Operando measurement of electrocatalyst potential on particulate photocatalysts for overall water splitting

Abstract

Photocatalytic water splitting using semiconductor particulates is an effective technique for solar-energy conversion to chemical energy in the form of hydrogen molecules. The photocatalytic reactions proceed via two half reactions: the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). The active sites in these reactions are electrocatalysts that have been deposited on particulate photocatalyst surfaces. It is important to understand the electrocatalyst potential during the photocatalytic reactions to understand the reaction mechanism. Several measuring methods have been developed for photoelectrodes, but it is still challenging to measure the electrocatalyst potential directly during unbiased overall water splitting with particulate photocatalysts. This study presents an inverted photocatalyst structure to evaluate the operating potential of CoOOH electrocatalysts during overall water splitting. The structure consists of Al-doped SrTiO₃ (SrTiO₃:Al) photocatalyst powder deposited on a CoOOH electrode. In addition, we estimated the fraction of holes that reach the SrTiO₃:Al photocatalyst surface after carrier generation in the bulk from the light-intensity dependence of the CoOOH electrocatalyst potential balanced with the hole quasi-Fermi level in the photocatalyst. The hydrogen production rate was found to be controlled by modulating the potential applied to the CoOOH electrode, which perturbs the hole quasi-Fermi level in the SrTiO₃:Al photocatalyst.