Kinds Of Electrolyte Solutions Research Articles

In Situ Grazing Incidence Surface X-ray Diffraction Study of Li2O Ultra-thin Film Formation on Li and Its Effect of Suppressing Dendrite Formation during Charging and Discharging

When a Li film deposited on a Ni(111) single-crystal was immersed in three kinds of electrolyte solutions, a uniform Li2O ultra-thin film was formed only in the O2-saturated tetraglyme solution containing 1 M LiNO3 and 50 mM LiBr. It was clarified by an in situ grazing incidence surface X-ray diffraction measurement. We found that this Li2O ultra-thin film stably exists during an electrochemically dissolution/deposition reaction, i.e., discharging/charging cycles at the anode of the Li-O2 battery, and effectively suppresses dendrite formation.

Cu-Based MOF for Simultaneous Determination of Trace Tl (I) and Hg (II) by Stripping Voltammetry

In this study, blue octahedral crystal of Cu-based metal-organic framework (Cu-MOF) was synthesized through a simple solvothermal method. The Cu-MOF was used as a modifier on GCE for the simultaneous determination of Tl (I) and Hg (II) at the trace level by square wave anodic stripping voltammetry (SWASV). The synthesized Cu-MOF was characterized by scanning electron microscope (SEM), transition electron microscope (TEM), X-ray diffraction (XRD), and electrochemical impedance spectroscopy (EIS). The parameters affecting the electrochemical process, such as the kind of electrolyte solution, KCl concentration, the potential, and the time for accumulation were investigated in detail. Under the optimal conditions, the present sensor showed excellent electrochemical performance for Tl (I) and Hg (II) in the leaner ranges from 0.5–700 ppb and 1–400 ppb, respectively. Low detection limits of 0.11 ppb for Tl (I) and 0.17 ppb for Hg (II) were achieved. The method is successfully applied to the determination of Tl (I) and Hg (II) in real samples and good recoveries are obtained from different spiked samples.

Effects of Solid Electrolyte Interphases Formed on Cu Eqcm Electrodes on Lithium Electrodeposition/Dissolution Reaction

Introduction With the increasing concern for energy problems, the demand for secondary battery with high safety, low cost, long life, and high energy density has been rising. The lithium metal is attracting worldwide attention as an anode material for next-generation lithium-based secondary battery such as a lithium air battery (LAB) because of its high capacity (3860 mA h g-1) and negative reduction potential (-3.04 V vs. SHE). However, the formation of lithium dendrites, which cause short circuit, low Coulombic efficiency, and short cycling lifespan, on the electrode surface is one of the biggest issues to practically use the LAB. During lithium deposition, moreover, solid electrolyte interphase (SEI), which is produced by the decomposition of solvents and/or electrolytes, is also accumulated on electrode. In order to suppress lithium dendrite formation [1], we are trying to produce the ideal SEI, which has high lithium ion conductivity, low electron conductivity, and uniform composition with an appropriated thickness [2]. In this study, Electrochemical Quartz Microbalance (EQCM) technique, which provides us with the mass change (Δm) [3,4] and the resonance resistance change (ΔR) [5,6] was employed to investigate SEI formation, lithium deposition, and charge/discharge cycles on Cu electrode. Tetraglyme (G4) which has relatively high flash point and wide potential window with Li[N(SO2CF3)2] (LiTFSI), Li[N(SO2F)2] (LiFSI), or LiOSO2CF3(LiTFS) was utilized as an electrolyte solution. Experimental After ultrasonically cleaning with ultra-pure water and drying with nitrogen flow, a Cu EQCM electrode (surface area: 0.196 cm2) as a working electrode was set to EQCM electrochemical cell with lithium sheet (99.999%) as a counter electrode in argon gas filled glove box (moisture < 0.5 ppm, oxygen concentration < 1 ppm) at room temperature, followed by input of electrolyte solution such as 1 M LiTFSI in G4, 1 M LiFSI in G4, and 1 M LiTFS in G4. Native-SEI formation, lithium deposition, and charge/discharge cycles were conducted as described below in the thermostatic chamber kept at 15 °C. After native-SEI formation and lithium deposition, electrochemical impedance spectroscopy (EIS) was measured. Native-SEI formation: After 3 h at open circuit potential (~3 V vs. Li/Li+), constant current electrolysis was performed at -0.01 mA cm-2or -1 mA cm-2with a cutoff potential of -0.04 V. During electrolysis, the potential, Δm, and ΔR were recorded.Lithium deposition: Lithium was deposited on the native-SEI covered Cu electrode at a constant current density of -0.1 mA cm-2for 1 h. Charge/discharge cycles: A charge/discharge measurements at ±0.1 mA cm-2for 6 min was performed with a 6-min rest at 0 mA cm-2. Results and Discussion According to the EQCM results, native-SEI was hardly formed at a constant current of -1.0 mA cm-2in all three electrolyte solutions. In these cases, relatively small amounts of lithium was deposited/dissolved in the charge/discharge cycle measurements. At -0.01 mA cm-2, on the other hand, appropriate amounts of the native-SEI was formed in all solutions and ideal behaviors were observed in the charge/discharge cycle measurements. Based on the EIS results, we found that the ideal SEI, i.e., the SEI with high lithium ion conductivity and low electron conductivity, formed at -0.01 mA cm-2. The differences in the three kinds of electrolyte solutions were discussed in details.

