Phosphoric acid impurities in phosphoric acid fuel cell electrolytes. 2: Effects on the oxygen reduction reaction at platinum electrodes

• Published in: Journal of the Electrochemical Society 1994-12, Vol.141:12
• Main Authors: Sugishima, Noboru, Hinatsu, J.T., Foulkes, F.R.
• Format: Article
• Language: English
• Subjects: 30 DIRECT ENERGY CONVERSION; ACID ELECTROLYTE FUEL CELLS; CATALYTIC EFFECTS; CHEMICAL REACTIONS; DIRECT ENERGY CONVERTERS; ELECTROCHEMICAL CELLS; FUEL CELLS; HYDROGEN COMPOUNDS; INORGANIC ACIDS 300505 > Fuel Cells-- Electrochemistry, Mass Transfer & Thermodynamics; PHOSPHOROUS ACID; REDOX REACTIONS; VOLTAMETRY
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.2059335

The effects of phosphorus acid additions on the oxygen reduction reaction at platinum electrodes in concentrated phosphoric acid were studied. The oxygen reduction currents decreased, and the Tafel slopes became more negative upon the addition of small concentrations of phosphorus acid. In addition,the phosphorus acid oxidation current tended to complete with the oxygen reduction current. These effects became more pronounced at higher phosphorus acid concentrations and at higher temperatures. Upon the addition of phosphorus acid the number of electrons involved in the oxygen reduction reaction decreased from a value close to four to a value approaching two, suggesting promotion of a two-electron reduction to peroxide. Therefore, in studies of the electrochemical reduction of oxygen in hot concentrated phosphoric acid or in fuel cell systems using hot concentrated phosphoric acid as electrolyte, it is recommended that precautions be taken against the inadvertent formation of the phosphorus acid. The removal of phosphorus acid from concentrated phosphoric acid by repeated potential cycling at 100 mV/s between + 0.5 and +1.50 V (vs. dynamic hydrogen electrode) was demonstrated.