Electrocatalysts for Zinc-Air Batteries Featuring Single Molybdenum Atoms in a Nitrogen-Doped Carbon Framework.

Bifunctional catalysts can facilitate two different electrochemical reactions with conflicting characteristics. Here, a highly reversible bifunctional electrocatalyst for rechargeable zinc-air batteries (ZABs) is reported featuring a "core-shell structure" in which N-doped graphene sheets wrap around vanadium molybdenum oxynitride nanoparticles. Single Mo atoms are released from the particle core during synthesis and anchored to electronegative N-dopant species in the graphitic shell. The resultant Mo single-atom catalysts excel as active oxygen evolution reaction (OER) sites in pyrrolic-N and as active oxygen reduction reaction (ORR) sites in pyridinic-N environments. ZABs with such bifunctional and multicomponent single-atom catalysts deliver high power density (≈376.4 mW cm-2 ) and long cycle life of over 630 h, outperforming noble-metal-based benchmarks. Flexible ZABs that can tolerate a wide range of temperatures (-20 to 80 °C) under severe mechanical deformation are also demonstrated.

Dispersion and stability mechanism of Pt nanoparticles on transition-metal oxides.

The heterogeneous catalysts of Pt/transition-metal oxides are typically synthesized through calcination at 500 °C, and Pt nanoparticles are uniformly and highly dispersed when hydrogen peroxide (H2O2) is applied before calcination. The influence of H2O2 on the dispersion and the stability of Pt nanoparticles on titania-incorporated fumed silica (Pt/Ti-FS) supports was examined using X-ray absorption fine structure (XAFS) measurements at the Pt L3 and Ti K edges as well as density functional theory (DFT) calculations. The local structural and chemical properties around Pt and Ti atoms of Pt/Ti-FS with and without H2O2 treatment were monitored using in-situ XAFS during heating from room temperature to 500 °C. XAFS revealed that the Pt nanoparticles of H2O2-Pt/Ti-FS are highly stable and that the Ti atoms of H2O2-Pt/Ti-FS support form into a distorted-anatase TiO2. DFT calculations showed that Pt atoms bond more stably to oxidized-TiO2 surfaces than they do to bare- and reduced-TiO2 surfaces. XAFS measurements and DFT calculations clarified that the presence of extra oxygen atoms due to the H2O2 treatment plays a critical role in the strong bonding of Pt atoms to TiO2 surfaces.

Association between the National Health Insurance coverage benefit extension policy and clinical outcomes of ventilated patients: a retrospective study.

BACKGROUND: This study aimed to investigate the association between the Korean National Health Insurance coverage benefit extension policy and clinical outcomes of patients who were ventilated owing to various respiratory diseases. METHODS: Data from 515 patients (male, 69.7%; mean age, 69.8±12.1 years; in-hospital mortality rate, 28.3%) who were hospitalized in a respiratory intensive care unit were retrospectively analyzed over 5 years. RESULTS: Of total enrolled patients, 356 (69.1%) had one benefit items under this policy during their hospital stay. They had significantly higher medical expenditure (total: median, 23,683 vs. 12,742 U.S. dollars [USD], P<0.001), out-of-pocket (median, 5,932 vs. 4,081 USD; P<0.001), and a lower percentage of out-of-pocket medical expenditure relative to total medical expenditure (median, 26.0% vs. 32.2%; P<0.001). Patients without benefit items associated with higher in-hospital mortality (hazard ratio [HR], 2.794; 95% confidence interval [CI], 1.980-3.941; P<0.001). In analysis of patients with benefit items, patients with three items ("cancer," "tuberculosis," and "disability") had significantly lower out-of-pocket medical expenditure (3,441 vs. 6,517 USD, P<0.001), and a lower percentage of out-of-pocket medical expenditure relative to total medical expenditure (17.2% vs. 27.7%, P<0.001). They were associated with higher in-hospital mortality (HR, 3.904; 95% CI, 2.533-6.039; P<0.001). CONCLUSIONS: Our study showed patients with benefit items had more medical resources and associated improved in-hospital survival. Patients with the aforementioned three benefit items had lower out-of-pocket medical expenditure due to the implementation of this policy, but higher in-hospital mortality.

Reduction of Transition-Metal Columbite-Tantalite as a Highly Efficient Electrocatalyst for Water Splitting.

We successfully report a liquid-liquid chemical reduction and hydrothermal synthesis of a highly stable columbite-tantalite electrocatalyst with remarkable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance in acidic media. The reduced Fe0.79Mn0.21Nb0.16Ta0.84O6 (CTr) electrocatalyst shows a low overpotential of 84.23 mV at 10 mA cm-2 and 103.7 achieved at 20 mA cm-2 current density in situ for the HER and OER, respectively. The electrocatalyst also exhibited low Tafel slopes of 104.97 mV/dec for the HER and 57.67 mV/dec for the OER, verifying their rapid catalytic kinetics. The electrolyzer maintained a cell voltage of 1.5 V and potential-time stability close to that of Pt/C and RuO2. Complementary first-principles density functional theory calculations identify the Mn sites as most active sites on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface, predicting a moderate Gibbs free energy of hydrogen adsorption (ΔGH* ≈ 0.08 eV) and a low overpotential of η = 0.47 V. The |ΔGMnH*| = 0.08 eV on the Fe0.75Mn0.25Ta1.875Nb0.125O6 (100) surface is similar to that of the well-known and highly efficient Pt catalyst (|ΔGPtH*| ≈ 0.09 eV).

