Boosting solid oxide H2O and CO2 co-electrolysis on Sr2−xFe1.5−yMo0.5NiyO6±δ by in situ exsolution of FeNi alloy nanoparticles

Abstract

Mixed ionic electronic conducting perovskite oxides are promising alternative fuel electrodes for steam and/or carbon dioxide co-electrolysis in solid oxide cells. Among these, molybdenum-doped strontium ferrites (Sr₂Fe_1.5Mo_0.5O_6±δ, SFM) are particularly important due to their high redox stability and catalytic properties. Herein, we have functionalized such SFM-based fuel electrodes by promoting exsolution of Fe and FeNi alloy nanoparticles through Ni-doping at their B-site and introduction of A-site deficiency. In situ NEXAFS under reducing conditions indicated that A-site deficiency and Ni doping promote Fe exsolution, leading to the formation of Fe-rich, FeNi bimetallic nanoparticles, with the composition influenced by perovskite stoichiometry. The electrochemical characterizations revealed that both doping and exsolution significantly reduce cell polarization resistance, which enhanced the electrode's electrical efficiency for H₂O–CO₂ co-electrolysis (25% H₂O, 25% CO₂) in the absence of hydrogen or carbon monoxide safe gas. Specifically, Ni-doping combined with FeNi or FeNi₃ exsolution improved by almost three times the electrocatalytic performance of the bare SFM, with current densities reaching up to 1.3 A cm⁻² at 1.6 V and 800 °C in a ZrO₂-based electrolyte-supported cell. The surface characterization revealed an increase in oxygen exchange rate kinetics and CO₂ adsorption capacity in the modified samples which may explain the enhanced performance. Our results provide valuable insight into the required strategy for developing highly efficient fuel electrodes through the combination of rational doping and redox exsolution to advance sustainable electrochemical syngas production from SOECs.