Surface Passivation of TiO₂ Nanowires Using a Facile Precursor-Treatment Approach for Photoelectrochemical Water Oxidation

We developed a facile precursor-treatment approach for effective surface passivation of rutile TiO₂ nanowire photoanode to improve its performance in photoelectrochemical (PEC) water oxidation. The approach was demonstrated by treating rutile TiO₂ nanowires with titanium precursor solutions (TiCl₄, Ti­(OBu)₄, or Ti­(OiP)₄) followed by a postannealing process, which resulted in the additional deposition of anatase TiO₂ layer on the nanowire surface. Compared to pristine TiO₂, all the precursor-treated TiO₂ nanowire electrodes exhibited a significantly enhanced photocurrent density under white light illumination. Among the three precursor-treated samples, Ti­(OBu)₄-treated TiO₂ nanowires achieved the largest enhancement of photocurrent generation, which is approximately a 3-fold increase over pristine TiO₂. Monochromatic incident photon-to-electron conversion efficiency (IPCE) measurements showed that the improvement of PEC performance was dominated by the enhanced photoactivity of TiO₂ in the UV region. The photovoltage and electrochemical impedance spectroscopy (EIS) measurements showed that the enhanced photoactivity can be attributed to the improved charge transfer as a result of effective surface state passivation. This work demonstrates a facile, low-cost, and efficient method for preparing highly photoactive TiO₂ nanowire electrodes for PEC water oxidation. This approach could also potentially be used for other photoconversion applications, such as TiO₂ based dye-sensitized solar cells, as well as photocatalytic systems