Characterization and use of aqueous caesium chloride as an ultra-concentrated salt bridge

Five strong aqueous binary electrolytes — one symmetrical (CsCl) and four unsymmetrical (Li₂SO₄, K₂SO₄, Rb₂SO₄, Cs₂SO₄) — have been examined, for possible use as salt bridges for the minimization of liquid junction potentials (E _L), up to the highest concentrations practicable, by the method of homoionic transference cells: Pt–Ir | Cl₂ | CsCl (m ₂) CsCl (m ₁) | Cl₂ | Pt–Ir and Hg | Hg₂Cl₂ | CsCl (m ₂) CsCl (m ₁) | Hg₂Cl₂ | Hg for CsCl, and Hg | Hg₂SO₄ | Me₂SO₄ (m ₂) Me₂SO₄ (m ₁) | Hg₂SO₄ | Hg for the Me₂SO₄ sulphates where Me=Li, K, Rb and Cs. CsCl, K₂SO₄, Rb₂SO₄, and Cs₂SO₄, prove to belong to the class obeying close equality of transference numbers for their ions, that is,t ₊= |t _–|=0.5, over the whole concentration range (namely, from infinite dilution up to saturation). This result qualifies aqueous CsCl as an unrivalled salt bridge, whose equitransference is obeyed more stringently than any other salt. This is now demonstrated experimentally over the whole molality range, the saturation molality being as high as 11.30 mol kg^–1 at 25°C. The observed propertyt ₊=|t _–|=0.5 excludes K₂SO₄, Rb₂SO₄, and Cs₂SO₄, as possible salt bridges because the equitransference conditions for minimization ofE _L's are ₊ = |_–| = l/(z ₊ + |z _–|) = 0.333, i.e.,t ₊=0.333 andt _–=2t ₊=0.667. Finally, Li₂SO₄, though behaving quite differently from the other three sulphates studied, does not sufficiently approach the required conditions, contrary to what one might have hoped from its known infinite-dilution transference numbers.     

Ion and solvent transfers at homoionic junctions between concentrated electrolyte solutions

A unified treatment of liquid junction potentials and membrane potentials which accounts for both ionic and solvent transfers at homoionic junctions between ultra concentrated electrolyte solutions, also in terms of the primary hydration parameters and the Stokes-Robinson hydration theory, is described. Application to the determination of cation transference numbers, ₊, water transference numbers, _w, and primary hydration numbers,h, is described as a rational scheme for characterization of concentrated electrolytes as possible new salt bridges for the minimization of liquid junction potentials in electroanalysis. Examples of application of this scheme are presented based on multiple regression analysis of electromotive force measurements of such homoionic concentration cell as Ir | Cl₂ | HCl (m ₂) HCl (m ₁) | Cl₂ | Ir and Hg | Hg₂SO₄ | Li₂SO₄ (m ₂) Li₂SO₄ (m ₁) | Hg₂SO₄ | Hg, with fixedm ₁ molality and variedm ₂ molality. Based on the electromotive force of analogous homoionic transference cells but with interposed membranes, application of the present procedure can be extended to the determination of ion and solvent transport parameters, notably the degree of permselectivity, of membranes for use either as selective sensors in electroanalysis or selective separators in industrial electrochemistry.     

Synthesis and Properties of Polyimides Based on an Ether Ketone Diamine, 4,4'-Bis(4-aminophenoxy)benzophenone

A diamime monomer with ether-ketone group, 4,4'-Bis(4-aminophenoxy)benzophenone (II) was prepared through the nucleophilic substitution reaction of 1-chloro-4-nitrobenzene with 4,4'-Dihydroxybenzophenone in the presence of potassium carbonate in N,N-dimethylformamide, followed by catalytic reduction with hydrazine and Pd/C. Polyimides (PI) V _a–f (H), V _a–f (C) and copolyimides (co-PI) V _{b–d/m(e–f)} were synthesized from II and six kinds of commercial aromatic dianhydrides (III _a–f )via thermal or chemical imidization method. Poly(amic acid) (IV _a–f )had inherent viscosities range from 0.81 to 0.98 dL/g. PI of thermal imidization method was showed poor solubility even sulfuric acid. But PI of chemical imidization method V _e,f (C) and (co-PI(C)) could be dissolved. The reason is that the ketone group of poly(amic acid) segments linked with the terminal amino group of polymer chains during thermal imidization. PI films V _a–f (H) had tensile strengths of 101–118 MPa, elongations to break of 11–32%, and initial moduli of 2.1–2.8 GPa. The glass transition temperatures of V series were in the range of 252–278°C, and the temperatures of 10% weight loss (T ₁₀) were above 529°C and their residues more than 50% at 800°C in nitrogen. V series also measured the color, dielectric constants and moisture absorptions. Their films had cutoff wavelengths between 378–421 nm, b ^* values ranging from 16.4 to 77.1, dielectric constants of 3.47–3.85 (1 MHz), and moisture absorptions in the range of 0.31–0.46 wt%.     

