The Faradaic impedance of the lithium-sulphur dioxide system. A kinetic interpretation

Impedance measurements have been made on Li/SO₂(C) cells containing an acetonitrile-based electrolyte in a range of states from newly assembled to completely discharged. The cell behaviour can be explained if it is assumed that the lithium is an irreversible electrode and that the SO₂ electrode is reversible. The nominal exchange current density on the lithium is 0.7 mA cm^–2 and 0.37 for the cell Li/LiBr(2.35 mol dm^–3), CH₃CN, S₂O ₄ ^2– ¦SO₂(6.25 mol dm^–3)C     

An efficient method for solving the model equations of a two dimensional packed bed electrode

A theoretical and experimental study of a flow-by packed bed electrochemical reactor consisting of graphite particles is given. The mathematical model describes the two dimensional distributions of electrode potential and reactant concentration in the reactor, and includes the influence of lateral dispersion between the feeder electrode and membrane. A new efficient numerical method, based on central finite difference and orthogonal collocation is used to solve the model. Results of the model simulations agree well with experimental measurement of the potential distribution for the ferrocyanide/ferricyanide system.List of symbols a specific surface area of packed bed electrode (cm^–1) - c _i concentration of speciesi(i = 2 for cathodic species) (mol dm^–3) - c _i0 inlet concentration of speciesi (mol dm^–3) - C dimensionless concentration - c _s concentration on the electrode surface (mol dm^–3) - C _s dimensionless concentration on the electrode surface - D _s effective diffusion coefficient (cm²s^–1) - Da Damköhler number - F Faraday's constant (96 487 C mol^–1 of electrons) - i current density (A m^–2) - i ₀ exchange current density (A m^–2) - I number of equation - j ₂ electrochemical reaction rate per unit area (mol cm^–2 s^–1) - J number of node point - k _a average local mass transfer coefficient (cm s^–1) - n number of moles of electrons - N number of inner collocation points - N ₂ flux of species 2 (mol cm^–2 s^–1) - Pe Peclet number - R gas constant (8.314 J mol^–1 K^–1) - Sh _m modified Sherwood number - T temperature (K) - u _a average axial velocity (cm s^–1) - x lateral coordinate (cm) - x ₀ electrode depth (cm) - X dimensionless depth of electrode - y axial coordinate (cm) - y ₀ electrode length (cm) - Y dimensionless length of electrode - z ₀ electrode width (cm) Greek symbols aspect ratio - _a anodic transfer coefficient - _c cathodic transfer coefficient - overpotential (V) - stoichiometric coefficient - dimensionless rate constant - ₂ effective conductivity of electrolyte (^–1 cm^–1) - ₁ potential of electrode (V) - ₂ potential of electrolyte (V) - _eq equilibrium potential (V) - dimensionless potential     

Characterization of reticulate,three — dimensional electrodes

A study has been made of the mass transfer characteristics of a reticulate, three-dimensional electrode, obtained by metallization of polyurethane foams. The assumed chemical model has been copper deposition from diluted solutions in 1 M H₂SO₄. Preliminary investigations of the performances of this electrode, assembled in a filter-press type cell, have given interesting results: with 0.01 M CuSO₄ solutions the current density is 85 mA cm^–2 when the flow rate is 14 cm s^–1.List of symbols a area for unit volume (cm^–1) - C copper concentration (mM cm^–3) - c _L copper concentration in cathode effluent (mM cm^–3) - c ₀ copper concentration of feed (mM cm^–3) - C ₀ ⁰ initial copper concentration of feed (mM cm^–3) - d pore diameter (cm) - D diffusion coefficient (cm²s^–1) - F Faraday's constant (mcoul me _q ^–1 ) - i electrolytic current density on diaphragm area basis (mA cm^–2) - I overall current (mA) - K _m mass transfer coefficient (cm s^–1) - n number of electrons transferred in electrode reaction (me_q mM^–1) - P ] volumetric flux (cm³s^–1) - Q total volume of solution (cm³) - (Re) Reynold's number - S section of electrode normal to the flux (cm²) - (Sc) Schmidt's number - (Sh) Sherwood's number - t time - T temperature - u linear velocity of solution (cm s^–1) - V volume of electrode (cm³) - divergence operator - void fraction - u/K _m a(cm) - electrical specific conductivity of electrolyte (^–1 cm^–1) - _S potential of the solution (mV) - density of the solution (g cm^–3) - v kinematic viscosity (cm²s^–1)     

