To confirm that the phenomenon is generalizable to other materials, we extended our investigation to Fe2O3, a well-studied semiconductor photoanode known for having slow hole transfer. We deposited a 100 nm a-TiO2 layer onto an Fe2O3 photoanode with and without a PEI layer using the same method explained before. The XPS and SEM measurements showed the same trend compared to BiVO4 (Supplementary Fig. and), and the Fe2O3/TiO2 also exhibited a very low photocurrent in the microampere scale (0.0018 mA cm -2 at 1.6 V vs. RHE) similar to that of BiVO4/TiO2 (Supplementary Fig. ). However, we observed improved PEC performance and the dramatic shift in onset potential with a thicker PEI interfacial layer under the TiO2 protective layer (Supplementary Fig. ), which indicates that the thickness of PEI significantly influences PEC performance of the hybrid PEI/TiO2 layer.