Joule heating induced local electrodeposition for microelectronic circuits

A fundamental study is performed for local electrodeposition of copper utilizing thermal potential induced by Joule heating. The feasibility of the process for microelectronic applications is assessed by both experiment and mathematical modeling. The results of the investigation show that (i) a copper wire is coated under conditions of a.c. 50 Hz Joule heating in electrolyte containing 1.0 M CuSO₄ and 0.5m H₂SO₄ with relatively high deposition rate of about 0.4 µm min^–1, (ii) the Joule heating current should be kept below the boiling point of the solution to realize uniform deposition, and (iii) results of calculations by the present model based on one-dimensional heat conduction agree well with experimental results.Nomenclature D diameter of wire (m) - D ₀ initial diameter of wire (m) - F Faraday constant (96 487 C mol¹ ) - g acceleration due to gravity (9.807 m s²) - Gr Grashof number - H thickness of electrodeposit (m) - I current (A) - i ₀ exchange current density (Am^–2) - i _n current density normal to electode (Am^–2) - J current density (I/S) (Am^–2) - L length of wire (m) - M molar concentration of electrolyte (mol dm^–3 or M) - m atomic weight (kg mol^–1) - n number of electrons participating - n unit normal vector to boundary - Nu Nusselt number - Pr Prandtl number - q heat per unit volume (W m^–3) - R universal gas constant (8.314 3 J mol^–1 K^–1) - (r, z) cylindrical coordinate (m) - S cross section of wire (m²) - T temperature (K) - T ₀ fixed temperature at both ends of wire (K) - T _y temperature of electrolyte (K) - t time (s) - x longitudinal coordinate over wire (m) Greek symbols heat transfer coefficient (W m^–2 K^–1 - _a,c anodic (a) and cathodic (c) transfer coefficient - thermal expansion coefficient of solution (K^–1) - specific heat (J kg^–1K^–1) - potential (V) - _e electrode potential (V) - thermal conductivity (W m^–1 K^–1 ) - _y ionic conductivity of electrolyte (^–1m^–1) - _e electronic conductivity of electrode (^–1 m^–1) - kinematic viscosity (m²s^–1) - surface overpotential ( _e – ) (V) - time constant (s) - density (kg m^–3) This work was presented at The 7th International Microelectronics Conference, Yokohama, Japan (1992).     

Identification of optimum conditions for zinc electrowinning in high-purity synthetic electrolytes

The optimum conditions for zinc electrowinning in synthetic acidic zinc sulphate electrolytes (0.8 M ZnSO₄+1.07 M H₂SO₄) were determined using response surface statistical analysis. The coulombic efficiency (QE) was optimized with respect to temperature (T), current density (J) and electrode rotation rate (n). For an electrolyte prepared from AR zinc sulphate and Aristar sulphuric acid, containing trace lead and nickel, QE reached a maximum of 98.8% on a zinc substrate under the following conditions:T=50°C,J=500 A m^–2,n=35s^–1. For a very-high-purity electrolyte, prepared by dissolution of 99.9999% zinc in Aristar sulphuric acid, a maximum QE of 98.4% was predicted and obtained at:T61°C,J890 A m^–2,n38s^–1. Using a statistical response surface model calculated during the optimization process, QE contours giving an overall view of electrolyte performance were constructed. The QE responses were determined principally byT andJ, with significant interaction betweenn andJ orT andJ, depending on the impurity composition of the electrolyte. The model was also used to predict the QE response of the above electrolytes under conditions similar to industrial practice.     

Gas induced bath circulation in aluminium reduction cells

Gas induced bath circulation in the interpolar gap of aluminium cells was studied in a room temperature physical model and by computer simulation. The circulation velocity increased with increasing gas formation rate, increasing angle of inclination and decreasing bath viscosity, while it was less affected by anode immersion depth, interpolar distance (in the normal range), and convection in the metal. A typical bath velocity near the cathode was 0.05 m s^–1. The flow velocity decreased with decreasing bubble size. The results were fitted to a simple semi-empirical expression, and the velocities measured in the model experiments were in good agreement with the findings of the computer simulation.Nomenclature A Surface area (m²) - c _D Drag coefficient (l) - c _pr Concentration of 1-propanol (ml/1000 ml) - d _e Equivalent diameter of gas bubble (m) - F Faraday constant (96 487 C mol^–1) - g Acceleration due to gravity (9.82 m s^–2) - g Gravity component along anode surface (m s^–2) - h Vertical dimension of gas-filled layer (m) - H Anode immersion depth (m) - i Current density (A m^–2) - k Turbulent energy (m² s^–2) - P Pressure (N m^–2) - q Gas formation rate (m³ s^–1 m^–2) - R Universal gas constant (8.314 J mol^–1 K^–1) - t Time (s) - U Liquid velocity parallel to anode surface (m s^–1) - U _b Bubble velocity parallel to anode surface (m s^–1) - U _rel Relative velocity between bubble and liquid (m s^–1) - V Liquid velocity perpendicular to anode surface (m s^–1) - x Distance from centre of anode (m) - y Vertical distance from cathode (m) - Y Interpolar distance (m) - Angle of inclination referred to the horizontal (deg.) - Dissipation rate of turbulent energy (m² s^–3) - Volume fraction of liquid (1) - v Kinematic viscosity / (m² s^–1) - Dynamic viscosity (kg m^–1 s^–1) - _t Turbulent viscosity (kg m^–1 s^–1) - Density of liquid (kg m^–3) - /g9 Kinematic surface tension (m³ s^–2) - Bubble void fraction (1) Paper presented at the 2nd International Symposium on Electrolytic Bubbles organized jointly by the Electrochemical Technology Group of the Society of Chemical Industry and the Electrochemistry Group of the Royal Society of Chemistry and held at Imperial College, London, 31st May and 1st June 1988.     

