Enhanced Charge Separation of TiO2 Nanotubes Photoelectrode for Efficient Conversion of CO2

Abstract

For the production of TiO2 nanotubes (TNTs) efficient photoelectrodes they must have efficient charge separation by trapping holes and transfer of electrons. In this study, MnOx and Pd codecorated TNTs photoelectrodes were successfully constructed using a simple impregnation method, followed by an electrochemical deposition process. The photocatalytic activities for CO2 conversion by the optimized TNTs photoelectrode (10Pd/0.8Mn/TNTs) were increased by 2.8 times to produce 40.3 ± 2.5 mg L–1 acetic acid, and by 2.5 times to generate 24.6 ± 1.9 mg L–1 formic acid compared to a bare TNTs photoelectrode. The optimized photoelectrode also showed the highest transient photocurrent of 1.15 mA cm–2. The improved performance was due to the elevated charge separation through bidirectional modulation of photogenerated holes and electrons, on the basis of the steady-state surface photovoltage and analysis with the formed •OH concentrations, electrochemical reduction tests with N2 or CO2 atmospheres, and electrochemical impedance spectra. The decorated MnOx effectively trapped the photogenerated holes, and the decorated Pd facilitated photogenerated electron transfer and promoted visible light absorption. The decorated MnOx and Pd also played catalytic roles in the redox reactions involved with the photogenerated charge carriers.