Novel synthesis of reduced PdO-WO3 hybrids for enhanced photoelectrochemical water splitting

Abstract

In this study, a novel synthesis approach for WO3 nanoparticles and their hybrids is proposed, followed by an investigation of their photoelectrochemical performance for water splitting applications. The surface modification of WO3 nanoparticles is carried out by immersing them in a Pd precursor solution, followed by calcination to obtain PdO-WO3 hybrid nanoparticles. Subsequently, the PdO-WO3 is reduced in a hydrogen (H2) environment to prepare PdOx-WO3-y hybrid material. XPS analysis revealed that H2 reduction converts residual metallic Pd to PdH and simultaneously generates oxygen vacancy defects in WO3 hybrid nanoparticles, as confirmed by EPR analysis. Additionally, TPR analysis further confirms the H2-induced reduction in the PdO-WO3 hybrid at a lowered temperature of 150 °C. The optical band gap energy of PdOx-WO3-y hybrid nanoparticles is slightly reduced (by 0.06 eV) compared to that of the PdO-WO3 reference sample. Photoelectrochemical measurements were conducted to assess the impact of these tailored modifications on the performance of conventional PdO-WO3 nanoparticles. The reduced PdOx-WO3-y catalyst exhibits an approximatly ∼22 % improvement in incident photon-to-current conversion efficiency (IPCE), over the unreduced PdO-WO3. The PEC efficiency improvement was attributed to the composite electronic structure changes introduced during the annealing process. Mott-Schottky measurements confirm that the reductive treatment consolidates the material’s two distinct flat band potentials (Efb) into with a single intermediate energy level and increases the charge carrier concentration. This study presents a straightforward method to generate oxygen vacancy defects in hybrid metal oxides and provides a convenient method for band gap engineering for photoelectrocatalytic applications.