Choked two-phase flow during electrochemical machining

A one-dimensional, two-phase fluid flow theory is formulated for the electrolyte-gas mixture behaviour in the interelectrode gap during electrochemical machining. The condition for generating the choked two-phase flow is described by an analytical formula. The initiation of choked two-phase flow in a flat, axially symmetric cavity is discussed.Nomenclature A(s) total area (cross-section of interelectrode gap (m²) - A _g,A _f cross-section of interelectrode gap filled with gas and electrolyte, respectively (m²) - c _p specific heat of electrolyte (J kg^–1 K^–1) - d diameter of inlet tube for flat radial cathode (tool (m) - d _g,d _f,d _m densities of gas, electrolyte and anode metal, respectively (kg m^–3) - d _R density ratio (see Equation 28) - D outer diameter of flat tool (m) - E voltage drop in interelectrode gap (V) - E _A,E _C potentials of anode and cathode (V) - Eu Euler number (see Equation 29) - f multiplier of dp/ds (see Equation 27) - f _r tool feed rate (m s^–1) - F Faraday constant, 96487 (A s mol^–1) - g(s) thickness of interelectrode gap (m) - g ₀,g _e inlet and outlet (exit) values ofg(s) (m) - h _a,h _f enthalpies of anode metal and electrolyte, respectively (J kg^–1) - L length of gap (m) - m _a mass flux rate for anode dissolution (kg m^–2 s^–1) - M _g,c molar mass of hydrogen or inert gas present in electrolyte (kg mol^–1) - i current density (A cm^–2) - I total current (A) - p(s) static pressure in interelectrode gap (Pa) - p ₀,p _e static pressures at inlet and outlet of the gap, respectively (Pa) - P(s) perimeter of the tool at distances (m) - R _g gas constant, 8.31471 J mol^–1 K^–1 - Re _M Reynolds number (see Equation 23) - s coordinate along gap (m) - T(s) electrolyte temperature in interelectrode gap (K) - T ₀,T _e temperatures at inlet and outlet parts of gap (K) - _g, _f linear velocities of gas and electrolyte, respectively (m s^–1) - V _a velocity of anode dissolution (m s^–1) - V _c velocity of tool (cathode) (m s^–1) - volume flow rates of gas and electrolyte, respectively (m³ s^–1) - y _g,y _f part of the interelectrode gap filled with gas or electrolyte, respectively (m) - _M limiting volume fraction of gas in electrolyte, calculated as right-hand side of Equation 30c - (s) volume fraction of gas in electrolyte - ₀, _e volume fractions of gas at inlet and outlet, respectively - _R temperature coefficient of specific resistivity, see Equation 12 (K^–1) - _a, _c electrochemical equivalents for dissolution of anode material and for gas evolution on cathode (kg C^–1) - angle (see Fig. 1) - _f kinematic viscosity of electrolyte (m² s^–1) - _M specific resistivity of gas-electrolyte mixture (m) - _f,0 specific resistivity of electrolyte at inlet (m) - slip ratio (for bubbles in the electrolyte)     

Long service life IrO2/Ta2O5 electrodes for electroflotation

Ti/IrO₂-Ta₂O₅ electrodes prepared by thermal decomposition of the respective chlorides were successfully employed as oxygen evolving electrodes for electroflotation of waste water contaminated with dispersed peptides and oils. Service lives and rates of dissolution of the Ti/IrO₂-Ta₂O₅ electrodes were measured by means of accelerated life tests, e.g. electrolysis in 0.5M H₂SO₄ at 25°C and j = 2 A cm^–2. The steady-state rate of dissolution of the IrO₂ active layer was reached after 600–700 h (0.095 g Ir h^–1 cm^–2) which is 200–300 times lower than the initial dissolution rate. The steady-state rate of dissolution of iridium was found to be proportional to the applied current density (in the range 0.5–3 A cm^–2 ). The oxygen overpotential increased slightly during electrolysis (59–82 mV for j = 0.1 A cm^–2 ) and the increase was higher for the lower content of iridium in an active surface layer. The service life of Ti/IrO₂ (65 mol%)-Ta₂O₅ (35 mol%) in industrial conditions of electrochemical devices was estimated to be greater than five years.List of symbols a constant in Tafel equation (mV) - b slope in Tafel equation (mV dec^–1) - E potential (V) - f mole fraction of iridium in the active layer - j current density (A cm^–2) - l number of layers - m _Ir content of iridium in the active layer (mg cm^–2) - r dissolution rate of the IrO₂ active layer (g Ir h^–1 cm^–2) - T _c calcination temperature (°C) - _{O 2} oxygen overpotential (mV) - _{O 2} difference in oxygen overpotential (mV) - _A service life in accelerated service life tests (h) - _S service life in accelerated service life tests related to 0.1 mg Ir cm^–2 (h) - _p polarization time in accelerated service life tests (h)     

