Space charge governs the kinetics of metal exsolution

30 January 2023, Version 2
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

Nanostructured composite electrode materials play a major role in the field of catalysis and electrochemistry. Self‐assembly of metallic nanoparticles on oxide supports via metal exsolution relies on the transport of reducible dopants towards the perovskite surface to provide accessible catalytic centers at the solid/gas interface. However, it is unclear if exsolution can be driven from the oxide bulk or if the process is limited to surfaces and interfaces, where strong electrostatic gradients and space charges typically control the properties of oxides. Here we reveal that the nature of the surface‐dopant interaction is the main determining factor for the exsolution kinetics of nickel in SrTi0.9Nb0.05Ni0.05O3‐ẟ and that the exsolution depth is strongly limited to the near‐surface region of the perovskite oxide. Electrostatic interaction of dopants with surface space charge regions forming upon thermal annealing result in strong surface passivation i.e. a retarded exsolution response. We furthermore demonstrate the controllability of the exsolution response via engineering of the perovskite surface chemistry. Our findings indicate that tailoring the electrostatic gradients at the perovskite surface is an essential step to improve exsolution type materials in catalytic converters.

Keywords

metal exsolution
space charge
nanoparticles
surface potential
catalysis

Supplementary materials

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Supporting Information
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RHEED analysis of the thin film growth. XRD analysis of the (002) diffraction peak of a 20 nm thick as-prepared STNNi thin film. Details on the cation depth profiling by SIMS. Surface morphology of reduced STNNi thin films after different times of oxidizing pre-annealing. XRD analysis of the (002) diffraction peak after different times of oxidzing annealing. Ratio of the integrated peak areas of the Sr 3d and Ti 2p core-level spectra obtained by NAP-XPS analysis over the course of an oxidizing annealing procedure. Control of the perovskite termination layer via oxide RHEED-PLD epitaxy and ananlysis of the exsolution behavior. of Surface morphology of an STNNi thin film after oxidizing annealing. Supplementary analysis of NAP-XPS data obtained under systematically varying redox conditions. Surface morphology of surface engineered STNNi with a top layer of either n-type or p-type defect chemistry (stack-geometry). Details on the finite-element electrostatic space charge simulations.
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