Endogenous Nanoparticles Strain Perovskite Host Lattice Providing Oxygen Capacity and Driving Oxygen Exchange and CH₄ Conversion to Syngas

Abstract

Particles dispersed on the surface of oxide supports have enabled a wealth of applications in electro-photo-and heterogeneous catalysis. Dispersing nanoparticles within the bulk of oxides is, however, synthetically much more challenging and therefore less explored, but could open new dimensions to control material properties analogous to substitutional doping of ions in crystal lattices.Here we demonstrate such a concept allowing extensive, controlled growth of metallic nanoparticles, at nanoscale proximity, within a perovskite oxide lattice as well as on its surface. By employing operando techniques, we show that in the emergent nanostructure, the endogenous nanoparticles and the perovskite lattice become reciprocally strained and seamlessly connected, enabling enhanced oxygen exchange. Additionally, even deeply embedded nanoparticles can reversibly exchange oxygen with a methane stream, driving its redox conversion to syngas with remarkable selectivity and long term cyclability while surface particles are present. These results not only exemplify the means to create extensive, self-strained nanoarchitectures with enhanced oxygen transport and storage capabilities, but also demonstrate that deeply submerged, redoxactive nanoparticles could be entirely accessible to reaction environments, driving redox transformations and thus offering intriguing new alternatives to design materials underpinning several energy conversion technologies.

Progress and Opportunities for Exsolution in Electrochemistry

“…Therefore, low-cation transport properties and lower oxygen partial pressures (pO 2 ) should favor internal nucleation. This concept was recently expanded upon by exsolving particles both on the surface and in the subsurface layers in La 0.8 Ce 0.1 Ni 0.4 Ti 0.6 Ni 0.4 O 3 , thus reciprocally straining the subsurface particles with the perovskite and significantly enhancing oxygen exchange [32]. While the application of this later discovery was not electrochemical in nature, the concept of enhanced oxygen mobility via subsurface growth may have applications in electrochemical oxygen reduction electrodes.…”

Combining Exsolution and Infiltration for Redox, Low Temperature CH4 Conversion to Syngas

“…In order to prepare an exsolved system that contains both surface (exo) and bulk (endo) particles we chose La 0.8 Ce 0.1 Ni 0.4 Ti 0.6 O 3 based on the design principles reported before [18]. The XRD pattern and corresponding Rietveld analysis of the as-prepared material are shown in Figure 2a.…”

“…Exsolution has been recently employed in chemical looping applications, specifically in chemical looping methane partial oxidation (CLPO), because of the emergent materials' properties that arise from this particular synthesis method [9][10][11][12][13], like coke resistance, redox stability and enhanced activity [14][15][16][17]. We have recently proven that by evolving the exsolution concept, we can design systems that have both particles on the surface (exo-particles) and in the bulk (endo-particles) [18]. In these systems the exo-particles activate methane, the endo-particles act as oxygen reservoirs and the perovskite matrix mediates oxygen transfer between the two.…”

“…Exsolving from samples with different microstructures. (a) Microstructure (SEM) analysis of the fine powder (fP), the coarse powder (cP) and the pellet (pP) after reduction at 1000 C for 10 h. Inserts of XRD patterns of the samples after reduction indicating with • the main perovskite peak at ~32°, with ∎ the La2TiO5 phase[18] at ~27° and with * the Ni metal peak at ~44°. (b) Nanostructure (SEM) analysis of the fP, cP and the pP after reduction at 1000 C for 10 h. (c) Particle size analysis and population for the samples.…”

Low temperature methane conversion with perovskite-supported exo/endo-particles

“…[14][15][16] We have recently demonstrated that the exsolution concept can be controlled to produce systems with particles on the surface as well as in the bulk, leading to oxygen carrier materials that can selectively convert methane to syngas by chemical looping at 600 C, much lower than similar chemical lopping processes. 17 To further lower this temperature, one would have to increase the surface reactivity of the material as well as increase the oxygen transport through the bulk. One way of achieving these goals simultaneously would be by incorporating Co in the previously designed systems because Co has been shown to improve oxide-ion transport in perovskites.…”