Effect of carbon dioxide on the performance of Ni/PTFE and Ag/PTFE electrodes in an alkaline fuel cell

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° 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° C, 72° C). All experiments showed no degrading effect on the Ag/PTFE electrode with the exception of one at 25° 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.