Trace analyses of gaseous products formed during heat treatment of high stage H2SO4-GICs and expanded graphite

H₂SO₄-GICs samples prepared by different methods were heated to 1000 °C under flow of air using heating rates of 2, 10 and 20 K/min Gaseous products of decomposition were analysed using FTIR spectra recorded during the thermal process. It was detected that S–O species started evolving from graphite gallery above 500 °C, not depending on the method of GIC preparation. High expansion of H₂SO₄-GIC was observed when the intercalate evolved from the intercalated graphite before its abrupt oxidation to CO₂. The disordered structure of graphite layers in H₂SO₄-GIC leads to easy release of S–O species without exfoliation effect. It was observed that using 2 K/min heating rate the time needed for intercalate to release from graphite gallery is shorter than that needed for its exfoliation. Therefore, the exfoliation process should be conducted using high heating rate.     

Effect of Gd2O3 on the hydrogen evolution property of nickel–cobalt coatings electrodeposited on titanium substrate

The effect of rare earth compound, Gd₂O₃, on the microstructure and the hydrogen evolution property of Ni–Co alloy electrode was studied. The morphology and microstructure were characterized by SEM and XRD, respectively, and the electrocatalytic efficiency was evaluated on the basis of electrochemical data obtained from steady-state polarization curves, Tafel curves and electrochemical impedance spectroscopy measurements carried out in 0.50 M Na₂SO₄+0.10 M H₂SO₄ solution. It was found that the embedded Gd₂O₃ particles largely enhanced the electrocatalytic activity of Ni–Co alloy electrode to hydrogen evolution reaction.     

Optical,structural characterization and dielectric relaxation of [C2H5NH3]2ZnCl4 compound

ABSTRACT

The new organic-inorganic compound [C₂H₅NH₃]₂ZnCl₄ has been grown by the slow evaporation at room temperature. The zero-dimensional (0-D) structure for this compound was determined by the single X-ray diffraction. It crystallizes at room temperature in the non-centrosymmetric space group Pna2₁ and consists of ethylammonium cations [C₂H₅NH₃]⁺ and [ZnCl₄]^2? tetrahedra anions. That is interconnected by means of hydrogen bonding contacts N-H···Cl. The molecular geometry and vibrational frequencies of [ZnCl₄]^2? and [C₂H₅NH₃]⁺ in the ground state was calculated using density functional method (B3LYP) with 6–31G(d) and 6–311G (d,p) basis set. The optimized geometric bond lengths and bond angles, obtained by using B3LYP/6–311G (d,p), show the best agreement with the experimental data. The optical absorbance was measured in order to deduce the absorption coefficient α, optical band gap E_g. The optical band gap is determined by extrapolating the plotted graph of (αhυ)^1/2 vs. (hυ). The large value of indirect optical band gap energy indicates the insulating nature of this material. Moreover, the extinction coefficient, refractive index and the dielectric permittivity of [C₂H₅NH₃]₂ZnCl₄ compound were calculated and the results are discussed. The evolution of the dielectric loss as a function of frequency revealed a distribution of relaxation times, probably ascribed to the reorientational dynamics of alkyl chains in this compound, and then analyzed with the Cole–Cole formalism.     

Atomic force microscopy for the surface structure of the CuCl2-graphite intercalation compound

Atomic force microscopy (AFM) has been used to image the surface structure of a CuCl₂-graphite intercalation compound. We have obtained the first AFM image of CuCl₂ molecules on a CuCl₂GIC surface with an atomic resolution in air at room temperature, which shows an incommensurate superlattice structure (a = 0.39 nm) having a close resemblance to the bulk of this compound.     