Effect of thiourea,benzotriazole and 4,5-dithiaoctane-1,8-disulphonic acid on the kinetics of copper deposition from dilute acid sulphate solutions

The effects of thiourea (TU), benzotriazole (BTA) and 4,5-dithiaoctane-1,8-disulphonic acid (DTODSA) on the deposition of copper from dilute acid sulphate solutions have been studied using potential sweep techniques. Tafel slopes and exchange current densities were determined in the presence and absence of these organic additives. TU and BTA were found to inhibit the copper deposition reaction; increases in the BTA concentration gave a systematic lowering of the exchange current density, whilst TU behaved in a less predictable manner. For BTA and TU concentrations of 10^–5 mol dm^–3,j ₀ values of 0.0027 ± 0.0001 and 0.0028 ± 0.0002 mA cm^–2 were obtained compared to a value of 0.0083 ± 0.0003 mA cm^–2 for the additive free acid sulphate solution. In contrast, in the presence of DTODSA, an increased exchange current of 0.043 ± 0.0003 mA cm^–2 was observed. The presence of additives gave rise to measured Tafel slopes of –164, –180 and –190 mV for TU, BTA and DTODSA, respectively, compared to that of –120 mV for copper sulphate alone.List of symbols A electrode area (cm²) - b _C cathodic Tafel slope (mV) - c _B bulk concentration (mol cm^–3) - D Diffusion coefficient (cm² s^–1) - F Faraday constant (A s mol^–1) - I _L Limiting current (A) - j Current density (A cm^–2) - j _CT Charge transfer current density (A cm^–2) - j ₀ Exchange current density (A cm^–2) - k _L Mass transport coefficient (cm s^–1) - R Molar gas constant (J K^–1 mol^–1) - T Temperature (K) - z Number of electrons (dimensionless) Greek symbols _C Cathodic transfer coefficient (dimensionless) - Overpotential (V) - v Kinematic viscosity (cm² s^–1) - Rotation rate (rad s^–1)     

Effective conductivities of an FeS positive in LiCl-KCl eutectic electrolyte at different states of charge

The effective conductivities of an FeS positive electrode in an Li-Al/FeS cell were determined for different states of charge and discharge in LiCl-KCl eutectic electrolyte at 450° C. The data obtained experimentally were compared with those obtained in 67.4 mol% LiCl-KCl electrolyte and theoretically predicted profiles. The electrode resistance profiles indicate that precipitation of KC1, in addition to formation of Li₂S, in the positive electrode causes high internal resistance and limits the discharge capacity.Nomenclature C _i,b Bulk concentration of speciesi outside the electrode (mol cm^–3) - C _i,p Concentration of speciesz in the pore solution (mol cm^–3) - D _i Diffusion coefficient of speciesi (cm² sec^–1) - F Faraday's constant (96 487 C equiv^–1) - I Current density (A cm^–1) - k _j Conductivity ratio defined ask _j /k _c - K _m,j Conductivity ratio defined asK _m,j /k _c - L Electrode thickness per unit volume (cm) - R _i,diffu Rate of concentration change of speciesi due to diffusion (mol s^–1cm^–3) - R _i,migra Rate of concentration change of speciesi due to migration (mol s^–1 cm^–3) - R _i,precip Rate of concentration change of speciesi due to precipitation (mol s^–1cm^–3) - R _i,reac Rate of concentration change of speciesi due to reaction (mol s^–1cm^–3) - t Time (s) - t _i ^Cl Transference number of speciesi relative to Cl^– - ¯ _j Molar volume ofj (cm³mol^–1) - w _LiCl Mass fraction of LiCl - x _i Mole fraction of speciesi - (x _LiCl)_KCl,sat Mole fraction of LiCl in LiCl-KCl electrolyte saturated with KC1 - (x _LiCl)_LiCl,sat Mole fraction of LiCl in LiCl-KCl electrolyte saturated with LiCl - _i Rate constant of production or consumption of speciesi - Void fraction or porosity - _j Volume fraction of solid phasej - _ps Volume fraction of precipitated salt - K _c Conductivity of continuous phase, e.g. electrolyte (^–1 cm^–1) - k _j Conductivity of solid phasej (^–1 cm^–1) - K _m,j Effective conductivity for a mixture of conductive solid phasej and the electrolyte at a given volume fraction of phasej (^–1 cm^–1) - Density of electrolyte (g cm^–3) - Effective conductivity of FeS electrode at a state of discharge (^–1 cm^–1) - Effective resistivity of FeS electrode at a state of discharge ( cm)     

