The effect of carbon dioxide as impurity in hydrogen and oxygen on the performance of electrodes was studied in a half cell arranged at different concentrations and temperatures. The presence of CO2 in hydrogen was investigated on Ni/PTFE at different concentrations (0-4%) and three temperatures (28, 52, 72-degrees-C). Carbon dioxide was found to increase the overpotential due to ionic concentration polarization, but this effect was completely reversible. Impurity levels of CO2 up to 1% in oxygen had no effects on the Ag/PTFE electrode in the short term. Long term performance tests were carried out with CO2 impurity in oxygen at two different concentrations (0.03%, 1%) and at two different temperatures (25-degrees-C, 72-degrees-C). All experiments showed no degrading effect on the Ag/PTFE electrode with the exception of one at 25-degrees-C with 1% CO2. At this run a steady drop of current density was observed due to the formation of K2CO3 in the micropores which was verified by XRD. In all runs the concentration of KOH electrolyte was kept constant at 25%. The effect of adding K2CO3 to KOH was also investigated and no loss in electrode currents was observed for 48 h on both Ni/PTFE and Ag/PTFE electrodes.