Facile synthesis of Co-N4-doped mesoporous carbon for oxygen reduction reaction

The oxygen reduction reaction (ORR) is a critical factor in fuel cells that has attracted significant research attention. Non-precious metal catalysts have improved the ORR activity considerably, but they still exhibit poorer ORR performance than commercial Pt-based catalysts. In this study, Co-N-4-doped mesoporous carbon (Co-N-4-MC) was prepared for the ORR using cobalt-azides as the Co-N-4-containing precursor, and ordered mesoporous silica SBA-15 as a template for achieving mesoporous structures. The Co-N-4-MC electrode exhibited remarkable ORR activity in an alkaline medium (a half-wave potential of -0.15 V vs. MMO, only similar to 19 mV deviation from the commercial Pt/C catalyst), high selectivity (electron-transfer number similar to 4) and excellent electrochemical stability (similar to 8 mV negative shift of the half-wave potential after 1000 cycles). The good performance of the Co-N-4- MC electrode was attributed to the synergetic effects of N-4, C and Co. In particular, the existence of graphitic pores in the Co-N-4-MC catalyst facilitated the diffusion of O-2 to the catalytic active sites, which benefited the progression of the ORR on the Co-N-4-MC catalyst. (C) 2017 The Electrochemical Society

Theory of enhanced performance emerging in a sparsely-connected competitive population

We provide an analytic theory to explain Anghel et al.'s recent numerical finding whereby a maximum in the global performance emerges for a sparsely-connected competitive population [Phys. Rev. Lett. 92, 058701 (2004)]. We show that the effect originates in the highly-correlated dynamics of strategy choice, and can be significantly enhanced using a simple modification to the model.Comment: This revised version will appear in PRE as a Rapid Com

Pretreatment of lignocellulosic wheat straw in ethanolwater co-solvents

Pretreatment is the key process for lignocellulosic biomass conversion, which is necessary to alter the structure of biomass to make cellulose and hemicellulose more accessible to the enzymes that convert the carbohydrate polymers into fermentable sugars. The present study reports the use of 15 ml ethanol-water co-solvents (1:1, v/v) for the pretreatment of lignocellulosic biomass (1.5 g) to produce cellulosic residual solid under varying conditions of temperature (220-310 °C) and time (20-100 min). Kinetic analysis was performed to examine the decomposition behavior of biomass in the co-solvents. The results showed that the optimal conditions for the pretreatment were 250 °C and 40 min. The maximum yield of residual solid under the optimized pretreatment conditions was 49.6% (0.744 g), which consisted of 91.4% holocellulose (cellulose and hemicellulose). Microstructure analysis showed that the compact monolithic structure of biomass had decomposed into a loose filamentous structure

Investigation of the Electrochemical Properties of CoAl-Layered Double Hydroxide/Ni(OH)2

Layered double hydroxides (LDH) as active electrode materials have become the focus of research in energy storage applications. The manufacturing of excellent electrochemical performance of the LDH electrode is still a challenge. In this paper, the production of CoAl-LDH@Ni(OH)2 is carried out in two steps, including hydrothermal and electrodeposition techniques. The prominent features of this electrode material are shown in the structural and morphological aspects, and the electrochemical properties are investigated by improving the conductivity and cycle stability. The core of this experimental study is to investigate the properties of the materials by depositing different amounts of nickel hydroxide and changing the loading of the active materials. The experimental results show that the specific capacity is 1810.5F·g−1 at 2 A/g current density and the cycle stability remained at 76% at 30 A g−1 for 3000 cycles. Moreover, a solid-state asymmetric supercapacitor with CoAl-LDH@Ni(OH)2 as the positive electrode and multi-walled carbon nanotube coated on the nickel foam as the negative electrode delivers high energy density (16.72 Wh kg−1 at the power density of 350.01 W kg−1). This study indicates the advantages of the design and synthesis of layered double hydroxides, a composite with excellent electrochemical properties that has potential applications in energy storage

Influence of various experimental parameters on the capacitive removal of phosphate from aqueous solutions using LDHs/AC composite electrodes

The efficient uptake of phosphate from aqueous solutions was achieved on layered double hydroxides (LDHs)-based electrodes via capacitive desalination in our previous study. The current follow-up work was mainly carried out to study the influence of various experimental parameters on the capacitive removal of phosphate using LDHs/activated carbon (LDHs/AC) composite electrodes. A series of batch experiments were implemented to investigate the experimental factors, including Mg2+/Al3+ ratios (2, 3, and 4), trivalent metal cations (Al3+, Fe3+, Cr3+), initial solution pH (from 3 to 10), coexisting anions (NO3-, Cl-, SO42-), and ion strengths, in capacitive deionization. The electrode materials before and after capacitive deionization were characterized to reinforce the analysis of the adsorption mechanisms by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray, cyclic voltammetry, and electrochemical impedance spectroscopy. Results indicated that the Mg-Al LDHs/AC electrodes exhibited higher phosphate adsorption capacity (80.43 mg PO43-/g), more regular morphology, and higher degree of crystallinity than that of Mg-Fe LDHs/AC and Mg-Cr LDHs/AC. Increasing Mg2+/Al3+ ratios enhanced the adsorption capacity of phosphate. The uptake of phosphate by Mg-Al LDHs/AC under circumneutral pH and low ion strength reached the maximum level. Furthermore, the presence of coexisting anions lowered the adsorption capacity of phosphate mainly due to the occurrence of a compressed electrical double layer. Therefore, the influence of different experimental parameters on phosphate removal via capacitive deionization by Mg-Al LDHs/AC necessitates a systematic investigation to optimize the preparation conditions of LDHs-based electrodes and several important operating parameters