Oxygen reduction on stainless steel

Oxygen reduction was studied on AISI 304 stainless steel in 0.51 m NaCl solution at pH values ranging from 4 to 10. A rotating disc electrode was employed. It was found that oxygen reduction is under mixed activation-diffusion control. The reaction order with respect to oxygen was found to be one. The values of the Tafel slope depend on the potential scan direction and pH of the solution, and range from – 115 to – 180 mV dec^–1. The apparent number of electrons exchanged was calculated to be four, indicating the absence of H₂O₂ formation.Nomenclature B =0.62 nFcD ^2/3 –^1/6 - c bulk concentration of dissolved oxygen (mol dm^–3) - D molecular diffusion coefficient of oxygen (cm² s^–1) - E electrode potential (V) - EH standard electrode potential (V) - E _H ⁰ Faraday constant (96 500 As mol^–1) - I current (A) - j current density (A cm^–2) - j _k kinetic current density (A cm^–2) - j _L limiting current density (A cm^–2) - m reaction order with respect to dissolved oxygen molecule - M molar mass (g mol^–1) - n number of transferred electrons per molecule oxygen - density (g cm^–3) - kinematic viscosity (cm² s^–1) - angular velocity (s^–1)     

Zinc removal from dilute solutions using a rotating cylinder electrode reactor

Mine residue recycling processes produce dilute zinc solutions suitable for metal recovery. The rotating cylinder electrode reactor behaviour sequentially followed charge transfer and diffusion control mechanisms, even with solutions contaminated with metals or organic substances. Zinc removal at low pH (0) and low concentration (2 mg dm^–3) is demonstrated. Under galvanostatic operation, the zinc deposition current efficiency in the charge transfer control region attains values up to 77.3%, whereas in the diffusion control region it decreases rapidly to values as low as 0.1%. When a potentio-static mode is used, less energy is required to deposit zinc, even at low current efficiency. The results and possible problems for continuous reactor operation under conditions of powder formation are identified and discussed using knowledge from other zinc industries such as electrowinning, plating and batteries.List of symbols A _c cylinder electrode active surface (cm²) - A _d disc electrode active surface (cm²) - c _H analytical sulfuric acid concentration (mol cm^–3) - c _Zn analytical zinc sulphate concentration (mol cm^–3) - d cylinder electrode diameter (cm) - D zinc diffusion coefficient (cm² s^–1) - F Faraday constant (96 500 C mol^–1) - I total current (A) - I _H hydrogen production current (A) - I ₁ zinc deposition limiting current (A) - j critical hydrogen current density (A cm^–2) - k zinc mass transfer coefficient (cm s^–1) - K Wark's rule constant - n number of electrons exchanged in the zinc deposition reaction - Re Reynolds number (d ²/2) - Sc Schmidt number (/D) - Sh Sherwood number (kd/D) - t time (s) - V electrolyte volume in the RCER (cm³) - solution kinematic viscosity (cm² s^–1) - zinc deposition current efficiency - rotation speed (rad s^–1)     

