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.

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.

Mechanical Properties and Chemical Durability of Nafion/Sulfonated Graphene Oxide/Cerium Oxide Composite Membranes for Fuel-Cell Applications.

To improve both the mechanical and chemical durability of Nafion membranes for polymer electrolyte membrane fuel-cells (PEMFCs), Nafion composite membranes containing sulfonated graphene oxide (SGO) and cerium oxide (CeO2; ceria) were prepared by solution casting. The structure and chemical composition of SGO were investigated by FT-IR and XPS. The effect of the sulfonation, addition of SGO and ceria on the mechanical properties, proton conductivity, and chemical stability were evaluated. The addition of SGO gave rise to an increase in the number of sulfonic acid groups in Nafion, resulting in a higher tensile strength and proton conductivity compared to that of graphene oxide (GO). Although the addition of ceria was found to decrease the tensile strength and proton conductivity, Nafion/SGO/ceria composite membranes exhibited a higher tensile strength and proton conductivity than recast Nafion. Measurement of the weight loss and SEM observations of the composite membranes after immersing in Fenton's reagent indicate an excellent radical scavenging ability of ceria under radical degradation conditions.

Association between Medical Costs and the ProVent Model in Patients Requiring Prolonged Mechanical Ventilation.

BACKGROUND: The purpose of this study was to determine whether components of the ProVent model can predict the high medical costs in Korean patients requiring at least 21 days of mechanical ventilation (prolonged mechanical ventilation [PMV]). METHODS: Retrospective data from 302 patients (61.6% male; median age, 63.0 years) who had received PMV in the past 5 years were analyzed. To determine the relationship between medical cost per patient and components of the ProVent model, we collected the following data on day 21 of mechanical ventilation (MV): age, blood platelet count, requirement for hemodialysis, and requirement for vasopressors. RESULTS: The mortality rate in the intensive care unit (ICU) was 31.5%. The average medical costs per patient during ICU and total hospital (ICU and general ward) stay were 35,105 and 41,110 US dollars (USD), respectively. The following components of the ProVent model were associated with higher medical costs during ICU stay: age <50 years (average 42,731 USD vs. 33,710 USD, p=0.001), thrombocytopenia on day 21 of MV (36,237 USD vs. 34,783 USD, p=0.009), and requirement for hemodialysis on day 21 of MV (57,864 USD vs. 33,509 USD, p<0.001). As the number of these three components increased, a positive correlation was found betweeen medical costs and ICU stay based on the Pearson's correlation coefficient (γ) (γ=0.367, p<0.001). CONCLUSION: The ProVent model can be used to predict high medical costs in PMV patients during ICU stay. The highest medical costs were for patients who required hemodialysis on day 21 of MV.

Clinical Utility of Rapid Pathogen Identification for Detecting the Causative Organisms in Sepsis: A Single-Center Study in Korea.

PURPOSE: The aim of this pre- and postintervention cohort study was evaluating how effectively rapid pathogen identification with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) detected the causative organisms in sepsis. METHODS: All consecutive adult patients who had bacteremia within 72 h of intensive care unit admission and met ≥2 quick Sequential Organ Failure Assessment criteria at intensive care unit admission were analyzed. The patients whose microorganisms were identified via MALDI-TOF MS between March 2014 and February 2016 formed the postintervention group. The patients whose microorganisms were identified by using conventional methods between March 2011 and February 2013 formed the preintervention group. RESULTS: The postintervention group (n=58) had a shorter mean time from blood draw to receiving the antimicrobial susceptibility results than the preintervention group (n=40) (90.2 ± 32.1 vs. 108.7 ± 43.1 h; p=0.02). The postintervention group was also more likely to have received active antimicrobial therapy by the time the susceptibility report became available (77% vs. 47%; p=0.005). Its 28-day mortality was also lower (40% vs. 70%; p=0.003). Univariate analysis showed that identification via MALDI-TOF MS (odds ratio, 0.28; 95% confidence interval, 0.12-0.66; p=0.004) and active therapy (odds ratio, 0.38; 95% confidence interval, 0.16-0.95; p=0.04) were associated with lower 28-day mortality. CONCLUSION: Rapid microorganism identification via MALDI-TOF MS followed by appropriate antimicrobial therapy may improve the clinical outcomes of patients with sepsis.

Clinical Application of Modified Burns Wean Assessment Program Scores at First Spontaneous Breathing Trial in Weaning Patients from Mechanical Ventilation.

BACKGROUND: The purpose of this study was to evaluate the clinical application of modified Burns Wean Assessment Program (m-BWAP) scoring at first spontaneous breathing trial (SBT) as a predictor of successful liberation from mechanical ventilation (MV) in patients with endotracheal intubation. METHODS: Patients requiring MV for more than 72 hours and undergoing more than one SBT in a medical intensive care unit (ICU) were prospectively enrolled over a 3-year period. The m-BWAP score at first SBT was obtained by a critical care nursing practitioner. RESULTS: A total of 103 subjects were included in this study. Their median age was 69 years (range, 22 to 87 years) and 72 subjects (69.9%) were male. The median duration from admission to first SBT was 5 days (range, 3 to 26 days), and the rate of final successful liberation from MV was 84.5% (n=87). In the total group of patients, the successful liberation from MV group at first SBT (n=65) had significantly higher m-BWAP scores than did the unsuccessful group (median, 60; range, 43 to 80 vs. median, 53; range, 33 to 70; P<0.001). Also, the area under the m-BWAP curve for predicting successful liberation of MV was 0.748 (95% confidence interval, 0.650 to 0.847), while the cutoff value based on Youden's index was 53 (sensitivity, 76%; specificity, 64%). CONCLUSIONS: The present data show that the m-BWAP score represents a good predictor of weaning success in patients with an endotracheal tube in place at first SBT.

