Abstract
The impedance diagram of fuel-cell hydrogen electrodes has been established at different temperatures and current densities. An equivalent electric circuit simulating the a.c. behaviour of electrodes is proposed which accounts fully for the experimental results. The computed adjustment of its elements allows the evaluation of the wet surface of catalyst, of the part played by diffusion in the reaction and of the catalytic activity of the electrode in the electro-oxidation of hydrogen. Using this technique the evaluation of the specific surface area of Raney nickel is possible by
in situ
measurements, which is of great use in probing catalyst aging. The method also gives a value for the electrocatalytic activity, which cannot be determined by any other method. One thus has the means to compare the activities of various catalysts.