Perovskite cathode with self-exsolved CoFe nanoparticles for efficient hydrogen evolution in ammonia solid oxide electrolysis cell

Ammonia electrolysis via solid oxide cell (NH₃-SOEC) offers a promising hydrogen production route with low electricity consumption and carbon-free operation. However, compared with conventional solid oxide electrolysis cell, suitable cathode materials remain to explore due to differences in cathodic kinetics and potential. Here, a series of Co-doped Sr₂Fe_1.5-xCo_xMo_0.5O_6-δ (SFCxM, x = 0, 0.1, 0.2, and 0.3) catalysts were synthesized and applied as NH₃-SOEC cathodes. Rivetingly, CoFe nanoparticles were self-exsolved in situ during electrolysis, as confirmed by SEM, XRD, TEM, EDX, and XPS, which is favourable for enhancing the catalytic activity. Among SFCxM, SFC0.2M exhibited the highest nanoparticle density and oxygen vacancy concentration, which can be attributed to lower-temperature reduction site due to Co doping, facilitating greater nanoparticle exsolution. Superior water adsorption and hydrogen desorption, along with markedly lower ohmic and polarization resistances, collectively endowed SFC0.2M with optimal performances, as evidenced by its achievement -1.37 A·cm^-2 and 0.6 V at 750 °C. As a result, SFC0.2M was confirmed as a robust NH₃-SOEC cathode material through stability testing. This work demonstrated an effective Co-doped perovskite cathode for NH₃-SOEC and provided insights for designing advanced cathode materials for solid oxide electrolysis cell.