Effect of N 2 + ion implantation on the electrochemical corrosion behaviour of Fe−Ni alloy in. 1N H2SO4 solution

A three sweep potentiokinetic technique was employed to study the electrochemical corrosion behaviour of Fe-50 at % Ni in .1N H₂SO₄ solution. The as received foil did not show any passivation but it was observed in case of Fe?Ni samples implanted with N₂ ⁺ ions at an energy of 100keV. Also it was seen that the primary passivation potential E_pp and the critical current density in the corrosion experiment decrease as the implanted nitrogen ion dose increases from 5*10¹⁵ to 1*10¹⁷ ions/cm². The identification of products formed during corrosion experiment has been attempted with the help of conversion electron Mössbauer spectroscopy (CEMS), X-ray diffraction (XRD) and X-ray photoemission spectroscopic (XPS) techniques, and the possible mechanism of reactions is discussed with reference to their results.     

Quantized conductance behavior of Pt metal nanoconstrictions under electrochemical potential control

We studied the quantized conductance behavior of mechanically fabricated Pt nanoconstrictions under electrochemical potential control in H₂SO₄, Na₂SO₄, and NaOH solutions. There was no clear feature in the conductance histogram, when the electrochemical potential of the nanoconstrictions was kept at the double layer or the under potential deposited hydrogen potential. At the hydrogen evolution potential, the conductance histograms showed clear features around 0.5 and 1 G₀ in the H₂SO₄ solution. In Na₂SO₄, and NaOH solutions, a 1 G₀ feature with a shoulder appeared in the histogram. The quantized conductance behavior of Pt nanoconstrictions could be controlled by the electrochemical potential and solution pH.     

石墨/Li（Ni1/3Co1/3Mn1/3）O2电池充放电过程中电极材料的XRD研究

利用XRD系统地研究了石墨/Li（Ni_1/3Co_1/3Mn_1/3）O₂ 18650型锂离子电池充放电过程中正负极活性材料的晶体结构和微结构的变化.已观测到,由于Li原子的脱嵌,使得LiMO₂点阵参数a缩小,c增大,微应变增大,衍射强度比I₁₀₄/I₁₀₁和I₀₁₂/I₁₀₁降低;此外,由于Li原子的嵌入,2H-石墨的点阵参数a和c,以及微应变ε和堆垛无序度P都增加.同时,讨论了活性材料Li（Ni_1/3Co_1/3Mn_1/3）O₂和石墨在电池充放电过程中的嵌脱锂的物理机理.在充电时,正极Li（Ni_1/3Co_1/3Mn_1/3）O₂中处于（000）位的Li原子优先脱离晶体点阵,继后才是位于（2/3 1/3 1/3）和（1/3 2/3 2/3）位的Li原子离开点阵.锂嵌入石墨,优先进入碳原子六方网格面间的间隙位置,当负极的堆垛无序度达到一定值后,3R相逐渐析出.当电池满充或过充时,在六方石墨中形成LiC₁₂和LiC₆相.放电时,与上述过程相反,但并非是完全可逆的. 关键词： 锂离子电池 微结构 X射线衍射 嵌脱锂物理机理     

Chemical stability study of Li2SO4 on the operation condition of a H2/O2 fuel cell

The chemical stability of Li₂SO₄ on the operation condition of a H₂/O₂ fuel cell has been investigated in this work. Thermodynamic calculation indicates Li₂SO₄ can react with H₂ at high temperature. The H₂/O₂ fuel cell using Li₂SO₄–α-Al₂O₃ as electrolyte exhibits good performance, but the stability of performance is not good. XRD analysis indicates that Li₂SO₄ reacts with H₂ at high temperature. Therefore, the Li₂SO₄-based proton conductors are not suitable for electrolytes for H₂/O₂ fuel cells.     

