A surface and cross-sectional morphology were analyzed with a Hitachi SU-7000 fieldemission scanning electron microscope (SEM) and Zeiss Gemini 450 SEM. The Bi and V contents in electrolytes after stability test were evaluated with a Varian inductively coupled plasma-optical emission spectrometer (ICP-OES). High-resolution X-ray photoelectron spectroscopy (XPS) spectra of the photoanodes was obtained by Thermo Fisher K-Alpha XPS instrument, and valence state XPS analysis to confirm "leaky" state was carried out with minutes when exposed to air. Therefore, the HOPG was measured against an Aluminium metal mirror with native Al2O3 layer on the surface. The work function of the Al/Al2O3 (~3.90 eV) was stable for several hours and even days. Open-source Gwyddion software package as well as the Asylum Research build in software were used to further analyze the AFM pictures and determine the average work function of the surface.