Role of carbon protective layer on the photoelectrochemical performance of drop-casted CuBi2O4 photocathodes for water splitting

Multinay p-type semiconductor oxide CuBi2O4 is a potential photocathode for solar water splitting due to its favorable band gap (1.5 to 1.8 eV) and positive flat band potential of above 1 VRHE. In this work, we report a facile drop-casted CuBi2O4 photocathode protected with low-cost carbon layer for improving its stability as well as enhancing charge carrier transfer. The drop-casted CuBi2O4 was annealed at three different temperatures (450 °C, 550 °C, and 650 °C) to optimize its crystallinity and morphology. The sample annealed at 550 °C exhibited better photoelectrochemical activity compared to other annealed temperatures due to its better crystallinity and morphology as revealed by XRD and FESEM, respectively. A thin protective carbon film of about 100 nm to 150 nm coated on CuBi2O4 showed an improved photoelectrochemical performance compared to bare CuBi2O4 with better stability. The optimized photocathodes at 550 °C produced maximum photocurrents of up to − 0.32 mA/cm2 and −0.56 mA/cm2 at +0.35 VRHE in pH 12.5 for CuBi2O4 and CuBi2O4/Carbon, respectively. The enhanced photocurrent was further supported by EIS spectra showing a better interfacial charge transfer as a result of minimized surface defects for CuBi2O4/Carbon. The photocurrent was further improved after depositing MoS2 co-catalyst but the stability of co-catalyst was inferior due to dissolution of the co-catalyst. The results show a promising low-cost route for protecting copper-based photocathodes for improving their stability in aqueous environment. [Display omitted] •Drop-casted CuBi2O4 optimized at 550 °C shows good PEC performance.•Carbon protected CuBi2O4 yielded ~1.75 folds higher photocurrent than bare CuBi2O4.•Carbon layer improved stability and facilitated electron shuttling to electrolyte.