High-Temperature Current Collection Enabled by the in Situ Phase Transformation of Cobalt-Nickel Foam for Solid Oxide Fuel Cells.

For the commercial development of solid oxide fuel cells (SOFCs), cathode current collection has been one of the most challenging issues because it is extremely difficult to form continuous electric paths between two rigid components in a high-temperature oxidizing atmosphere. Herein, we present a Co-Ni foam as an innovative cathode current collector that fulfills all strict thermochemical and thermomechanical requirements for use in SOFCs. The Co-Ni foam is originally in the form of a metal alloy, offering excellent mechanical properties and manufacturing tolerance during stack assembly and startup processes. Then, it is converted to the conductive spinel oxide in situ during operation and provides nearly ideal structural and chemical characteristics as a current collector, gas distributor, and load-bearing component. The functionality and durability of the Co-Ni foam are verified by unit cell test and 1 kW-class stack operation, demonstrating performance that is equivalent to that of precious metals as well as an exceptional stability under dynamic conditions with severe temperature and current variations. This work highlights a cost-effective technique to achieve highly reliable electric contacts over the large area using the in situ metal-to-ceramic phase transformation that could be applied to various high-temperature electrochemical devices.