ZnO-CdS-Ag2S double S-scheme heterojunctions with significant hydrogen evolution reaction and dye degradation properties

Abstract

Here in, we report a new methodology for the fabrication of free template ternary ZnO-CdS-Ag2S nanohybrids with superior photocatalyst properties for the hydrogen evolution reaction (HER) and dye degradation. Firstly, ZnO nanorods (NRs) were synthesized using a solvothermal method and used as a seed template for the growth of CdS-Ag2S QDs. The CdS-Ag2S QDs were grown using two different methods of microwave irradiation and photochemical treatment using thioglycolic acid (TGA) as both capping agent and digestive reactant. Structural characterizations proved the formation of the ternary structure with both methods of synthesis. XPS analyses revealed that photochemical approach results in the formation of a ternary composite with higher ZnO nanoparticles concentration. Electrochemical studies inferred that samples prepared using photochemical treatment have the least of charge transfer resistance, large surface area of 132 m2/g, large electrochemical surface area and higher electrochemical performance. Linear sweep voltammetry obtained current densities of magnitude of 100 mA cm−2 at bias −0.475 V vs. RHE, onset potential of −0.238 V, and Tafel slope of 45 mV/dec. Moreover, samples prepared using photochemical approach showed also high cyclic HER stability and reproducibility of the same results from the same ink after storing for six months. This method of synthesis can be applied for the synthesis of multi-functional ternary metal oxide-QD-QD nanocomposites for energy conversion applications. A S-scheme band diagram is suggested to infer the internal charge separation mechanism and high HER and photocatalyst activities of the ternary compound.