Influence of electrolyte composition on deactivation mechanism of a Ti/Ru0.25Ir0.25Ti0.5O2 electrode

Deactivation of a RuO₂-IrO₂-TiO₂/Ti electrode was investigated during an accelerated life test in H₂SO₄ and NaCl solutions using cyclic voltammetry, electrochemical impedance spectroscopy, and SEM/energy dispersive spectroscopy. It is found that the deactivation mechanism depends on electrolyte composition. Intensive Ru/Ir dissolution from the oxide coating and the growth of an insulating TiO₂ interlayer are the main deactivation mechanisms of anode in H₂SO₄ and NaCl solutions, respectively. The results indicate that the determining factor in deactivation mechanism is the morphology factor of oxide anode in different solutions which restrains the diffusion process of electrolyte into coating inner layers.     

Nanophase ZnV2O4 as stable and high capacity Li insertion electrode for Li-ion battery

Spinel ZnV₂O₄ nanoparticles are synthesized by a hydrothermal method and its properties are characterized using XRD, SEM, TEM, and electrochemical test. The structural and morphological characterizations show that ZnV₂O₄ sample has high purity and well crystallization with crystal size less than 20 nm. The as prepared electrode shows stable capacity over 660 mAh g⁻¹ in the voltage range of 0.01–3.0 V at 50 mA g⁻¹. The reaction mechanism with lithium ion is also investigated through ex-XRD and -TEM. It shows that the pristine ZnV₂O₄ is transformed to isostructural spinel Li_xV₂O₄ (x close to 7.6) and metal Zn phase during the first lithiation process. Then the spinel Li_xV₂O₄ seems to perform a topotactic intercalation reaction mechanism and that the in-situ formed Li_xV₂O₄ can still keep its spinel matrix while allowing more than 5.7 lithium reversibly into/out over 50 cycles.     

Effect of the surface treatment of the TiO2 fillers on the properties of hexanoyl chitosan/polystyrene blend-based composite polymer electrolytes

Surface treatment of TiO₂ was done by immersing filler particles in 2 and 4 % sulphuric acid (H₂SO₄) aqueous solutions. Untreated, 2 and 4 % H₂SO₄-treated TiO₂ were referred as neutral, weakly acidic, and acidic TiO₂, respectively. Composite polymer electrolytes (CPEs) based on hexanoyl chitosan–polystyrene blend were prepared by using lithium trifluromethanesulfonate (LiCF₃SO₃) as the doping salt and three different types of the TiO₂ fillers. X-ray diffraction (XRD) results showed that the addition of TiO₂ reduced the crystalline fraction of the electrolytes. The conductivity performance of the CPEs varied in the order: acidic?<?weakly acidic?<?TiO₂ free?<?neutral TiO₂. A model based on the interaction between Lewis acid–base sites of TiO₂ with ionic species of LiCF₃SO₃ has been proposed to understand the conductivity mechanism brought about by the different types of fillers. The conductivity enhancement by neutral TiO₂ is attributed to the increase in the mobility of Li⁺ cations. Acidic TiO₂ decreased the conductivity by decreasing the anionic contribution. The conductivity variation with filler content was discussed on the basis of the number of free ions.     

Metallic reflectance of AsF5-graphite intercalation compounds

Room temperature measurements of the 0.07–2.0 eV optical reflectance of carefully prepared stage 1–4 AsF₅-graphite intercalation compounds have been performed. Stages 1–3 show simple metallic behavior with a well-defined plasma edge. Curve fits to the data give good agreement between dc and optical conductivities for stage 1 and 2. Comparison between stage 2 data for AsF₅ and HNO₃ compounds suggests that the higher conductivity of the former arises from a longer carrier relaxation time rather than from a greater carrier density.     

Charge storage performance of lithiated iron phosphate/activated carbon composite as symmetrical electrode for electrochemical capacitor

In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO₄)-activated carbon (AC) composite as the core electrode material in 1.0 M Na₂SO₃ and 1.0 M Li₂SO₄ aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO₄ loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na₂SO₃. The improvement in the capacitive performance of the 40 wt% LiFePO₄–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H⁺, OH⁻, Na⁺ and SO₃²⁻ and Li⁺ ions in LiFePO₄ lattices. In contrast, it appears that the incorporation of LiFePO₄ into AC electrodes does not increase the charge storage capability when Li₂SO₄ is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO₄²⁻ only exhibits EDLC in the Fe-based electrodes. Additionally, Li⁺ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na⁺ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO₄ loading on a Na₂SO₃ neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications.     

