Phosphorous Acid Impurities in Phosphoric Acid Fuel Cell Electrolytes: I . Voltammetric Study of Impurity Formation

Abstract

A study of the anodic impurity peak that appears in the cyclic voltammograms of platinum electrodes in highly purified, hot, concentrated phosphoric acid is reported. The results indicate that this anodic impurity peak corresponds to the anodic oxidation of phosphorous acid. This phosphorous acid impurity appears to be formed at cathodic potentials by the reaction of the phosphoric acid electrolyte with adsorbed hydrogen. The electrochemical formation and anodic oxida-tion of the phosphorous acid impurity are enhanced at the elevated temperatures found in phosphoric acid fuel cells. Phosphoric acid fuel cells employ concentrated phospho-ric acid electrolyte at a temperature of about 200 ~ 1'2 Since the performance of these fuel cell systems is limited by the polarization of the carbon-supported platinum cathodes, the oxygen reduction reaction on platinum in hot phospho-ric acid has been a topic of active research interest for some time, and continues to be so. ~'3- ~ Impurities in the elec-trolyte can affect he reduction of oxygen to water by effec-tively terminating the reaction at H202 z-s; therefore, the