Charge carrier separation in nanostructured TiO2 photoelectrodes for water splitting

Abstract

There is intense interest in developing new novel nanostructured photoanodes for water splitting. It is therefore important that methods to analyze the effect of nanostructuring on water splitting yields are developed in order to rationalize the relative merits of this approach for different materials. In this study the dependence of charge separation efficiency (η_sep) on potential during photoelectrochemical water splitting at pH 2 has been quantified in a model electrode system (nanocrystalline, mesoporous TiO₂) using two independent methods. These are (i) analysis of incident photon conversion efficiency (IPCE) measurements and (ii) transient absorption (TA) spectroscopy measurements. The techniques provide good agreement with each other and show that a low maximum value of η_sep (∼0.18) is the primary cause of the low IPCE for water oxidation on these nc-TiO₂ electrodes.