The constrained densification of ceramic interlayers in solid oxide fuel cells (SOFCs) is strongly influenced by the interplay between constraint effects and diffusion kinetics. While elevated sintering temperatures are commonly employed to overcome stress-retarded densification, they simultaneously accelerate interfacial interdiffusion and reaction-layer formation, creating a long-standing trade-off between microstructural integrity and chemical stability. Here, we demonstrate a chemo-mechanical regulation strategy that effectively mitigates the conflict between these competing processes through concurrent enhancement of sintering kinetics and regulation of green-state packing homogeneity. By combining Co₃O₄-assisted sintering activation with cold isostatic pressing (CIP), ultrathin Gd-doped ceria (GDC) interlayers achieve an apparent relative density of 98.5% after constrained sintering, enabling densification at 1200 °C, below the temperatures commonly reported for constrained GDC films processed without sintering activation. The resulting dense and continuous interlayer limits Ce–Zr interdiffusion during fabrication and mitigates Sr-related interfacial reactions and reaction-layer formation during operation. Consequently, the optimized anode-supported SOFC delivers a peak power density of 1.36 W·cm⁻² at 800 °C and exhibits a normalized degradation rate of 0.48% per 1000 h, calculated from the stabilized 200–460 h operation period at 750 °C. Accelerated thermal aging at 850 °C for 600 h further supports the stability of the engineered heterointerface. The chemo-mechanical strategy was successfully extended to 10 cm × 10 cm cells, supporting their compatibility with scalable wet-processing routes. This work provides a chemo-mechanical perspective for mitigating the interplay between constrained densification and interfacial reactivity in multilayer ceramic systems.

Reversible protonic ceramic electrochemical cells (R-PCECs), which are capable of efficiently converting electrical and chemical energy in mutual directions, are considered highly promising alternatives for bidirectional electrical energy generation or storage. However, the sluggish electrocatalytic activity at low temperatures and unsatisfactory operational durability of oxygen electrodes remain the primary challenges to the commercial application of R-PCECs. Here, the degradation mechanism of the BaFe_0.4Co_0.4Zr_0.1Y_0.1O_3−δ (BFCZY) oxygen electrode under humid conditions is systematically investigated. This degradation can be attributed to the formation of BaCO₃ caused by water-facilitated Ba segregation. The activity and stability of the BFCZY oxygen electrode are significantly improved through heterointerface engineering by infiltrating the BaCoO₃ (BCO) catalyst. At 600 °C in 30 vol% H₂O–air, heterointerface engineering decreases the polarization resistance of the BFCZY electrode by half (from 0.42 to 0.21 Ω·cm²) and the decay rate by more than one order of magnitude (from 0.384 to 0.026 Ω·cm²/100 h). Moreover, an R-PCEC with a BCO–BFCZY oxygen electrode exhibited high activity and stability in both fuel cell and water electrolysis modes. The substantially increased electrocatalytic activity and stability of the oxygen electrode are attributed primarily to the improved surface oxygen exchange process and inhibited Ba segregation.