Catalytic effect of water,water dimer,water trimer,HCOOH, H2SO4, CH3CH2COOH and HN(NO2)2 on the isomerisation of HN(NO2)2 to O2NNN(O)OH: a mechanism study

In this article, the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH without and with catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂) have been investigated theoretically at the CBS-QB3 level of theory. Our results show that the catalyst X (X = H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄ and CH₃CH₂COOH) shows different positive catalytic effects on reducing the apparent activation energy of the isomerisation reaction processes. Such different catalytic effects are mainly related to the number of hydrogen bonds and the size of the ring structure in X (X = H₂O, (H₂O)₂ and (H₂O)₃)-assisted transition states, as well as different values of pK_a for H₂SO₄, HCOOH and CH₃CH₂COOH. Very interesting is also the fact that H₂SO₄-assisted reaction is the most favourable for the hydrogen transfer from HN(NO₂)₂ to O₂NNN(O)OH, due to the smallest pK_a (?3.0) value of H₂SO₄ than H₂O, HCOOH, H₂SO₄ and CH₃CH₂COOH, and also because of the largest ∠X???H???Y (the angle between the hydrogen bond donor and acceptor) involved in H₂SO₄-assisted transition state. Compared to the self-catalysis of the isomerisation mechanisms of HN(NO₂)₂ to O₂NNN(O)OH, the apparent activation energy of H₂SO₄-assisted channel also reduces by 9.6 kcal?mol^?1, indicating that H₂SO₄ can affect the isomerisation of HN(NO₂)₂ to O₂NNN(O)OH, most obvious among all the catalysts H₂O, (H₂O)₂, (H₂O)₃, HCOOH, H₂SO₄, CH₃CH₂COOH and HN(NO₂)₂.     

Pseudo-capacitance on exfoliated carbon fiber in sulfuric acid electrolyte

The specific capacitance of exfoliated carbon fibers (ExCF) which were synthesized from pitch-based carbon fibers showed a strong dependence with the concentration of sulfuric acid electrolyte and reached 1.4 F/m² in 18 M H₂SO₄ solution. Since the capacitance value is quite large compared with the case of conventional activated carbons, faradic reactions (charge transfer reactions) are the cause of pseudo-capacitance. ExCF, however, gave a featureless cyclic voltammogram in 18 M H₂SO₄ solution. In the case of exfoliated natural graphite, the intercalation of H₂SO₄ molecules is evidenced by redox peaks observed in the voltammograms in the same conditions. Therefore, a strong interaction between the H₂SO₄ molecules and the ExCF surface might be the reason for the origin of pseudo-capacitance with ExCF in H₂SO₄ electrolyte. PACS 81.05.Uw; 82.45.Fk; 82.47.Uv     

Product speciation and aquation after the reaction of 51Cr(VI) with concentrated HCl or H2SO4

The present study was undertaken to investigate the reaction of Cr(VI) in concentrated hydrochloric acid or concentrated sulfuric acid, as well as to evaluate the products formed when complexing anions are present during the reaction. The results show that trace level Cr(VI) is rapidly reduced to Cr(III) in both 37% HCI and 98% H₂SO₄ in the absence of conventional reducing agents and that the initial products are, respectively, CrCl₃(H₂O)₃ and Cr(H₂O)₂(SO₄) ₂ ^- }, which undergo slow aquation reactions at pH 1, giving Cr(H₂O) ₆ ³⁺ .     

