135HIGHLIGHTS 2020

STRAIN-ACTIVATED MATERIALS BY ENDO-/EXO- NANOPARTICLES

Particles dispersed on the surface of oxide supports (exo-) have enabled a wealth of applications in electro-, photo- and heterogeneous catalysis. Here, operando X-ray diffraction is used to reveal how nanoparticles can additionally be dispersed within the support itself (endo-), unlocking dramatic enhancements in ion transport and exchange by strain arising from their crystallographic mismatch with the support.

Metallic nanoparticles dispersed on the surface of oxide supports (e.g., perovskite oxides) have proven to be instrumental in controlling and tailoring the surface reactivity of materials for a wide variety of catalytic applications, especially in energy conversion technologies. This work shows that nanoparticles can additionally be dispersed within the support itself, leading to strain on the particles themselves as well as on the bulk perovskite. This could lead to the ability to tailor materials, in particular through strain engineering, which has been shown to control multiple properties including oxide ion, electron and thermal transport, catalytic reactivity and magnetic properties.

Generally, it is challenging to produce such structures, and any efforts made so far have been through assembling metallic nanoclusters together with a non-metallic host lattice, which poses limitations as to the types of materials that can be used and to the nanostructures that can be produced. However, such a concept can also be made possible through exsolution a disassembly method that has been proven to produce nanoparticles with enhanced surface properties such as anti-coking behaviour and long-term stability due to crystallographic alignment and strain [1]. By employing the exsolution concept outside its conventional area of application of surface modification,

Fig. 118: Systems with exo-/endo-particles. a) 3D model of a catalyst particle with nanoparticles dispersed on its surface and within its bulk. b) SEM micrographs of cross-section view after exsolution revealing surface and bulk particles. c) Room-temperature XRD of samples

reduced at different reduction temperatures. d) From left: Ni metal peak from (c) deconvoluted into surface and bulk particles contribution using Rietveld refinement, Ni metal particle size distribution, and domain size distribution calculated by image analysis.

e) Detail of the Ni peak from XRD pattern with corresponding total (surface and bulk) Ni content (wt.%) calculated by Rietveld refinement. Schematic illustrations of samples without (left) and with (right) bulk particles.