The Effect of Phosphoric Acid Concentration on Electrocatalysis

Abstract

Phosphoric acid is the electrolyte used in the most advanced fuel cell developed for power generation and for on‐site integrated energy systems. Oxygen reduction kinetics in this electrolyte are relatively poor and thus limit the efficiency of such fuel cells. Therefore, in order to better understand oxygen interactions with platinum in these cells, oxygen adsorption and the kinetics of oxygen reduction reaction (ORR) were studied utilizing a Pt rotating disk electrode in several concentrations of highly purified . Although the kinetics of the ORR remained first order in all concentrations, it was found that its Tafel slope increased from ∼110 mV/dec in low concentrations to ∼134 mV/dec in 85 w/o. Anodic adsorption isotherms indicated that the higher concentrations also hindered adsorption of oxygen from solution. These effects were attributed to the blockage of electroactive sites by the adsorption of molecules.