Performance Prediction of High-Entropy Perovskites LaSrMnCoFeO with Automated High-Throughput Characterization of Combinatorial Libraries and Machine Learning.

Perovskite oxides form a large family of materials with applications across various fields, owing to their structural and chemical flexibility. Efficient exploration of this extensive compositional space is now achievable through automated high-throughput experimentation combined with machine learning. In this study, we investigate the composition-structure-performance relationships of high-entropy LaSrMnCoFeO perovskite oxides (0 < x, y, z <1; x+y+z≈1) for application as oxygen electrodes in Solid Oxide Cells.

Revealing Local Grain Boundary Chemistry and Correlating it with Local Mass Transport in Mixed-Conducting Perovskite Electrodes.

Grain boundary (GB) mass transport, and chemistry exert a pronounced influence on both the performance and stability of electrodes for solid oxide electrochemical cells. Lanthanum strontium cobalt ferrite (LSCF6428) is applied as a model mixed ionic and electronic conducting (MIEC) perovskite oxide. The cation-vacancy distribution at the GBs is studied at both single and multi-grain scales using high-resolution characterization techniques and computational approaches.

Studying Surface Chemistry of Mixed Conducting Perovskite Oxide Electrodes with Synchrotron-Based Soft X-rays.

A fundamental understanding of the electrochemical reactions and surface chemistry at the solid-gas interface and is critical for electrode materials applied in electrochemical and catalytic applications. Here, the surface reactions and surface composition of a model of mixed ionic and electronic conducting (MIEC) perovskite oxide, (LaSr)CrFeO (LSCrF8255), were investigated using synchrotron-based near-ambient pressure (AP) X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine-structure spectroscopy (NEXAFS). The measurements were conducted with a surface temperature of 500 °C under 1 mbar of dry oxygen and water vapor, to reflect the implementation of the materials for oxygen reduction/evolution and HO electrolysis in the applications such as solid oxide fuel cell (SOFC) and electrolyzers.

Surface Decorations on Mixed Ionic and Electronic Conductors: Effects on Surface Potential, Defects, and the Oxygen Exchange Kinetics.

The oxygen exchange kinetics of epitaxial PrCeO electrodes was modified by decoration with submonolayer amounts of different basic (SrO, CaO) and acidic (SnO, TiO) binary oxides. The oxygen exchange reaction (OER) rate and the total conductivity were measured by PLD impedance spectroscopy (-PLD), which allows to directly track changes of electrochemical properties after each deposited pulse of surface decoration. The surface chemistry of the electrodes was investigated by near-ambient pressure XPS measurements (NAP-XPS) at elevated temperatures and by low-energy ion scattering (LEIS).

Electronic and ionic effects of sulphur and other acidic adsorbates on the surface of an SOFC cathode material.

The effects of sulphur adsorbates and other typical solid oxide fuel cell (SOFC) poisons on the electronic and ionic properties of an SrO-terminated (La,Sr)CoO (LSC) surface and on its oxygen exchange kinetics have been investigated experimentally with near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS), low energy ion scattering (LEIS) and impedance spectroscopy as well as computationally with density functional theory (DFT). The experiment shows that trace amounts of sulphur in measurement atmospheres form SO adsorbates and strongly deactivate a pristine LSC surface. They induce a work function increase, indicating a changing surface potential and a surface dipole.

Correlating Surface Crystal Orientation and Gas Kinetics in Perovskite Oxide Electrodes.

Solid-gas interactions at electrode surfaces determine the efficiency of solid-oxide fuel cells and electrolyzers. Here, the correlation between surface-gas kinetics and the crystal orientation of perovskite electrodes is studied in the model system La Sr Co Fe O . The gas-exchange kinetics are characterized by synthesizing epitaxial half-cell geometries where three single-variant surfaces are produced [i.

Kinetics of competing exchange of oxygen and water at the surface of functional oxides.

The presence of water vapour in the input gas stream influences the performance of air electrodes of solid oxide cells. In this work, the oxygen transport kinetics were determined by isotopic exchange depth profiling at 350 °C on polycrystalline La0.6Sr0.

