(642e) Co-Deposition of Pt and Ceria In Supercritical Carbon Dioxide for Direct Methanol Fuel Cell Anode Catalyst
AIChE Annual Meeting
Thursday, November 20, 2008 - 1:58pm to 2:20pm
One of the challenges for fabrication of direct methanol fuel cells (DMFC) is to construct electrodes with improved electrocatalysts. It has been recognized that carbon monoxide, the byproduct of the methanol oxidation reaction, is problematic because it poisons the platinum catalyst thereby decreasing its activity. However, the addition of cerium oxide as an oxygen donor to the carbon monoxide has improved the methanol oxidation performance. Therefore, it is necessary to develop a cost effective and efficient method to prepare the platinum and ceria anode for the use in DMFC.
Supercritical fluid deposition (SFD) is a novel technique that yields conformal metal, metal oxide and alloy films on topographically complex surfaces. Supercritical fluids can exhibit gas-like transport properties and liquid-like densities. Because many organometallic compounds are soluble in SCFs, such as carbon dioxide, SFD provides orders of magnitude higher precursor concentrations than traditional chemical vapor deposition (CVD). After the deposition reaction, the reaction chamber is simply depressurized to remove the reaction byproducts to obtain the high purity films.
In this work, we show that SFD can further be utilized to deposit platinum and ceria simultaneously and at reduced temperatures. Dimethyl(1,5-cyclooctadiene) platinum (II) and tetrakis(2,2,6,6-tetramethyl-3,5-heptanedionato) cerium (IV) are used as the platinum and ceria precursors, respectively. Hydrogen is used as the reducing agent for the platinum precursor while hydrolysis is responsible for the conversion of cerium precursor to ceria. Platinum and ceria were deposited on TaN substrates and carbon glass. Characterization by means of XRD, XPS, profilometry, SEM and EDS were performed. In separate experiments, we have found that ceria deposition occurs at temperatures greater than 250oC and platinum deposition at temperatures as low as 40oC. However, for this process it is found that platinum catalyzes the deposition of ceria and allows for co-deposition at reduced temperatures of 60oC. Initial results indicate that co-deposition of platinum and ceria in supercritical carbon dioxide is a feasible and advantageous method for the fabrication of DMFC anodes.