Heterogeneous doping of visible-light-responsive Y2Ti2O5S2 for enhanced hydrogen evolution

Abstract

Y₂Ti₂O₅S₂, a stable oxysulfide photocatalyst with a bandgap energy of 1.9 eV, has been studied for the purpose of H₂ production via sunlight-driven water splitting. Although this material absorbs a wide range of wavelengths, the light-driven hydrogen evolution activity of Y₂Ti₂O₅S₂ remains low due to ineffective charge carrier separation. The present study improved the charge separation in Y₂Ti₂O₅S₂via heterogeneous doping with lower valency Sc³⁺ at Ti⁴⁺ sites. This doping combined with flux- and etching-treatments incorporated Sc³⁺ ions into the Y₂Ti₂O₅S₂ surface without degrading the bulk crystallinity of the material or generating by-products. The optimized Sc-doped Y₂Ti₂O₅S₂ was 3.4 times more active than pristine Y₂Ti₂O₅S₂ during photocatalytic H₂ evolution. Transient diffuse-reflectance spectroscopy and theoretical modelling established that Sc doping provided a shallower trap state distribution above the valence band of Y₂Ti₂O₅S₂ and facilitated hole detrapping. This effect promoted surface oxidation reactions and thereby enhanced the photocatalytic properties of the oxysulfide.