We therefore investigated the carrier dynamics of the BiVO4 photoanode and hybrid PEI/TiO2 through dual-working electrode (DWE) analysis to evaluate hole transfer efficiency. We carried out operando open-circuit potential (OCP) measurement with the DWE to determine the energetics of the majority carriers of BiVO4 and TiO2 under dark and light conditions. In the measurement, BiVO4/TiO2 showed identical Fermi levels for BiVO4 and TiO2 under dark conditions, indicating Fermi level equilibration between the two semiconductor materials (Fig. ). We also observed a slight shift in the Fermi level of BiVO4 under illumination due to the accumulation of photogenerated electrons, and the Fermi level of BiVO4 decreased and returned to equilibrium with TiO2 after turning off the light.