Obtaining high-performance cathodes is critical for protonic ceramic fuel cells (PCFCs), as cathode performance significantly impacts fuel cell performance. A full understanding of the interactions among the diverse properties of cathode materials would benefit cathode design. In this study, PrBaFe₂O_6−δ (PBF) was doped with various dopants, including cobalt (Co), Ni, Cu, Zn, and Mn. Experiments and first-principles calculations are used to study the key properties of dopant-modified PrBaFe₂O_6−δ, including oxygen vacancy (V_O) creation, hydration ability, proton mobility, and oxygen reduction reaction (ORR) activity. There is no perfect dopant that can improve every property to its full potential. Instead, different dopants can impact different properties of the material. Co-dopant has the best cathode performance since it balances the material’s instinctive properties, even though it does not provide a significant advantage in the formation of V_O. PCFC utilizing Co-doped PrBaFe₂O_6−δ cathode has a high performance of 1680 mW·cm⁻² at 700 °C, which is greater than that of the other dopant-tailored PrBaFe₂O_6−δ cathodes reported in this study and is one of the largest ever recorded for PrBaFe₂O_6−δ-based cathodes for PCFCs. Co-doped PrBaFe₂O_6−δ cathode is further demonstrated to be robust, with excellent operational stability. This study not only provides a potential cathode candidate for PCFCs but also suggests an intriguing approach to cathode design by carefully examining and balancing different vital properties of the material.

BaCe_0.8Fe_0.1Ni_0.1O_3−δ (BCFN) in a perovskite structure is impregnated consecutively by BCFN solution and BCFN suspension into a phase-inversion prepared NiO–Gd_0.1Ce_0.9O_2−δ (GDC) scaffold as an anode for solid oxide fuel cells (SOFCs) with on-cell dry reforming of methane (DRM). The whole pore surface of the scaffold is covered by small BCFN particles formed by BCFN solution impregnation; the large pores near the scaffold surface are filled by BCFN aerogels with a high specific surface area produced by BCFN suspension impregnation, which act as a catalytic layer for on-cell DRM. After reduction, the anode consists of a Ni–GDC scaffold and BCFN particles with exsolved FeNi₃ nanoparticles. This BCFN-impregnated Ni–GDC anode has higher electrical conductivity, electrochemical activity, and resistance to carbon deposition, with which the cell shows maximum power densities between 1.44 and 0.92 W·cm⁻² when using H₂ and between 1.09 and 0.50 W·cm⁻² when using CO₂–CH₄ at temperatures ranging from 750 to 600 °C. A stable performance at 400 mA·cm⁻² and 700 °C is achieved using 45% CO₂–45% CH₄–10% N₂ for more than 400 h without carbon deposition, benefiting from the impregnated BCFN aerogel with a high specific surface area and water adsorbability.

Reliable and economical energy storage technologies are urgently required to ensure sustainable energy supply. Hydrogen (H₂) is an energy carrier that can be produced environment-friendly by renewable power to split water (H₂O) via electrochemical cells. By this way, electric energy is stored as chemical energy of H₂, and the storage can be large-scale and economical. Among the electrochemical technologies for H₂O electrolysis, solid oxide electrolysis cells (SOECs) operated at temperatures above 500 ℃ have the benefits of high energy conversion efficiency and economic feasibility. In addition to the H₂O electrolysis, SOECs can also be employed for CO₂ electrolysis and H₂O–CO₂ co-electrolysis to produce value-added chemicals of great economic and environmental significance. However, the SOEC technology is not yet fully ready for commercial deployment because of material limitations of the key components, such as electrolytes, air electrodes, and fuel electrodes. As is well known, the reactions in SOEC are, in principle, inverse to the reactions in solid oxide fuel cells (SOFCs). Component materials of SOECs are currently adopted from SOFC materials. However, their performance stability issues are evident, and need to be overcome by materials development in line with the unique requirements of the SOEC materials. Key topics discussed in this review include SOEC critical materials and their optimization, material degradation and its safeguards, future research directions, and commercialization challenges, from both traditional oxygen ion (O²⁻)-conducting SOEC (O-SOEC) and proton (H⁺)-conducting SOEC (H-SOEC) perspectives. It is worth to believe that H₂O or/and CO₂ electrolysis by SOECs provides a viable solution for future energy storage and conversion.

Slow oxygen reduction reaction (ORR) involving proton transport remains the limiting factor for electrochemical performance of proton-conducting cathodes. To further reduce the operating temperature of protonic ceramic fuel cells (PCFCs), developing triple-conducting cathodes with excellent electrochemical performance is required. In this study, K-doped BaCo_0.4Fe_0.4Zr_0.2O_3−δ (BCFZ442) series were developed and used as the cathodes of the PCFCs, and their crystal structure, conductivity, hydration capability, and electrochemical performance were characterized in detail. Among them, Ba_0.9K_0.1Co_0.4Fe_0.4Zr_0.2O_3−δ (K10) cathode has the best electrochemical performance, which can be attributed to its high electron (e⁻)/oxygen ion (O²⁻)/H⁺ conductivity and proton uptake capacity. At 750 ℃, the polarization resistance of the K10 cathode is only 0.009 Ω·cm², the peak power density (PPD) of the single cell with the K10 cathode is close to 1 W·cm⁻², and there is no significant degradation within 150 h. Excellent electrochemical performance and durability make K10 a promising cathode material for the PCFCs. This work can provide a guidance for further improving the proton transport capability of the triple-conducting oxides, which is of great significance for developing the PCFC cathodes with excellent electrochemical performance.