UNSTEADY-STATE PERFORMANCE OF POROUS GAS-DIFFUSION NI-ELECTRODE IN ALKALINE FUEL-CELLS

The traditional approach of using steady-state techniques to determine the performance of the electrodes of fuel cells may have two main set -backs. Firstly, steady state techniques are not suitable for use in c ases where the electrochemical system does not come to equilibrium. Se condly, most steady state methods employ impedance techniques. These i mpedance methods, however, are known to give only overall values. Some of the intrinsic parameters of the electrode (such as the exchange cu rrent density and capacitance) can also be obtained from unsteady-stat e techniques. In this study, an unsteady state technique in the form o f exponential decay current was put in a galvanostatic mode and used t o determine the exchange current density and double layer capacitance of the hydrogen porous gas diffusion electrodes of the alkaline fuel c ell. In addition, the effects of temperature on the determined paramet ers are discussed. In order to compare the results (using the same exp erimental conditions), a triangular wave current also in a galvanostat ic mode was employed in a separate investigation. The ranges of values obtained for the exchange current density and the double layer capaci tance are (1.1-11.9) X 10(-6) A/cm2 and (91-104) X 10(-3)F, respective ly, for the temperature range of 30-70-degrees-C. The activation energ y was found to be 4.15 kcal/gmol and the surface roughness factor at 7 0-degrees-C was 34 x 10(-4) cm2/cm2, for Raney Ni-electrocatalyst.