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/cm(2) 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/cm(2)). 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.

Automated summary

This study converted the surface of Cu2O film to CuO by thermal oxidation, forming a Cu2O/CuO heterojunction with fewer interface defects to enhance the efficiency of photoelectrochemical water splitting. The performance of Cu2O/CuO can be further improved by depositing a Pt co-catalyst layer.