A multi-species transport model for one-dimensional TiO2 nanotube array photoanode of photocatalytic fuel cell

Abstract

One-dimensional TiO2 nanotube array photoanode used in photocatalytic fuel cells exhibits excellent performance. However, a fundamental understanding of multi-species transport coupled with photoelectrochemical reactions in this type of photoanode remains unclear. In this work, a multi-species transport model with the consideration of the electron/hole transport in the nanotube wall, the organics/hydroxyl ion transport in the pore space and the photoelectrochemical reaction at the semiconductor/electrolyte interface is developed for one-dimensional TiO2 nanotube array photoanode. The simulated result is in good agreement with the experimental data. Effects of operation conditions and nanotube structures are also studied. It is found that increasing the organics/hydroxyl ion concentrations improves the photoanode performance because of enhanced mass transport. The increase of illumination intensity allows for more electron-hole pairs to be generated, leading to the improved photoanode performance. Decreasing the wavelength results in the lowered photoanode performance. Thinner nanotube wall thickness yields better performance, while there exists an optimum nanotube layer thickness leading to the optimum performance. The results obtained not only shed light on the characteristics of multi-species transport coupled with photoelectrochemical reactions but also benefits the design and operation of one-dimensional TiO2 nanotube array photoanode.