Analysis of an Electrolyte’s pH-Dependent Performance during Solar Water Splitting

Abstract

The redox reaction is related to the pH of the electrolyte owing to protonation/deprotonation during photoelectrochemical (PEC) water splitting. However, the influence of electrolyte pH on water splitting is not clear, especially the mechanism of the solid–liquid interface mass transfer and carrier transport process under strong acid and alkaline conditions. Herein, a comprehensive series of PEC characterization methods including the linear sweep voltammetry, electrochemical impedance spectroscopy (EIS), Mott–Schottky, and intensity-modulated photocurrent/photovoltage spectroscopy (IMPS/IMVS) were deployed to reveal the effect of pH on the carrier transport at the solid–liquid interface layer using TiO2 and Sb2Se3 as the photoanode and photocathode, respectively. Our results indicated that the photocurrent density under alkaline conditions can be as much as six times greater than that under acidic conditions for Sb2Se3, while for the TiO2 photoanode, the photocurrent under strong alkaline conditions was approximately four times greater compared to that under acidic conditions. The relationship between the photocurrent density and electrolyte pH was investigated by injecting acidic and alkaline electrolytes through the electrode surface using a multichannel syringe pump. According to the EIS results, a rise in the pH reduces the impedance of the electrolyte/electrode interface and improves the carrier separation efficiency. Interestingly, the carrier collection efficiency, which is defined by the carrier lifetime and transport time, was enhanced with a rise in electrolyte pH. Our work provides a general approach to identify the relationship between electrolyte pH and carrier dynamics at the electrolyte/electrode interface by electrolyte regulation using a microchannel reactor.