1. Introduction

Exsolution is a beneficial process that promotes the uniform growth of highly dispersed catalytically active nanoparticles partially embedded in surface sockets of the host oxide, enhancing their stability. Perovskite oxides (ABO₃) are widely favored as host materials due to their remarkable structural flexibility, allowing for various element substitutions and controlled crystal defect chemistry, which are crucial for manipulating the exsolution process. Their stability under redox conditions and high temperatures makes them highly suitable for energy conversion applications such as solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs). Nickel is one of the most effective exsolvable species owing to its high reducibility, favorable incorporation as a B-site dopant, and excellent catalytic activity. The in-situ formation of Ni nanoparticles enhances the electrochemical activity of perovskite-based electrodes while providing a cost-effective alternative to noble metals. [1,2]

2. Materials and Methods

In this study, we investigate Ni exsolution from La(Mn,Cr)O₃-based perovskites with controlled A-site doping and defect chemistry through Sr substitution. Ni-doped La(Mn,Cr)O₃ powders were synthesized by Solution Combustion Synthesis. The obtained materials were characterized by X-ray diffraction (XRD) combined with Rietveld refinement, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and High-Energy Resolution Fluorescence Detected X-ray Absorption Near Edge Structure (HERFD-XANES) spectroscopy at the Ni K-edge. The powders were reduced under 5% H₂-containing atmosphere to promote exsolution.

3. Results and Discussion

Thermogravimetric analysis under reducing conditions revealed significant differences in mass loss behavior among the investigated compositions, which can be attributed to variations in oxygen vacancy formation and the onset of Ni exsolution. These results indicate a strong dependence of the reducibility of the perovskite lattice on dopant concentration and A-site defectivity.

HERFD-XANES measurements provided direct insight into the evolution of the Ni oxidation state during reduction. The spectra clearly show the progressive reduction of Ni species and the formation of metallic Ni. The extent of metallic Ni formation was found to depend on composition and defect chemistry, highlighting the role of Sr doping in controlling the exsolution process. SEM analysis of the reduced samples confirmed the formation of highly dispersed Ni nanoparticles exsolved at the perovskite surface. The particle size and surface density were closely related to the A-site chemistry, the overall defect structure of the host lattice, and the reduction conditions. These findings demonstrate a clear correlation between compositional tuning, defect chemistry, and exsolution dynamics, which ultimately govern the microstructural evolution of the materials. The combined structural, spectroscopic, and microstructural characterization provides a comprehensive understanding of the mechanisms driving Ni exsolution in this family of perovskites and supports their suitability as durable and efficient fuel electrodes for SOFC and SOEC applications. [3]

4. Conclusions

The final goal of this investigation is to establish structure–property relationships across a twelve-composition series by varying dopant concentrations and defect chemistry to control the exsolution process and microstructural evolution of La(Mn,Cr)O₃-based perovskites. The results elucidate the interplay between crystal chemistry, defect chemistry, and Ni exsolution behavior. HERFD-XANES demonstrates the formation of metallic Ni upon reduction, while SEM confirms the development of well-dispersed exsolved nanoparticles. By correlating A-site chemistry and Ni content with nanoparticle formation and stability, this work contributes to the rational design of exsolution-based fuel electrode materials with enhanced performance and long-term durability for SOFC and SOEC technologies.