Solid electrolyte cell using the electrolyte of the CuCl-CuI-RbCl system

The electrochemical behaviour of a solid electrolyte cell Cu,X/X/Cu_1.75Se (X = Rb₄Cu₁₆I₇Cl₁₃) has been examined. The open circuit voltage was 0.2680 V at 25° C. The cell yielded a current of several microamperes at ambient temperature. Some charge-discharge cycles were possible. The failure of the cell was ascribed to the anode, owing to a decrease of the activity of metallic copper as well as a low rate of the charge transfer reaction, copper/copper ion.     

Nanometer-thick films of titanium oxide acting as electrolyte in the polymer electrolyte fuel cell

0-18 nm-thick titanium, zirconium and tantalum oxide films are thermally evaporated on Nafion 117 membranes, and used as thin spacer electrolyte layers between the Nafion and a 3 nm Pt catalyst film. Electrochemical characterisation of the films in terms of oxygen reduction activity, high frequency impedance and cyclic voltammetry in nitrogen is performed in a fuel cell at 80 °C and full humidification. Titanium oxide films with thicknesses up to 18 nm are shown to conduct protons, whereas zirconium oxide and tantalum oxide block proton transport already at a thickness of 1.5 nm. The performance for oxygen reduction is higher for a bi-layered film of 3 nm platinum on 1.5 or 18 nm titanium oxide, than for a pure 3 nm platinum film with no spacer layer. The improvement in oxygen reduction performance is ascribed to a higher active surface area of platinum, i.e. no beneficial effect of combining platinum with zirconium, tantalum or titanium oxides on the intrinsic oxygen reduction activity is seen. The results suggest that TiO₂ may be used as electrolyte in fuel cell electrodes, and that low-temperature proton exchange fuel cells could be possible using TiO₂ as electrolyte.     

Modeling the permittivity of electrolyte solutions

Solution of a strong electrolyte in a high‐density polar fluid gives rise to a dielectric saturation that decreases the orientation polarizability of the solvent molecules in close proximity to the ions wherefore the relative permittivity in this region is determined solely by the atomic and electronic polarization. This causes a substantial decrease in the static permittivity of the solution. By considering the dielectric saturation, a model for the permittivity of an electrolyte solution have been developed and the parameters, the relative permittivities at dielectric saturation in close proximity to the ions, for 17 ions in water at 298.15 K were determined. By scaling these relative permittivities in proportion to the permittivity of the solvent, the model could be extended to calculate the permittivity of solutions of electrolytes in methanol and admixtures of water and ethanol. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2854–2860, 2015     

Theory of the double-layer effect on the rate of charge transfer across an electrolyte/electrolyte interface

Effect of the electric double-layer structure on the rate equations of charge (ion or electron) transfer across an electrolyte/electrolyte solution interface is discussed. The electric double layer is considered as composed of the inner layer sandwiched by two diffuse layers in both side. The charge transfer reaction is considered as taking place between two chemical species at the planes of contact of the inner layer with the two respective diffuse layers. A steady-state ionic transport in the diffuse layers (Levich correction) is assumed. Two ideal processes; inner layer rate-determining process and diffuse layer rate-determining process are addressed.     

Voltage of a solid electrolyte galvanic cell in terms of the activity of the mobile species of the electrolyte

The voltage of a solid electrolyte galvanic cell is not related to the activity of the mobile ions in the electrolyte which is why this activity is not a measurable quantity. Any different view contradicts fundamental relationships inherent in solid state electrochemistry.     

On the conductivity of phosphoric acid electrolyte

The specific electric conductivity and viscosity of 7.5–100 wt% aqueous phosphoric acid electrolyte have been measured in the temperature range 25–200°C. The product of conductivity and viscosity was found to decrease exponentially with increasing temperature. This suggests that the electric conduction in phosphoric acid follows the Grotthus proton switching mechanism. The measured conductivity data were correlated by the following empirical equation: $$\begin{array}{*{20}c} {k\mu = {\rm A} exp [BT]}\\ {A = 702.7X^{1.5} - 1734.2X^2 + 1446.5X^{2.5} - 350.7X^3 }\\ {B = - 0.010163 + 0.011634X - 0.08313X^2 }\\ \end{array}$$ wherek is conductivity in mho cm^?1; μ is viscosity in centipoise;T is the absolute temperature in K; andX is mole fraction of phosphoric acid in the electrolyte. The standard deviation for the percentage difference between the calculated and experimental values of 188 data points was less than 7.5%.     

