Electrocatalysis of modified carbon materials.

摘要

Carbon electrodes were superficially and bulk modified. The catalytic activity of the modified electrodes depended on the pretreatment procedures, the type of dopants and their loading level. These modified electrodes were applied to the oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER).; ORR in alkaline solutions was investigated on surface modified GC electrodes and HOPG basal plane surfaces. The modification included polishing, laser irradiation, electrochemical pretreatment, fracturing, and adsorption of certain species. These pretreatment affected the first electron reduction kinetics in the ORR mechanism. ORR was subject to H/D isotope effect. Surface-OH type oxide was most probably responsible for the increased activity. Catalysis by the {dollar}>{dollar}C = O groups or a quinone mediated reaction mechanism was unlikely under current conditions.; A low temperature route to the preparation of homogeneously doped glassy carbon (DGC) materials was developed. A variety of dopants, including Pt, Fe, F and Cl, were dispersed in the GC matrix at a fairly high level {dollar}(sim{dollar}15 wt%). In the case of Pt-DGC, nanoscale platinum clusters {dollar}(sim{dollar}20A) were incorporated in the GC matrix and the material showed very efficient catalytic activities for both ORR and HER. The supported Pt-DGC catalyst was applied to Polymer Electrolyte Membrane (PEM) fuel cell studies where they demonstrated as a viable catalyst for the fuel cell applications. The activity of the Pt-DGC catalyst depended on the precursor, the support, the pyrolysis environment and temperature and the degree of precursor dispersion. A properly prepared Pt-DGC catalyst showed comparable activity as the commercial ETEK and Pt black catalysts, while the Pt-DGC catalyst was more flexible in preparation because the precursor was soluble. The activity was correlated with the catalyst's structure by means of Extended X-ray Absorption Fine Structure spectroscopy and Transmission Electron Microscopy.; The F and Cl doped GC materials exhibited similar physical and electrochemical properties as the conventional GC materials. The addition of F into the Pt-DGC structure did not enhance its activity. The Fe-DGC material was different from either pure GC, pure Fe or the simple combination of the two components. ORR on Fe-DGC was catalyzed by the incorporated Fe species.