A plausible schematic diagram is presented in Fig. 8B by the
function of PEC for WO3/BiVO4 as a photo-anode and Cu2O/Ag as
a photo-cathode under visible light irradiation. Under visible light
irradiation and bias potential, at a photo-anode a number of holes
(h+) are generated to oxidize MB to CO2. The electrons from the
photo anode were derived by bias potential, while at the photo
cathode the reduction would take place efficiently by the electron
transfer from the Cu2O conduction band to Ag particles. Therefore,
the high efficiency of the degradation of MB was achieved.