Scanning electrochemical microscopy characterization of bimetallic Pt-M (M = Pd, Ru, Ir) catalysts for hydrogen oxidation

A combinatorial screening method, combined with scanning electrochemical microscopy (SECM) in a tip-generation-substrate-collection (TG-SC) mode, was applied to systematically and rapidly identify potential bimetallic catalysts (Pt-M, M=Pd, Ru, Ir) for the hydrogen oxidation reaction (HOR). The catalytic oxidation of hydrogen on the candidate catalysts was further examined during cyclic voltammetric scans of the substrate with a tip close to the substrate. The quantitative rate of hydrogen oxidation on the candidate substrates was determined for different substrate potentials from SECM approach curves by fitting to a theoretical model. SECM screening results revealed that Pt4Pd6, Pt9Ru1 and Pt3Ir7 were the optimum composition of the catalysts from the Pt-Pd, Pt-Ru and Pt-ir bimetallic systems for hydrogen sensors. The catalytic activity of the candidate catalysts in HOR was highly dependent on the substrate potential. The kinetic parameters for HOR were obtained on Pt4Pd6 (Tafel slope = 124 mV, k degrees = 0.19 cm/s, alpha = 0.52), Pt9Ru1 (Tafel slope = 140 mV, k degrees = 0.08 cm/s, alpha = 0.58) and Pt3Ir7 (Tafel slope= 114 mV, k degrees = 0.11 cm/s, alpha = 0.48) and compared with Pt (Tafel slope= 118 mV, k degrees = 0.17 cm/s, alpha = 0.5). Among the bimetallic catalysts studied. Pt4Pd6 exhibited the highest activity toward HOR with a high standard rate constant value in a wide range of applied potentials. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.