Ultrathin films on copper(i) oxide water splitting photocathodes: a study on performance and stability

TLDR

Cu2O photocathodes for water splitting suffer photocorrosion, requiring protective overlayers that provide favorable band alignment and chemical stability, yet long‑term deactivation occurs through overlayer etching and platinum catalyst loss. The study investigates which factors influence photocurrent performance and stability of Cu2O photocathodes with ultrathin overlayers. Ultrathin wide‑band‑gap oxide overlayers are deposited by atomic layer deposition to form a p–n junction for charge extraction and to protect Cu2O, and the study examines how deposition temperature, electrolyte pH/composition, and post‑annealing affect performance. A semi‑crystalline TiO₂ overlayer achieved 62 % stability over 10 h of testing without re‑platinization.

Abstract

The utilisation of Cu2O photocathodes for photoelectrochemical water splitting requires their stabilisation due to photocorrosion in aqueous electrolytes. Ultrathin films of wide band gap semiconducting oxides deposited by atomic layer deposition (ALD) on top of cuprous oxide can perform the dual function of both facilitating charge extraction (through the creation of a p–n junction) and protecting the absorber material from the aqueous electrolyte, thereby suppressing corrosion in favor of hydrogen generation. The factors that determine the photocurrent performance as well as the stability of these photoelectrodes are examined. Specifically, the influence of ALD deposition temperature, electrolyte pH, electrolyte composition as well as post-deposition annealing treatments was studied. The successful development of protective overlayers must fulfil the dual requirements of favourable band alignments as well as chemical stability. At long time scales, the deactivation of the photocathodes proceeds through etching of the amorphous overlayer, accompanied by the loss of the platinum catalyst particles. Through the deposition of a semi-crystalline TiO2 overlayer, 62% stability over 10 hours of testing has been demonstrated without re-platinization.