Carbon quantum dots based charge bridge between photoanode and electrocatalysts for efficiency water oxidation

Highlights: • The charge transfer between electrocatalysts and photoanode is improved. • CQDs was found to increase the charge separation efficiency evidenced by surface photovoltage spectra. • CQDs as a charge bridge enhance water oxidation by promoting hole separation and transfer. Due to its earth abundant and excellent stability, metal oxide semiconductor attracts great attention in photoelectrochemical water splitting. However, its performance is restricted due to the high recombination rate of electron-hole pairs even modified with electrocatalysts. In this work, carbon quantum dots are studied as the charge bridge to boost the charge transfer kinetics of cobalt phosphate (Co-Pi)/Fe₂O₃ photoanode at the photoanode/electrocatalyst interface. Our results show that carbon quantum dots significantly improve the charge transfer and charge separation efficiency of Co-Pi/Fe₂O₃ photoanode. The photocurrent is substantially enhanced to 4.9 mA/cm² at 0.6 V (vs. Ag/AgCl) which is much higher than Co-Pi/Fe₂O₃ photoanode 3.7 mA/cm² in the same situation. These results provide a strategy to improve photoanode performance by facilitating the electrical contact at the photoanode/electrocatalyst interface with carbon quantum dots.