WETTING-IN STUDIES ON ALKALINE-FUEL-CELL CATHODES USING A POTENTIOSTATIC-GALVANOSTATIC EXPERIMENTAL-DESIGN

The influence of potential and current on electrolyte intrusion during the initiation phase of poly(tetrafluoroethylene)-(PTFE)-bonded bonded carbon cathodes has been studied. A potentiostatic-galvanostatic experimental design was used. This was attained by varying the oxygen concentration using a computerized control circuit. The intrusion depth was determined by an electron microscope element-mapping method, and the amount of intruded electrolyte was determined by weighing. The wetting-in of the electrodes was found to depend strongly on potential and less on applied current density. A combination of electrocapillarity and electro-osmosis is proposed as an explanation of the results. The experiments have also revealed interesting phenomena concerning electrolyte and three-dimensional current-density distribution during the initiation phase. From the results, a mechanism for the sudden failure (flooding) of PTFE-bonded carbon cathodes at the end of their service life is suggested.