Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O Nanoparticles.

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood.

UV-Driven Oxygen Surface Exchange and Stoichiometry Changes in a Thin-Film, Nondilute Mixed Ionic Electronic Conductor, Sr(Ti,Fe)O.

Enabling light-controlled ionic devices requires insight into photoionic responses in technologically relevant materials. Mixed-conducting perovskites containing nondilute Fe─serving as electrodes, catalysts, and sensors─can support large, electronically accommodated excursions in oxygen content, typically controlled by temperature, bias, and gas atmosphere. Instead, we investigated the ability of low-fluence, above-bandgap illumination to adjust oxygen stoichiometry and drive oxygen fluxes in nondilute Sr(TiFe)O ( = 0.

Defect Engineering in Composition and Valence Band Center of Y(YRu)O Pyrochlore Electrocatalysts for Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) takes place in various types of electrochemical devices that are pivotal for the conversion and storage of renewable energy. This paper describes a strategy in the design of solid-state structures of OER electrocatalysts through controlling the cation substitution on the active metal site and consequently valence band center position of site-mixed Y(YRu)O pyrochlore to achieve high catalytic activity. We found that partially replacing the B-site Ru cation with A-site Y in pyrochlore-structured YRuO modifies the oxidation state of B-site Ru from 4 to 5, as observed by electron paramagnetic resonance (EPR) spectroscopy but does not continuously increase the oxygen vacancy concentration in these oxygen substoichiometric compositions, as quantified by thermogravimetric analysis (TGA) decomposition studies.

High-Temperature 2D Optical Relaxation Visualizes Enhanced Oxygen Exchange Kinetics at Metal-Mixed Conducting Oxide Interfaces.

Solid-state heterointerfaces are of interest for emergent local behavior that is distinct from either bulk parent compound. One technologically relevant example is the case of mixed ionic/electronic conductor (MIEC)-metal interfaces, which play an important role in electrochemistry. Metal-MIEC composite electrodes can demonstrate improved catalytic activity vs single-phase MIECs, improving fuel cell efficiency.

Dislocation-Mediated Conductivity in Oxides: Progress, Challenges, and Opportunities.

Dislocations in ionic solids are topological extended defects that modulate composition, strain, and charge over multiple length scales. As such, they provide an extra degree of freedom to tailor ionic and electronic transport beyond limits inherent in bulk doping. Heterogeneity of transport paths as well as the ability to dynamically reconfigure structure and properties through multiple stimuli lend dislocations to particular potential applications including memory, switching, non-Ohmic electronics, capacitive charge storage, and single-atom catalysis.

Simultaneous Electrical, Electrochemical, and Optical Relaxation Measurements of Oxygen Surface Exchange Coefficients: Sr(Ti,Fe)O Film Crystallization Case Study.

The oxygen surface exchange coefficient () dictates the efficiency and response time of many mixed conductors, so its accurate, continuous measurement in realistic conditions, enabling rational tailoring, is necessary. However, recent results showed that values determined by a thin-film optical transmission relaxation (OTR) method were orders of magnitude lower than those extracted from the cross-cell AC-impedance spectroscopy (AC-IS) approach, and similar discrepancies among methods exist in the literature. OTR has also detected dramatic increases in in situ during crystallization.

Integrating primary and secondary care to optimize hepatitis C treatment: development and evaluation of a multidisciplinary educational Masterclass series.

Background: It is increasingly being recognized that the elimination of HCV requires a multidisciplinary approach and effective cooperation between primary and secondary care.

Objectives: As part of a project (HepCare Europe) to integrate primary and secondary care for patients at risk of or infected with HCV, we developed a multidisciplinary educational Masterclass series for healthcare professionals (HCPs) working in primary care in Dublin and Bucharest. This article aims to describe and evaluate the series and examine how this model might be implemented into practice.

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.

Tailoring Nonstoichiometry and Mixed Ionic Electronic Conductivity in PrCeO/SrTiO Heterostructures.

The oxygen deficiency or excess, as reflected in the nonstoichiometry of oxide films, plays a crucial role in their functional properties for applications such as micro solid oxide fuel cells, catalysis, sensors, ferroelectrics, and memristors. High concentrations of oxygen vacancies may be beneficial or detrimental according to the application, and hence there is interest in controlling the oxygen content of films without resorting to compositional changes. Here, we demonstrate that substantial changes in the nonstoichiometry of PrCeO (PCO), a model mixed ionic electronic conductor, can be achieved by fabricating multilayers with an inert material, SrTiO (STO).

In Situ Method Correlating Raman Vibrational Characteristics to Chemical Expansion via Oxygen Nonstoichiometry of Perovskite Thin Films.

Effective integration of perovskite films into devices requires knowledge of their electro-chemomechanical properties. Raman spectroscopy is an excellent tool for probing such properties as the films' vibrational characteristics couple to the lattice volumetric changes during chemical expansion. While lattice volumetric changes are typically accessed by analyzing Raman shifts as a function of pressure, stress, or temperature, such methods can be impractical for thin films and do not capture information on chemical expansion.