Enhanced phosphate removal under an electric field via multiple mechanisms on MgAl-LDHs/AC composite electrode

Phosphorus removal is essential to avoid eutrophication in water bodies. Layered double hydroxides (LDHs) are widely used to scavenge phosphate through intercalated ion exchange or surface complexation. Moreover, LDHs have attracted increasing attention as electrode modifiers for supercapacitors. Researchers have begun to re-delve the electrosorption technology according to the fundamental principle of electrical double layers. Herein, we propose a new phosphate removal method inspired by the adsorption characteristic and electrical double-layer capacitive properties of LDHs through electrosorption via capacitive deionization. We present a series of experiments to study the enhanced phosphate removal under an electric field via multiple mechanisms on the MgAl-LDHs/AC electrode. The uptake of phosphate by MgAl-LDHs/AC was investigated as a function of phosphate concentration, applied voltage, electrode materials, and temperature. The MgAl-LDHs/AC electrode possessed a salt removal capacity of 67.92 mg PO43−·g−1 (1.2 V, 250 mg·L−1 KH2PO4, 30 °C). The electrosorption kinetics of phosphate ions onto the capacitive deionization electrode followed the pseudo-second-order kinetics model rather than the pseudo-first-order kinetics model. Furthermore, the adsorption isotherms of phosphate on the MgAl-LDHs/AC electrode fitted the Freundlich model better than the Langmuir model. The proposed method could be used for phosphate removal

Gamma-ray emission from the globular clusters Liller 1, M80, NGC 6139, NGC 6541, NGC 6624, and NGC 6752

Globular clusters (GCs) are emerging as a new class of gamma-ray emitters, thanks to the data obtained from the Fermi Gamma-ray Space Telescope. By now, eight GCs are known to emit gamma-rays at energies >100~MeV. Based on the stellar encounter rate of the GCs, we identify potential gamma-ray emitting GCs out of all known GCs that have not been studied in details before. In this paper, we report the discovery of a number of new gamma-ray GCs: Liller 1, NGC 6624, and NGC 6752, and evidence for gamma-ray emission from M80, NGC 6139, and NGC 6541, in which gamma-rays were found within the GC tidal radius. With one of the highest metallicity among all GCs in the Milky Way, the gamma-ray luminosity of Liller 1 is found to be the highest of all known gamma-ray GCs. In addition, we confirm a previous report of significant gamma-ray emitting region next to NGC 6441. We briefly discuss the observed offset of gamma-rays from some GC cores. The increasing number of known gamma-ray GCs at distances out to ~10 kpc is important for us to understand the gamma-ray emitting mechanism and provides an alternative probe to the underlying millisecond pulsar populations of the GCs.Comment: 22 pages, 7 figures, 2 tables; ApJ, in pres

Can Palestine Banks Develop Credit Risk Management According to Basel III?

In this paper, we investigated Palestine bank sector ability to develop credit risk management systems based on international standards (Basel Capital Accord). First, we evaluate the credit risk management systems and strategies that the operating bank in Palestinian banking system mandate. Second, we used the analytical description methodology to describe the new Basel accord for effective banking supervision. Our study showed that despite the banks prefer to use the Standardized Approach in measuring credit risk according to Basel committee approaches, it is still difficult for Palestinian banks to measure credit risks according to Basel III approaches. Keywords: Basel III approach, capital adequacy, Risk management, Palestine Monetary Authorities (PMA

Basel III, And Banking Risk; Do Basel III Factors Could Predict the Risk of Middle-Eastern Countries?

The research is financed by the Nation Natural Science Foundation of China under number 71173060. Abstract The global financial crisis in 2008 shows that the successive agreements Basel I, and II failed to stop the global financial collapse. Therefore, this research tries to answer the study question that; can Basel III enhancement give the banking sectors stability? Our data includes 324 listed from the largest banks across Middle East. Results from PLS-SEM analyses demonstrate bank risk is positive relationship related to charter value, information systems and Internal/External control systems. We find negative relationship among bank risk and market discipline. Following our finding, the result shows there is no relationship between bank risk and bank capital and the results suggest that Charter Value is the most important predictor of bank risk. Keywords: Basel III, Bank Risk, Bank capital, charter value, information system, control system, market discipline, Middle East

Strongly Asymmetric Tricriticality of Quenched Random-Field Systems

In view of the recently seen dramatic effect of quenched random bonds on tricritical systems, we have conducted a renormalization-group study on the effect of quenched random fields on the tricritical phase diagram of the spin-1 Ising model in $d=3$. We find that random fields convert first-order phase transitions into second-order, in fact more effectively than random bonds. The coexistence region is extremely flat, attesting to an unusually small tricritical exponent $\beta_u$; moreover, an extreme asymmetry of the phase diagram is very striking. To accomodate this asymmetry, the second-order boundary exhibits reentrance.Comment: revtex, 4 pages, 2 figs, submitted to PR