Another Application of SOFC systems is in the transportation sector. The polymer electrolyte membrane (PEM) fuel cell is generally regarded as the fuel cell of choice for transportation applications. PEM fuel cells require pure H2, with no CO, as the fuel to operate successfully. However, presently no H2 infrastructure exists, and on-board reformer systems to produce H2 from existing fuel base (gasoline, diesel) are technically challenging, complex, and expensive. Furthermore, it is difficult to eliminate the CO entirely from the reformate stream. In contrast, SOFCs can use CO along with H2 as fuel, and their higher operating temperature and availability of water on the anode side makes on-cell or in-stack reformation of hydrocarbon fuels feasible. Also, no noble metal catalysts are used in SOFCs reducing cost of the cells. The initial application of SOFCs in the transportation sector will be for on-board auxiliary power units (APUs). Such APUs, operating on existing fuel base, will supply the everincreasing electrical power demands of luxury automobiles, recreational vehicles, and heavy-duty trucks. Delphi Corporation has developed a 5 kW APU using anode-supported planar SOFCs.11 This unit is intended to operate on gasoline or diesel, which is reformed through catalytic partial oxidation. The building blocks of such an APU consist of an SOFC stack, fuel reformation system, waste energy recovery system, thermal management system, process air supply system, control system, and power electronics and energy storage (battery) system. Delphi has reduced the mass and volume in successive generation APU units to meet the stringent automotive requirements; the remaining issues of start up time and tolerance to thermal cycling are presently being worked on.