Enhanced photocatalytic H2 evolution on ultrathin Cd0.5Zn0.5S nanosheets without a hole scavenger: Combined analysis of surface reaction kinetics and energy-level alignment

Abstract The surface photocatalytic water splitting kinetics of ultrathin Cd0.5Zn0.5S nanosheets without hole scavengers is critically examined, focusing on the effects of the pH and NaOH as an electrolyte. In aqueous NaOH, hole scavenging from Cd0.5Zn0.5S is enhanced, which reduces catalyst photocorrosion. Based on the Langmuir-Hinshelwood model, OH− adsorption on Cd0.5Zn0.5S is the rate-limiting step of the whole process, and the reaction rate increases with increase in pH and temperature. The hydrogen evolution reaction (HER) activity of Cd0.5Zn0.5S reaches 12.44 and ∼ 20 mmol‧g−1‧h−1 at 303.15 K and 313.15 K (6 M NaOH, 0.5 h), respectively, two orders of magnitude higher than that in pure water. At high pH, direct OH− oxidation is favored, enhancing water splitting and indicating that water oxidation shifts to a ∙OH production pathway with activation energy approximately of 23.73 kJ‧ mol−1. Promisingly, this strategy to improve H2 production rates is applicable to other chalcogenide photocatalysts (CdS, Cd0.5Mn0.5S, ZnSe and Cd0.5Zn0.5Se).