7520
Langmuir 2000, 16, 7520-7523
Core-Shell Gold Nanoparticle Assembly as Novel Electrocatalyst of CO Oxidation Mathew M. Maye, Yongbing Lou, and Chuan-Jian Zhong* Department of Chemistry, State University of New York at Binghamton, Binghamton, New York 13902 Received April 4, 2000. In Final Form: June 19, 2000 This paper reports findings of an investigation of the electrocatalytic oxidation of carbon monoxide (CO) that occurs at nanocrystal gold cores with thiolate monolayer encapsulation and within a core-shell network assembly. The core-shell and network combinations allow the manipulation of core size properties and enhance the stability of nanosized catalysts against the propensity of aggregation while being catalytically active. Using alkanedithiolate-linked thin films assembled from two different gold core sizes (2 and 5 nm), we have demonstrated that the capped nanosites are both electrochemically accessible and catalytically active to CO oxidation upon electrochemical activation. Cyclic voltammetric data are presented for assessing the electrocatalytic properties. The results have important implications for the design and tailoring of nanosized gold catalysts via manipulating core-shell chemistry. We wish to report in this paper findings from an exploration of thiolate-encapsulated gold nanoparticles as catalysts on electrodes for the electrooxidation of carbon monoxide (CO). The catalytically active gold nanocrystal cores are under thiolate monolayer encapsulation and within a network assembly, as schematically depicted in Scheme 1. Although gold is a poor catalyst in bulk form, nanometer-sized gold exhibits excellent catalytic activities.1,2 One important attribute of the nanosized catalysts is the high surface area and interface-dominated properties that differ from atomic, molecule, and bulk counterparts. Recently, Goodman and co-workers3 studied the activationsize correlation of gold nanoparticles in gas-phase CO oxidation using a number of surface techniques including STM and reactionrate measurements. The high catalytic activity was revealed to link to a band gap of a metallic-insulator transition in the range of a few nanometers range. Although the intriguing nanosizeassociated electronic effects and catalytic activities have many potential applications,2 one important area of research interests involve the understanding of the mechanistic aspects in the catalytic oxidation of CO. This catalytic reaction system has broad technological and fundamental importance, including the purification of air in gas products and in long-duration space travel, conversion in automobile exhaust systems, and new fuel-cell technology based on the electrooxidation of methanol and other hydrocarbons.1,2 The propensity for poisoning at traditional platinum group catalysts by adsorbed CO-like intermediate species is a long-standing problem.4,5 Haruta and co-workers5 recently demonstrated that bare gold nanoparticles (