Fabrication of Uniformly Sized Gold Nanoparticles on Glassy Carbon by Simple Electrochemical Method

Gold nanoparticles (AuNPs) can be fabricated on glassy carbon (GC) cathode by a galvanostatic electrolysis that employs an Au wire as anode. This electrolysis is essentially similar to a simple method that has been used to prepare platinum nanoparticles (Electrochim. Acta, 129, 152 (2014)): it is performed under the conditions that the electrolysis of water occurs in strong acid solutions such as H2SO4 and HNO3. The Au anode, where oxygen evolution occurs, dissolves to form Au ions and the GC cathode, where hydrogen evolution occurs, reduces them. Although the method is simple in principle, the prepared AuNPs are uniform in size and well dispersed on the GC surface. The size and number density of AuNPs depend on the electrolysis conditions such as the applied current and electrolysis time. The characteristics also depend on the kind of electrolyte solution: the size and density are larger when the solution is 0.5 M H2SO4 than when it is 0.5 M HNO3. This is because the dissolution rate of Au anode (i.e., the formation rate of Au ions) in H2SO4 solution is faster than that in HNO3 solution, which has been confirmed by quartz crystal microbalance.

Pre-Treatment Effects on Electrochemical Lithium Deposition/Dissolution Processesstudied By Electrochemical Quartz Crystal Microbalance