A wall-jet electrode reactor and its application to the study of electrode reaction mechanisms Part I: Design and construction

A wall jet electrode reactor possessing a laminar flow regime, suitable for mechanistic studies, is reported. This reactor is different from those described in the literature in the size of its working electrode surface area. The reactor is evaluated by means of mass transport-limited current measurements using as a model reaction the reduction of ferricyanide ions at a platinum electrode surface from a 0.01 m K₃Fe(CN)₆-0.01 m K₄Fe(CN)₆ solution containing 1 m KCl as supporting electrolyte. The dependence of the mass transport-limited current on the crucial reactor parameters — the volume flow rate V _f (m³ s^–1), the nozzle diameter a (m) and the radius of the working electrode R (m) — is established and verified by theoretical predictions. The reactor is shown to have the desired wall jet hydrodynamics for: 1.6 × 10^–6 V _f 4.3 × 10^–6 m³ s^–1, 1.5 × 10^–3 a 3 × 10^–3 m and 1.5 × 10^–2 R 2 × 10^–2 m.List of symbols a nozzle diameter (m) - C _A concentration of A in the bulk (mol m^–3) - D _A diffusion coefficient of A (m² s^–1) - F Faraday's constant (C mol^–1) - dynamic viscosity (gm^–1 s^–1) - H distance between the working electrode and the tip of the nozzle (m) - I _lim mass-transport-limited current (A) - k _r constant linking the typical velocity of the wall-jet to the mean velocity in the nozzle - v kinematic viscosity (m² s^–1) - n number of electrons exchanged - density (g m^–3) - R radius of the working electrode (m) - t time (s) - V _f volume flow rate (m^–3 s^–1)     

Synthesis of cube-like Ag/AgCl plasmonic photocatalyst with enhanced visible light photocatalytic activity

Cube-like Ag/AgCl plasmonic photocatalyst was successfully synthesized through a one-pot precipitation method by simply adding an aqueous solution of AgNO₃ into the natural hot spring, wherein the hot spring acted as the chlorine source. The cube-like Ag/AgCl with a size of 0.5–0.9 μm exhibited enhanced visible light photocatalytic performance for the degradation of organic MO dye due to the localized surface plasmon resonance (LSPR) of the photoexcited Ag species. The trapping experiments confirmed that O₂⁻ and h⁺ were the main active species during the photocatalytic process.     

A parametric study of copper deposition in a fluidized bed electrode

The behaviour of a fluidized bed electrode of copper particles in an electrolyte of deoxygenated 5×10^–1 mol dm^–3Na₂SO₄–10^–3mol dm^–3H₂SO₄ containing low levels of Cu(II), is described as a function of applied potential, bed depth, flow rate, particle size range, Cu(II) concentration and temperature. The observed (cross sectional) current densities were more than two orders of magnitude greater than in the absence of the bed, and current efficiencies for copper deposition were typically 99%.No wholly mass transport limited currents were obtained, due to the range of overpotentials within the bed. The dependence of the cell current on the experimental variables (excluding temperature) was determined by regression analysis. The values of exponents for some of the variables are close to those expected, while others (for concentration and flow rate) reveal interactions between the experimental parameters. Nevertheless the values of the correlation coefficient matrix are low (except for the term relating expansion and flow rate), so that cross terms may be neglected in modelling the system at the first level of approximation.Nomenclature d mean particle diameter (mm) - E electrode potential, ( _m– _s)_r+(x) (V vs ref) wherer denotes the value of ( _m- _s) at the reversible potential - I (membrane) current density (A m^–2) - L static bed depth (mm) - M concentration of electroactive species (mol dm^–3) - T catholyte temperature (K) - u catholyte flow rate (mm s^–1) - x distance in the bed from the feeder electrode atx=0 - XL expanded bed depth (mm) - bed expansion (fraction of static bed depth) - _m metal phase potential (V) - _s solution phase potential (V) - _m metal phase resistivity (ohm m) - _s solution phase effective resistivity (ohm m) - overpotential (V)     

