Ultra-Low Loading of Ru Clusters over Graphitic Carbon Nitride: A Drastic Enhancement in Photocatalytic Hydrogen Evolution Activity

The photocatalytic activity of graphitic carbon nitride (g-C3N4) was dramatically enhanced by ultra-low loading of Ru6 clusters (0.01 wt %). This was accomplished via the equilibrium adsorption of a Ru(NO)(NO3)(3) precursor followed by annealing at 550 degrees C under an inert atmosphere. Varying both the type of Ru precursor and the annealing temperature permitted tuning of the local structure of the Ru centers between single site and nanoparticle morphologies. These variations in structure played a crucial role in determining the H-2 evolution activity of the material in aqueous media under visible light irradiation (lambda >420 nm) in the presence of Pt cocatalyst. The ultra-low loading of Ru6 clusters led to a more than twenty-fold increase in activity compared to that for bare g-C3N4 owing to synergic effects. These effects included increases in the surface area by exfoliation as well as suppression of the recombination of electron-hole pairs and improved charge migration, as demonstrated by analyses of the photoluminescence and photo-electrochemical properties of the catalyst.