Rapid Plasma Exsolution from an A‐site Deficient Perovskite Oxide at Room Temperature

Abstract

and catalysis, capable of producing supported nanoparticles in a single synthesis step. [2][3][4][5][6][7] Exsolution was first observed on stoichiometric perovskite oxides where nanoparticles could be produced from transition metals present on the B-site of the perovskite oxide. This mechanism was initially referred to as solid-state recrystallization or self-regeneration. [8] Recently, however, the use of defect chemistry to synthesize the host oxides has revived the interest in exsolution because it allows a greater number of active cations, enhanced surface nucleation and nanoparticle growth and an overall faster and better controlled process. [3,9,10] Furthermore, the defect chemistry also allows for a structure that does not change when the reaction conditions change from oxidizing to reducing thus producing extremely controllable and stable catalysts. These advances have triggered fast growing research activities in the exsolution of nanoparticles and their application for environmental catalysis, solid oxide fuel cells, electrolysers, and chemical looping. [11][12][13][14][15][16][17][18][19] Exsolution is now an established term that refers to the growth of nanoparticles via the supply of metallic ionic species from an oxide host. This allows the formation of well anchored and partially embedded nanoparticles (socketed) on the support oxide, while also exhibiting crystallographic alignment. The application interest in exsolved nanoparticles High-performance nanoparticle platforms can drive catalysis progress to new horizons, delivering environmental and energy targets. Nanoparticle exsolution offers unprecedented opportunities that are limited by current demanding process conditions. Unraveling new exsolution pathways, particularly at low-temperatures, represents an important milestone that will enable improved sustainable synthetic route, more control of catalysis microstructure as well as new application opportunities. Herein it is demonstrated that plasma direct exsolution at room temperature represents just such a step change in the synthesis. Moreover, the factors that most affect the exsolution process are identified. It is shown that the surface defects produced initiate exsolution under a brief ion bombardment of an argon low-pressure and lowtemperature plasma. This results in controlled nanoparticles with diameters ≈19-22 nm with very high number densities thus creating a highly active catalytic material for CO oxidation which rivals traditionally created exsolved samples.

Roadmap on exsolution for energy applications

“…Regarding irradiation, Kyriakou et al employed N 2 plasma treatment to facilitate exsolution, and found that the plasma-assisted exsolution can generate Ni nanoparticles that have up to ten times higher particle density compared to thermal chemical exsolution [37]. Recently, Khalid et al have leveraged argon plasma treatment to promote Ni exsolution out of La 0.43 Ca 0.37 Ti 0.94 Ni 0.06 O 2.955 at room temperature [39]. Finally, in terms of thermal control of exsolution, Sun et al have utilized ultrafast thermal annealing (i.e.…”

“…Additionally, employing extrinsic techniques to control the crystal faces on the surface i.e. particle shape would make possible the design of highly active, selective and tailored materials [11,39,186], enabling a functional diversity that will allow for more efficient CL processes. As mentioned above, preparation method plays a key role in the nano and microstructure of these materials and modification of the current synthesis methods would impact on the microstructure of the backbone matrixes.…”

Recent advances in exsolved perovskite oxide construction: exsolution theory, modulation, challenges, and prospects

“…In addition to plasma discharge, the activated N-containing species also participated in stripping oxygen from the perovskite. Khalid et al 105 found that in low-temperature plasma under an argon atmosphere, the perovskite La 0.43 Ca 0.37 Ti 0.94 Ni 0.06 O 2.955 with A-site deficiency achieved large particle densities with a diameter range of 19–22 nm at room temperature within 15 min. The schematic illustration of the plasma-driven exsolution of Ni nanoparticles is shown in Fig.…”

Ion irradiation to control size, composition and dispersion of metal nanoparticle exsolution

“…2,3 Since ultrafine (e.g., sub-5 nm) 16,17 and multi-element 18 nanoparticles can have higher catalytic activities, it is desirable to exsolve nanoparticles with tunable composition (multicomponent) and with tunable (reduced) size. Researchers have tried various methods, such as doping, 19,20 plasma treatment, 21,22 and electrochemistry 23,24 (see Table S1, ESI † for a more comprehensive summary) to tailor exsolution. While significant progress has been made, most strategies proposed thus far still rely on choosing a specific host oxide composition for metal exsolution.…”