Real-time insight into the multistage mechanism of nanoparticle exsolution from a perovskite host surface

Abstract

In exsolution, nanoparticles form by emerging from oxide hosts by application of redox driving forces, leading to transformative advances in stability, activity, and efficiency over deposition techniques, and resulting in a wide range of new opportunities for catalytic, energy and net-zero-related technologies. However, the mechanism of exsolved nanoparticle nucleation and perovskite structural evolution, has, to date, remained unclear. Herein, we shed light on this elusive process by following in real time Ir nanoparticle emergence from a SrTiO3 host oxide lattice, using in situ high-resolution electron microscopy in combination with computational simulations and machine learning analytics. We show that nucleation occurs via atom clustering, in tandem with host evolution, revealing the participation of surface defects and host lattice restructuring in trapping Ir atoms to initiate nanoparticle formation and growth. These insights provide a theoretical platform and practical recommendations to further the development of highly functional and broadly applicable exsolvable materials.

In situ passivation of Fe nanoparticles exsolved from perovskite cathodes through zinc doping for CO2 electrolysis

“…This passivation effect can optimize the particle size of exsolved Fe NPs, and modify the surface interaction between in situ exsolved particles and the perovskite substrate, which greatly prevents the agglomeration of Fe NPs from occurring during the reduction process. 14–16 Consequently, this ensures a sufficient number of catalytic active sites for the CO 2 RR and enhances the stability of the perovskite during long-term operation.…”

“…However, the continuous stripping of exsolved NPs from the perovskite matrix can lead to phase transformation and even scaffold collapse. 14,15 Additionally, the uninterrupted reduction process can result in coarsening and agglomeration of NPs, ultimately affecting the performance for the CO 2 RR. Lv et al provided direct insights into the emergence, growth, and coarsening processes of CoFe-alloy on Sr 2 Fe 1.5 Mo 0.5 O 6− δ (SFM) under H 2 .…”

Enhanced Stability of Iridium Nanocatalysts via Exsolution for the CO2 Reforming of Methane

“…This is expected, as the higher reduction temperature would result in a higher degree of reduction of the material as well as the increased mobility of Ir ions toward the surface. 41,42 As confirmation, a relatively high amount of Ir in its oxide forms is still found in the sample after reduction at 600 °C (Ir (III),(IV) :Ti = 0.6%:99.4%), which is lowered (Ir (III),(IV) :Ti = 0.2%:99.8%) after reduction in 5% H 2 /Ar at 900 °C for the same time scale (10 h). When the catalytic activity of the two samples for the dry reforming of methane was compared, the sample reduced at 900 °C showed higher activity, as shown in Figure 1h and i.…”

Co-Exsolution of Ni-Based Alloy Catalysts for the Valorization of Carbon Dioxide and Methane

“…The separation of a solid phase from a homogeneous solid solution, known as exsolution, is a fascinating phenomenon with wide-ranging applications in geology, chemistry, − and materials engineering . In the field of catalysis, exsolution is being explored to create “smart” or “intelligent” nanocatalysts with improved sinter resistance, coke resistance, and impurity resistance. ,− The exsolved catalyst nanoparticles are formed under a reducing environment (Figure a) and can regenerate after exposure to an oxidizing environment, making them highly advantageous in energy-intensive reactions. − ,, Their unique properties of improved dispersion, thermal stability, and compositional malleability compared to those of conventional synthesis strategies (Figure b) are particularly useful for valorizing CO 2 into chemical commodities and fuels.…”

“…The A cation is typically composed of lanthanide (La, Ce, Pr, and Nd) or alkaline earth metals (Ca, Sr, and Ba), while the B cations consist of smaller transition metals, often used as substitutional sites for catalytic dopant metals . Under thermo- or electro-reductive conditions, the perovskite oxides undergo exsolution, a partial decomposition process where B cations diffuse from the bulk and nucleate on the surface. ,, The transport of cations from the bulk to the surface is mediated by defects, such as grain boundaries and oxygen vacancies. , The B-cation metal is reduced to its zerovalent state, leading to particle growth and the formation of catalyst nanoparticles. These nanoparticles are partially submerged or “socketed” in the perovskite oxide support, improving the metal–support interaction and retarding particle coalescence sintering. , The nanoparticles can move in and out of the perovskite matrix under reducing and oxidation conditions, allowing for their regeneration. , …”