VOLTAGE OSCILLATIONS OF H2-CO SYSTEM

A Pt catalyst in a porous fuel cell anode is poisoned by adsorption of CO from a H2-CO fuel mixture. Under constant current conditions, this forces the electrode to high potentials. The electrode may reach potentials sufficiently high to oxidize the adsorbed CO and initiate a period of efficient electro-oxidation of the H2 in the fuel mixture. Natural oscillations of potential are caused by repeated poisoning and reactivation of the electrode. More efficient activation of the electrode at high currents can result in a lower time-averaged anode potential at high current than at lower currents. The frequency of natural oscillations of the H2-CO system is relatively independent of the current density, but is dependent on the partial pressure of CO. The oscillatory behavior is explained on the basis of poisoning of an electrode system having a passivation-type polarization curve. The maximum rate of potential increase is correlated with the charging of the double layer by the imposed constant current. The maximum rate of potential recovery is explained by the charging, or collapsing, of the double layer by the electrode reaction current. © 1969, The Electrochemical Society, Inc. All rights reserved.