Atomic Layer Deposition (ALD) Co-Deposited Pt-Ru Binary and Pt Skin Catalysts for Concentrated Methanol Oxidation

In this study, we demonstrate a novel approach atomic layer deposition (ALD) for the synthesis and investigation of Pt-Ru catalyst structures toward the oxidation of stoichiometric (1:1) methanol solutions in advanced direct methanol fuel cells. Two types of thin-film materials are investigated as catalysts for methanol oxidation: Pt-Ru films of varying ruthenium content that are co-deposited by ALD, and Pt skin catalysts made by depositing porous platinum layers of different thickness by ALD on sputtered ruthenium films. MeCpPtMe3 and Ru(Cp)(2) are used as precursors for Pt and Ru ALD, respectively, together with pure O-2 as the counter reactant. The electrochemical behavior of the co-deposited Pt-Ru catalysts and the Pt skin catalysts for methanol oxidation is characterized using chronoamperometry and cyclic voltammetry in a 0.5 M H2SO4/16.6 M CH3OH electrolyte at room temperature. The results illustrate that the optimal stoichiometric Pt: Ru ratio for the co-deposited catalysts is 1:1, which is consistent with our previous study on sputtered Pt-Ru catalysts using the same CH3OH concentration. Moreover, we report that the catalytic activity of sputtered ruthenium catalysts toward methanol oxidation is strongly enhanced by the ALD Pt overlayer, with such skin catalysts displaying superior catalytic activity over pure platinum. The mechanistic aspects of our observations are discussed.