Nickel-iron anode substrate for smart solid oxide fuel cells with a self-protecting function against reoxidation

Development of highly reliable solid oxide fuel cells (SOFCs) is strongly requested, and the introduction of a self-protecting function is an ideal approach to increase the reliability of SOFCs. A highly porous (>33%) Ni-Fe metal substrate, which has well-developed nanopores, is prepared by reduction of NiO-Fe₂O₃. In an oxidizing atmosphere, a thin layer of Fe₂O₃ forms on the surface of the substrate. As a result, the porous morphology changes at the surface and becomes denser. This morphological change occurs only at the surface and prevents oxidation of Ni in the bulk of the substrate. Furthermore, the surface morphology returns to its original state following reduction. Therefore, despite the fact that Ni is readily oxidized, Ni metal phase is sustained in the Ni-Fe bimetallic alloy substrate even after 480 h oxidation in air. The cell power density is also stably sustained after a few reduction-reoxidation cycles. Here, we report that Ni-Fe bimetal alloy substrate exhibits a self-protecting function against reoxidation of the substrate, which would otherwise lead to a permanent failure of the cell.