Maximizing Photoelectrochemical Performance in Metal-Oxide Hybrid Composites via Amorphous Exsolution-A New Exsolution Mechanism for Heterogeneous Catalysis.

Exsolution generates metal nanoparticles anchored within crystalline oxide supports, ensuring efficient exposure, uniform dispersion, and strong nanoparticle-perovskite interactions. Increased doping level in the perovskite is essential for further enhancing performance in renewable energy applications; however, this is constrained by limited surface exsolution, structural instability, and sluggish charge transfer. Here, hybrid composites are fabricated by vacuum-annealing a solution containing SrTiO3 photoanode and Co cocatalyst precursors for photoelectrochemical water-splitting. In situ transmission electron microscopy identifies uniform, high-density Co particles exsolving from amorphous SrTiO3 films, followed by film-crystallization at elevated temperatures. This unique process extracts entire Co dopants with complete structural stability, even at Co doping levels exceeding 30%, and upon air exposure, the Co particles embedded in the film oxidize to CoO, forming a Schottky junction at the interface. These conditions maximize photoelectrochemical activity and stability, surpassing those achieved by Co post-deposition and Co exsolution from crystalline oxides. Theoretical calculations demonstrate in the amorphous state, dopant─O bonds become weaker while Ti─O bonds remain strong, promoting selective exsolution. As expected from the calculations, nearly all of the 30% Fe dopants exsolve from SrTiO3 in an H2 environment, despite the strong Fe─O bond's low exsolution tendency. These analyses unravel the mechanisms driving the amorphous exsolution.

Tuning Reconstruction Level of Precatalysts to Design Advanced Oxygen Evolution Electrocatalysts.

Surface reconstruction engineering is an effective strategy to promote the catalytic activities of electrocatalysts, especially for water oxidation. Taking advantage of the physicochemical properties of precatalysts by manipulating their structural self-reconstruction levels provide a promising methodology for achieving suitable catalysts. In this review, we focus on recent advances in research related to the rational control of the process and level of surface transformation ultimately to design advanced oxygen evolution electrocatalysts. We start by discussing the original contributions to surface changes during electrochemical reactions and related factors that can influence the electrocatalytic properties of materials. We then present an overview of current developments and a summary of recently proposed strategies to boost electrochemical performance outcomes by the controlling structural self-reconstruction process. By conveying these insights, processes, general trends, and challenges, this review will further our understanding of surface reconstruction processes and facilitate the development of high-performance electrocatalysts beyond water oxidation.

Growth Kinetics of Individual Co Particles Ex-solved on SrTi0.75Co0.25O3-δ Polycrystalline Perovskite Thin Films.

A precise control of the size, density, and distribution of metal nanoparticles dispersed on functional oxide supports is critical for promoting catalytic activity and stability in renewable energy and catalysis devices. Here, we measure the growth kinetics of individual Co particles ex-solved on SrTi0.75Co0.25O3-δ polycrystalline thin films under a high vacuum, and at various temperatures and grain sizes using in situ transmission electron microscopy. The ex-solution preferentially occurs at grain boundaries and corners which appear essential for controlling particle density and distribution, and enabling low temperature ex-solution. The particle reaches a saturated size after a few minutes, and the size depends on temperature. Quantitative measurements with a kinetic model determine the rate limiting step, vacancy formation enthalpy, ex-solution enthalpy, and activation energy for particle growth. The ex-solved particles are tightly socketed, preventing interactions among them over 800 °C. Furthermore, we obtain the first direct clarification of the active reaction site for CO oxidation-the Co-oxide interface, agreeing well with density functional theory calculations.

Manipulation of Nanoscale Intergranular Phases for High Proton Conduction and Decomposition Tolerance in BaCeO3 Polycrystals.

In many ion-conducting polycrystalline oxides, grain boundaries are generally accepted as rate-limiting obstacles to rapid ionic diffusion, often resulting in overall sluggish transport. Consequently, based on a precise understanding of the structural and compositional features at grain boundaries, systematic control of the polycrystalline microstructure is a key factor to achieve better ionic conduction performance. In this study, we clarify that a nanometer-thick amorphous phase at most grain boundaries in proton-conducting BaCeO3 polycrystals is responsible for substantial retardation of proton migration and moreover is very reactive with water and carbon dioxide gas. By a combination of atomic-scale chemical analysis and physical imaging, we demonstrate that highly densified BaCeO3 polycrystals free of a grain-boundary amorphous phase can be easily fabricated by a conventional ceramic process and show sufficiently high proton conductivity together with significantly improved chemical stability. These findings emphasize the value of direct identification of intergranular phases and subsequent manipulation of their distribution in ion-conducting oxide polycrystals.

Oxygen diffusion and surface exchange in the mixed conducting oxides SrTi1-yFeyO3-δ.

Oxygen transport in the mixed ionic-electronic conducting perovskite-oxides SrTi1-yFeyO3-δ (with y = 0.5 and y = 1.0) was studied by oxygen isotope exchange measurements. Experiments were performed on thin-film samples that were grown by Pulsed Laser Deposition (PLD) on MgO substrates. Isotope penetration profiles were introduced by 18O2/16O2 exchanges into the plane of the films at various temperatures in the range 773 < T/K < 973 at an oxygen activity aO2 = 0.5. Isotope profiles were determined subsequently by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and their analysis yielded tracer diffusion coefficients D* and oxygen surface exchange coefficients k*. Activation energies for oxygen diffusion ΔHD* and surface exchange ΔHk* were obtained. Isothermal values of D* and values of ΔHD* are compared with literature data as a function of Fe content. D* is seen to increase monotonically with Fe content; ΔHD* shows more complex behaviour. D* and ΔHD* are also compared with the predictions of defect-chemical models. Analogous comparisons with literature data for k* and ΔHk* indicate, in contrast to prior studies, no mechanistic difference between electron-poor and electron-rich materials. It is concluded that the single operative mechanism of surface exchange for the entire series of STF compositions requires conduction-band electrons (minority electronic charge-carriers).