Berberine as a natural source inhibitor for mild steel in 1 M H2SO4

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H₂SO₄ was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy disperse spectrometer (EDS). The weight loss results showed that berberine is an excellent corrosion inhibitor for mild steel immersed in 1 M H₂SO₄. Potentiodynamic curves suggested that berberine suppressed both cathodic and anodic processes for its concentrations higher than 1.0 × 10⁻⁴ M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H₂SO₄ containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increased with the inhibitor concentration rising. A good fit to Flory-Huggins isotherm was obtained between surface coverage degree and inhibitor concentration. The surface morphology and EDS analysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by the weight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.     

Structure and lithium storage performances of nickel hydroxides synthesized with different nickel salts

Nickel hydroxides with hierarchical micro-nano structures are prepared by a facile homogeneous precipitation method with different nickel salts (Ni(NO₃)₂·6H₂O, NiCl₂·6H₂O, and NiSO₄·6H₂O) as raw materials. The effect of nickel sources on the microstructure and lithium storage performance of the nickel hydroxides is studied. It is found that all the three prepared samples are α-nickel hydroxide. The nickel hydroxides synthesized with Ni(NO₃)₂·6H₂ or NiCl₂·6H₂O show a similar particle size of 20–30 μm and are composed of very thin nano-sheets, while the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O shows a larger particle size (30–50 μm) and consists of very thin nano-walls. When applied as anode materials for lithium-ion batteries (LIBs), the nickel hydroxide synthesized with NiSO₄·6H₂O exhibits the highest discharge capacity, but its cyclic stability is very poor. The nickel hydroxides synthesized with NiCl₂·6H₂O exhibit higher discharge capacity than the nickel hydroxides synthesized with Ni(NO₃)₂·6H₂O, and both of them show much improved cyclic stability and rate capability as compared to the nickel hydroxide synthesized with Ni(SO₄)₂·6H₂O. Moreover, pseudocapacitive behavior makes a great contribution to the electrochemical energy storage of the three samples. The discrepancies of lithium storage performance of the three samples are analyzed by ex-situ XRD, FT-IR, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) tests.     

Fabrication of belt-like VO2(M)@C core-shell structured composite to improve the electrochemical properties of VO2(M)

VO₂(M) nanobelts encapsulated into carbon core–shell structured composite (VO₂(M)@C) was successfully synthesized by the thermal treatment with the precursor V₃O₇·H₂O@C composite under the inert atmosphere. The as-obtained sample was characterized by XRD, EDS, EA, FT-IR, Raman, SEM and TEM measurements. The core exhibited monoclinic phase VO₂(M) and the carbon coated on the surface of VO₂(M) was amorphous. The average thickness of carbon was about 18.5 nm. The possible formation mechanism of VO₂(M)@C was proposed as that the reaction underwent the solid state reaction by the interface reaction between V₃O₇ core and carbon shell. Furthermore, VO₂(M) and VO₂(M)@C composite were explored as the cathode materials to apply in lithium-ion batteries, indicating that the VO₂(M)@C composite electrode exhibited the better electrochemical properties than that of pure VO₂(M), achieving the aim of improving the electrochemical properties of VO₂(M).     

Langmuir-Blodgett self-assembly and electrochemical catalytic property of FePt magnetic nano-monolayer

Dispersed-well FePt nanoparticles with particle size ~5 nm have been prepared by hydrazine hydrate reduction of H₂PtCl₆·6H₂O and FeCl₂·4H₂O in ethanol–water system. By employing as-synthesized FePt nanoparticles, the monolayer can be formed by LB Technique. The structural, magnetic properties and electrochemical properties of FePt monolayer were respectively studied by XRD, TEM, VSM and CHI 820 electrochemical workstation. The as-synthesized particle has a chemically disordered fcc structure and can be transformed into chemically ordered fct structure after annealing treatment above 400°C. The coercivity of ordered fct FePt phase can be up to 2515Oe. CVs of 0.5 M H₂SO₄/0.5M CH₃OH on GCE modified with FePt nanoparticles monolayer films illustrate that the as-synthesized FePt is a kind of active electrochemical catalyst.