Improved photoelectrochemical water oxidation kinetics using a TiO₂ nanorod array photoanode decorated with graphene oxide in a neutral pH solution

We prepared TiO₂ nanorod (NR) arrays on a fluorine-doped tin oxide substrate and decorated with graphene oxide (GO) to study their photoelectrochemical (PEC) water oxidation activities in two different electrolytes. The PEC performances of GO-decorated TiO₂ NR photoanodes were characterized by optical and electrochemical impedance spectroscopy measurements. In 1 M KOH, the photocurrent density of the TiO₂ NR film decreased after deposition of GO, while in the neutral pH electrolyte (phosphate buffered 0.5 M Na₂SO₄), the TiO₂ NR photoanode showed enhanced performance after deposition with the 2 wt% GO solution. This was a consequence of the decrease in charge transfer resistance between the electrode surface and the electrolyte. The improvement of photocurrents by GO decoration was obvious near the onset potential of the photocurrents in the neutral pH electrolyte. These opposite contributions of GO on the TiO₂ NR photoanodes suggest that GO can promote water oxidation effectively in a neutral electrolyte because depending on the pH of the electrolyte, different chemical species interact with the surface of the photoanode in the water oxidation reaction.