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

Abstract

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_0.1Ce_0.9O_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_0.1Ce_0.9O_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.