Introduction High capacity battery like lithium air battery (LAB) is demanded for electric car and clean energy battery. Lithium is known as an ideal anode material because of its high theoretical capacity (3860 mA h g-1) and the most negative reduction potential (-3.04 V vs. SHE). However, during charging process, lithium dendrite, which leads to short circuit and/or explosion, is produced. In order to avoid dendritic lithium deposition, the way using solid electrolyte interphase (SEI), which is formed by decomposition of electrolytes and/or solvents on the anode surface during charging/discharging processes, is expected. Relatively flat and flexible SEI with higher lithium ion conductivity and less electron conductivity leads to better battery performance [1]. Electrochemical quartz crystal microbalance (EQCM) technique provides us not only ng leveled mass change (Δm) at the electrode surface from frequency change but also electrode surface area change (ΔA) and/or density/viscosity change (Δρ/Δη) at the electrode/electrolyte solution interface from resonance resistance change (ΔR) [2-5]. In addition, we can get mass per electron (MPE) value from this technique and then, this technique is quite useful to study the electrochemical lithium deposition/dissolution processes. In this study, we focused on the "pre-SEI" formed by potential pre-cycling before lithium deposition on the Cu EQCM electrode. As compared with the case without pre-SEI, we found that much more ideal MPE values in the case with pre-SEI were obtained in the three electrolyte solutions [6]. Experimental Using three kinds of electrolyte solutions containing 1 M lithium salts, such as 1 M LiPF6 in tetraglyme (G4), 1 M LiTFSI in G4, and 1 M LiFSI in G4, we measured cyclic voltammograms (CVs) of Cu EQCM electrode and we got simultaneously Δm andΔR. In the case without pre-SEI, the potential was negatively scanned from open circuit potential (OCP) to -0.1 V (vs. Li/Li+), where lithium deposition is already started, and then cycled between -0.1 V and +0.35 V. In the case with pre-SEI, the potential was negatively scanned from OCP to 0 V, where lithium deposition is not started yet, cycled between 0 V and +0.35 V for two cycles, and then, cycled between -0.1 V and +0.35 V. All the electrochemical measurements were carried out in the glove box, in which argon gas was filled. The SEI components were evaluated by IR and XPS. Results and discussion When the electrode potential was negatively scanned from OCP, small cathodic peaks due to the electrochemical reductive decomposition of unavoidable water, unavoidable dissolved oxygen, and electrolytes were observed around +2.0 V, +1.5 V, and +0.5 V, respectively, in all the solutions, with increases of Δm and ΔR. During pre-SEI formation, Δm and ΔR also increased although no conspicuous current peaks were observed. From IR and XPS, components of the SEI prepared from the three electrolyte solutions were almost same as each other. On the basis of the MPE values during lithium deposition and dissolution, it is concluded that the formation of the pre-SEI layers, which have the appropriate thickness and lithium ion conductivity with a relatively flat surface, is effective in regulating the lithium deposition/dissolution processes.

Fabrication of Uniformly Sized Gold Nanoparticles on Glassy Carbon By Simple Electrochemical Method

