Modelling TiO2 photoanodes for PEC water splitting: Decoupling the influence of intrinsic material properties and film thickness

Abstract

Semiconductor metal oxides are intensively studied in electrodes for photoelectrochemical (PEC) water splitting. On a series of nanoparticulate TiO2 photoanodes, we analyze specific fabrication variables by means of data fitting. First, the experimental outcome is gathered using PEC characterization techniques, mostly cyclic voltammetry and transient photocurrent measurements. Subsequently, we apply models to gain insights into the involved charge trapping and transfer phenomena. We find that capacitance coefficients and the switch-on transient kinetics depend on the TiO2 layer thickness, respectively indicating surface mechanisms and stationary regimes that are mediated by light accessibility. On the contrary, exponential factors of capacitance are independent of thickness, but reflect changes in the density of electron states with different sintering atmospheres. Also, the transfer resistance in the electrolyte side is indirectly influenced by sintering. Through meticulous quantitative analysis of trends, we stablish simple mathematical relationships that connect thickness-dependent parameters. This knowledge delves into fundamental mechanisms governing the TiO2 photoelectrode behaviour, and aims to facilitate further improvements in the efficiency of materials and electrodes for green hydrogen production.