Understanding the stability of CuxO photocathodes for photoelectrochemical water splitting: Insights by operando XAS

Photoelectrochemical energy conversion is a promising solution for sustainable energy production by harnessing solar energy to produce clean fuels like hydrogen (H2). H2, as a clean and renewable energy vector, can be produced from water using solar energy in one step. In this work, CuxO electrode was synthesized by thermal treatment and used as photocathode, after the deposition on metallic Cu to improve the PEC water splitting performance. The synthesized photocathodes were characterized by XRD, SEM, XAS and then their electrochemical performances were investigated. Two CuxO electrodes were alternatively used as working electrode (WE) and counter electrode (CE), recording the photocurrent of the WE in each switching process. This procedure has been applied with the aim of improving the lifetime of the CuxO electrode, since CuxO is easily reduced during the PEC water splitting. Interestingly, the cathode photocurrent increases in the third switching process, reaching a maximum and then decreases. Therefore, operando X-ray absorption near edge structure spectrum (XANES) was used to track the effective composition of the photocathodes during the hydrogen production, applying a sequence of polarization potentials in order to mimic the described switching process during PEC water splitting. This work provides a method to investigate the semiconductors behaviour during their role of photoanode/photocathode, including possible photocorrosion phenomena.