Proton conducting fuel cells (PCFC) are recently among the most promising strategies for tackling the key issue of Solid Oxide Fuel Cells (SOFC) development, namely their high operating temperatures. Their advantage lies mainly in the superior values of protonic conductivity at the low-temperature range, compared to the oxygen ions. However, unveiling the full potential of PCFC technology is currently limited by the performance of air electrode materials. Firstly, the catalytically active zone is often restricted, when only a mixed oxygen ion–electron conductor (MIEC) is applied. This constraint is overcome by the development of triple, proton-oxygen-electron conductors, which allow for the transport of all involved species across the volume of the electrode, thus extending the active region to the whole surface area. Yet, their design is still burdened with multiple challenges involving competition between their transport properties, electrochemical activity, stability, and functional properties. While Ba-based systems are well-recognized for their protonic conductivity, they tend to suffer from several stability-related issues, such as being prone to CO₂ interactions, Ba diffusion, or transformation to hexagonal phases. Similarly, incorporating transition metals, especially Co, meant to introduce the electronic contribution to conductivity and enhance electrochemical performance, deteriorates protonic conductivity, and adversely increases TEC values, compromising the functional properties.

Herein, we address these challenges and propose modifications of B-site lattice configuration in the established perovskite triple conductor BaCo_0.4­Fe_0.4­Zr_0.1Y_0.1O_3-δ (BCFZY), aimed at enhancement of proton uptake and catalytic activity. We present three new perovskite-structured triple-conducting materials: BaCo_0.4­Fe_0.4­Zr_0.1Zn_0.1O_3-δ, BaCo_0.4­Fe_0.4­Ce_0.1Y_0.1O_3-δ, BaCo_0.4­Fe_0.4­Ce_0.1Zn_0.1O_3-δ, synthesized by the modified Pechini method. The proposed modifications result in an increase in oxygen deficiency, which may be correlated with improved catalytic activity. By comparative studies under dry and humidified atmosphere, we confirm the presence of triple conductivity in the studied systems. The results for modified systems demonstrate enhanced stability of protonic defects and indicate higher proton uptake. Moreover, the changes in total conductivity under varied atmospheres further allow us to identify the mechanism of protonic defect formation. Additional analysis, including measurements of the Seebeck coefficient, attempts to explore the modifications’ influence on the defect structure, as particularly the Ce-substitution exhibits recognizable impact, despite involving only 10% of the B-site sublattice. As we verify by dilatometric measurements and in-situ high-temperature XRD, the improvements of transport properties come without deterioration of the thermomechanical behavior. The chemical stability is tested against both PCFC and O-SOFC electrolytes. Finally, by EIS measurements, we study how the observed enhancements are reflected in the electrochemical performance as PCFC electrodes.

Overall, our analysis indicates the three newly proposed triple-conductors as viable candidates for PCFC air electrodes and illustrates an effective approach to the design of a new generation of cathode materials.