X-ray photoelectron spectroscopic study of the activation of molecularly-linked gold nanoparticle catalysts

This paper reports the results of a study on the activation of core-shell assembled gold nanoparticle catalysts using X-ray photoelectron spectroscopy (XPS). The goal is to determine the surface reconstitution of the nanostructured catalysts upon electrochemical activation for the electrocatalytic oxidation of methanol. The decanethiolate-capped gold nanoparticles of 2-5 nm core sizes were assembled as catalyst thin films on electrode surfaces using 1,9-nonanedithiol and 11-mercaptoundecanoic acid as model molecular linkers. The XPS results have provided two important insights into the surface reconstitution of the activated nanostructure. First, the capping/linking thiolates or dithiolates are partially removed to produce the catalytic access, with the degree of removal being dependent on the nature of the molecular linker. Second, oxygenated species are detected on the activated gold nanocrystals, demonstrating the formation of surface gold oxide and its participation in the electrocatalytic oxidation of methanol. The findings are also correlated with results from studies of surface microscopic morphology and interfacial mass flux and provide further insights into issues related to the design and preparation of highly active nanostructured gold catalysts.