Reactivation of chromia poisoned oxygen exchange kinetics in mixed conducting solid oxide fuel cell electrodes by serial infiltration of lithia

Solid oxide fuel cells have the potential to render the conversion from fuel to electrical energy more efficienct while lowering emissions. The technology, however, suffers from performance degradation due to cathode poisoning by chromia from metal interconnects. We confirm the deleterious impact of chromia on the performance of the model mixed conducting cathode material Pr 0.1 Ce 0.9 O 2− δ by examining the oxygen exchange coefficient ( k chem ) via electrical conductivity relaxation measurements, and the area-specific resistance (ASR) by electrochemical impedance spectroscopy. Liquid Cr-infiltration decreases k chem 20-fold and the oxygen exchange component of ASR increases 20-fold while maintaining the same activation energy. We then demonstrate the ability to not only recover initial k chem and ASR values, but improve properties above those exhibited by the pristine specimen through subsequent Li-infiltration, leading to enhancement of k chem by more than three orders of magnitude and reduction in oxygen exchange component of the ASR by over a factor 100. We attribute these dramatic changes to the depletion of electrons induced by the acidic Cr-infiltrant on the Pr 0.1 Ce 0.9 O 2− δ surface and the recovery to accumulation of electrons from the basic Li-infiltrant. These results point to acidity as a key descriptor in addressing the long-standing challenge of reactive surface poisoning in applications reliant on rapid oxygen exchange and recovery behavior. The ability to achieve remarkable levels of recovery of electrocatalytic surfaces by controlling the relative acidity of surface species is demonstrated for the first time. The ability to recover the oxygen reduction reaction of poisoned metal oxide surfaces, central to many energy related applications, is demonstrated by controlling relative surface acidity.