Nanoparticles (NPs) of noble metals such as gold and platinum are utilized in a wide range of applications in various fields because of their unique catalytic, electronic, and optical properties. Furthermore, NPs have large surface area to volume ratios, which leads to an increase in catalytic efficiency and also to a cost-reduction. A variety of methods using chemical reactions are currently available for synthesizing NPs in solution phase and also for controlling their shapes and surface properties. In the field of electrochemistry, platinum NPs (PtNPs) deposited on carbon materials such as graphite, glassy carbon, and carbon blacks have been extensively studied because they are useful as efficient electrocatalysts for fuel cells, water electrolysis, and so on. Nishimura et al. have developed a variable method for preparing shape-controlled PtNPs on graphite surface [1]. In the method, a constant current is applied between a Pt anode and a graphite cathode. This galvanostatic electrolysis was performed under the conditions that the water electrolysis (2H2O → 2H2 + O2) occurred in strong acid solutions such as H2SO4 and HNO3. During the electrolysis, the Pt anode dissolved to form Pt ions and the graphite cathode reduced them. The method was cost friendly because PtNPs were obtained without any reducing and stabilizing agents, and also because 72 % of dissolved Pt ions were electrodeposited as PtNPs. This simple method produced not only tetragonal nanoparticles which were enclosed by (111) planes, that is, thermodynamically stable nanoparticles, but also cubic nanoparticles enclosed by (100) planes. Interestingly, the cubic nanoparticles were preferentially obtained by controlling current densities of the cathode and anode. In our previous report [2], we have shown that gold NPs (AuNPs) can be produced by galvanostatic electrolysis using an Au anode and a graphite cathode. This electrolysis was essentially the same as the simple method that has been used to prepare PtNPs [1]. The Au anode, where oxygen evolution occurred, dissolved to form Au ions (Au → Au3+ + 3e-) and the graphite cathode, where hydrogen evolution occurred, reduced them (Au3+ + 3e- → Au). The number density of AuNPs depended on the kind of electrolyte solution: it was higher when the electrolysis was conducted in 0.5 M H2SO4 solution than in 0.5 M HNO3 solution. This was because the rate of Au dissolution (or the formation rate of Au3+), which was directly measured using quartz crystal microbalance, was higher in the H2SO4 solution than in the HNO3 solution. It is interesting that this dependence was opposite to the one for PtNPs: PtNPs were effectively obtained in the HNO3 solution compared with in the H2SO4 solution [1]. In this present work, we show AuNPs can be produced on glassy carbon (GC) by the galvanostatic electrolysis. The use of GC as cathodes facilitates us to observe AuNPs by scanning electron microscope (SEM) because the surface of GC is smoother than that of graphite. Figure 1 show SEM images of GC cathodes taken after the electrolysis. Uniformly seized AuNPs are clearly observed after the electrolysis is conducted for a long time, e.g., 120 minutes (compare panel a1 with a2), which will be discussed in the presentation. On the other hand, AuNPs can be produced without using Au anode when the electrolysis solution contains HAuCl4 (panels b1 and b2). A graphite plate is used as the anode for this electrolysis to avoid the formation of Au ions from the anode. The size of AuNPs is larger than that produced in the electrolysis without HAuCl4. The difference in the size of AuNPs will be also discussed in the presentation. REFERENCES [1] T. Nishimura, T. Nakade, T. Morikawa, H. Inoue, Electrochimi. Acta, 129 (2014) 152–159. [2] Y. Mukouyama, Y. Fukuda, T. Nishimura, ECS Trans., 80 (2017) 1425-1431. FIGURE CAPTION Figure 1. SEM images of GC cathodes taken after galvanostatic electrolysis at a cathodic current density of 10 mA cm-2. The electrolysis was conducted at 30℃ for (left) 30 minutes and (right) 120 minutes. (a1 and a2) Electrolysis solution: 0.5 M H2SO4. Anode: Au wire. Anodic current density: 2.5 mA cm-2. (b1 and b2) Electrolysis solution: 0.5 M H2SO4 + 0.1 mM HAuCl4. Anode: graphite plate. Anodic current density: 0.49 mA cm-2. Figure 1

Conductivity enhancement of silver nanowire networks via simple electrolyte solution treatment and solvent washing

As a promising replacement material for indium tin oxide in flexible electronics, silver nanowires (AgNWs) usually need complicated post-treatment to reduce the high contact resistance across the intersections when used as transparent conductive films. In this work, a widely applicable nano-joining method for improving the overall conductivity of AgNW networks with different kinds of electrolyte solutions is presented. By treatment with an electrolyte solution with appropriate ionic strengths, the insulating surfactant layer (polyvinylpyrrolidone, PVP) on the AgNWs could be desorbed, and the AgNW network could be densified. The sheet resistance of the AgNW film on a glass slide is reduced by 60.9% (from 67.5 to 26.4 Ohm sq−1) with a transmittance of 92.5%. High-resolution transmission electron microscopy analysis indicates that atomic diffusion occurs at the intersection of two AgNWs. Thus, metallurgical bonding on the nanometer scale is achieved across the junctions of the AgNWs, leading to a significant enhancement in the conductivity of the AgNW network.

A Simple Electrochemical Method for Preparing Gold Nanoparticles on Graphite

Au nanoparticles (AuNPs) can be prepared by a galvanostatic electrolysis which employs gold wire and graphite plate as anode and cathode, respectively. This electrolysis is similar to a simple method that has been used to prepare PtNPs (Electrochim. Acta, 129, 152 (2014)): it is performed under the conditions that the electrolysis of water occurs in strong acid solutions such as H2SO4 and HNO3. The Au anode, where oxygen evolution occurs, dissolves to form Au ions (Au → Au3+ + 3e-) and the graphite cathode, where hydrogen evolution occurs, reduces them (Au3+ + 3e- → Au). This work repots how the amount of AuNPs depends on the electrolysis conditions such as the current densities of the anode and cathode, and the kind of electrolyte solution.