Self-diffusion in garnet-type LiLaZrO solid electrolytes.

Tetragonal garnet-type LiLaZrO is an important candidate solid electrolyte for all-solid-state lithium ion batteries because of its high ionic conductivity and large electrochemical potential window. Here we employ atomistic simulation methods to show that the most favourable disorder process in LiLaZrO involves loss of LiO resulting in lithium and oxygen vacancies, which promote vacancy mediated self-diffusion. The activation energy for lithium migration (0.

Surface Restructuring of Thin-Film Electrodes Based on Thermal History and Its Significance for the Catalytic Activity and Stability at the Gas/Solid and Solid/Solid Interfaces.

Electrodes in solid-state energy devices are subjected to a variety of thermal treatments, from film processing to device operation at high temperatures. All these treatments influence the chemical activity and stability of the films, as the thermally induced chemical restructuring shapes the microstructure and the morphology. Here, we investigate the correlation between the oxygen reduction reaction (ORR) activity and thermal history in complex transition metal oxides, in particular, LaSrCoO (LSC64) thin films deposited by pulsed laser deposition.

A CO -Tolerant Perovskite Oxide with High Oxide Ion and Electronic Conductivity.

Mixed ionic-electronic conductors (MIECs) that display high oxide ion conductivity (σ ) and electronic conductivity (σ ) constitute an important family of electrocatalysts for a variety of applications including fuel cells and oxygen separation membranes. Often MIECs exhibit sufficient σ but inadequate σ . It has been a long-standing challenge to develop MIECs with both high σ and stability under device operation conditions.

Designing Optimal Perovskite Structure for High Ionic Conduction.

Solid-oxide fuel/electrolyzer cells are limited by a dearth of electrolyte materials with low ohmic loss and an incomplete understanding of the structure-property relationships that would enable the rational design of better materials. Here, using epitaxial thin-film growth, synchrotron radiation, impedance spectroscopy, and density-functional theory, the impact of structural parameters (i.e.

Oxygen transport and surface exchange mechanisms in LSCrF-ScCeSZ dual-phase ceramics.

For the mechanisms by which the oxygen gets incorporated in a dual-phase composite system, three hypotheses, i.e. cation inter-diffusion, spillover type and self-cleaning of the perovskite-structured phase, have been provided in the literature.

Unveiling the Outstanding Oxygen Mass Transport Properties of Mn-Rich Perovskites in Grain Boundary-Dominated LaSr(Mn Co )O Nanostructures.

Ion transport in solid-state devices is of great interest for current and future energy and information technologies. A superior enhancement of several orders of magnitude of the oxygen diffusivity has been recently reported for grain boundaries in lanthanum-strontium manganites. However, the significance and extent of this unique phenomenon are not yet established.

Electrical conductivity and oxygen diffusion behaviour of the (LaSr)CrFeO (x = 0.3, 0.5 and 0.7) A-site deficient perovskites.

Lanthanum strontium chromite ferrite ((La0.8Sr0.2)0.

Interface Effects on the Ionic Conductivity of Doped Ceria-Yttria-Stabilized Zirconia Heterostructures.

Multilayered heterostructures of CeSmO and YZrO of a high crystallographic quality were fabricated on (001)-oriented MgO single crystal substrates. Keeping the total thickness of the heterostructures constant, the number of ceria-zirconia bilayers was increased while reducing the thickness of each layer. At each interface Ce was found primarily in the reduced, 3+ oxidation state in a layer extending about 2 nm from the interface.

Electronic properties and surface reactivity of SrO-terminated SrTiO and SrO-terminated iron-doped SrTiO.

Surface reactivity and near-surface electronic properties of SrO-terminated SrTiO and iron doped SrTiO were studied with first principle methods. We have investigated the density of states (DOS) of bulk SrTiO and compared it to DOS of iron-doped SrTiO with different oxidation states of iron corresponding to varying oxygen vacancy content within the bulk material. The obtained bulk DOS was compared to near-surface DOS, i.

Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

O and H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCoO (PBCO) in flowing air containing 200 mbar of HO. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10 cms) at this temperature and that the presence of water (HO), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3.