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.

Clinical Application of the Quick Sepsis-Related Organ Failure Assessment Score at Intensive Care Unit Admission in Patients with Bacteremia: A Single-Center Experience of Korea.

BACKGROUND: We evaluated the clinical usefulness of the quick Sepsis-Related Organ Failure Assessment (qSOFA) score (based on the 2016 definition of sepsis) at intensive care unit admission in Korean patients with bacteremia. METHODS: We retrospectively analyzed clinical data from 236 patients between March 2011 and February 2016. In addition to the qSOFA, the Modified Early Warning score (MEWS) and systemic inflammatory response syndrome (SIRS) criteria were calculated. RESULTS: The patients' median age was 69 years, and 61.0% were male. Of the patients, 127 (53.8%) had a qSOFA score ≥2 points. They had significantly higher rates of septic shock, thrombocytopenia, and hyperlactatemia, and increased requirements for ventilator care, neuromuscular blocking agents, vasopressors, and hemodialysis within 72 hours after intensive care unit admission. They also had a significantly higher 28-day mortality rate. When analyzed using common thresholds (MEWS ≥5 and ≥2 SIRS criteria), patients with a MEWS ≥5 had the same results as those with a qSOFA score ≥2 (P < 0.05). However, patients with ≥2 SIRS criteria showed no significant differences. CONCLUSIONS: Our results show that a qSOFA score ≥2 at admission is a useful screening tool for predicting disease severity and medical resource usage within 72 hours after admission, and for predicting 28-day mortality rates in patients with bacteremia. In addition, qSOFA scores may be more useful than SIRS criteria in terms of prognostic utility.

Clinical application of the ProVent score in Korean patients requiring prolonged mechanical ventilation: A 10-year experience in a university-affiliated tertiary hospital.

PURPOSE: We evaluated the clinical usefulness of a prognostic scoring system ("the ProVent score") in Korean patients requiring prolonged mechanical ventilation. MATERIAL AND METHODS: We retrospectively analyzed the data of 184 patients in a medical intensive care unit of a tertiary care hospital between January 2004 and December 2013. RESULTS: The patients' median age was 65 years, and 66.8% were male. One-year mortality was 67.4%. On day 21 of mechanical ventilation, the ProVent score was 0 in 13 patients (7.1%), 1 in 39 patients (21.2%), 2 in 73 patients (39.7%), 3 in 42 patients (22.8%), and greater than or equal to 4 in 17 patients (9.2%). For patients with a ProVent score ranging from 0 to greater than or equal to 4, 1-year mortality was 46.2%, 53.8%, 68.5%, 76.2%, and 88.2%, respectively. The Kaplan-Meier curves of 1-year survival for each ProVent score showed statistically significant differences (log-rank test: P = .001). Logistic regression analysis showed that only thrombocytopenia was independently associated with 1-year mortality in our cohort (odds ratio = 4.786, P < .001). CONCLUSIONS: In our study, the ProVent score could be applied to predict 1-year mortality for patients requiring prolonged mechanical ventilation in Korea. Among variables contributing to this score, only thrombocytopenia was an independent prognostic factor for 1-year mortality.

Outcomes and prognostic factors in patients with prolonged acute mechanical ventilation: A single-center study in Korea.

PURPOSE: The purpose of the study is to evaluate outcomes and objective parameters related to poor prognosis in patients who were defined as prolonged acute mechanical ventilation (PAMV; ventilator care ≥96 hours) in the medical intensive care unit of a university-affiliated tertiary care hospital in Korea. MATERIAL AND METHODS: We analyzed retrospectively clinical data gathered from the medical records on day 4 of MV between 2008 and 2013. In total, 311 were categorized as PAMV. RESULTS: Their median age was 67 years (range, 18-93 years), and 71.7% were male. The 28-day mortality rate after intensive care unit admission was 34.7%. Four variables on day 4 of mechanical ventilation (need for neuromuscular blockers [hazard ratio {HR}, 2.432; 95% confidence interval, 1.337-4.422], need for vasopressors [HR, 2.312; 95% confidence interval, 1.258-4.248], need for hemodialyses [HR, 1.913; 95% confidence interval, 1.018-3.595], and body mass index ≤21 kg/m(2) [HR, 1.827; 95% confidence interval, 1.015-3.288]) were independent factors associated with mortality based on a Cox proportional hazards model. As the number of these prognostic factors increased, the survival rate decreased. CONCLUSIONS: Four clinical factors (body mass index ≤21, requirement for neuromuscular blockers, vasopressors, and hemodialysis) on day 4 of mechanical ventilation were associated with 28-day mortality in PAMV patients.

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.