The photoelectrochemical properties of highly crystalline and phase-pure BiOCl microplatelets synthesised via a room temperature ionic liquid method are reported. X-ray crystallography reveals a tetragonal BiOCl phase, while high resolution electron microscopy shows sheet-like structures with a cross section of approximately 5 μm and thickness in the range of 500 nm. Diffuse reflectance spectroscopy shows a direct bandgap transition at 3.34 eV. Electrochemical measurements of as-prepared BiOCl powders deposited onto fluorine-doped tin oxide electrodes show a sharp cathodic current at − 0.10 V vs RHE at pH 10, which is linked to electron injection into the conduction band edge. Photoelectrochemical measurements in the presence of Na2SO3 as hole-acceptor in solution exhibit a strong potential dependence, switching from cathodic to anodic photocurrents at potentials around 0.70 V vs RHE. The positive photocurrent is associated with SO32 − oxidation, while the unexpected negative photocurrents are linked to cathodic material decomposition.