Improvement of CO tolerance of proton exchange membrane (PEM) fuel cells by a pulsing technique

Proton exchange membrane (PEM) fuel cells are currently being developed as alternative energy conversion systems for vehicular as well as for stationary power applications. The supply of hydrogen obtained by the reforming of alcohols or hydrocarbons to PEM fuel cells requires an extensive gas clean-up, as contaminants such as CO are poisonous to the employed catalysts. A new method of operating PEM fuel cells with reformed hydrogen with reduced requirements for gas cleaning is presented. The pulse technique allows the direct feeding of reformate gas into the fuel cell without a significant loss of performance. The electrical pulses increase the anode potential to values at which the CO is oxidised to CO2. In this way the catalyst surface is continuously cleaned and the loss of cell voltage is minimised. The optimised operating parameters for the pulses (namely pulse amplitude, duration and frequency) were investigated and determined as a function of CO content in the feed gas. It was found that the optimised pulse duration is not changed significantly for the different CO contents investigated (100, 1000 and 10000 ppm). In contrast, the pulse frequency needs to be adjusted to obtain CO tolerance at different CO concentrations in the hydrogen gas. This operating method greatly increases the design options of fuel cell systems for different applications.