Electrolytic process optimization by simultaneous-modular flowsheeting

A procedure is described for computer-assisted optimization of an electrolytic process flowsheet. Material, energy, and economic balances for all process units were incorporated in a nonlinear optimization routine for predicting the minimum selling price based on a discounted cash flow rate of return on investment. The optimization utilized a simultaneous-modular approach which was incorporated into the public version of the Aspen flowsheeting package, and used an infeasible path convergence method based on successive quadratic programming procedures. Electrolyte vapour-liquid equilibrium data were estimated by the non-random two-liquid model. The Lagrangian multipliers of the constraint equations were used to determine the sensitivity of the optimum to key process variables. The method was illustrated by evaluation of two process flowsheets for electrosynthesis of methyl ethyl ketone (MEK) from 1-butene based on pilot-plant performance reported in the patent literature.List of symbols A _c cell cost factor ($ cell^–1) - A _H heat exchanger cost factor ($ m^–2) - A _p pump cost factor ($ sl^–1) - A _R rectifier cost factor ($ kVA^–1) - A _T tank cost factor ($l ^–0.5) - A _cm cell maintenance factor ($ A^–1 y^–1) - A _cl cell labour ($ cell^–1 y^–1) - A _cw cooling water cost ($ m^–3) - A _e electricity cost ($ kWh^–) - A _m membrane cost ($ cell^–1 y^–1) - A _om other maintenance factor, fraction of plant capital less cell cost - C _p cooling water heat capacity (kJ kg^–1 °C^–1) - H operating hours per year - I _C current to each cell (A) - I _TOT total current to all cells (A) - L _A Lang factor for auxiliaries - L _C Lang factor for cells - L _R Lang factor for rectifiers - N number of cells in plant - Q heat removal load (kJ h^–1) - R production rate (kgh^–1) - T _cw cooling water temperature rise (°C) - T _LM cooler log mean temperature difference (°C) - U heat transfer coefficient for cooler (kW m^–2 °C^–1) - v _c electrolyte flow to each cell (l ^-1) - v _C cell voltage (V) - _R rectifier efficiency - cooling water density (kg m^–3) - _T surge tank residence time (s)     

Electrochemical reduction of silver thiosulphate complexes Part I: Thermodynamic aspects of solution composition

Deposition of silver from electrolyte solutions is of major importance in the industrial applications of photographic development and electroplating. Prior to the kinetic study of the reduction of silver thiosulphate complexes, the concentrations, activities and activity coefficients of all components formed in AgNO₃-Na₂S₂O₃-NaNO₃ solutions are calculated, starting from the measurement of the equilibrium potential. In view of the high ionic strength of the solutions (greater than 0.1 mol kg^–1), the ion interaction model is applied for the estimation of the activity coefficients, inevitably imposing the use of an iterative calculation routine. The activity coefficients are shown to comply with known thermodynamic laws, supporting the appropriateness of the model, together with the approximations.List of symbols a activity (m) - c concentration (m) - d density (kg dm^–3) - h hydration number - m molality (mol kg^–1) - x molfraction - y activity coefficient (molarity scale) - z charge of an ion - E ₀ equilibrium potential vs NHE (V) - I ionic strength (m or mol kg^–1) - M molecular weight (kg dm^–3) - T temperature (K) Greek symbols stability constant - activity coefficient (molality scale) - stoichiometric coefficient - osmotic coefficient Indices Indices f free (uncomplexed) - s solvent - t total - – (or a) anion - + (or c) cation - ± mean quantity     

Modelling of time-dependent performance criteria in a three-dimensional cell system during batch recirculation copper recovery

A three-dimensional electrode cell with cross-flow of current and electrolyte is modelled for galvanostatic and pseudopotentiostatic operation. The model is based on the electrodeposition of copper from acidified copper sulphate solution onto copper particles, with an initial concentration ensuring a diffusion-controlled process and operating in a batch recycle mode. Plug flow through the cell and perfect mixing of the electrolyte in the reservoir are assumed. Based on the model, the behaviour of reacting ion concentration, current efficiency, cell voltage, specific energy consumption and process time on selected independent variables is analysed for both galvanostatic and pseudopotentiostatic modes of operation. From the results presented it is possible to identify the optimal values of parameters for copper electrowinning.List of symbols a specific surface area (m^–1) - A cross-sectional area (mu²) - a _a Tafel constant for anode overpotential (V) - a _II Tofel constant for hydrogen evolution overpotential (V) - b _a Tafel coefficient for anode overpotential (V decade^–1) - b _H Tafel coefficient for hydrogen evolution overpotential (V decade^–1) - C _e concentration at the electrode surface (m) - C _L cell outlet concentration (m) - C ₀ cell inlet concentration (m) - C ₀ ⁰ initial cell inlet concentration att = 0 (m) - d _p particle diameter (m) - e, e _p current efficiency and pump efficiency, respectively - E specific energy consumption (Wh mol^–1) - E solution phase potential drop through the cathode (V) - F Faraday number (C mol^–1) - h interelectrode distance (m) - i, i _L current density and limiting current density, respectively (A m^–2) - I, I _L current and limiting current, respectively (A) - I _H partial current for hydrogen evolution (A) - k _L mass transfer coefficient (m s^–1) - L bed height (m) - l bed depth (m) - M molecular weight (g mol^–1) - N power per unit of electrode area (W m^–2) - n exponent in Equation 19 - P pressure drop in the cell (N m^–2) - Q electrolyte flow rate (m³ h^–1) - R Universal gas constant (J mol^–1 K^–1) - r _e electrochemical reaction rate (mol m^–2 h^–1) - t _c critical time for operating current to reach instantaneous limiting current (s) - t _p process time to reach specified degree of conversion (s) - T temperature (K) - u electrolyte velocity (m s^–1) - U total cell voltage (V) - U ₀ reversible decomposition potential (V) - U _ohm ohmic voltage drop between anode and threedimensional cathode (V) - V volume of electrolyte (m³) - z number of transferred electrons Greek letters ratio of the operating and limiting currents - _{A, a} anodic activation overpotential (V) - _{c, e} cathodic concentration overpotential (V) - bed voidage - _H void fraction of hydrogen bubbles in cathode - constant (Equation 2) - ₀ electrolyte conductivity (ohm^–1 m^–1) - v electrolyte kinematic viscosity (m² s^–1) - _d diaphragm voltage drop (V) - _H voltage drop due to hydrogen bubble containing electrolyte in cathode (V) - electrolyte density (kg m^–3) - _p particle density (kg M^–3) - reservoir residence time (s)     

