M–Au/TiO2 (M = Ag, Pd, and Pt) nanophotocatalyst for overall solar water splitting: role of interfaces

Abstract

M–Au/TiO₂ (M = Ag, Pd, Pt) composites were prepared through a facile one-pot photodeposition synthesis and evaluated for solar water splitting (SWS) with and without a sacrificial agent. The M–Au combination exhibits a dominant role in augmenting the H₂ generation activity by forming a bi-metallic system. Degussa P25 was used as a TiO₂ substrate to photodeposit Au followed by Au + M (M = Ag/Pd/Pt). The SWS activity of the M–Au/TiO₂ was determined through photocatalytic H₂ production in the presence of methanol as a sacrificial agent under one sun conditions with an AM1.5 filter. The highest H₂ yield was observed for Pt_0.5–Au₁/TiO₂ and was around 1.3 ± 0.07 mmol h⁻¹ g⁻¹, with an apparent quantum yield (AQY) of 6.4%. Pt_0.5–Au₁/TiO₂ also demonstrated the same activity for 25 cycles of five hours each for 125 h. Critically, the same Pt_0.5–Au₁/TiO₂ catalyst was active in overall SWS (OSWS) without any sacrificial agent, with an AQY = 0.8%. The amount of Au and/or Pt was varied to obtain the optimum composition and it was found that the Pt_0.5–Au₁/TiO₂ composition exhibits the best activity. Detailed characterization by physico-chemical, spectral and microscopy measurements was carried out to obtain an in-depth understanding of the origin of the photocatalytic activity of Pt_0.5–Au₁/TiO₂. These in-depth studies show that gold interacts predominantly with oxygen vacancies present on titania surfaces, and Pt preferentially interacts with gold for an effective electron–hole pair separation at Pt–Au interfaces and electron storage in metal particles. The Pt in Pt_0.5–Au₁/TiO₂ is electronically and catalytically different from the Pt in Pt/TiO₂ and it is predicted that the former suppresses the oxygen reduction reaction.