New insight on the study of electrocatalytic oxidation of methanol on some Pt group metals: Important methodological aspects

The synthesis of novel Pt-containing catalysts to achieve the high electrocatalytic activity in methanol oxidation reaction is the one of important directions in modern direct methanol fuel cells research and design. However, the comparison of results of electrochemical experiments shown in various works for different compositions of catalyst is practically impossible due to various conditions of experiments used by different authors’ groups. Hence, the importance of the methodology in study of electrochemical properties of Pt-containing catalysts discussed in the current work becomes evident. The Pt/C and PtRu/C commercial catalysts and also model systems with Pd, Rh, Ru, PtRu particles electrodeposited on glassy carbon electrode surface were used to specify the methodological aspects of comparative characterization of catalysts with various composition. The role of several important factors such as the methodology of electroactive surface area estimation, the nature of model acid electrolyte, polarization mode (potential range using in CV), polarization regime used for modeling of catalyst work in DMFC, medium pH and influence of methanol oxidation intermediates was discussed. It is shown that CO desorption is more appropriate method (with proposed modifications) for ECSA estimation; HClO4 is more favorable electrolyte for model experiments with catalysts when Nafion suspension is used as a binding agent. The polarization in CV mode in the potential range including the hydrogen adsorption region leads to local (near the electrode) pH changes, which results in increase in concentration (correlates with forward peak current density) of main electroactive species, gem-diolate, in methanol solution. The use of diluted methanol solutions allows to increase the efficiency of fuel consumption and decrease the overpotential of methanol oxidation reaction due to more favorable ratio of concentrations of electroactive and oxygen species adsorbed on the electrode surface.