The introduction of oxygen vacancies of BiOCl is conducted at various temperatures in helium atmosphere, the gas flow rate and ramping rate are 50 ml min -1 and 5 °C min -1 , respectively. The annealing samples are denoted as BOC-H-x (x indicates annealing temperature in °C). In addition, for comparison, BiOCl annealed at 300 °C in oxygen for 12 h is denoted as BOC-O-300.