Silver and yttrium co-doped ZnO nanoparticles as a potential water splitting photocatalyst for the H₂ evolution reaction

Herein, we present the preparation of silver and yttrium co-doped ZnO (Ag-Y-ZnO) nanoparticles by a sol-gel process. The obtained catalysts are systematically characterized using a variety of standard techniques, including x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDX), Brunauer–Emmett–Teller (BET), diffuse reflectance spectra (DRS), photoluinescnce (PL), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). XRD analysis confirms the successful doping of Y ions into the lattice of ZnO with a slight negative peak shift while Ag appears in its metallic form on the surface of ZnO. The (Ag, Y) co-doping into ZnO decreased the crystallite size from 47.4 nm to 40.2 nm, promoted the optical response from 381 nm to 413 nm in the visible region, and inhibited the recombination rate of electron-hole pairs. Among all prepared catalysts, the Ag-Y-ZnO exhibits an optimum photocatalytic H₂ evolution rate of 587.4 μmolh⁻¹g⁻¹, and 425.4 μmolh⁻¹g⁻¹ through water-methanol mixture under visible and UV light illumination, respectively. This catalyst manifests 49 and 3.32 times enhancement for cumulative (4 h) and initial H₂ evolution rates, respectively, and credit to the red shift in the light absorption, inhibited recombination of photoinduced chare carriers, and abundant actives sites accessible for H₂ evolution reaction. Furthermore, the recycling tests verify the strong stability of the as-prepared Ag-Y-ZnO catalyst. The plausible mechanism for the increased photocatalytic activity of the Ag-Y-ZnO catalyst is also proposed and discussed. Graphical Abstract: [Figure not available: see fulltext.]