Hasil untuk "Physical and theoretical chemistry"

Nicholas R. Cross, Tiras Y. Lin, Nicholas W. Brady et al.

Abstract Lithium metal is a sought after battery material for its high energy density due to the low electrochemical potential and density. However, lithium metal is also highly reactive, which results in a strong propensity for dendrite formation. The Sand’s time has previously been used to predict the time of dendrite initiation on metals that do not form a solid-electrolyte interphase (SEI), but it has been shown that the Sand’s time is not accurate for lithium electrodes when using transport parameters associated with the electrolyte. Thus, we built a numerical model to simulate lithium ion transport through a growing SEI to predict the Sand’s time. The numerical model is shown to be more accurate than previous analytical solutions, especially for low current densities. We then analyze the sensitivity of the Sand’s time to different SEI properties and the chemical potential gradients present in the SEI, driving lithium transport. The results showed that high lithium concentration has a greater impact at high current density, while fast diffusivity is more important at low current density. Lastly, we modeled the influence of surface roughness on the plating evolution and chemical potential gradients when an SEI is present in comparison to the electrolyte. As a result, we demonstrate that the SEI plays a critical role in lithium electrode stability, and that improved characterization techniques are needed to better understand transport through the SEI and increase lithium metal utilization in energy storage devices.

Juan C. Mejuto

<i>Compounds</i> has existed as a scientific publication in the field of chemistry for five years now [...]

Qiang Zhang, Xuedong Zhao, Yunhua Hou et al.

The uniform dispersion of the catalyst is a key factor for the preparation of high-performance microbial fuel cell (MFC) cathodes. Herein, we self-assemble the amino ligand onto the surface of the carbon cloth (CC) by a one-pot method and complex the copper ions to form an amino-functionalized copper metal-organic framework (Cu-MOF-NH2) as a cathode catalyst for the MFC. The positive charge and polarity of the amino group improve the interaction between the Cu-MOF-NH2 and the carbon-based electrode, achieving high dispersion and high catalytic activity of the Cu-MOF-NH2. The application results show that the Cu-NOF-NH2 modified cathode provides a maximum power density of 0.64 Wm-2 for the MFC, which is 3.2 times higher than that of the CC base cathode. This work has explored a facile preparation method for a highly dispersed non-precious metal catalyst applied to a cathode, which has certain guiding significance for the large-scale popularization and application of MFCs.

V.M. Samsonov, I.V. Talyzin

The geometric instability of nanoscale island films is interpreted as a manifestation of the solid state wetting phenomenon, and instability of continuous extended films with nanosized thickness as a consequence of the solid state dewetting. Using molecular dynamics experiment, regularities and mechanisms are investigated of spreading of Pb solid nanoparticles on different Cu faces at a temperature 10 K below the melting temperature of nanoparticles of the chosen size ( 10 nm). The results obtained in molecular dynamics experiments are compared with experimental data for Pb microparticles of 5 - 10 μm in size. It has been also established that in the same «island – substrate» system both solid state wetting and solid state dewetting phenomena can simultaneously take place.

Hengzheng Li, Yanjiang Li, Guangzhen Zhao et al.

ZIF-67 derivatives show promising applications in energy storage owing to their high surface area and excellent electrochemical performance. In this work, an N-doped carbon-coated CoMoO4 nanoparticle (CMO@NC) polyhedron was prepared by hydrothermal treatment and calcination. The structural and morphological properties of the obtained samples were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and N2 adsorption/desorption isotherms. In terms of electrochemical performance, CMO@NC exhibits a remarkable specific capacitance of 267.3 F g-1 at 0.5 A g-1. Moreover, a hybrid supercapacitor device with CMO@NC as the positive electrode material and active carbon (AC) as the negative electrode material was observed to achieve a specific capacitance of 114 F g-1 at 0.5 A g-1, with a stable operational voltage of 1.5 V and a maximum energy density of 35.4 Wh kg-1 at a power density of 1041 W kg-1. The specific capacitance retention can reach up to 82.4 % after 5000 cycles, as determined by GCD measurements, indicating outstanding cycling stability and potential application prospects in supercapacitors.