Electrochemical mass transfer studies in open cavities

Experimental measurements on free convection mass transfer in open cavities are described. The electrochemical deposition of copper at the inner surface of a cathodically polarized copper cylinder, open at one end and immersed in acidified copper sulphate was used to make the measurements. The effects on the rate of mass transfer of the concentration of the copper sulphate, the viscosity of the solution, the angle of orientation, and the dimensions of the cylinder were investigated. The data are presented as an empirical relation between the Sherwood number, the Rayleigh number, the Schmidt number, the angle of orientation and the ratio of the diameter to the depth of the cylinder. Comparison of the results with the available heat transfer data was not entirely satisfactory for a number of reasons that are discussed in the paper.Nomenclature C _b bulk concentration of Cu⁺⁺ (mol cm^–3) - C _b bulk concentration of H₂SO₄ (mol cm^–3) - C _o concentration of Cu⁺⁺ at cathode (mol cm^–3) - C _o concentration of H₂SO₄ at cathode (mol cm^–3) - D cavity diameter (cm) - D diffusivity of CuSO₄ (cm² s^–1) - D diffusivity of H₂SO₄ (cm² s^–1) - Gr Grashof number [dimensionless] (=Ra/Sc) - g acceleration due to gravity (=981 cm s^–2) - H cavity depth (cm) - h coefficient of heat transfer (Wm ^–2 K^–1) - i _L limiting current density (mA cm^–2) - K mass transfer coefficient (cm s^–1) - K ₁,K ₂ parameters in Equation 1 depending on the angle of orientation () of the cavity (see Table 3 for values) [dimensionless] - k thermal conductivity (W m^–1 K^–1) - L ^* characteristic dimension of the system (=D for cylindrical cavity) (cm) - m exponent on the Rayleigh number in Equation 1 (see Table 3 for values) [dimensionless] - Nu Nusselt number (=hL ^* k^–1) [dimensionless] - n exponent on the Schmidt number in Equation 1 (see Table 3 for values) [dimensionless] - Pr Prandtl number (=v/k) [dimensionless] - Ra Rayleigh number (defined in Equation 2) [dimensionless] - Sc Schmidt number (=v/D) [dimensionless] - Sh Sherwood number (=KD/D) [dimensionless] - ^t H⁺ transference number for H⁺ [dimensionless] - ^t Cu⁺⁺ transference number for Cu⁺⁺ [dimensionless] - specific densification coefficient for CuSO₄ [(1/)/C] (cm³ mol^–1) - specific densification coefficient for H₂SO₄ [(1/)/C] (cm³ mol^–1) - k thermal diffusivity (cm² s^–1) - dynamic viscosity of the electrolyte (g cm^–1 s^–1) - kinematic viscosity of the electrolyte (= /)(cm² s^–1) - density of the electrolyte (g cm^–3) - angle of orientation of the cavity measured between the axis of the cavity and gravitational vector (see Fig. 1) [degrees] - parameter of Hasegawaet al. [4] (=(2H/D))5/4 Pr^{– 1/2}) [dimensionless]     

