Photoelectrochemical Manifestation of Photoelectron Transport Properties of Vertically Aligned Nanotubular TiO2 Photoanodes

A simple photoelectrochemical method was proposed to quantitatively evaluate the electron transport process of photoelectrocatalytic oxidation of water at vertically aligned nanotubular TiO2 photoanodes. The photoelectrocatalysis reaction resistance (R=k/J(sph)+R(0)=R(I)+R(0)) was measured and used to express the electron transport characteristics of a nanotubular TiO(2) electrode. The overall resistance was found to consist of a variant (R(I)) and an invariant component (R(0)). R(I) was found to be inversely proportional to the saturation photocurrent and it depends on the experimental conditions. The proportional constant, k, represents the minimum applied potential bias required to remove 100 % of the photogenerated electrons from the photocatalyst layer and was found to be independent of the anodization time. The invariant component of the resistance (R(0)) is an inherent property of the semiconductor photocatalyst that represents the sum of Ohmic contact impedance at the conducting substrate/TiO2 interface and crystalline boundary impedance. The magnitude of R(0) linearly increased with anodization time. The real saturated photocurrent density (J(real-sphd)) was found to be independent of R(0) indicating that the electron collection efficiency is independent of the nanotube length.