Xiqing Zhao, Jun Xiong, Shaowei Zhu et al.

A thorough investigation of a polymer was performed for corrosion of mild steel in 1M HCl solution using electrochemical and surface studies. Infra-red spectroscopy was completed in reflectance mode to detect the adsorption of the polymer on the metal surface. Scanning electrochemical microscopy (SECM) studies were made to detect the localized corrosion reaction at the working electrode. Electrochemical impedance spectroscopy revealed that the efficiency of corrosion inhibition was improved after the addition of polymer in the solution. Polarization studies suggested that the polymer belong to the mixed category mitigators. Scanning electrochemical microscopy (SECM) studies suggested that the surface was insulating in presence of polymer thereby protecting the surface. Scanning electron microscope (SEM) suggested that the surface was less corroded in presence of polymer.

Fubin Ma, Yan Zhang, Hongjuan Wang et al.

Chitooligosacharide derivatives with different carboxymethylation degrees and grafting degrees of Schiff base were synthesized. Their inhibition property for carbon steel in 3.5% NaCl was tested by weight loss measurement, electrochemical measurements. The corrosion morphology of the specimens was examined by scanning electron microscope (SEM). The inhibition mechanism was analyzed by adsorption isotherm fitting and quantum chemical calculation. The results indicated that carboxymethylation improved the inhibition effect by increasing the compounds’ solubility; while grafting of Schiff base increased the amount of effective active groups directly but had bad effect on the solubility. The molecules adsorbed on the carbon steel surface by physisorption and chemiadsorption according to Temkin adsorption isotherm and acted as a mixed type inhibitor.

Chang Liu, Shang Li, Yijing Xing et al.

Polyaniline (PANI) nanofibers were synthesized on carbon paper by electrochemical method, then heat-treated at temperatures of 800°C, 900°C, 1000°C and 1100°C to obtain a gas diffusion electrode (GDE). Fourier Transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the catalysts. The metal-free C-N catalyst with a reticular structure was coated on carbon paper. The ORR (oxygen reduction reaction) activity of metal-free C-N catalysts was evaluated by cyclic voltammetry (CV) and rotating disk electrode (RDE) in HClO4. The results showed that the catalysts heat-treated at 1000°C had the best ORR activity and better stability compared with the commercial Pt-based catalysts in acidic medium. The result of XPS showed that the activity of metal-free C-N catalysts was related to the pyridinic-type nitrogen. Finally, the advantages and disadvantages of these catalysts were discussed for further investigation.

Yan Wang, Wei Chen, Dahai Pan et al.

In this work, ordered mesoporous Ni/Al2O3 catalysts were prepared by the solvent evaporation induced self–assembly (EISA) method. The synthesized Ni/Al2O3 catalysts were characterized by XRD, elemental distribution analyses, N2 adsorption and TEM. Ni/Al2O3 modified glassy carbon electrode was used to investigate the electrocatalytic oxidation of methanol in 0.1 M NaOH solution by cyclic voltammetry (CV) and chronoamperometry (CA). CVs results showed good electrocatalytic activity of Ni/Al2O3 for methanol electrooxidation in alkaline electrolytes. The good methanol electrooxidation activity of Ni/Al2O3 could be attributed to its synergetic effects between high dispersion of nickel and the ordered mesoporous structure that facilitates the diffusion of methanol and products. The CV and CA results suggest methanol electrooxidation is an irreversible process and a diffusion controlled process. The rate constant for the catalytic reaction of methanol is calculated to be 1.66× 106 cm3 mol–1 s–1.

Kai An, Chengqiang An, Chuanning Yang et al.

To improve the corrosion resistance of electro-galvanized (EG) steel, the EG steel was initially treated by utilizing the phosphating with phosphate and then sealed by the technique of post-sealing with silicate solution. The surface morphology and elemental composition of the three samples were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of the phosphating and post-sealing treatment on the corrosion resistance of EG steel was investigated by neutral salt spray test (NSS), potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The results showed that, after phosphating, the porous phosphate crystals formed on the surface of the electro-galvanized steel, and additionally, due to the existence of sodium silicate which adequately filled into the phosphate pores, a complete layer of silicate film formed on the phosphate coating, the corrosion resistance ability of EG steel was enhanced further. The phosphating and post-sealing treatment reduced the corrosion current density of EG steel by one order of magnitude, besides, the impedance values were increased obviously. In particular, the anodic oxidation and the cathodic reduction of zinc were inhibited during corrosion process, the active dissolution of zinc was much lower, improving remarkably the corrosion of the EG steel.

