The significance of temperature-dependent potential shift corrections for the activity of methanol electro-oxidation at Pt/Ru nanoparticles in the range of 23 C to 70 C
Snow, David E.
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Temperature effects on the electrochemical oxidation of methanol over PtRu nanoparticle catalyst materials were investigated with the aim of assessing errors introduced in the measurement of reaction rate and activation energy (Ea) due to uncompensated thermal drift at the reference electrode. Experiments employed PtRu black nanoparticles containing 50 at. % Ru. Focus was on the use of a commercial catalyst (Johnson Matthey (JM), Ward Hill, MA). Some results from in-house prepared catalyst are also reported. The active surface area of the immobilized catalyst was determined by CO stripping voltammetry based on reaction of a pre-adsorbed CO monolayer. Accurate measurements of temperature at the reference electrode were made and mathematical corrections applied to compensate for shifts in the reference potential caused by temperature gradients across the electrode. Experiments were performed for temperatures in the range of 23°C to 70° C. Potentials were measured with respect to a reversible hydrogen electrode (RHE) reference and reported in volts as VRHE. Methanol oxidation rates were evaluated in potential step experiments. The activation energy for the oxidation of methanol in 0.1 M H2SO4 at JM PtRu black (50 at. % Ru) ranged from 60 kJ/mol to 87 kJ/mol at potentials between 0.5 VRHE and 0.3 VRHE. Corrections applied to similar measurements performed on a sonochemically prepared PtRu catalyst gave values for Ea in the range of 45 kJ/mol to 55 kJ/mol. Accounting for thermal drift in the reference potential resulted in a change in Ea averaging ± 2 kJ/mol, which is not significant in comparison to the margin of error in values for Ea reported in the literature (± 7 kJ/mol).