Kinetics of copper electrodeposition in citrate electrolytes

The kinetics of copper electrocrystallization in citrate electrolytes (0.5M CuSO₄, 0.01 to 2M sodium citrate) and citrate ammonia electrolytes (up to pH 10.5) were investigated. The addition of citrate strongly inhibits the copper reduction. For citrate concentrations ranging from 0.6 to 0.8 M, the impedance plots exhibit two separate capacitive features. The low frequency loop has a characteristic frequency which depends mainly on the electrode rotation speed. Its size increases with increasing current density or citrate concentration and decreases with increasing electrode rotation speed. A reaction path is proposed to account for the main features of the reduction kinetics (polarization curves, current dependence of the current efficiency and impedance plots) observed in the range 0.5 to 0.8 M citrate concentrations. This involves the reduction of cupric complex species into a compound that can be either included as a whole into the deposit or decomplexed to produce the metal deposit. The resulting excess free complexing ions at the interface would adsorb and inhibit the reduction of complexed species. With a charge transfer reaction occurring in two steps coupled by the soluble Cu(I) intermediate which is able to diffuse into the solution, this model can also account for the low current efficiencies observed in citrate ammonia electrolytes and their dependencies upon the current density and electrode rotation speed.Nomenclature b, b ₁, b ₁ ^* Tafel coefficients (V^–1) - bulk concentration of complexed species (mol cm^–3) - (si*) concentration of intermediate C^* atx=0 (mol cm^–3) - C concentration of (Cu Cit H)^2– atx=0 (mol cm^–3) - C C variation due to E - C concentration of complexing agent (Cit)^3- at the distancex (mol cm^–3) - C _o concentrationC atx=0 (mol cm^–3) - C _o C _o variation due to E - Cv _s bulk concentrationC (mol cm^–3) - (Cit H), (Cu), (Compl) molecular weights (g) - C _dl double layer capacitance (F cm^–2) - D diffusion coefficient of (Cit)^3- (cm²s^–1) - D ₁ diffusion coefficient of C^* (cm²s^–1) - E electrode potential (V) - f ₁ frequency in Equation 25 (s^–1) - F Faraday's constant (96 500 A smol^–1) - i, i ₁, i ₁ ^* current densities (A cm^–2) - i i variation due to E - Im(Z) imaginary part ofZ - j - k ₁, k ₁ ^* , K₁, K ₁ ^* , K₂, K rate constants (cms^–1) - K rate constant (s^–1) - K ₃ rate constant (cm³ A^–1s^–1) - R _t transfer resistance (cm²) - R _p polarization resistance (cm²) - Re(Z) real part ofZ - t time (s) - x distance from the electrode (cm) - Z _f faradaic impedance (cm²) - Z electrode impedance (cm²) Greek symbols maximal surface concentration of complexing species (molcm^–2) - thickness of Nernst diffusion layer (cm) - , ₁, ₂ current efficiencies - angular frequency (rads^–1) - electrode rotation speed (revmin^–1) - =K ^–1(s) - _d diffusion time constant (s) - electrode coverage by adsorbed complexing species - (in0) electrode coverage due toC _s - variation due to E     

Potentiodynamic electrodeposition of paint (EDP)

Potentiodynamic electropainting at a rotating iron disc electrode has been investigated with three different EDP resins, two anodic from the acrylate type and one cathodic from the epoxide type, and a wide variation of conditions. Voltage scan rate ( _s=1 to 200 Vs^–1), voltage range (40 to 200V) and electrode rotation speed (n=60 and 1000rpm) were the most important parameters. The (cyclic) voltammetric curves obtained generally exhibit three characteristic features: (1) The current rises steeply at the start of the experiment. Bath resistance transforms the potentiodynamic curve simultaneously into a galvanodynamic curve. After a transition time, , a critical pH is attained at the phase boundary and electrocoagulation occurs. This leads to a rapidly decreasing current density. The sharp c.d. maximum thus established has a peak voltage,U _p, which increases with _s according to the relation logU _P 1/3 log _s in accordance with theory. (2) At high voltages, a limiting current density is observed, increasing with the square root of _s. This could be quantitatively interpreted in terms of dynamic growth of film thickness governed by Ohmic ion transport in the film. The preceding part of theU/j curve declines withj t _–1/2, which indicates the prevalence of space charge effects. (3) Ohmic lines are measured in the course of the first reverse scan and in all quasi steady state follow up cycles. They are flatter by a factor of 1000 in regard to the initial Ohmic line and reflect low voltage Ohmic behaviour of the EDP-film. At high voltages positive current deviations occur due to Child's law. The curves can be measured easily and reproducibly. Due to their salient features it is proposed to use them for characterization of EDP-paints.Nomenclature a current density scan rate (mAcm^–2s^–1) - A electrode area (cm²) - c ^* critical hydrogen ion- (or hydroxyl ion-) concentration at the electrode for electrocoagulation (mol dm^–3) - C _A capacitance of EDP-film per unit area (Fcm^–2) - E electric field strength (Vcm^–1) - I cell current (mA) - j current density, c.d. (mA cm^–2) - j _c capacitance current density (mA cm^–2) - j ^lim limiting current density (mA cm^–2) - j _p peak current density (Section3) (mA cm–2) - J _r residual current density (mA cm^–2) - j ^* critical current density (for EDP) (mA cm^–2) - K constant in Equations 9 and 10 (Vs^1/2) - L _F thickness of polymer film (cm) - L _sc thickness of space charge layer (cm) - m _e electrochemical equivalent (gC^–1 - n _c exponent in Child's law - n rotating disc electrode rotation speed (rpm) - N particle number concentration (cm^–3) - R _B bath resistance () - R _F film resistance () - s density (g cm^–3) - transition time (s) - U (cell) voltage (V) - U _max maximum voltage, point of reversion of voltage scan direction (V) - U _p peak voltage, section3 (V) - _s voltage scan (or sweep) rate (Vs^–1)     

