Solid oxide fuel cells (SOFCs) have the potential to be one of the cleanest and most efficient energy technologies for direct conversion of chemical fuels to electricity. Economically competitive SOFC systems appear poised for commercialization, but widespread market penetration will require continuous innovation of materials and fabrication processes to enhance system lifetime and reduce cost. One early technical opportunity is minimization of resistance to the oxygen reduction reaction (ORR) at the cathode, which contributes the most to performance degradation and efficiency loss in the existing SOFCs, especially at temperatures <700 °C. Detailed study over the past 15 years has revealed the positive impact of catalyst infiltration on SOFC cathode performance, both in power density and durability metrics. However, realizable performance improvements rely upon strongly-coupled relationships in materials and morphology between the infiltrate and the backbone, and therefore efficacious systems cannot be simply generated with a set of simple heuristics. This article reviews recent progress in enhancing SOFC cathode performance by surface modification through a solution-based infiltration process, focusing on two backbone architectures – inherently functional and skeletal – infiltrated using wet-chemistry processes. An efficient cathode consists of a porous mixed-conducting backbone and an active coating catalyst; the porous backbone provides excellent ionic and electronic conductivity, while the infiltrated surface coating possesses high catalytic activity and stability. As available, performance comparisons are emphasized and reaction schematics for specific infiltrate/backbone systems are summarized. While significant progress has been achieved in enhancing surface catalytic activity and durability, the detailed mechanisms of performance enhancement are insufficiently understood to obtain critical insights and a scientific basis for rational design of more efficient catalysts and novel electrode architectures. Recent progress in characterization of surfaces and interfaces is briefly discussed with challenges and perspectives in surface modification of SOFC electrodes. Surface modification through infiltration is expected to play an increasingly important role in current and next-generation commercial SOFC development, and this review illustrates the sophisticated technical considerations required to inform judicious selection of an infiltrate for a given SOFC system.

The protonic ceramic electrochemical cell (PCEC) is an emerging and attractive technology that converts energy between power and hydrogen using solid oxide proton conductors at intermediate temperatures. To achieve efficient electrochemical hydrogen and power production with stable operation, highly robust and durable electrodes are urgently desired to facilitate water oxidation and oxygen reduction reactions, which are the critical steps for both electrolysis and fuel cell operation, especially at reduced temperatures. In this study, a triple conducting oxide of PrNi_0.5Co_0.5O_3-δ perovskite is developed as an oxygen electrode, presenting superior electrochemical performance at 400~600 °C. More importantly, the self-sustainable and reversible operation is successfully demonstrated by converting the generated hydrogen in electrolysis mode to electricity without any hydrogen addition. The excellent electrocatalytic activity is attributed to the considerable proton conduction, as confirmed by hydrogen permeation experiment, remarkable hydration behavior and computations.