Oxygen reduction reaction on Pt electrode in mixture of brØnsted acid and room temperature molten salts at medium temperature

Abstract

Oxygen reduction reaction (ORR) on Pt in mixtures of Brønsted acid and room temperature molten salts based on triflate anion has been investigated as a fundamental study for an application to medium temperature polymer electrolyte fuel cells. The ORR was determined by the slow scan voltammetry and the rotating ring disk electrode voltammetry under oxygen atmosphere on a Pt electrode. The oxygen reduction current in a mixture of trifluoromethanesulfonic acid (HTf) and 1-ethyl-3-methylimidazolium triflate (EMITf) was larger than that in a mixture of HTf and 2-ethylimidazolium triflate (2EtHImTf) and 85 wt.% aqueous phosphoric acid at 140 °C The 63.5 kJ mol-1 of the activation energy of the ORR at Pt/HTf-EMITf was larger than that of HTf in water at reversible potential. Hydrogen peroxide was not detected as a byproduct in the range from 0.1 to 1.1 V vs. RHE by RRDE measurement. Consequently, HTf-EMITf would be a good electrolyte for the medium temperature fuel cells.