Hidayahtun Nur Amirah Mustafa, Illyas Md Isa, Noorshida Mohd Ali et al.

The ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIMBr) based graphene composite paste electrode (GrPE) was fabricated and applied for the determination of hydroquinone. By using square wave voltammetry, the electrochemical response of hydroquinone on EMIMBr-GrPE was greatly enhanced in 0.7 M phosphate buffer solution (pH 7.0). Under optimized conditions, the proposed electrode showed a linear relationship with concentration in the range of 1.0×10-6 to 1.0×10-2 m hydroquinone with limit of detection of 2.77x10’7 M. The interferences of Ba2+, Cu2+, Na+, K+, NO3’, Cl’, SO42’, glycine, glucose, fructose and sucrose were negligible. Electrochemical impedance spectroscopy indicated that the charge transfer at the electrode’solution interface was excellent. The proposed electrode was successfully applied to determine of hydroquinone in wastewater and cosmetic creams with range of recovery 97 - 104%.

Jingfang Hu, Guowei Gao, Shanhong Xia

A mediator-type bioelectrochemical sensor was developed by using polypyrrole (PPy) immobilized ferricyanide (FC) as mediator and immobilized Pseudomonas aeruginosa (P. aeruginosa) as a biosensing film for biochemical oxygen demand (BOD) fast detection. The sensor chip consists of a three-electrode system, with Au working electrode (WE), Pt counter electrode (CE) and Pt pseudoreference electrode (RE) compactly integrated as a disposable using micro-electro-mechanism system (MEMS) technology. The FC mediator and P. Aeruginosa microorganisms have been embedded in PPy matrix on gold microelectrode surface during the electropolymerization of pyrrole monomer using electrochemical cyclic voltammetry (CV) method. This bioelectrochemical sensor responds to BOD due to yielded ferrocyanide during catalytic reduction by metabolic reactions of microorganisms. A good linear correlation with chemically determined BOD values was obtained from 5 to 100 mg/L with fast response time. The proposed sensor in this paper is significant for BOD fast detection.

E. Frey, A. Sygula, N. Hammer

Zhiyong Wang, Xiaoli Liu, Mangxin Yang et al.

In this work, we reported a simple and sensitive electrochemical method for nitrite detection via Griess reaction. Specifically, naphthylethylenediamine (NEA) was immobilized onto the gold electrode to form positively charged self-assembled monolayers (SAMs). The positive charges on electrode facilitated the access of the negatively charged [Fe(CN)6]3-/4- probes to the electrode surface. The nitrite-mediated Griess reaction between NEA and sulphanilic acid (SA) on the electrode surface leaded to the formation of negatively charged SAMs, which produced a barrier for the electron transfer between the redox probe and the electrode. The results were demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy. The increase in the impedance of NEA-modified electrodes is proportional to the increase of nitrite concentration. A detection limit of 20 nM for nitrite detection was achieved.

Thomas E. Rufford, K. Ida Chan, Stanley H. Huang et al.

Helium is a unique gas with a wide range of important medical, scientific and industrial applications based on helium's extremely low boiling temperature, inert and non-flammable nature and small molecular size. The only practical sources of helium are from certain natural gas (NG) fields. As world demand for helium rapidly increases, the value of NG fields that contain it even in very small amounts is likely to rise significantly if the helium can be recovered efficiently. However, recovering the helium from the NG using conventional cryogenic distillation processes is expensive and energy intensive. We review the scope for improving the efficiency of the conventional helium recovery and upgrade processes, and evaluate the potential of emerging technologies based on adsorption or membrane separations for helium upgrade and purification. Helium recovery and purification processes are comparable in many ways with systems designed for hydrogen purification and thus, many of recent technological advances for H 2 separation from CH 4 N 2 and CO 2 may be applicable to a helium recovery process. Furthermore, some recent patents and pilot plant studies indicate there exist several opportunities for the development of advanced materials, such as helium-selective adsorbents, and optimized process operations for the recovery of helium from NG.

