Harnessing a Thermo-Compensating Effect to Stabilize Heterojunctions: An Effective Strategy for Durable Reversible Protonic Ceramic Fuel Cells

Reversible protonic ceramic fuel cells (R-PCFCs) have emerged as a promising energy conversion technology. However, the thermal expansion mismatch between the electrode and electrolyte induces interfacial stress, weakening bonding strength and endangering device durability. Herein, we designed a composite air electrode with a thermal compensatory effect by integrating the active phase PrBa0.6Ca0.4Co1.5Fe0.5O5-δ (PBCCF) and functional phase NdMnO3-δ (NM) for stable interfacial bonding. The unique thermomechanical behavior originates from the negative thermal expansion caused by the lattice phase transition of NM during heating. This characteristic effectively alleviates interfacial delamination caused by thermal stress accumulation due to the high thermal expansion coefficient of PBCCF. The results show that the single cell with the composite electrode PN82 (80 wt % PBCCF and 20 wt % NM) maintains tight interfacial bonding with negligible performance degradation after thermal cycling over 100 h, far outperforming the PBCCF cell (failed at 78 h). Moreover, the cell achieves a current density of 1.17 A cm–2 in the electrolysis mode (1.3 V) and a peak power density of 521.97 mW cm–2 in the fuel cell mode at 650 °C. These findings establish an effective strategy for stabilizing heterojunctions in high-temperature electrochemical devices and pioneer a new route for thermomechanical stress regulation of high-expansion perovskite energy materials.