Photocurrents under irradiation for all samples annealed in He are significantly higher than that of the as-prepared sample, reaching up to 1.17 µA cm -2 for BOC-H-300, which is 7 times higher than that of BiOCl (0.13 µA cm -2 ). In contrast, O2-annealing seems to be detrimental as the photocurrent for sample BOC-O-300 drops to 0.08 µA cm -2 . The maximum theoretically achievable photocurrent density of BiOCl (3.2 eV) is around 500 µA cm -2 under 100 mW cm -2 simulated solar light illumination . However, the practical photocurrent will strongly be limited by light absorption, separation and transport of charge carriers as well as the rate of the surface redox reactions . Although bulk defects may act as recombination centers for photogenerated charge carriers and are thus unfavorable for photoelectrochemical activity ,