Metal vacancies in semiconductor oxides enhance hole mobility for efficient photoelectrochemical water splitting

Achieving efficient carrier separation in transition-metal-oxide semiconductors is crucial for their applications in optoelectronic and catalytic devices. However, the substantial disparity in mobility between holes and electrons heavily limits device performance. Here we develop a general strategy for enhancing hole mobility via reducing their effective mass through metal vacancy (VM) management. The introduction of VM yields remarkable improvements in hole mobility: 430% for WO3, 350% for TiO2 and 270% for Bi2O3. To illustrate the importance of this finding, we applied the VM concept to photoelectrochemical water splitting, where efficient carrier separation is highly coveted. In particular, VM-WO3 achieves a 4.4-fold enhancement in photo-to-current efficiency, yielding a performance of 4.8 mA cm−2 for both small- and large-scale photoelectrodes with exceptional stability for over 120 h. Efficient charge carrier separation is a substantial roadblock to achieving high performance in photoelectrochemical systems based on transition-metal oxides. Here a metal vacancy strategy is used to enhance hole mobility, resulting in general enhancement of photocurrent density in WO3, TiO2 and Bi2O3 photoanodes.