance of Cu2O/CuO can be greatly enhanced by depositing a Pt co-catalyst layer. The photocurrent density of Cu2O/CuO/Pt composites was 4.6 times higher than pristine Cu2O. More exciting, the stability of Cu2O with the CuO and Pt co-catalyst only presents a decline of 20% under illumination for 3600 s. This work points to the effective means of thermal oxidation that can form a heterojunction with relatively fewer interface defects and provides a strategy for the performance improvement of Cu2O photocathode in PEC water reduction.