It was assumed that the presence of C and N in hybrid PEI/TiO2 could influence the intrinsic properties of amorphous TiO2, thereby contributing to facile hole transfer. To elucidate the intrinsic properties of the hybrid PEI/TiO2, we conducted electron energy-loss spectroscopy (EELS) for BiVO4/TiO2 and BiVO4/PEI/TiO2 photoanode. This analysis aimed to characterize the defect band of a-TiO2, which is crucial for facilitating hole transfer from light absorbers to drive water oxidation. In EELS analysis, Cs-corrected TEM was used with a line scan technique for depth profiling analysis to investigate the oxidation state of Ti and O within both the amorphous TiO2 and the hybrid PEI/TiO2 layer (Fig. ). EELS analysis of BiVO4/TiO2 showed two primary peaks in the Ti L-edge (459.74 and 465 eV) and O K-edge spectrum (531.4 and 542.65 eV), and we verified that the position of each peak remained consistent regardless of the depth (Fig. and Supplementary Fig. ). However, in the case of BiVO4/PEI/TiO2, while there were no depth-dependent peak variations, we observed an overall shift of Ti peaks towards the low-energy region (Fig. and Supplementary Fig. ). The low-energy shift of Ti is known to occur due to the reduction of Ti 4+ in TiO2, which suggests that the hybrid PEI/TiO2 exhibits a higher Ti 3+ population with an excess electron compared to normal a-TiO2. The reduction of Ti was also confirmed through kelvin probe force microscopy (KPFM) measurements for both normal TiO2 and hybrid PEI/TiO2. The KPFM measurements revealed work functions of 4.82 eV, 4.57 eV, and 4.41 eV for the BiVO4, BiVO4/TiO2, and BiVO4/PEI/TiO2 photoanodes, respectively (Supplementary Fig. ). The lower work function value of hybrid PEI/TiO2 indicates the reduction of TiO2, which coincides with the results obtained from EELS analysis.