Optimization of an electrochemical hydrogen-chlorine energy storage system

A mathematical model is presented for the optimization of the hydrogen-chlorine energy storage system. Numerical calculations have been made for a 20 MW plant being operated with a cycle of 10 h charge and 10h discharge. Optimal operating parameters, such as electrolyte concentration, cell temperature and current densities, are determined to minimize the investment of capital equipment.Nomenclature A _ex design heat transfer area of heat exchanger (m²) - a _F electrode area (m²) - heat capacity of liquid chlorine (J kg^–1K^–1) - heat capacity of hydrogen gas at constant volume (J kg^–1 K^–1) - c _p,hcl heat capacity of aqueous HCl (J kg^–1 K^–1) - C _$acid cost coefficient of HCl/Cl₂ storage ($ m^–1.4) - C _$ex cost coefficient of heat exchanger ($ m^–1.9) - C _$F cost coefficient of cell stack ($ m^–2) - cost coefficient of H₂ storage ($ m^–1.6) - C _$j cost coefficient of equipmentj ($/unit capacity) - C _$pipe cost coefficient of pipe ($ m^–1) - C _$pump cost coefficient of pump ($ J^–0.98 s^–0.98) - E cell voltage (V) - F Faraday constant (9.65 × 10⁷ C kg-equiv^–1) - F _j design capacity of equipmentj (unit capacity) - G _D design electrolyte flow rate (m³ h^–1) - heat of formation of liquid chlorine (J kg-mol^–1 C1₂) - H _f ⁰ ,_HCl heat of formation of aqueous HCl (J kg-mol^–1HCl) - H _m total mechanical energy losses (J) - I total current flow through cell (A) - i operating current density of cell stack (A m^–2) - L length of pipeline (m) - N number of parallel pipelines - n_HCl change in the amount of HCl (kg-mole) - P pressure of HCl/Cl₂ storage (kPa) - p ₁ H₂ storage pressure at the beginning of charge (kPa) - p ₂ H₂ storage pressure at the end of charge (kPa) - –Q _ex heat removed through the heat exchanger (J) - R universal gas constant (8314 J kg-mol^–1 K^–1) - the solubility of chlorine in aqueous HCl (kg-mole Cl₂ m^–3 solution) - T electrolyte temperature (K) - T ₂ electrolyte temperature at the end of charge (K) - T _max maximum electrolyte temperature (K) - T _min minimum electrolyte temperature (K) - t final time (h) - t _ex the length of time for the heat exchanger operation (h) - Uit _ex overall heat transfer coefficient (J h^–1 m^–2 K^–1) - V _acid volume of HCl/Cl₂ storage (m³) - } volume of H₂ storage (m³) - v design linear velocity of electrolyte (m s^–1) - amount of liquid chloride at timet (kg) - amount of liquid chlorine at timet ₀ (kg) - w _hcl amount of aqueous HCl solution at timet (kg) - W _p design brake power of pump (J s^–1) - X electrolyte concentration of HCl at timet (wt fraction) - X _f electrolyte concentration of HCl at the end of charge (wt fraction) - X _i electrolyte concentration of HCl at the beginning of charge (wt fraction) - X ₀ electrolyte concentration of HCl at timet ₀ (wt fraction) - Y objective function to be minimized ($ kW^–1 h^–1) - _j the scale-up exponent of equipmentj - overall electric-to-electric efficiency (%) - _acid safety factor of HCl/Cl₂ storage - fractional excess of liquid chlorine - _p pump efficiency - average density of HCl solution over the discharge period (kg m^–3)     

Electrode heat balances of electrochemical cells: application to NaCl electrolysis

This paper deals with a method of estimating single electrode heat balances during the electrolysis of molten NaCl-ZnCl₂ in a cell using a-alumina diaphragm. By measuring the thermoelectric power of the thermogalvanic cells: (T) Na/-alumina/NaCl-ZnCl₂/-alumina/Na(T+dT) and (T) C,Cl₂/NaCl-ZnCl₂/Cl₂,C(T+dT) the single electrode Peltier heat for sodium deposition and for chlorine evolution at 370° C were estimated to be –0.026±0.001 JC^–1 and+0.614±0.096 J C^–1, respectively.     

A study of transport of hydroxyl ion in a chlor-alkali diaphragm

The loss of hydroxyl ions by diffusion and back migration to the anolyte compartment is the major source of efficiency loss in a chlor-alkali diaphragm cell. The transfer rate of hydroxyl ions across the diaphragm depends on diaphragm properties and electrolyte flow rate inside the diaphragm. This work examines the concentration distribution of hydroxyl ions across the diaphragm in a laboratory cell. A numerical computation is carried out to optimize the diaphragm structure and current density based on the minimum production cost of chlorine. The optimum current density is found to be 50% lower than the present operating current density in the chlor-alkali industry.Nomenclature A _p apparent cross-sectional area of the diaphragm (m²) - A _T true cross-sectional area of the pores (m²) - C _OH concentration of the hydroxyl ion at any pointx along thex-direction (kg mol m^–3) - C _K catholyte concentration (kg mol m^–3) - C dimensionless concentration given in Equation 11 - C _D unit diaphragm cost ($ kg^–1) - C _E unit direct electrical energy cost ($ kg^–1) - C ₁ unit specific investment cost ($ kg^–1) - D diffusion coefficient of the hydroxyl ion (m² s^–1) - E ₀ open circuit voltage (V) - E total cell voltage (V) - F Faraday's constants (96 487 C g equiv^–1) - i _P apparent current density based on apparent area of the diaphragm,A _P (A m^–2) - i _T true current density based on true crosssectional area of the pores,A _T (A m^–2) - I magnitude of total current through the cell (A) - (IR)_BUS voltage drop in the bus-bar (V) - (IR)_SOLN voltage drop in the solution (V) - (IR)_DIA voltage drop in the diaphragm (V) - N _OH flux of hydroxyl ion (kg mol m^–2 s^–1) - K _S average conductivity of the solution (ohm^–1 m^–1) - k ₁ energy cost ($ kWh^–1) - K ₂ capital cost of the electrolyte cell ($ m^–2) - K ₃ cost coefficient of diaphragm ($ m^–2) - K ₅ unit cost of the raw material ($ kg^–1) - l effective pore length (m) - l ₁ distance between the anode and the cathode (m) - L life period of the diaphragm (yr) - molecular weight of chlorine gas (kg) - M _NaCl molecular weight of sodium chloride (kg) - n number of years of amortization which in principle is given by the life time of the cell (yr) - N _C total number of cells (dimensionless) - p production rate of chlorine gas (kg yr^–1) - R resistance (ohm) - r ₀ resistance of the solution (ohm) - S annual interest rate (%) - U _OH– mobility of hydroxyl ion (kg mol m²V^–1 C^–1 s^–1) - electrolyte velocity along the x-direction inside diaphragm (m s^–1) - _S superficial velocity (m s^–1) - V _W volume of water lost from the catholyte compartment due to evaporation and cathodic reaction (m³ s^–1) - x axial coordinate - Z valence of hydroxyl ion (kg equiv kg^–1 mol^–1) - diaphragm thickness (m) - porosity (%) - current efficiency (dimensionless) - _a anodic overpotential (V) - _c cathodic overpotential (V) - tortuosity factor (dimensionless)     

