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 bonde d carbon cathodes has been studied. A potentiostatic-galvanostatic exp erimental design was used. This was attained by varying the oxygen con centration using a computerized control circuit. The intrusion depth w as determined by an electron microscope element-mapping method, and th e amount of intruded electrolyte was determined by weighing. The wetti ng-in of the electrodes was found to depend strongly on potential and less on applied current density. A combination of electrocapillarity a nd electro-osmosis is proposed as an explanation of the results. The e xperiments have also revealed interesting phenomena concerning electro lyte and three-dimensional current-density distribution during the ini tiation phase. From the results, a mechanism for the sudden failure (f looding) of PTFE-bonded carbon cathodes at the end of their service li fe is suggested.