Over the last decade, exsolution has emerged as a powerful new method for decorating oxide supports with uniformly dispersed nanoparticles for energy and catalytic applications. Due to their exceptional anchorage, resilience to various degradation mechanisms, as well as numerous ways in which they can be produced, transformed and applied, exsolved nanoparticles have set new standards for nanoparticles in terms of activity, durability and functionality. In conjunction with multifunctional supports such as perovskite oxides, exsolution becomes a powerful platform for the design of advanced energy materials. In the following sections, we review the current status of the exsolution approach, seeking to facilitate transfer of ideas between different fields of application. We also explore future directions of research, particularly noting the multi-scale development required to take the concept forward, from fundamentals through operando studies to pilot scale demonstrations.

Perovskites are very promising materials for a wide range of applications (such as catalysis, solid oxide fuel cells…) due to beneficial general properties (e.g. stability at high temperatures) and tunability – doping both A- and B-site cations opens the path to a materials design approach that allows specific properties to be finely tuned towards applications. A major asset of perovskites is the ability to form nanoparticles on the surface under certain conditions in a process called “exsolution”. Exsolution leads to the decoration of the material's surface with finely dispersed nanoparticles (which can be metallic or oxidic – depending on the experimental conditions) made from B-site cations of the perovskite lattice (here, doping comes into play, as B-site doping allows control over the constitution of the nanoparticles). In fact, the ability to undergo exsolution is one of the main reasons that perovskites are currently a hot topic of intensive research in catalysis and related fields. Exsolution on perovskites has been heavily researched in the last couple of years: various potential catalysts have been tested with different reactions, the oxide backbone materials and the exsolved nanoparticles have been investigated with a multitude of different methods, and the effect of different exsolution parameters on the resulting nanoparticles has been studied. Despite all this, to our knowledge no comprehensive effort was made so far to evaluate these studies with respect to the effect that the exsolution conditions have on anchorage and morphology of the nanoparticles. Therefore, this highlight aims to provide an overview of nanoparticles exsolved from oxide-based perovskites with a focus on the conditions leading to nanoparticle exsolution.

Perovskite-type oxides are highly flexible materials that show properties that are beneficial for application in reverse water-gas shift processes (rWGS). Due to their stable nature, the ability to incorporate catalytically active dopants in their lattice structure, and the corresponding feature of nanoparticle exsolution, they are promising candidates for a materials design approach. On an industrial level, the rWGS has proven to be an excellent choice for the efficient utilisation of CO₂ as an abundant and renewable carbon source, reflected by the current research on novel and improved catalyst materials. In the current study, a correlation between rWGS reaction environments (CO₂ to H₂ ratios and temperature), surface morphology, and catalytic activity of three perovskite catalysts (Nd_0.6Ca_0.4Fe_0.9Co_0.1O_3-δ, Nd_0.6Ca_0.4Fe_0.97Co_0.03O_3-δ, and Nd_0.6Ca_0.4Fe_0.97Ni_0.03O_3-δ) is investigated, combining catalytic measurements with SEM and NAP-XPS. The materials were found to react dynamically to the conditions showing both activation due to in situ nanoparticle exsolution and deactivation via CaCO₃ formation. This phenomenon could be influenced by choice of material and conditions: less reductive conditions (larger CO₂ to H₂ or lower temperature) lead to smaller exsolved particles and reduced carbonate formation. However, the B-site doping was also important; only with 10% Co-doping, a predominant activation could be achieved.

Our research reveals the deactivating effect of metal exsolution on high-temperature CO₂ electrolysis.

Understanding the behaviour of active catalyst sites at the atomic level is crucial for optimizing catalytic performance. Here, the evolution of Pt and Cu dopants in Au₂₅ clusters on CeO₂ supports is investigated in the water-gas shift (WGS) reaction, using operando XAFS and DRIFTS. Different behaviour is observed for the Cu and Pt dopants during the pretreatment and reaction. The Cu migrates and builds clusters on the support, whereas the Pt creates single-atom active sites on the surface of the cluster, leading to better performance. Doping with both metals induces strong interactions and pretreatment and reaction conditions lead to the growth of the Au clusters, thereby affecting their catalytic behaviour. This highlights importance of understanding the behaviour of atoms at different stages of catalyst evolution. These insights into the atomic dynamics at the different stages are crucial for the precise optimisation of catalysts, which ultimately enables improved catalytic performance.