A highly efficient nanoporous non-doped BiVO4 photoelectrode with high photocurrent and low onset potential for photoelectrochemical water splitting was achieved by using molecular catalyst and amorphous TiO2 stabilization layer. This BiVO4 photoelectrode co-catalyzed by molecular catalyst of Ir-COOH exhibits the photo electrochemical performance comparable to the limitation values obtained in Na2SO3 sacrifice agent. Interestingly, the BiVO4/Ir-COOH exhibits more efficient interface charge transfer than BiVO4/IrOx as measured by intensity modulated photocurrent spectroscopy (IMPS) and intensity modulated photovoltage spectroscopy (IMVS) although the Ir-COOH molecular catalyst shows much lower electrochemically catalytic activities than the state-of-the-art IrOx, nanoparticles for water splitting. The Ir-COOH/BiVO4 was further stabilized by double amorphous TiO2 layers with little impact on charge transfer. In all, it is promising to achieve high efficiency water splitting by using molecular catalysts to co-catalyze nanostructure photoelectrodes with short diffusion length and such system can be stabilized by amorphous TiO2 layer.