Carbon dots enhance the interface electron transfer and photoelectrochemical kinetics in TiO2 photoanode

Photoelectrochemical (PEC) water splitting is one of the most promising strategies to turn solar energy into chemical fuels. The low efficiency of photo-generated charge separation caused by fast electron-hole recombination is regarded as a challenge that hinders the further improvement of TiO2 photoanode performance in PEC cells. Here, the nitrogen-doped carbon dots (N-CDs) anchored TiO2 photoanodes were fabricated by one-step hydrothermal method. The in-situ transient photovoltage (TPV) technology shows that electron-trap effect is formed in TiO2 photoanode due to the existence of N-CDs. Meanwhile, the enhancement of photo-generated charge separation efficiency was proven as the charge extraction of TiO2 is promoted by ~160% after anchoring N-CDs. Besides, N-CDs increase the conductivity of TiO2 photoanode and promote the efficiency of photo-generated charge transfer. In addition, the impedance of TiO2 photoanode and its interface are reduced by ~ 34% and ~ 66%, respectively. Under AM 1.5G light intensity and 1.23 V vs. RHE, the highest photocurrent densities of TiO2/N-CDs (TNCD-15 mg) is 3.09 mA cm−2 in 1.0 M NaOH, which is ~ 3.22 times as high as that of the primitive TiO2. This work explains the mechanism of anchoring N-CDs to improve PEC performance through in-situ characterization, which provides a new idea for PEC material design to achieve higher PEC performances.