Tuning negative thermal expansion in Sm0.85Zn0.15MnO3−δ via synthesis optimization for enhancing the stability of heterostructured solid oxide fuel cell cathodes

• First successful synthesis of single-phase NTE perovskite Sm0.85Zn0.15MnO3−δ via sol–gel method, eliminating unwanted ZnO phase. • Achieved negative TEC of approximately −6.5 × 10−6 K−1 in the 400–850°C range, enabling precise TEC matching with LSGM electrolyte (mismatch reduced to 1%). • SBSCCO + 10wt% SZM15 composite cathode showed ~70% lower polarization resistance (0.019 Ω·cm² at 900°C) and excellent long-term stability over 100 h. • Demonstrated high peak power density of 680 mW·cm⁻² in an anode-supported fuel cell at 850°C, validating NTE additives as a promising strategy for IT-SOFCs.