Investigations In Progress To Further Reduce Cell Cost

Elimination of one of the cell components (calcia-stabilized zirconia support tube) and replacement of one EVD step by plasma spraying (for depositing interconnection) has resulted in a major reduction in the cost of the AES cells and the cost of electricity ($/kW) produced by using such cells. Investigations are underway to further reduce the cost of these cells by reducing the cost of materials used in SOFCs and replacing another EVD step (for depositing fuel electrode) by a more cost-effective sintering approach.

Over 90% of the weight of an AES cell is that of the doped lanthanum manganite air electrode tube. Presently, the air electrode material is synthesized using high purity component oxides such as I^O, and MnOr Over 70% reduction in the cost of air electrode raw materials is possible if mixed lanthanides are used instead of pure lanthanum compounds to synthesize the air electrode powder. AES cells have now been fabricated using air electrode powder synthesized using mixed lanthanides. The performance of an initial cell with air electrode fabricated using mixed lanthanides at 400 mA/cmJ was only about 8% lower, primarily due to non-optimized processing conditions and a slightly higher resistivity of the mixed lanthanides air electrode material. Further adjustments in the composition of the air electrode material synthesized using mixed lanthanides are expected to result in lower air electrode resistivity and a cell performance equivalent to that of cells using high purity air electrode material synthesized using pure lanthanum oxide.

Investigations to deposit Ni-YSZ fuel electrode by a non-EVD process have also shown great promise. Deposition of a Ni-YSZ slurry over the YSZ electrolyte followed by sintering has yielded fuel electrodes that are equivalent in electrical conductivity to those fabricated by the EVD process. Cells fabricated with only one-EVD step (sintered fuel electrode, plasma sprayed interconnection, and EVD electrolyte) have shown electrical performance equivalent to those of the two-EVD steps (plasma sprayed interconnection, EVD electrolyte,, and EVD fuel electrode) cells. In fact, the sintered fuel electrode polarization is even lower than the already very low (7-15 mV) EVD fuel electrode polarization. This is believed to be due to a larger contact area and a greater number of electrochemically active sites at the electrolyte/sintered fuel electrode interface. This fuel electrode sintering process is currently being scaled up for cell manufacturing.

In the very near future, the AES cell production process will use EVD for only the electrolyte. The EVD process deposits very thin (20 to 40 |am thick), gas-tight electrolyte film over the porous air electrode, reliably, uniformly, and in acceptable cycle time. Nonetheless, deposition of the YSZ electrolyte film by a non-EVD technique such as colloidal/electrophoretic deposition of YSZ over porous air electrode tube followed by sintering is also being investigated.

0 0

Post a comment