[en] The deactivation behaviour of Ni/PTFE electrodes operating with hydrogen gas containing CO impurity was studied in half cell experiments under potentiostatic conditions. The decay of electrode current densities with respect to time is measured. It is observed that the electrode is deactivated and the electrode current densities reached lower steady state values when subjected to CO impurities in the hydrogen stream. The recovery, which is only partial under all conditions except at 72 deg C, after removal of the contaminant CO impurities, is also recorded. A total of 12 runs were carried out at 3 different temperatures. The effect of the CO impurity concentration is investigated at each temperature. The effects of electrode overpotential and electrolyte concentration are also studied. 9 figs., 1 tab., 14 refs