Effects of the Alkyl Chain Length of Imidazolium Iodide in the Electrolyte Solution on the Performance of Black-Dye-Based Dye-Sensitized Solar Cells

Five kinds of electrolyte solutions containing the imidazolium iodide with a different alkyl chain length (DMImI, EMImI, MPImI, DMPImI and HMImI; DMImI=1,3-dimethylimidazolium iodide, EMImI=1-ethyl-3-methylimidazolium iodide, MPImI=1-methyl-3-n-propylimidazolium iodide, DMPImI=1,2-dimethyl-3-n-propylimidazolium iodide, HMImI=1-n-hexyl-3-methylimidazolium iodide) have been prepared to investigate the effects of the alkyl chain length of the imidazolium iodide on the performance of dye-sensitized solar cells (DSCs) with Black dye and D131. The photocurrent density (Jsc) increased and the fill factor (FF) decreased with increasing the alkyl chain length of the imidazolium iodide. Electrochemical impedance spectroscopic measurements of the DSCs revealed that the conduction band energy of TiO2 shifted to the positive direction and the diffusion resistance of the redox couple in the electrolyte solution increased with increasing the alkyl chain length of the imidazolium iodide. Therefore, the observed increment of the Jsc value seems to be attributed mainly to the conduction band energy shift of TiO2, and the observed decrement of the FF value would be caused by increasing the diffusion resistance of the redox couple in the electrolyte solution.The conversion efficiency of the DSCs was found to depend on the ion conductivity of the electrolyte solution, which is closely related to the alkyl chain length of the imidazolium iodide. This study demonstrated that the conversion efficiency could be improved by using EMImI instead of the conventional imidazolium iodide (DMPImI) due to the larger ion conductivity with a slightly higher conduction band energy of TiO2.

Evaluation of Micro Plasma Formed in the Narrow Gap in Electrolyte Solution

Microplasma was formed in a gap hole made in a quartz plate immersed in various kinds of electrolyte solutions at different concentrations. High-voltage AC was applied to the solution by using a pair of contact- or non-contact electrodes at both sides of the gap hole to ignite microplasma generation. Spectra of the light emitted from the microplasma showed elemental emission lines of the species contained in the solution, and their intensities depended on not only their concentration but also plasma conditions such as plasma temperature. A non-equilibrium plasma state was confirmed from estimated temperature of electrons and OH• radicals in the order of thousand and 10 thousand Kelvins. Deformation of the gap hole was observed depending on the polarization condition and species, probably due to high-temperature plasma and also dielectric loss in the gap hole.

Theoretical calculation on the membrane potential of charged porous membranes in 1-1, 1-2, 2-1 and 2-2 electrolyte solutions

The space-charge (SC) model and the Teorell–Meyer–Sievers (TMS) model are widely employed to calculate the membrane potential of charged porous membranes in 1-1 electrolyte solutions, but few works with the other kinds of electrolyte solutions have been reported. In this article, membrane potentials for 1-1, 1-2, 2-1 and 2-2 electrolyte solutions have been calculated numerically based on the two models using parameters of concentration, pore radius and surface charge density. The results suggest that equivalent electrolyte concentration is more suitable to characterize the membrane potential in different kinds of electrolyte solutions than electrolyte concentration. Membrane potential approaches to the Nernst potential in the low concentration region, which indicates membrane potential in monovalent cation electrolyte solution is twice as large as that in divalent cation electrolyte solution. In the high concentration region, membrane potential is close to the diffusion potential, which implies membrane potential would be reversed if the diffusion coefficient ratio of coion and counterion is larger than 1.0. While in the intermediate concentration region, membrane potential as a function of electrolyte concentration is almost linear. In the comparison of the SC and TMS models, theoretical predictions by the two models for 1-2, 2-1 and 2-2 electrolyte solutions appear to be similar to those for 1-1 electrolyte solutions reported earlier by Westermann-Clark and Christoforou [3]. The two models coincide with each other when the radius, r p, is less than 5.0 nm and the dimensionless charge density in the pore wall, q 0 is less than 1.0. Otherwise, the TMS model would overestimate the membrane potential. Furthermore, the membrane potential shows dependence on the ratio of the volume charge density to equivalent electrolyte concentration, ξ f, q 0 and r p by the SC model, but only varies with ξ f irrespective of q 0 and r p by the TMS model. These findings have a significant influence on the establishment of an appropriate theory to evaluate membrane potentials in different electrolyte solutions.

