Impact of SO2 on NiFe Nanoparticle Exsolution and Dissolution from LaFe0.9Ni0.1O3 Perovskite Oxides

Abstract

Ni-doped LaFeO₃ perovskite oxide is a promising cathode material for solid oxide electrolysis cells (SOECs) designed for CO₂/H₂O coelectrolysis. The performance of LaFe_0.9Ni_0.1O₃ is being investigated under real-world conditions that include exposure to acid gases, such as SO₂, relevant to SOEC operation. Experiments show that LaFe_0.9Ni_0.1O₃ exsolves NiFe nanoparticles, along with the formation of surface SO₄^2– and SO₃^2– 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.