Effects of Metal-Doping and Surface Modification on Hydrogen Production Activity of Metal Nanoclusters

Identification of an efficient hydrogen evolution reaction (HER) electrocatalyst is one of the challenging tasks in the development of alternative energies to replace fossil fuel. Although many efforts to develop active HER catalysts, it is still difficult to answer what are the main factors that influence on HER activities. Among many researches, two factors are commonly accepted;that is, thermoneutral binding step with H+ (∆GH = ~0 eV) on solid metal catalysts and proton shuttling effect of secondary coordinated ligand of molecular catalysts. Ligand protected Au nanoclusters that show both metallic and molecular-like properties exhibit distinctive electrochemical and HER features. The HER activities of Au nanoclusters could be improved by doping of foreign metal and surface modification. In this presentation, we report electronic structures and catalytic properties of Au25(SR)18 and bimetallic PtAu24(SR)18 nanoclusters (SR = thiolate). The modified catalytic activities were demonstrated by linear sweep voltammetry and controlled potential electrolysis. HER turnover frequency (TOF) of Au25(C6S)18, where C6S is hexanthiolate, dramatically increased from 8.8 s-1 to 33.4 s-1 at -0.6 V vs. RHE upon doping of Pt into Au25(C6S)18 to form PtAu24(C6S)18. The TOF of Pt-doped nanocluster was further increased by introducing proton-relaying sulfonate ligands, leading to TOF of 100 s-1 at -0.6 V.