Effects of NH3 and tertiary ammoniums on Au/C catalyst in glycerol electrooxidation in alkaline media

Abstract

The poisoning effect of ammonia, trimethyl ammonium (TMA), and triethyl ammonium (TEA) on an Au/C catalyst in glycerol electrooxidation was investigated by using cyclic voltammetry, chronoamperometry (CA), and chronopotentiometry (CP) techniques. These ternary ammoniums are the possible degradation products of quaternary ammonium functional groups that are mainly contained in anion exchange membranes (AEMs) used in fuel cells. The most poisonous species was NH3, followed by TEA and TMA, which is consistent with their pK a trends. Via a cyclic voltammogram, poisoning effects were observed from the shift of the potentials at maximum current density, the recovery of oxidation currents in negative scans, and the drops in current density as compared to the ammonium-free electrolyte. The maximum current density decreased about 44 % in the presence of 1 mM NH3, but it showed only small effects for TMA and TEA at this concentration. The poisoning effects of TMA and TEA were more pronounced at a concentration of 10 mM. TEA displayed harsh effects in the CA and CP results. The cause of the current drop was the strong adsorption of these species in the same potential region of glycerol electrooxidation. Finally, the results suggested the use of methyl-substituted amines as a functional group in an AEM when Au was used as the electrocatalyst.