Charge transfer in iron oxide photoanode modified with carbon nanotubes for photoelectrochemical water oxidation: An electrochemical impedance study

Iron oxide photoanode was modified with multi-wall carbon nanotubes (MWCNTs) to improve the charge transport property of iron oxide in the photoelectrochemical water oxidation under solar light. The MWCNT-modified Fe2O3 electrode exhibited markedly increased photocurrent generation (by 66%) relative to unmodified Fe2O3 electrode. Electrochemical impedance spectroscopy demonstrated that MWCNT modification dramatically decreased resistance over the entire electrode and increased capacitance at the interface between carbon nanotubes and conducting substrate. The Mott-Schottky analysis showed that the flat band potential of the Fe2O3 electrode shifted to a more positive potential in the MWCNT-modified anode, indicating the charge migration from Fe2O3 to MWCNT. Thus the role of the MWCNT as an expressway for electron transport has been clearly demonstrated, which would help charge separation and improve photoelectrochemical water oxidation efficiency of the poorly conducting Fe2O3 electrode.