Photoelectrochemical and Impedance Spectroscopy Investigation of Water Oxidation Reaction over Coordination Polymers Decorated TiO2 Nanotubes Arrays Electrodes

Abstract

Loading a cocatalyst onto a photoelectrodes is a wide spread strategy to enhance the efficiency of the photoelectrochemical water splitting process [(Yang, Wang, Han, & Li, 2012)]; however, its performance is strongly dependent of the method employed to form the heterojunction between cocatalyst and photoelectrode, as well as the alignment of their energetic levels to separate successfully the photogenerated charge carriers. In this study, we report water splitting photoanodes constituted from TiO2 nanotubes arrays decorated with coordination polymers as cocatalyst. Highly ordered TiO2 nanotubes were synthesized by the electrochemical anodization process of titanium (Ti) foil in a 0.2 M NH4F, ethylene glycol/10% H2O electrolyte under constant anodization time and applied potential. Coordination polymers were deposited onto TiO2 nanotubes by using the low cost successive layer adsorption and reaction (SILAR) method. Cocatalyst was successfully deposited on TiO2 nanotubes with tunable loading amounts by controlling the deposition cycles of SILAR. The structural characterization, morphology, elemental composition and light absorption capability of the samples were characterized by XRD, RAMAN, FT-IR, FE-SEM, EDX and UV–Vis methods respectively. Furthermore, the semiconducting properties of the modified TiO2 nanotubes were also estimated from Mott-Schottky plots. It was found that under illumination, the cocatalyst can efficiently collect photogenerated holes from the TiO2 nanotubes electrodes promoting charge separation and lowering the onset potential which yields an increased water oxidation efficiency. Yang, J., Wang, D., Han, H., & Li, C. (2012). Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis. Accounts of Chemical Research, 46(8), 1900–1909. https://doi.org/10.1021/ar300227e