M. Farjallah, C. Ghanmi, H. Berriche

Petr Hodek, Pavel Trefil, Jiri Simunek et al.

Chicken antibodies isolated from egg yolks (IgY) are a suitable alternative to conventional antibodies from blood of experimental animals. Main advantages of IgY are: (i) larger amounts of IgY could be prepared from repeatedly laid chicken eggs, (ii) collection of eggs is a non-invasive procedure contrary to bleeding of mammals, and (iii) a better response of chicken to mammalian antigens due to the larger evolutionary distance. Here, we report a cost- and labor-effective two-step procedure consisting of yolk extraction by tap water (8-fold dilution, freezing, and filtration) followed by a specific precipitation of IgY at pH 4 with sodium chloride in the final concentration of 8.8%. Using this procedure, the highly purified antibody (97%) was prepared. Resulting IgY preparations are acceptable for a wide range of applications as it was prepared using only bio-compatible chemicals. The purification protocol was developed and optimized in terms of the time, materials and the necessary manipulations.

Shou-Heng Liu, H. Paul Wang

Speciation of copper with ethylenediaminetetraacetic acid (EDTA) during electrotreatments of a contaminated soil nearby printed circuit board recycling plants has been studied by in-situ extended X-ray absorption fine structural (EXAFS) and X-ray absorption near edge structural (XANES) spectroscopies. The least-square fits of the copper XANES spectra indicated that the main copper species in the contaminated soil were CuCO3 (41%), CuO (40%) and adsorbed copper (Cu/SiO2) (19%). By EXAFS studies, it was found that the bond distance of Cu-(O)-Si was 3.25 Å with a coordination number (CN) of 1.0 in the second shells, suggesting a chemical interaction between copper and the soil surfaces. In the presence of EDTA (0.05 M), a Cu-EDTA complex having the equatorial and axial Cu-O bond distances of 1.96 Å and 2.21 Å, respectively was observed. Interestingly, after 180 min of the electrotreatments, the axial Cu-O bond distance was increased by 0.1 Å. The perturbation might be attributed to the possibility that the weak-field carboxylic acid groups of EDTA in the equatorial plane of Cu(II) were replaced by the strong-field water molecules. In addition, about 36% of total copper in the soil was dissolved into the aqueous phase and 67% (or 24% of total copper) of which were migrated to the cathode under the electric field (5 V/cm). This work demonstrates the utilization of in-situ X-ray absorption spectroscopy for tracking and revealing speciation and possible reaction pathways of copper with EDTA in the contaminated soil under an electric field.

A.M. Shah, A.A. Rahim, S.A. Hamid et al.

Inhibition of copper corrosion by mangrove tannin has been investigated in aqueous 0.5 M hydrochloric acid solution using weight loss method, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) along with energy dispersive (EDX), atomic absorption spectroscopy (AAS) and ion chromatography (IC). Inhibition efficiency of 82 % was achieved with the addition of 3.0 g L-1 mangrove tannin from potentiodynamic polarisation measurements. Potentiodynamic curves showed that the presence of mangrove tannin in 0.5 M hydrochloric acid solution predominantly affected the cathodic process, decreased the corrosion current density and shifted the corrosion potential towards more negative values. Results obtained from the gravimetric (weight loss), potentiodynamic polarisation and impedance measurements showed similar trends of inhibition efficiency. AAS and IC analysis results showed that the concentrations of copper (II) ions and chloride ions in the electrolyte solutions decreased and increased, respectively, after the corrosion process, when the concentrations of mangrove tannin increased. Adsorption of mangrove tannin on the copper surface in 0.5 M hydrochloric acid solution fitted well with the Langmuir adsorption isotherm model. A change of morphology was observed after the addition of mangrove tannin as shown from SEM analysis.

Lixin Ning, Changbao Wu, Lanlan Li et al.