Effect of CO2, HCO3- and CO3-2 on Oxygen Reduction in Anion Exchange Membrane Fuel Cells

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The effect of carbonate and bicarbonate anions on the oxygen reduction reaction was investigated in four alkaline solutions (pH ∼ 14) on a Pt disk type electrode with varying concentrations of carbonate and bicarbonate. The addition of carbonate and bicarbonate had two primary effects on the observed voltammetric behavior: i) The Tafel slope shifts positive with increasing carbonate/bicarbonate concentration, indicating that the carbonate anions may compete for surface adsorption sites; and ii) The dissolved oxygen concentration and diffusion coefficient are depressed with increasing anion concentration. Finally, adding CO2 to the cathode stream of an anion exchange membrane fuel cell caused an improvement in the device performance under fully hydrated conditions, suggesting that the fuel cell was operating at least partially under the carbonate cycle.