Streaming effect of single electrolyte mass transfer in nanofiltration: potential application for the selective defluorination of brackish drinking waters

This work deals with electrical properties of nanosurfaces in contact with electrolyte solutions. Single halide ion solutions were studied by streaming potential (SP) measurements and observed retention (R obs) of the F −, Cl −, and Br − ions across nanofiltration (NF) membranes. The detailed understanding of an electrolyte solution mass transfer requires an intimate knowledge of the physicochemical interactions occurring between nanoporous materials and electrolyte solutions across the first-generation composite membranes called NF55, NF70 and NF90. These membranes are composed of a polysulfone mesoporous sublayer and a microporous skin layer in polyamide. In order to get a better understanding of these effects, it seems attractive to compare the mass transfer permeation of the monovalent ions F −, Cl −, and Br − with the electrokinetic characterizations deduced from a properly developed SP apparatus. SP measurements is a very simple method to show the intrinsinc charges on membrane pore walls. The membrane's electrical properties are studied with SP design modeling pH, ionic strength and kind of electrolyte solutions. We have observed that the isoelectric point (IEP) of the membrane materials is both dependent on the ionic strength and on the kind of electrolyte solution. The IEP in the presence of KCl is 4.4 at 0.0001 mol/L and 5.8 at 0.001 mol/L, showing an increasing adsorption of the cation K + by increasing its solution concentration. For a fixed concentration, the effect of the electrolyte solution has shown that a higher adsorption of Ca ++ occurs in comparison to K + and Na +. But the adsorption of these electrolyte solutions is essentially reversible as observed under dilution conditions. Furthermore SP measurements were used for the first time to characterize the transmembrane pressure ranges where a convective and/or a diffusional mass transfer occurs. Such an approach was developed to correlate the R obs of the halide ions F −, Cl − and Br − with the kind of mass transfer (diffusional and/or convective) occurring predominantly under transmembrane pressure variations. Thus the NF70 membrane shows at low pressure (under 3 bar) the order of R obs following the hydrated ionic radius: R obs .( F −)> R obs .( Cl −)> R obs .( Br −). For a higher pressure (> 3 bar) an inversion occurs between Cl − and Br −, but F − was not affected. These results open a new prospective area for selective defluorination of brackish drinking waters using NF membranes under low transmembrane pressure.

Studies on Spontaneous Charging/Discharging Processes of Polypyrrole in Aqueous Electrolyte Solutions

Spontaneous processes of polypyrrole (PPy) films in electrolyte solutions resulting from polymer oxidation by dissolved oxygen or polymer redox capacitance discharging and their influence on open circuit potentials were investigated. Chronopotentiometric and chronoamperometric methods were adapted to study these processes. Based on the data obtained and open circuit potential vs. time measurements, Tafel plots, rest (zero-current) potentials and dependences of discharging/charging current on time were determined. Currents resulting from discharge of oxidized polypyrrole are slightly higher for thicker films, while oxidation currents of neutral PPy increase additionally with rising H+ ions and oxygen concentrations. The influence of concentration and kind of electrolyte solution on recorded currents and rest potentials was also taken into consideration. Results of these experiments can be helpful in evaluation of the polymer charge stability. They are also of significance in the explanation of the dependence of open circuit potential of PPy on concentration of solution components, described in the literature, important for analytical applications of conducting polymers.