Oscillatory kinetics is commonly observed in the electrocatalytic oxidation of most species that can be used in fuel cell devices. Examples include formic acid, methanol, ethanol, ethylene glycol, and hydrogen/carbon monoxide mixtures, and most papers refer to half-cell experiments. We report in this paper the experimental investigation of the oscillatory dynamics in a proton exchange membrane ͑PEM͒ fuel cell at 30°C. The system consists of a Pt/C cathode fed with oxygen and a PtRu ͑1:1͒/C anode fed with H 2 mixed with 100 ppm of CO, and was studied at different cell currents and anode flow rates. Many different states including periodic and nonperiodic series were observed as a function of the cell current and the H 2 /CO flow rate. In general, aperiodic/ chaotic states were favored at high currents and low flow rates. The dynamics was further characterized in terms of the relationship between the oscillation amplitude and the subsequent time required for the anode to get poisoned by carbon monoxide. Results are discussed in terms of the mechanistic aspects of the carbon monoxide adsorption and oxidation.

Electrochemical reactions exhibit autosustained oscillatory states once the appropriate parameters are applied. As shown herein, the main impact of operating a reaction in an oscillatory state is the increased efficiency. The electroxidation of CO-containing hydrogen is analyzed because its oscillating mechanism mimics the oscillator known as hidden negative differential resistance (HNDR). With that, experimental results and the thermodynamic calculations of this contribution could be extended for other HNDR oscillators such as ethanol and methanol electroxidation. The enlarged efficiency results from a smaller chemical dissipation

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