Unstable Phenomena on Initial Performance of Phosphoric Acid Fuel Cell Cathode

Abstract

Early in operation of high current density, cathode potential of phosphoric acid fuel cell having well wet proofed catalyst layer is found to be unstable and to decrease rapidly at some operating conditions.
Previous impregnation of phosphoric acid in the catalyst layer is useful for stable operations at high current density. When weakly wet proofed catalyst layer is used, this initial unstable behavior at high current density does not apear. At the operation of high oxygen concentration, the potential of the cathode is also stable.
Operating temperature and the air flow rate are not effective on this initial unstable behavior. These decreased potential at initial operation recovers immediately after increasing oxygen concentration or decreasing current density. Decreased generating capability is held in nitrogen environment under open circuit potential until oxygen is supplied.
Potential decrease corresponds to increase of oxygen gain, that is, increase of concentration polarization. Oxygen shortage in the catalyst is suggested as the cause of this unstable behavior.