Effects of Calcination Temperature on the Activity of Au13/WO3 Photocatalysts in Photocatalytic H2O2 Production

Atomically-precise ligand-protected gold clusters have garnered wide attention as a catalytic active site in photocatalysis. Using the [Au13(dppe)5Cl2]Cl3 cluster (Au13 for convenience) deposited onto WO3, we investigated the effects of calcination temperature on the photocatalyst performance for H2O2 production. Heat treatments at different temperatures (160, 180 and 200 ºC) in air causes a gradual increase in Au size from 0.93 nm to 2.86 nm as verified using STEM imaging. Calcination at 160 °C still retains a majority of unaggregated clusters, while at 180 °C, both unaggregated clusters and aggregated particles are found in equal fraction (50:50), and at 200 °C a complete aggregation into larger Au particles occurs. The Au13/WO3-based photocatalysts only exhibit photoactivity in H2O2 production after calcination; WO3 and as-deposited Au13/WO3 are photocatalytically inactive. Transient photocurrent responses reveal that WO3 and Au13/WO3 exhibit the lowest photocurrent while calcined Au13/WO3 photocatalysts in the range of 160–200 °C show a dramatic enhancement in photocurrent indicating higher charge separation and transfer. The high activity of calcined Au13/WO3 is attributed to the existence of strong metal-support interaction that promotes charge separation and transfer, and formation of larger Au particles. Both rate constants of H2O2 formation (kf) and decomposition (kd) increase as the calcination temperature increases. The Au13/WO3 calcined at 200 °C displays the highest H2O2 production yield (2.1 mM) and rate (21 mM g-1 h-1) with apparent quantum yield of 1.27% under violet (405 nm) light irradiation. This work unravels the effects of calcination temperature on the photoactivity of Au13/WO3 photocatalyst for H2O2 synthesis.