Emergence of Rapid Oxygen Surface Exchange Kinetics during in Situ Crystallization of Mixed Conducting Thin Film Oxides.

The oxygen surface exchange kinetics of mixed ionic and electronic conducting oxides (MIECs) play a critical role in the efficiency of intermediate-to-high-temperature electrochemical devices. Although there is increasing interest in low-temperature preparation of MIEC thin films, the impact of the resultant varied degrees of crystallinity on the surface exchange kinetics has not been widely investigated. Here, we probe the effect of crystallization on oxygen surface exchange kinetics in situ, by applying an optical transmission relaxation (OTR) approach during annealing of amorphous films.

On the Theoretical and Experimental Control of Defect Chemistry and Electrical and Photoelectrochemical Properties of Hematite Nanostructures.

Hematite (α-FeO) is regarded as one of the most promising cost-effective and stable anode materials in photoelectrochemical applications, and its performance, like other transition-metal oxides, depends strongly on its electrical and defect properties. In this work, the electrical and thermomechanical properties of undoped and Sn-doped α-FeO nanoscale powders were characterized in situ at controlled temperatures ( T = 250 to 400 °C) and atmospheres ( pO = 10 to 1 atm O) to investigate their transport and defect properties. Frequency-dependent complex impedance spectra show that interfacial resistance between particles is negligible in comparison with particle resistance.

Oxygen surface exchange kinetics measurement by simultaneous optical transmission relaxation and impedance spectroscopy: Sr(Ti,Fe)O thin film case study.

We compare approaches to measure oxygen surface exchange kinetics, by simultaneous optical transmission relaxation (OTR) and AC-impedance spectroscopy (AC-IS), on the same mixed conducting SrTiFeO film. Surface exchange coefficients were evaluated as a function of oxygen activity in the film, controlled by gas partial pressure and/or DC bias applied across the ionically conducting yttria-stabilized zirconia substrate. Changes in measured light transmission through the film over time (relaxations) resulted from optical absorption changes in the film corresponding to changes in its oxygen and oxidized Fe (~Fe) concentrations; such relaxation profiles were successfully described by the equation for surface exchange-limited kinetics appropriate for the film geometry.

Roles of Bulk and Surface Chemistry in the Oxygen Exchange Kinetics and Related Properties of Mixed Conducting Perovskite Oxide Electrodes.

Mixed conducting perovskite oxides and related structures serving as electrodes for electrochemical oxygen incorporation and evolution in solid oxide fuel and electrolysis cells, respectively, play a significant role in determining the cell efficiency and lifetime. Desired improvements in catalytic activity for rapid surface oxygen exchange, fast bulk transport (electronic and ionic), and thermo-chemo-mechanical stability of oxygen electrodes will require increased understanding of the impact of both bulk and surface chemistry on these properties. This review highlights selected work at the International Institute for Carbon-Neutral Energy Research (I²CNER), Kyushu University, set in the context of work in the broader community, aiming to characterize and understand relationships between bulk and surface composition and oxygen electrode performance.

Tunable Mixed Ionic/Electronic Conductivity and Permittivity of Graphene Oxide Paper for Electrochemical Energy Conversion.

Graphene oxide (GO) is a two-dimensional graphitic carbon material functionalized with oxygen-containing surface functional groups. The material is of interest in energy conversion, sensing, chemical processing, gas barrier, and electronics applications. Multilayer GO paper has recently been applied as a new proton conducting membrane in low temperature fuel cells.

Discovery of a ternary pseudobrookite phase in the earth-abundant Ti-Zn-O system.

We combine theory with experiment in searching for "missing", stable materials within the Zn-Ti-O chemical system, leading to the discovery of a new pseudobrookite phase, ZnxTi3-xO5-δ. This ternary system was chosen for (1) technological relevance, (2) earth abundance, and (3) the fact that many compounds in this system are predicted from enthalpies of formation to be borderline stable, suggesting an important role of entropic contributions in their stabilization and making this chemical system a perfect test bed for exploring the limits of theoretical predictions. The initial set of exploratory experimental syntheses, via sintering in evacuated ampoules and quenching, resulted in a single phase ZnxTi3-xO5-δ composition with x ≈ 0.

Understanding chemical expansion in perovskite-structured oxides.

In this work, chemical expansion in perovskite oxides was characterized in detail, motivated, inter alia, by a desire to understand the lower chemical expansion coefficients observed for perovskites in comparison to fluorite-structured oxides. Changes in lattice parameter and in local atomic arrangements taking place during compositional changes of perovskites, i.e.

Barriers to and facilitators of hepatitis C testing, management, and treatment among current and former injecting drug users: a qualitative exploration.

Hepatitis C (HCV) infection is common among injecting drug users (IDUs), yet accessing of HCV care, particularly HCV treatment, is suboptimal. There has been little in-depth study of IDUs experiences of what enables or prevents them engaging at every level of HCV care, including testing, follow-up, management and treatment processes. This qualitative study aimed to explore these issues with current and former IDUs in the greater Dublin area, Ireland.