Transient phenomenological modelling of photoelectrochemical cells for water splitting: application to undoped hematite electrodes

A phenomenological model is proposed for a better understanding of the basic mechanismsof photoelectrochemical (PEC) cells. The main assumptions of the one-dimensionaltransient phenomenological model are: i) bulk recombination of the conduction bandelectrons with holes in the valence band; ii) the mobile charge transport takes place viadiffusion, which arises from the concentration profiles, and migration, caused bya macroscopic electric field; iii) negligible effects of microscopic electric fields in the celland screening effects, as well as negligible Helmholtz and diffuse layers. For modelingpurposes, the photoanode was assumed to be a homogeneous nanocrystalline hematitestructure, with thickness L, porosity 3p and tortuosity s. The TCO/semiconductor interfacewas modeled as an ideal ohmic contact, while the electrolyte/platinized TCO interface wasdescribed by a ButlereVolmer approach. An alkaline electrolyte solution was used,allowing the transport of the ionic species from the counter-electrode to the photoanode.The continuity and transport governing equations are defined for the mobile speciesinvolved: electrons in the conduction band of the semiconductor, holes in the valence bandand hydroxyl ions in the electrolyte. Simulated IeV characteristics were computed and thecorresponding results compared with the experimental values. The simulated results werein straight agreement with the experimental data