PHOSPHORUS-ACID IMPURITIES IN PHOSPHORIC-ACID FUEL-CELL ELECTROLYTES .1. VOLTAMMETRIC STUDY OF IMPURITY FORMATION

A study of the anodic impurity peak that appears in the cyclic voltamm ograms of platinum electrodes in highly purified, hot, concentrated ph osphoric acid is reported. The results indicate that this anodic impur ity 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 hydr ogen. The electrochemical formation and anodic oxidation of the phosph orous acid impurity are enhanced at the elevated temperatures found in phosphoric acid fuel cells.