Zeolite-templated Pt/C electrocatalysts

In an effort to reduce the amount of platinum required in low temperature fuel cells, we have prepared electrocatalysts of platinum nanoparticles-on-carbon through zeolite-templating methods. Several different zeolite structure-types, as well as clays and mesoporous silicas were investigated as hosts for the preparation of small Pt clusters through thermal decomposition of ion exchanged (NH3)4Pt(2+). Several factors relating to cluster confinement and mobility influence cluster size, and clusters below 1 nm with narrow size distribution have been prepared. To enable electrochemical application, the pores of the Pt cluster-containing zeolite were filled with electrically conductive carbon via infiltration with carbon precursors, polymerization, and pyrolysis. The zeolite host was then removed by acid digestion, to leave a micro-/mesoporous Pt/C electrocatalyst possessing Pt clusters of controlled size. Preliminary electrochemical evaluation of these catalysts is reported. The energetics of thermal decomposition of (NH3)(4)Pt2+ to form Pt clusters in zeolite X have been investigated through Differential Scanning Calorimetry, and apparent activation energies calculated. The relationship between (NH3)4Pt2+ decomposition and conditions of calcination has been explored in an effort to better control Pt cluster sizes. (C) 2007 Elsevier Inc. All rights reserved.