Initially, a 10 nm-thick permeable Au layer was deposited using sputtering onto each photoanode surface, which had been covered with epoxy resin (Epoxide-resin EA 9461, Loctite). To establish an additional contact for surface potential measurement of the TiO2 layer, a front contact was fabricated on the Au layer of the epoxy surface. The front contact was connected with a Cu foil and the Au layer using Ag paste and sealed by additional epoxy to protect the contact from the electrolyte. Open circuit potential (OCP) measurement was carried out using a dual-working electrode (DWE) through Bio-Logic SP-300 potentiostat with V2controlled PEIS measurements. A first and second working electrode (WE1 and WE2) were connected to the BiVO4 back contact and the TiO2 front contact, allowing to monitor changes in Fermi level and quasi electron Fermi level under dark and light illumination.