Data-driven discovery of thermo-mechanically compatible Mn-based air electrodes for high-performance reversible protonic ceramic cells

Reversible proton ceramic cells (RPCCs) are a transformative sustainable energy technology, offering potential for bidirectional power generation and hydrogen production at moderate tempeartures. However, thermal expansion coefficient (TEC) mismatch between air electrode and electrolyte impedes their actual implementation. This work pioneers a cobalt-free air electrode design through an integrated computational-experimental strategy. A machine learning framework (XGBoost) deciphers eight physicochemical properties governing TEC evolution, revealing Ca-substituted LnMnO_3-δ systems as optimal candidates. Subsequently, Pr_0.5Ca_0.5MnO_3-δ (PCM5) is identified with dual-functionality: a near-ideal TEC of 12.17 × 10⁻⁶ K⁻¹ matching state-of-the-art BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ electrolytes at 200–650 °C, coupled with maximizing electrochemical activity. First-principles calculation and electrical conductivity relaxation reveal extremely low proton migration energy (0.34 eV) and fast surface water exchange kinetics (k_chem,H = 2.32 × 10⁻³ cm s⁻¹ at 600 °C). The PCM5-based cell achieves a peak power density of 1.28 W cm⁻² and a electrolysis current density of 2.34 A cm⁻² at 1.3 V (650 °C), and excellent stability for 210 h in reversible mode. Most importantly, the cell demonstrates remarkable thermo-mechanical robustness through 140 accelerated thermal cycles with different heating/cooling rates (5, 10 and 15 °C min⁻¹), which is the most rigorous stability assessment reported. This study establishes a new paradigm of material design bridging electrochemical performance and thermo-mechanical reliability for next-generation RPCCs.