Oscillation phenomena on the cell voltage of PEFCs during CO poisoning

In case of operating a polymer electrolyte fuel cell (PEFC) with Pt-Ru allo y for the anode catalyst at low temperature, oscillation phenomena of the c ell voltages are often observed. In order to study the phenomenon with CO p oisoning in PEFCs, we used a "divided cell". In the "divided cell" which co nsisted of two single cells, fuel gas was supplied in series From the "upst ream cell" to the "downstream cell". Air was supplied in parallel to the bo th cells. An electric load was also connected in parallel. When fuel change d from pure hydrogen to CO containing gas, the current at the up stream cel l decreased and that at the downstream cell increased. This result indicate s that the CO poisoning occurred mainly in the upstream cell. In general, o scillations of the cell voltages were observed under low operation temperat ure (ex. below 60 degreesC) or GO-rich conditions. When the voltage oscilla tes, the current density of each cell in the divided cell also oscillates s ynchronized with the voltage oscillation. In all cases, CO concentration of fuel exhaust gas was lower than that of fuel inlet gas. These results indi cate that the oxidation reaction of CO with water occurs in the anode of th e PEFC. The ratio of oxidized CO with water is proportional to CO concentra tion in the inlet fuel gas.