Temperature-Dependence of Methanol Oxidation Rates at PtRu and Pt Electrodes

High temperature operation of direct methanol fuel cells is essential from the viewpoint of achieving a high performance with reduced amounts of Pt electrocatalysts used. A thin-layer flow cell of 0.1 mm gap is applied to evaluate the activity of PtRu (46 atom % Ru) alloy and Pt electrodes for methanol oxidation reaction (MOR) in a wide temperature range from 20 to 120°C in 1 M M solution under pressurized operation. The steady electrocatalytic activity could be evaluated by linear potential-sweep voltammetry under a certain electrolyte flow rate (>0.2 mL/s), which eliminated an effect of the oxidation current of hydrogen evolved at the proximate counter cathode. Onset potentials [ vs. reversible hydrogen electrode (RHE)] for the MOR shifted linearly to less positive potentials with elevating temperature, e.g. , from 0.45 V (at 20°C) to 0.34 V (at 120°C) on the PtRu electrode and from 0.66 to 0.52 V on the Pt electrode, respectively. A low apparent activation energy of 16 kJ/mol for the MOR was found on PtRu at 0.45 to 0.55 V, which was smaller than that of 24 kJ/mol on Pt at 0.70 V.