Impact of SO₂ on NiFe Nanoparticle Exsolution and Dissolution from LaFe_0.9Ni_0.1O₃ Perovskite Oxides

Ni-doped LaFeO3 perovskite oxide is a promising cathode material for solid oxide electrolysis cells (SOECs) designed for CO2/H2O coelectrolysis. The performance of LaFe0.9Ni0.1O3 is being investigated under real-world conditions that include exposure to acid gases, such as SO2, relevant to SOEC operation. Experiments show that LaFe0.9Ni0.1O3 exsolves NiFe nanoparticles, along with the formation of surface SO42– and SO32– after being exposed to 200 ppm of SO2. This suggests that the ionic diffusion of Ni3+ and Fe3+ between the bulk and the surface remains unaffected throughout the exsolution–dissolution–exsolution cycle. Thermochemical water splitting has been employed as a probe reaction to evaluate the catalytic properties of the exsolved NiFe nanoparticles. These nanoparticles demonstrated improved hydrogen production compared to bare perovskite oxide substrates. However, after exposure to SO2, the formation of Fe-rich NiFe nanoparticles led to poor thermocatalytic performance and rapid deactivation of the perovskite at elevated temperatures. Density functional theory (DFT) analysis was utilized to validate the experimental findings, indicating a significantly negative reaction energy for water splitting over exsolved Fe, as well as stronger binding of SO2 to Fe than to Ni. Computational analysis further suggests that the presence of surface sulfate promotes the formation of Fe-rich NiFe nanoparticles, aligning with the experimental results. Overall, this study clarifies how SO2 affects the structure of SOEC perovskite oxide candidate materials. Future engineering efforts should focus on enhancing nanoparticle exsolution and sulfur resistance, which is crucial for improving the hydrogen production capacity of La-based perovskite oxides for electro- and thermocatalytic water splitting in real environments containing acid gases.