Vacancy-Induced Electronic Structure Variation of Acceptors and Correlation with Proton Conduction in Perovskite Oxides.

In most proton-conducing perovskite oxides, the electrostatic attraction between negatively charged acceptor dopants and protonic defects having a positive charge is known to be a major cause of retardation of proton conduction, a phenomenon that is generally referred to as proton trapping. We experimentally show that proton trapping can be suppressed by clustering of positively charged oxygen vacancies to acceptors in BaZrO3-δ and BaCeO3-δ . In particular, to ensure the vacancy-acceptor association is effective against proton trapping, the valence electron density of acceptors should not significantly vary when the oxygen vacancies cluster, based on the weak hybridization between the valence d or p orbitals of acceptors and the 2p orbitals of oxygen.

Tibial Axis-to-Talus Distance: A Clinically Reliable Measurement for Sagittal Translation of the Talus in Total Ankle Arthroplasty.

Background: Sagittal talar translation is an important factor influencing the sagittal alignment of total ankle arthroplasty (TAA). Thus, accurate measurement of sagittal talar translation is crucial. This study proposes a simple method (tibiotalar distance [TTD]) that can quantify talar translation without being affected by the ankle and subtalar joint condition or the talar component position in patients with TAA. Methods: We enrolled 280 eligible patients (296 ankles) who underwent primary TAA between 2005 and 2019 and retrospectively reviewed them for sagittal talar translation. The TTD was measured for each patient on weight-bearing lateral ankle radiographs by 3 raters. In addition, we analyzed interrater and intrarater reliability for the TTD method. Results: We found that the TTD method could quantify the talar translation and was not affected by the preoperative condition of the ankle joint surface, subtalar joint pathologies, or the postoperative talar component position. The TTD method showed an excellent intraclass correlation coefficient (> 0.9) in all interrater and intrarater reliability analyses. In the analysis of 157 healthy, unoperated contralateral ankles, we identified that TTD showed a Gaussian distribution (p = 0.284) and a mean of 38.91 mm (normal range, 29.63-48.20 mm). Conclusions: The TTD method is a simple and reliable method that could be applied to patients with TAA to assess the sagittal talar translation regardless of the pre-and postoperative joint condition and implantation status.

Revitalizing Oxygen Reduction Reactivity of Composite Oxide Electrodes via Electrochemically Deposited PrOx Nanocatalysts.

Solid oxide fuel cells that operate at intermediate temperatures require efficient catalysts to enhance the inherently poor electrochemical activity of the composite electrodes. Here, a simple and practical electrochemical deposition method is presented for fabricating a PrOx overlayer on lanthanum strontium manganite-yttria-stabilized zirconia (LSM-YSZ) composite electrodes. The method requires less than four minutes for completion and can be carried out under at ambient temperature and pressure. Crucially, the treatment significantly improves the electrode's performance without requiring heat treatment or other supplementary processes. The PrOx-coated LSM-YSZ electrode exhibits an 89% decrease in polarization resistance at 650 °C (compared to an untreated electrode), maintaining a tenfold reduction after ≈400 h. Transmission line model analysis using impedance spectra confirms how PrOx coating improved the oxygen reduction reaction activity. Further, tests with anode-supported single cells reveal an outstanding peak power density compared to those of other LSM-YSZ-based cathodes (e.g., 418 mW cm-2 at 650 °C). Furthermore, it is demonstrated that multicomponent coating, such as (Pr,Ce)Ox, can also be obtained with this method. Overall, the observations offer a promising route for the development of high-performance solid oxide fuel cells.

Crystal structure optimization of copper oxides for the benzyl alcohol oxidation reaction.

In this work, experimental and theoretical analyses reveal that different types of Cu wires significantly change the adsorption properties of reactant molecules and the benzyl alcohol oxidation reaction performance. In particular, CuO nanowires in situ grown on Cu foam exhibit the best performance with a low potential of 1.39 V at a current density of 200 mA cm-2, high selectivity to benzoic acid production, and good operational stability.

Re-evaluation of battery-grade lithium purity toward sustainable batteries.

Recently, the cost of lithium-ion batteries has risen as the price of lithium raw materials has soared and fluctuated. Notably, the highest cost of lithium production comes from the impurity elimination process to satisfy the battery-grade purity of over 99.5%. Consequently, re-evaluating the impact of purity becomes imperative for affordable lithium-ion batteries. In this study, we unveil that a 1% Mg impurity in the lithium precursor proves beneficial for both the lithium production process and the electrochemical performance of resulting cathodes. This is attributed to the increased nucleation seeds and unexpected site-selective doping effects. Moreover, when extended to an industrial scale, low-grade lithium is found to reduce production costs and CO2 emissions by up to 19.4% and 9.0%, respectively. This work offers valuable insights into the genuine sustainability of lithium-ion batteries.