Construction of Multifunctional Nanoarchitectures in One Step on a Composite Fuel Catalyst through In Situ Exsolution of La0.5Sr0.5Fe0.8Ni0.1Nb0.1O3-δ

Exsolution on perovskite oxides: morphology and anchorage of nanoparticles

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.

A novel exsolution technique-twice lasers: rapidly aroused explosive exsolution of nanoparticles to boost electrochemical performance

The exsolution of nanoparticles (NPs) on material surfaces exhibits good performance with great potential in the field of catalysis. In this study, a method with twice lasers treatment (TLT) is proposed for the first time to rapidly promote the exsolution of Co NPs to the surface of (La_0.7Sr_0.3)_0.93Ti_0.93Co_0.07O₃(LSTC) by laser rapid heating to enhance the electrochemical performance of the LSTC. The entire process from precursor powder-stable perovskite crystal structure-Co NPs exsolution on the LSTC surface takes only ≈36 s by TLT. The Co NPs exsolution was confirmed by x-ray diffractometer, scanning electron microscopy and high-resolution transmission electron microscopy. After TLT, a large number of Co NPs reached 75 particlesμm^-2appeared on the surface of LSTC with the onset potential of 1.38 V, the overpotential of 214 mV, and the Tafel slope of 81.14 mV dec^-1, showing good catalytic activity and long-term stability. The novel process of using TLT to rapidly induce exsolution of NPs enables the rapid preparation of nanoparticle-decorated perovskite materials with better electrochemical properties, thus enriching exsolution technology and opening a new avenue for surface science research.

Ultrafast Ambient-Air Exsolution on Metal Oxide via Momentary Photothermal Effect

The process of exsolution for the synthesis of strongly anchored metal nanoparticles (NPs) on host oxide lattices has been proposed as a promising strategy for designing robust catalyst-support composite systems. However, because conventional exsolution processes occur in harsh reducing environments at high temperatures for long periods of time, the choice of support materials and dopant metals are limited to those with inherently high thermal and chemical stability. Herein, we report the exsolution of a series of noble metal catalysts (Pt, Rh, and Ir) from metal oxide nanofibers (WO₃ NFs) supports in an entirely ambient environment induced by intense pulsed light (IPL)-derived momentary photothermal treatment (>1000 °C). Since the exsolution process spans an extremely short period of time (<20 ms), unwanted structural artifacts such as decreased surface area and phase transition of the support materials are effectively suppressed. At the same time, exsolved NPs (<5 nm) with uniform size distributions could successfully be formed. To prove the practical utility of exsolved catalytic NPs functionalized on WO₃ NFs, the chemiresistive gas sensing characteristics of exsolved Pt-decorated WO₃ NFs were analyzed, exhibiting high durability (>200 cyclic exposures), enhanced response (R_air/R_gas > 800 @ 1 ppm/350 °C), and selectivity toward H₂S target gas. Altogether, we successfully demonstrated that ultrafast exsolution within a few milliseconds could be induced in ambient conditions using the IPL-derived momentary photothermal treatment and contributed to expanding the practical viability of the exsolution-based synthetic approaches for the production of highly stable catalyst systems.

A Flexible Method to Fabricate Exsolution-Based Nanoparticle-Decorated Materials in Seconds

Decorating metallic nanoparticles on the surface of oxide support is a promising approach to tailor the catalytic activity of perovskite. Here, for the first time using thermal shock to rapidly fabricate nanoparticle-decorated materials (NDMs) is proposed. Low-cost and size-tailorable carbon paper is used as the heating source during the thermal shock. It is reported that by thermal shock technique, only ≈13 s including heating and treating time is needed to fabricate the exsolution-based NDMs (the fastest method to date). Benefitted by the sufficiently provided driving force and the short treating time, as compared to the product prepared by the conventionally furnace-based method, higher particle density and smaller particle size of the exsolved catalysts are acquired for the thermal shock fabricated NDM, giving rise to a fascinating improvement (12-fold) of the electrochemical performance. This work develops a new technique to rapidly fabricate NDMs in an economic and high-throughput manner, profoundly improving the flexibility of the application of exsolution-based materials in electrochemical devices.

Progress of Exsolved Metal Nanoparticles on Oxides as High Performance (Electro)Catalysts for the Conversion of Small Molecules

Utilizing electricity and heat from renewable energy to convert small molecules into value-added chemicals through electro/thermal catalytic processes has enormous socioeconomic and environmental benefits. However, the lack of catalysts with high activity, good long-term stability, and low cost strongly inhibits the practical implementation of these processes. Oxides with exsolved metal nanoparticles have recently been emerging as promising catalysts with outstanding activity and stability for the conversion of small molecules, which provides new possibilities for application of the processes. In this review, it starts with an introduction on the mechanism of exsolution, discussing representative exsolution materials, the impacts of intrinsic material properties and external environmental conditions on the exsolution behavior, and the driving forces for exsolution. The performances of exsolution materials in various reactions, such as alkane reforming reaction, carbon monoxide oxidation, carbon dioxide utilization, high temperature steam electrolysis, and low temperature electrocatalysis, are then summarized. Finally, the challenges and future perspectives for the development of exsolution materials as high-performance catalysts are discussed.