Gas Research Institute Report Excerpt.
electrochem.org
"In comparing an SOFC system with a PEMFC system, both systems reform natural gas to hydrogen, although an SOFC can reform the natural gas internally within the anode compartment. Although the SOFC is not as sensitive to sulfur as the PEMFC, sulfur removal is required for both systems. Whereas the PEMFC system requires CO removal because of poisoning of the anode catalyst at levels above 10ppm, SOFC has the ability to handle large quantities of CO, which participates in the water-gas shift reaction in the anode compartment. Whereas the performance of the proton exchange membrane in PEMFC is very sensitive to membrane dehydration and thus required humidification of the anode and the cathode gas streams, water management is not an issue in the SOFC-based system as the performance of the solid electrolyte is not dependant on the presence of water.
The waste heat generated during the operation of the PEMFC is of low grade due to its relatively low temperature (70C-90C). As a result, it is limited to moderate heating of water to 50-55C. In contrast, because the waste heat generated during the operation of the SOFC is at high temperature (650-1000C) the high quality of waste heat can be used to aid in providing the energy necessary to drive the endothermic SR reaction as well as for domestic hot water and space heating.
While PEM fuel cells in general have relatively short start up times, the start up time of the PEMFC system is governed more by the time required to start up the fuel processor with its companion sulfur removal and CO preferential oxidation components. Thus the actual start-up time of a PEMFC system is LONGER, and thus more comparable to that of SOFC's.
In summary, SOFC's operate at higher electrical conversion efficiencies, do not require CO removal, do not require humidification of the anode and the cathode gases, and generate higher quality waste heat that can be better used for fuel reforming, space heat, or domestic hot water applications." |