Surface Chemistry of LaSrNbO and Its Implication for Proton Conduction.

Acceptor-doped LaNbO is a promising electrolyte material for proton-conducting fuel cell (PCFC) applications. As charge transfer processes govern device performance, the outermost surface of acceptor-doped LaNbO will play an important role in determining the overall cell performance. However, the surface composition is poorly characterized, and the understanding of its impact on the proton exchange process is rudimentary.

The effects of lattice strain, dislocations, and microstructure on the transport properties of YSZ films.

Enhanced conductivity in YSZ films has been of substantial interest over the last decade. In this paper we examine the effects of substrate lattice mismatch and film thickness on the strain in YSZ films and the resultant effect on the conductivity. 8 mol% YSZ films have been grown on MgO, AlO, LAO and NGO substrates, thereby controlling the lattice mismatch at the film/substrate interface.

Back-exchange: a novel approach to quantifying oxygen diffusion and surface exchange in ambient atmospheres.

A novel two-step Isotopic Exchange (IE) technique has been developed to investigate the influence of oxygen containing components of ambient air (such as HO and CO) on the effective surface exchange coefficient (k*) of a common mixed ionic electronic conductor material. The two step 'back-exchange' technique was used to introduce a tracer diffusion profile, which was subsequently measured using Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The isotopic fraction of oxygen in a dense sample as a function of distance from the surface, before and after the second exchange step, could then be used to determine the surface exchange coefficient in each atmosphere.

Investigating the Dendritic Growth during Full Cell Cycling of Garnet Electrolyte in Direct Contact with Li Metal.

All-solid-state batteries including a garnet ceramic as electrolyte are potential candidates to replace the currently used Li-ion technology, as they offer safer operation and higher energy storage performances. However, the development of ceramic electrolyte batteries faces several challenges at the electrode/electrolyte interfaces, which need to withstand high current densities to enable competing C-rates. In this work, we investigate the limits of the anode/electrolyte interface in a full cell that includes a Li-metal anode, LiFePO cathode, and garnet ceramic electrolyte.

Oxygen exchange and transport in dual phase ceramic composite electrodes.

Composites consisting of a perovskite-based electronic or mixed conductor with a fluorite-structured ionic conductor are often used as electrodes in solid oxide electrochemical energy conversion devices. After sintering the materials, there is often evidence for inter-reaction between the two phases, or inter-diffusion of cations or impurities between the two phases. We studied the (18)O exchange properties of a composite consisting of CGO and LSCF in a 50 : 50 ratio.

Relating surface chemistry and oxygen surface exchange in LnBaCo2O(5+δ) air electrodes.

The surface and near-surface chemical composition of electroceramic materials often shows significant deviations from that of the bulk. In particular, layered materials, such as cation-ordered LnBaCo2O(5+δ) perovskites (Ln = lanthanide), undergo surface and sub-surface restructuring due to the segregation of the divalent alkaline-earth cation. These processes can take place during synthesis and processing steps (e.

Accurate and precise measurement of oxygen isotopic fractions and diffusion profiles by selective attenuation of secondary ions (SASI).

The accuracy and precision of isotopic analysis in Time-of-Flight secondary ion mass spectrometry (ToF-SIMS) relies on the appropriate reduction of the dead-time and detector saturation effects, especially when analyzing species with high ion yields or present in high concentrations. Conventional approaches to avoid these problems are based on Poisson dead-time correction and/or an overall decrease of the total secondary ion intensity by reducing the target current. This ultimately leads to poor detection limits for the minor isotopes and high uncertainties of the measured isotopic ratios.

Probing the bulk ionic conductivity by thin film hetero-epitaxial engineering.

Highly textured thin films with small grain boundary regions can be used as model systems to directly measure the bulk conductivity of oxygen ion conducting oxides. Ionic conducting thin films and epitaxial heterostructures are also widely used to probe the effect of strain on the oxygen ion migration in oxide materials. For the purpose of these investigations a good lattice matching between the film and the substrate is required to promote the ordered film growth.