Novel electrolyte system: Porous polymeric support filled with liquid electrolyte

In this article, a novel electrolyte system composed of both porous polysulfone film and a propylene carbonate/LiCIO₄ liquid solution occupying the pore is suggested. Porous poly-sulfone acts as a support which imparts a good mechanical property and accommodation of a liquid electrolyte. Using this approach, we could enhance the conductivity and me-chanical property of the polymer electrolyte simultaneously. The maximum conductivity of this system was 3.93 × 10⁻³ S/cm at room temperature. The conductivity seems to be significantly affected by the amount of the uptake of the liquid electrolyte and also by the surface characteristics of the porous polysulfone. The path for ionic conduction is effectively formed with the increase in the uptake of the liquid electrolyte. Low-surface porosity and high-surface roughness is believed to reduce the ionic conduction. However, the denser surface layer of the support showed retarded evaporation of propylene carbonate under reduced pressure, indicating superior long-term stability. © 1996 John Wiley & Sons, Inc.     

Nature of the electrolyte and zirconium anodization

The characteristics of anodic zirconium oxides depend on the solution in which they are formed. The results of sequential anodizing in sulphate and borate solutions suggest that the rate determining step lies within the oxide films not at the interfaces.     

Enhanced thermal properties of the solid electrolyte interphase formed on graphite in an electrolyte with fluoroethylene carbonate

The influence of fluoroethylene carbonate (FEC) on the electrochemical and thermal properties of graphite anodes is examined. The dQ/dV graph of graphite/Li cells shows that the electrochemical reduction peak of an electrolyte shifts to higher potential in the presence of FEC. The DSC results for graphite anodes cycled in FEC-containing electrolytes clearly exhibit that an exothermic peak at around 120 °C mostly disappears. It is demonstrated by X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS) that SEI formed by the electrochemical reduction of FEC consists of a relatively high proportion of LiF and gives low interfacial resistance for graphite/Li/Li cells.     

The effect of electrolyte temperature on the passivity of solid electrolyte interphase formed on a graphite electrode

The effect of electrolyte temperature on the passivity of solid electrolyte interphase (SEI) was investigated in 1 M LiPF₆-ethylene carbonate/diethyl carbonate (50:50 vol.%) electrolyte, using galvanostatic charge-discharge experiment, and ac-impedance spectroscopy combined with Fourier transform infra-red spectroscopy, and high resolution transmission electron microscopy (HRTEM). The galvanostatic charge-discharge curves at 20 °C evidenced that the irreversible capacity loss during electrochemical cycling was markedly increased with rising SEI formation temperature from 0 to 40 °C. This implies that the higher the SEI formation temperature, the more were the graphite electrodes exposed to structural damages. From both increase of the relative amount of Li₂CO₃ to ROCO₂Li and decrease of resistance to the lithium transport through the SEI layer with increasing SEI formation temperature, it is reasonable to claim that, due to the enhanced gas evolution reactions during transformation of ROCO₂Li to Li₂CO₃, the rising SEI formation temperature increased the number of defect sites in the SEI layer. From the analysis of HRTEM images, no significant structural destruction in bulk graphite layer was observed after charge-discharge cycles. This means that solvated lithium ions were intercalated through the defect sites in the SEI, at most, into the surface region of the graphite layer.     