The mechanism of copper powder formation in potentiostatic deposition

A mechanism for copper powder formation in potentiostatic deposition is proposed, and the critical overpotential of copper powder formation is determined. A good agreement between theoretical and experimental results has been obtained.List of symbols C ₀ bulk concentration (mol cm^–3) - D diffusion coefficient (cm² s^–1) - F Faraday's constant (C mol^–1) - h height of protrusion (cm) - h _c height at which dendrites crack (cm) - h _i height (cm) - h ₀ initial height of protrusion (cm) - h _j,t elevation at pointj and timet (cm) - h _j,0 initial elevation at pointj (cm) - I limiting diffusion current (A) - I ₀ initial limiting diffusion current (A) - i limiting current density (A cm^–2) - i _d current density on the tip of dendrite of height h (A cm^–2) - i _t total current (A cm^–2) - j number - k proportionality factor [cm (mol cm^–3)^m] - k constant - M number of dendrites - m number - N number of elevated points - n number of electrons - p concentration exponent - Q _c quantity of electricity (C) - R gas constant (J mol^–1 K^–1) - S electrode surface area (cm²) - T temperature (K) - t time (s) - t _a longest time in which approximation h is valid (s) - t _i induction time (s) - V molar volume (cm³ mol^–1) - surface tension (J cm^–2) - thickness of diffusion layer (cm) - overpotential (V) - _c,p critical overpotential of powder formation (V) - fraction of flat surface - apparent induction time (s)     

Effect of sodium and potassium sulphates on zinc electrowinning

In order to evaluate the intrinsic effect of high concentrations of sodium and potassium sulphates in zinc electrowinning solutions, measurements of coulombic efficiency were carried out under mass transfer-controlled conditions in synthetic solutions of very high purity. A solution composition of 1 mol dm^–3 ZnSO₄+1.5 mol dm^–3 H₂SO₄ was employed with and without additions of 0.5 mol dm^–3 Na₂SO₄ and/or 0.25 mol dm^–3 K₂SO₄. With temperature and current density similar to plant practice (37° C, 650 A m^–2) and electrode rotation rates of 10 and 45 s^–1, the coulombic efficiency for three successive batch tests (200 mg zinc) increased by an average of 1.2% (from an average of 96.0%) for additions of 0.5 mol dm^–3 Na₂SO₄+0.25 mol dm^–3 K₂SO₄. The results were evaluated in terms of available theories, solution purity and predicted changes in solution composition (zinc and hydrogen ion activities) and physical properties following additions of Na₂SO₄/K₂SO₄. It was concluded that in the plant situation the increase in coulombic efficiency would probably be offset by an increase in cell voltage of about 2%, the net effect on power efficiency being a decrease of about 1%. The zinc deposit morphology and preferred orientation were also studied. The addition of sodium and/or potassium sulphate to the solution resulted in rougher, darker zinc deposits, a slight grain refining effect, and a change from random to predominantly basal (002), (004) crystal orientation (at 45 s^–1).     

Characterization of electroless Ni-Mo-P/SnO2/Ti electrodes for oxygen evolution in alkaline solution

