A homogeneous multi-species transport model for porous TiO2 photoanode of photocatalytic fuel cell

Understanding the characteristics of multi species transport coupled with photoelectrochemical reaction occurring in the porous TiO2 photoanode of photocatalytic fuel cell remains a fundamental challenge. In this work, therefore, a theoretical model describing the hole/electron/organics/ion transport coupled with photoelectrochemical reaction is developed. Numerical results are in good agreement with experimental data. Besides, effects of various design and operation parameters on the photoanode performance are systematically studied. The photoanode performance improves with increasing the light intensity and decreasing the wavelength under the illumination from the substrate/photoanode interface due to more photo-excited electron-hole pairs and enhanced photon absorption, respectively. Increasing the supplied methanol and hydroxyl ion concentrations can boost the photoanode performance because of enhanced mass transport that accelerates photoelectrochemical reaction. When the photoanode is illuminated from the substrate/photoanode interface to the photoanode, increasing the photoanode thickness leads to an improvement in the photoanode performance because more photons are absorbed to photo-excite more electron-hole pairs. But too large thickness shows ignorable contribution to the photoanode performance. While for the illumination from the photoanode/electrolyte interface to the photoanode, the photoanode performance decreases with increasing the photoanode thickness due to increased electron transfer resistance. This work provides a deep understanding of various species transport characteristics coupled with photoelectrochemical reaction, which is useful for the design and operation of the photoanode.