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 (V M ) management. The introduction of V M yields remarkable improvements in hole mobility: 430% for WO 3 , 350% for TiO 2 and 270% for Bi 2 O 3 . To illustrate the importance of this finding, we applied the V M concept to photoelectrochemical water splitting, where efficient carrier separation is highly coveted. In particular, V M -WO 3 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.