Partially exsolved iron from doped ceria as electrocatalysts for steam reduction in solid oxide electrolysis cell

Cerium-based oxides such as samarium-doped ceria (SDC) are promising ceramic electrocatalysts for steam-to-hydrogen conversion in solid oxide electrolysis cells (SOECs) due to their excellent redox stability under harsh cathodic conditions. To enhance their catalytic activity, an Fe-doping strategy is proposed to induce partial in situ exsolution, forming a novel FeSDC cathode with Fe nanoparticles embedded in the ceria matrix. Microstructural analysis reveals uniformly distributed Fe nanoparticles with sizes of 30–60 nm formed after reduction, exhibiting a semi-embedded morphology that provides abundant active sites for steam reduction. Density functional theory calculations indicate that Fe doping and exsolution increase H 2 O adsorption energy and elongate the O–H bond, suggesting activated adsorption and dissociation of H 2 O molecules. As a result, oxygen transport kinetics for the steam reduction reaction are significantly enhanced. At 750 °C, FeSDC exhibits a chemical surface exchange coefficient of 5.48 × 10 −5 cm s −1 , approximately 56% higher than that of undoped SDC. Single-cell tests demonstrate that the FeSDC cathode achieves a current density of 1.17 A cm −2 at 800 °C and 1.3 V under equimolar H 2 /H 2 O, about twice that of SDC. Moreover, the FeSDC-based cell delivers 1.47 A cm −2 under pure steam electrolysis. • In situ exsolved Fe nanoparticles form socket-like structure on FeSDC cathode. • DFT shows Fe doping and partial exsolution enhance H 2 O adsorption on SDC surfaces. • FeSDC exhibits 56% higher surface exchange coefficient than SDC at 750 °C. • FeSDC single cell delivers 1.47 A cm −2 in pure steam at 800 °C and 1.3 V.