Crystallization of Transition-Metal Oxides in Aqueous Solution beyond Ostwald Ripening.

The crystallization mechanism of transition-metal oxides (TMOs) in a solution was examined based on ZnO crystallization using in-situ x-ray absorption fine structure (XAFS) measurements at the Zn K edge and semi-empirical quantum chemistry (SEQC) simulations. The XAFS results quantitatively determine the local structural and chemical properties around a zinc atom at successive stages from Zn(NO3)2 to ZnO in an aqueous solution. The results also show that a zinc atom in Zn(NO3)2 ions dissolves in a solution and bonds with approximately three oxygen atoms at room temperature (RT). When hexamethylenetetramine (C6H12N4) is added to the solution at RT, a stable Zn-O complex consisting of six Zn(OH)2s is formed, which is a seed of ZnO crystals. The Zn-O complexes partially and fully form into a wurtzite ZnO at 60 and 80 °C, respectively. Based on the structural properties of Zn-O complexes determined by extended-XAFS (EXAFS), SEQC simulations clarify that Zn-O complexes consecutively develop from a linear structure to a polyhedral complex structure under the assistance of hydroxyls (OH-s) in an aqueous solution. In a solution with a sufficient concentration of OH-s, ZnO spontaneously grows through the merging of ZnO seeds (6Zn(OH)2s), reducing the total energy by the reactions of OH-s. ZnO crystallization suggests that the crystal growth of TMO can only be ascribed to Ostwald ripening when it exactly corresponds to the size growth of TMO particles.

Amorphous Cobalt Phyllosilicate with Layered Crystalline Motifs as Water Oxidation Catalyst.

The development of a high-performance oxygen evolution reaction (OER) catalyst is pivotal for the practical realization of a water-splitting system. Although an extensive search for OER catalysts has been performed in the past decades, cost-effective catalysts remain elusive. Herein, an amorphous cobalt phyllosilicate (ACP) with layered crystalline motif prepared by a room-temperature precipitation is introduced as a new OER catalyst; this material exhibits a remarkably low overpotential (η ≈ 367 mV for a current density of 10 mA cm-2 ). A structural investigation using X-ray absorption spectroscopy reveals that the amorphous structure contains layered motifs similar to the structure of CoOOH, which is demonstrated to be responsible for the OER catalysis based on density functional theory calculations. However, the calculations also reveal that the local environment of the active site in the layered crystalline motif in the ACP is significantly modulated by the silicate, leading to a substantial reduction of η of the OER compared with that of CoOOH. This work proposes amorphous phyllosilicates as a new group of efficient OER catalysts and suggests that tuning of the catalytic activity by introducing redox-inert groups may be a new unexplored avenue for the design of novel high-performance catalysts.

Animal models of periventricular leukomalacia.

Periventricular leukomalacia, specifically characterized as white matter injury, in neonates is strongly associated with the damage of pre-myelinating oligodendrocytes. Clinical data suggest that hypoxia-ischemia during delivery and intrauterine or neonatal infection-inflammation are important factors in the etiology of periventricular leukomalacia including cerebral palsy, a serious case exhibiting neurobehavioral deficits of periventricular leukomalacia. In order to explore the pathophysiological mechanisms of white matter injury and to better understand how infectious agents may affect the vulnerability of the immature brain to injury, novel animal models have been developed using hypoperfusion, microbes or bacterial products (lipopolysaccharide) and excitotoxins. Such efforts have developed rat models that produce predominantly white matter lesions by adopting combined hypoxia-ischemia technique on postnatal days 1-7, in which unilateral or bilateral carotid arteries of animals are occluded (ischemia) followed by 1-2 hour exposure to 6-8% oxygen environment (hypoxia). Furthermore, low doses of lipopolysaccharide that by themselves have no adverse-effects in 7-day-old rats, dramatically increase brain injury to hypoxic-ischemic challenge, implying that inflammation sensitizes the immature central nervous system. Therefore, among numerous models of periventricular leukomalacia, combination of hypoxia-ischemia-lipopolysaccharide might be one of the most-acceptable rodent models to induce extensive white matter injury and ensuing neurobehavioral deficits for the evaluation of candidate therapeutics.

Local structural and optical properties of ZnO nanoparticles.

This study examined the local structural and optical properties of ZnO nanoparticles (NPs) with mean diameters of 4.5 and 70 nm using extended X-ray absorption fine structure (EXAFS) measurements at the Zn K edge and photoluminescence (PL) measurements. EXAFS revealed that the average bond length of atomic pairs in the NPs was shorter than that of the powder. Furthermore, a substantial amount of structural disorder existed in the NPs. From the PL measurements, we observed the direct band gap peak of 3.41 eV from the 70 nm ZnO NPs at low temperatures. This blue shift was related to the structural property changes.