Ceres Power has been developing fuel cell stacks and mCHP systems based on its unique metal-supported SOFC design incorporating a gadolinia-doped ceria (CGO) electrolyte operating in the 450-600°C temperature range. The metal supports are lowcost ferritic stainless steel foils which are perforated using a laser to create a porous region for gas diffusion on the anode side, and an impermeable region around the perimeter for sealing. Conventional volume ceramic processing techniques are used for the deposition of the anode, bulk electrolyte, cathode active and cathode current-collector layers, which are all sintered in a nonreducing atmosphere. A proprietary technique has been developed for the deposition of a dense stabilized zirconia layer and a CGO barrier layer between the bulk CGO electrolyte and the cathode active layer, largely blocking the internal short-circuiting currents inherent in the use of ceria-based electrolytes due to the mixedconductivity of CGO when exposed to an anodic atmosphere. The use of this layer enables close-to-theoretical cell efficiencies to be obtained, whilst still maintaining the advantages of high ionic conductivity and sinterability which make CGO ideal for lowtemperature processing and operation. The present generation of cells being manufactured are designed to meet the commercial requirements for a wall mounted, natural gas fuelled mCHP product, producing an average of 140 mWcm -2 at 0.75 V/cell at 570°C and 60% fuel utilization, operating on steam-reformed natural gas. Open-circuit voltages are around 1.10V operating on hydrogen/nitrogen; close to theoretical values indicating the effective suppression of internal short-circuits. The unique metal supported design facilitates simple and robust hermetic sealing of the cell to the interconnect by welding, and layer-to layer sealing and isolation is achieved using a commercial gasket material, thus largely eliminating degradation due to thermal stress induced seal leakage found in conventional planar SOFC designs. The extreme robustness of the metal foil cell design has been demonstrated by thermally cycling welded cell/interconnect assemblies from 100-600°C (<5 min total cycle time) using an infrared heater and forced air cooling. After 100 cycles, there was no degradation of the gas tightness of the assembly (pressure-decay leak tester). These tested cells were then assembled into a short stack and tested, with electronic performance indistinguishable from a short stack of new cells.

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