Dual Functional CuO1-x Clusters for Enhanced Photocatalytic Activity and Stability of a Pt Cocatalyst in an Overall Water-Splitting Reaction

Photocatalytic overall water splitting to produce hydrogen is one of the most promising means to utilize solar energy and water. Pt has been widely used as the optimal cocatalyst in photocatalytic water splitting. However, it still has an obvious drawback that the H-2 evolution rate shows an obvious decrease for overall water splitting after a certain reaction time due to the back reaction between H-2 and O-2 to produce water. To date, the mechanism of the back reaction under solar-light irradiation is still unclear, and the method of preventing the back reaction has been rarely researched in recent years. Herein, a hybrid Pt/Cu1-x/TiO2 catalyst was prepared via an in situ photodeposition method. Compared to Pt/TiO2, the as-prepared Pt/CuO1-x/TiO2 showed enhanced photocatalytic activity and stability in the water-splitting reaction. Characterization results revealed that CuO1-x clusters are highly dispersed on the exposed TiO2 surface, and Pt particles are mainly deposited upon the CuO1-x clusters. The electrochemical hydrogen evolution reaction (HER) tests and transient photocurrent responses manifested the fast and efficient transfer of e(-) from CuO1-x, to Pt. It was found that O-2(-) plays an important role for the reverse reaction of photocatalytic water splitting. The CuO1-x clusters in the Pt/CuO1-x/TiO2 catalyst restrain the back reaction of water splitting due to the decreased formation of O-2- on the surface of TiO2 (like the Ying character in Taoism). In addition, the fast transfer of e(-) from TiO2 to CuO1-x and Pt particles accordingly improves the photocatalytic activity (like the Yang character in Taoism). These two characters of CuO1-x synergistically improve the photocatalytic activity and stability during the overall water-splitting process. This study reveals the mechanism on the back reaction of water splitting over Pt/TiO2 under solar-light irradiation and provides an innovative and practical way to efficiently enhance the photocatalytic activity and prevent the back reaction of water splitting.