Unraveling synergy of ternary alloy exsolution and oxygen vacancy regulation in Fe/Ni/Co-doped MnCr2O4 spinel for high-performance durable CO2–H2O co-electrolysis in SOECs

Spinel oxides are structurally stable and chemically compatible candidates for solid oxide electrolysis cell (SOEC) fuel electrodes, but their catalytic performance in CO 2 –H 2 O co-electrolysis is severely limited by low oxygen vacancies and inadequate electronic transport. Herein, a MnCr 2 O 4 spinel fuel electrode is rationally engineered via transition metal co-doping to enable composition-controlled in-situ exsolution of multicomponent alloy nanoparticles, thereby enhancing its electrical conductivity and catalytic activity. increase the catalytic performance and conductivity. By progressively introducing Fe, Ni, and Co into the MnCr 2 O 4 lattice, a series of compositionally tailored spinel oxides Mn 0.9 Fe 0.3 Cr 1.8 O 4− δ (MFC), Mn 0.9 (FeNi) 0.3 Cr 1.8 O 4− δ (MFNC), and Mn 0.9 (FeCoNi) 0.3 Cr 1.8 O 4− δ (MFNCC) have been successfully developed. Under reducing conditions, the in-situ exsolution of metallic Fe, Fe–Ni, and Fe–Ni–Co nanoparticles, accompanied by increased oxygen vacancy concentration, promotes CO 2 /H 2 O adsorption and charge-transfer kinetics. The synergistic combination of these effects enables the cell with the reduced MFNCC (R–MFNCC) fuel electrode to achieve current density of 0.99 A cm −2 at 1.5 V and 800 °C for CO 2 –H 2 O co-electrolysis, together with a tunable syngas production (H 2 /CO = 1.01–1.47) and stable operation over 120 h at 0.4 A cm −2 . This study highlights the power of integrating in-situ exsolution with defect engineering to unlock the catalytic potential of spinel oxides for durable SOEC applications.