Preparation of carbon-supported Pt-Pd electrocatalysts with improved physical properties using electroless deposition methods

Surface modification of a carbon support preceding deposition of catalytic Pd seed nuclei has been used to prepare Pt-Pd catalysts by the electroless deposition (ED) of Pt (onto the Pd surface) from a solution containing PtCl62- and dimethylamine borane reducing agent. Functionalization of a carbon support with nitric acid to form surface carboxylic acid groups is followed by pre-treatment in a pH 14 bath to convert the acid moieties to the corresponding carboxylate (RCOO-) groups. The negative surface charge results in an electrostatic attraction between the carboxylate groups and positively charged Pd2+ cations during wet impregnation to produce smaller catalytic Pd seed nuclei which act as deposition sites for Pt in the ED process. Analysis by TEM after Pt deposition indicated the Pt-Pd particle sizes were smaller and had a more narrow size distribution than a series of Pt-Rh/C catalysts prepared earlier in which there had been no such modification of the carbon surface [K.D. Beard, M.T. Schaal, J.W. Van Zee, J.R. Monnier, Applied Catalysis B: Environmental 72 (2007) 262]. Cyclic voltammetry experiments indicated the Pt-Pd/C catalysts have different (bi)sulfate anion adsorption properties than conventional Pt/C electrocatalysts, suggesting a possible change in the d-band electronic structure of the surface atoms. However, oxygen reduction activity of Pt-Pd/C is only comparable to that of the Pt/C catalyst. Regardless, the results have implications for using ED methods to decrease the amount of Pt used for the oxygen electrode in low temperature fuel cells. (C) 2008 Elsevier B.V. All rights reserved.