Multiwalled carbon nanotube (CNT)-supported Pt nanoparticles (Pt/CNT) were covered with silica layers by successive hydrolysis of 3-aminopropyl-triethoxysilane and tetraethoxysilane on CNTs with Pt metal precursors, followed by reduction with hydrogen. The Pt/CNT covered with silica layers was used as a cathode catalyst for a proton exchange membrane fuel cell (PEMFC). The activity of catalyst for the oxygen reduction reaction in a single-cell PEMFC was similar to that of Pt/CNT, in spite of the uniform coverage of Pt with silica layers, indicating that the coverage of Pt/CNT with silica layers did not appreciably decrease the catalytic activity. In addition, electrocatalyst showed high stability during potential cycling from 0.05 to vs reversible hydrogen electrode in an aqueous electrolyte, whereas Pt/CNT significantly deactivated during the experiment. The structural change of Pt species in these electrocatalysts during potential cycling was investigated by transmission electron microscopy images and -edge X-ray absorption fine structure. The crystallite size of Pt metal in did not change appreciably during the potential cycling, while Pt metal crystallites in Pt/CNT seriously aggregated. Silica layers enveloping Pt metal particles in prevent the dissolution and redeposition of Pt metal particles as well as the agglomeration of Pt metal particles on the supports.
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Takenaka et al. (2008) studied this question.
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