Leveraging Grain Boundary Effects for Nanostructured Electrode Layers in Symmetric Solid Oxide Fuel Cells

Abstract

While grain boundary engineering is attracting great interest as a potential strategy to fabricate highly electrochemically active materials, open questions remain in relation to the fundamental mechanisms of local property enhancement as well as to the potential technological impact of such nanostructuring strategies. In this paper, the ability to turn a predominantly electronic conductor into an excellent mixed-ionic electronic conductor by grain boundary doping is demonstrated for nanocrystalline films of lanthanum chromite. A four-orders-of-magnitude increase in the oxygen diffusion coefficient at grain boundaries is observed, and related  to local chemical changes. It is shown that grain boundary effects can be effectively exploited for technological purposes by fabricating a proof-of-concept symmetric solid oxide cell based on lanthanum chromite film electrodes. The cell is operated under reversible gas feeding conditions, exhibiting electrode self-healing characteristics. The results provide new insights on the fundamental aspects of fast grain boundary oxygen diffusion and validate grain boundary engineering as a technologically relevant strategy for the realization of solid oxide cells with enhanced performance.