Demonstrating feasibility of a high temperature polymer electrolyte membrane fuel cell operation with natural gas reformate composition

Experimental data on the performance of a single cell PBI-based HT-PEMFC operated with a fuel composition similar to natural gas reformate and oxygen enriched cathode air are presented. A test studying the effect of CO₂, H₂O and CO in the fuel on fuel cell performance revealed that the presence of CO₂ mainly worsens mass transport, H₂O improves proton conduction and CO influences reaction kinetics as well as causing mass transport limitations. A small increase of the O₂ concentration in the oxidant provided a boost on performance. Electrical efficiency of the fuel cell was improved from 36.6% with H₂/air operation up to 38.2% with synthetic reformate gas/30% O₂ enriched air. Three 1000 h long-term tests at constant load conditions were performed. The first test showed a degradation rate of ?21.4 μV/h and was operated with H₂/30% O₂. The second test was performed with the same kind of MEA but different fuel composition (54% H₂, 15% CO₂ and 31% H₂O) and exhibited a reduction of the degradation rate to ?5.5 μV/h. The main reason for this lifetime improvement is H₂O because its transport from anode to cathode may sweep along PA that soaks catalyst active sites and limits HOR. Moreover, water in rich H₂ reformate streams also relieves formation of CO from CO₂ via RWGS. The third test was performed with a different kind of MEA (extra PTFE content in GDE) but the same fuel composition than the second one. A higher degradation rate of ?22.2 μV/h was observed but it was mainly caused by unprotected shut-downs during operation. Two preliminary long-term tests were also performed with a fuel composition similar to natural gas reformate (54% H₂, 14% CO₂, 1% CO and 31% H₂O). These latest tests revealed that the fuel cell should be operated at higher temperatures to diminish CO catalyst coverage, and that anode purge with dry gases avoids water condensation in gas pipes. In addition, CO poisoning on anode catalyst is time dependent and operation at high current densities enhances CO catalyst coverage.