Electrochemical impedance spectroscopy (EIS) is capable to determine resistances and capacities in the semiconductor solution interface by fitting equivalent circuits. In our study, EIS was conducted at open circuit potential (OCP) in the dark. The BiOCl electrolyte interface can be fit in first approximation by a Randles equivalent circuit, describing charge transfer and diffusion processes (Fig. ). The smaller the diameters of the semicircles of the plots, the smaller is the charge transfer resistance and the higher is the charge transfer rate at the interface. Compared and flat band position (Efb) were measured and are summarized in Table . The band bending (Ubb) of BiOCl samples was calculated according to the formula: 𝑈𝑈 𝑏𝑏𝑏𝑏 = 𝑂𝑂𝑂𝑂𝑂𝑂 -𝐸𝐸 𝑓𝑓𝑏𝑏 . The larger upwards band bending results in a larger contact potential difference at the semiconductor-solution interface. In addition, the donor density can be estimated by the slope of the Mott-Schottky plot according to the formula below: