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

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 similar to 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 center dot OH production pathway with activation energy approximately of 23.73 kJ.mol(-1). Promisingly, this strategy to improve H-2 production rates is applicable to other chalcogenide photocatalysts (CdS, Cd0.5Zn0.5S, ZnSe and Cd0.5Zn0.5Se).

Automated summary

The study found that in NaOH solution, the hole scavenging capability of Cd0.5Zn0.5S is enhanced, which effectively reduces the photocorrosion of the catalyst and increases the reaction rate of water splitting. Furthermore, under high pH conditions, the water oxidation pathway shifts to direct OH- oxidation, promoting the splitting of water.