Electro-organic synthesis without supporting electrolyte: Possibilities of solid polymer electrolyte technology

The application of ion exchange membranes as solid polymer electrolytes (SPE) in fuel cells is state-of-the-art. This technology needs no supporting electrolyte; consequently it can be applied for electro-organic syntheses in order to save process steps. In this case the process is not predetermined to a maximized energy efficiency so that the selection of the cell design, of the electrode materials and of the operating conditions can be focused on a high selectivity of the electrode reactions. The electro-osmotic stream, which is caused by the solvation shells of the ions during their migration through the membrane, and hence is a typical property of SPE technology, has a significant effect on the electrode reactions. It generates enhanced mass transfer at the electrodes, which is beneficial for reaction selectivity. It can be influenced by the choice of, and possibly by the preparation of, the membrane. An additional remarkable advantage of SPE technology is the exceptional long durability of oxide coated electrodes. By combination of several process engineering methods stable operation of SPE cells has been realized, even for examples of non-aqueous reaction systems. Experiments up to 6000 h duration and in cells of up to 250 cm² membrane area show the potential for industrial application.     

Surface relaxation at the metal/electrolyte interface

X-ray diffraction is an ideal technique for the in situ study of single crystal metal surfaces in an electrochemical environment. In this paper, measurements of the low-index surfaces of Au and Pt are described, in particular with reference to surface expansion effects. Surface expansion can be probed potentiodynamically to correlate expansion with the adsorption/desorption of solution species. In general, the results are in good agreement with recent theoretical calculations. The X-ray technique can also give insight into electrocatalytic reactions as shown by the results for the adsorption and oxidation of CO on Pt(111).     

Passivity phenomena at the silicon/electrolyte interface

The current/potential behaviour of silicon in aqueous alkaline systems was investigated by potentiostatic techniques. In general, curves typical of metal passivity phenomena were obtained, although the effect of the semiconducting nature of silicon was evident. Corrosion and anodic dissolution rates correlated closely with the current/potential curves, but the decrease in corrosion rate after passivation was not as large as is observed with most passivated metal systems. The presence of the passivating oxide had a marked effect on the interfacial capacitance. The oxide itself is not a capacitive element in the interfacial circuit, but exerts an effect on the number of charge-trapping centres (surface states) at the termination of the silicon lattice.     

Ceria-based solid electrolyte exhibits superior mechanical and electric properties compared to zirconia-based solid electrolyte

The mechanical strength and electrical characteristics of 10 mol% gadolinium (Gd)-doped ceria (10GDC) and gadolinium-samarium (Gd–Sm) co-doped ceria ceramics treated by contact reduction were investigated. The observed increased strength of 10GDC was similar to the strength previously reported for ceria with and without Sm doping. X-ray photoelectron spectroscopy revealed that only the surface was reduced in the strengthened material. In addition, the strengthened ceramic displayed improved hardness at low test loads, which suggested the formation of a surface compression layer. The reducing conditions did not affect the electrical conductivity of the 10GDC material. Co-doping with 10 mol% each of Gd and Sm improved strength and conductivity compared with 10GDC and 20GDC. When the co-doped material was reduced, the electric conductivity remained identical; however, the mechanical strength improved, exceeding the strength of zirconia.     

Solvents in salt electrolyte: Benefits and possible use as electrolyte for lithium-ion battery

An EC/DEC [40:60% (v/v)] solvent mixture has been added in various amounts to the ionic liquid (IL) hexyltrimethylammonium bis(trifluoromethylsulfonyl)imide (N₁₁₁₆-NTf₂) in the presence of LiNTf₂ (lithium bis(trifluoromethylsulfonyl)imide) as lithium salt for possible use as electrolytes in lithium-ion batteries. These electrolytes exhibit a larger thermal stability than the reference electrolyte EC/DEC [40:60] + LiNTf₂ 1 M when the percentage of the IL exceeds 30% (v/v). All studied electrolytes are glass forming ones with an ideal glass transition temperature of ca. −85 °C(±5 °C), which has been determined by application of the VTF theory to conductivity and viscosity measurements and confirmed by DSC (T_g = −90 ± 5 °C). An electrochemical window of about 5 V versus Li/Li⁺ was measured at a glassy carbon electrode. The cycling ability of the optimized electrolyte N₁₁₁₆-NTf₂/EC:DEC (40/60% (v/v)) + 1 M LiNTf₂ has been investigated at a titanate oxide (Li₄Ti₅O₁₂) and a cobalt oxide (Li_xCoO₂) electrodes. Cycling the positive and the negative electrodes was conducted successfully with a high capacity and without any significant fading.