Investigation of interfacial reaction kinetics of I(aq) with Ag2O(s) on Ag substrate: Determining mass transport and surface reaction rates

The reaction kinetics of AgI formation by reaction of Ag₂O films with aqueous iodide were followed by monitoring the open-circuit potential (E_OC). Previous studies have shown that complete conversion of Ag₂O to AgI is indicated by an abrupt transition in the E_OC from a value close to the equilibrium potential for the Ag|Ag₂O|H₂O system to one close to that for Ag|AgI|I⁻, allowing an easy determination of the total reaction time, τ_f. The solid–solution interfacial kinetic parameters can then be determined by measuring τ_f as a function of the initial amount of Ag₂O and the I⁻ concentration. In this study, the application of the technique was extended to examine the effect of I⁻(aq) transport to an Ag₂O surface by measuring τ_f as a function of electrode rotation rate. By studying the chemical conversion as a function of electrode rotation rate we are able to separate mass transport effects from the reaction kinetics. The interfacial reaction follows kinetics typical of a sequential binary-reaction system consisting of mass transport to, followed by reaction at, the surface. The mass transport rate was proportional to the square root of the electrode rotation rate, consistent with the well-established diffusion-boundary layer model for a rotating disc. Varying the rotation rate allows a quantitative extrapolation of the data to the infinite rotation rate to determine the chemical reaction rate at the surface.     

Design characteristics of an aluminium-air battery with consumable wedge anodes

An attempt was made to optimize a mechanically rechargeable bipolar-cell battery, exemplified by an aluminium-air battery with self-perpetuating wedge anodes. The optimization involved current density of battery operation and some design parameters such as the anode thickness and the cell dimensions. It was shown that these parameters depend on the energy-to-power ratio selected by the user. The saline electrolyte aluminium-air battery was found to be essentially a low power-density/high energy-density power source. Energy densities of up to over 1500 W h kg^–1 are achievable for low power needs, indicating very long operations between recharging. It was also shown that aluminium should render significantly cheaper electric energy than any of the high-energy density metals.Nomenclature d anode plate thickness (cm) - d _p thickness of end-plates (cm) - d thickness of cell walls (cm) (see Fig. 1) - E energy density (W h kg^–1) - E _B total energy contained in the battery (k W h) - F the Faraday constant 26.8 A h mol^–1 - g _c weight of the air cathode per unit anode area (g cm^–2) - g _e excess electrolyte per unit electrode area (g cm^–2) - g _h weight of the hardware per unit anode area (g cm^–2) - g _m weight of metal per unit electrode area (g cm^–2) - _m g excess of unconsumable metal per unit electrode area (g cm^–2) - g ₀ sum of all the weights except that of consumable metal (g cm^–2) - g _ox weight of oxygen consumed withg _m (g cm^–2) - G total weight of battery (g) - G _m total amount of reserve metal per cell and per cm width (kg cm^–1) - G _m total weight of the wedges (kg) - G _r total weight of the reserve anode container except the metal (kg) - G free energy of oxidation of the metal (kW h mol^–1) - h _a height of the wedge (cm) - h _r reserve anode height (cm) - j current density (mA cm^–2) - J total current drawn from the battery (mA) - n number of electrolyte replacements between anode replacement - n _c number of cells in a battery - M atomic weight of the metal (kg mol^–1) - P power density (W kg^–1) - Q _e cost of metal in the cost of unit energy produced ($ kW^–1 h^–1) - Q _e ⁰ theoretical figure of merit of a metal ($ kW^–1 h^–1) - Q _m cost of metal per unit weight ($ kg^–1) - S _a total anode surface area (cm²) - U cell voltage without ohmic drop (V) - V cell voltage (V) - x width of battery (cm) - z number of electrons exchanged per atom of metal dissolved - interelectrode spacing (cm) - spacing between cover and top of a new reserve anode (cm) - _f material efficiency - _v voltage efficiency - _e conductivity of electrolyte (ohm^–1 cm^–1) - _e electrolyte density (g cm^–3) - _m density of metal (g cm^–3) - _p density of end-plates (g cm^–3) - _w density of cell-walls (g cm^–3)