Ni-Mo-P alloy electrodes, prepared by electroless plating, were characterized for application to oxygen evolution. The rate constants were estimated for oxygen evolution on electrodes prepared at various Mo-complex concentrations. The surface area and the crystallinity increase with increasing Mo content. The electrochemical characteristics of the electrodes were identified in relation to morphology and the structure of the surface. The results show that the electroless Ni-Mo-P electrode prepared at a Mo-complex concentration of 0.011 m provided the best electrocatalytic activity for oxygen evolution.List of symbols b Tafel slope (mV dec^–1) - b F/RT (mV^–1) - F Faraday constant (96 500 C mol^–1) - j current density (mA cm^–2) - k₁ reaction rate of Reaction 1, (mol^–1 cm³ s^–) - k ₁ = k₁C _OH ^–(mol cm^–2 s^–1) - k ₁₀ rate constant of Reaction 1 at = 0 (mol cm^–2 s^–1) - k_c1 rate constant of Reaction 2 (mol^–1 cm³ s^–1) - k _c1 = k_c1C _{H 2O} (mol cm^–2 s^–1) - k_c2 rate constant of chemical Reaction 3 (mol^–1 cm² s^–1) - k _c2 = k_c2² (mol cm^–2 s^–1) - k_c3 rate constant of Reaction 4 (mol^–1 cm² s^–1) - Q _a anodic capacity (mC) - Q _c cathodic capacity (mC) - R gas constant (8.314 J mol^–1 K^–1) - R _ct charge transfer resistance ( cm²) - R _ads charge transfer resistance due to adsorption effect ( cm²) - C _d1 double layer capacity (mF cm^–2) - _{C ads} double layer capacity due to adsorption effect (mF cm^–2) - T temperature (K) Greek symbols anodic transfer coefficient - _{O 2} oxygen overpotential (mV) - saturation concentration of surface oxide on nickel (mol cm^–2)     

Meniscus shape and lateral wetting at the hanging meniscus rotating disc (HMRD) electrode

The hanging meniscus rotating disc (HMRD) electrode is a configuration in which a cylinder of the electrode material is used without an insulating mantle. We have recently shown that the hydrodynamic behaviour of the HMRD is similar to that of the conventional rotating disc electrode and that this configuration can also be used to study the kinetics of simple charge transfer reactions. In this paper experimental data on the change of meniscus shape upon meniscus height and rotation for different electrode materials are presented and analysed in relation to lateral wetting and stability.List of symbols A electrode area (cm²) - C ₀ ^* bulk concentration (mol cm^–3) - D ₀ diffusion coefficient (cm²s^–1) - f force on a cylinder supporting a hanging meniscus (dyn) - F Faraday (96 500 Cmol^–1) - g gravitational acceleration (cm s^–2) - h height (cm) - h _m meniscus height (cm) - h ₀ critical meniscus height (cm) - i total current (A) - i _L limiting current (A) - i _max kinetic current (A) - k proportionality constant (cm^–1) - K dimensionless constant - n number of electrons exchanged - R _eff effective radius of the electrode (cm) - R ₀ geometric radius of the electrode (cm) - V volume of the meniscus above the general level of the liquid surface (cm³) Greek letters ₀ thickness of hydrodynamic boundary layer (cm) - surface tension (dyn cm^–1) - kinematic viscosity (cm²s^–1) - density difference between the liquid and its surrounding fluid (gcm^–3) - _C normal contact angle - _L local contact angle 0_L + 90° - electrode rotation rate (s^–1)     

Investigation of hydrodynamic test systems for the selection of high flow rate resistant materials

Flow-dependent corrosion phenomena can be studied in the laboratory and on a pilot plant scale by a number of methods, of which the rotating disc, the rotating cylinder, the coaxial cylinder and the tubular flow test are the most important. These methods are discussed with regard to mass transfer characteristics and their applicability to flow-dependent corrosion processes and erosion corrosion. To exemplify the application of such methods to materials selection for seawater pumps, corrosion data of non-alloyed and low alloy cast iron are presented.Nomenclature (Sh) Sherwood number - (Re) Reynolds number - n exponential of Reynolds number - shear stress (Pa) - dynamic viscosity (Pa s) - du/dy velocity gradient (s^–1) - mass density (kg m^–3) - f friction factor - (Sc) Schmidt number - i _cor,i _c corrosion current density (mA cm^–2) - i _lim limiting current density (mA cm^–2) - u _cor corrosion rate (mm y^–1 or g m^–2d^–1) - u flow rate (ms^–1) - k constant - u _ph phase boundary rate (gm^–2d^–1) - z number of electrons exchanged - F Faraday number (96 487 As mol^–1) - D diffusion coefficient (m²s^–1) - c concentration (kmol m^–3) - L characteristic length (m) - kinematic viscosity (m² s^–1) - h gap width (m) - v volume rate (m³s^–1) - m rotation rate (min^–1) - u _rel relative rate of co-axial cylinders (m s^–1) - _H electrode potential versus SHE (V)     

Development of a novel redox flow battery for electricity storage system

A novel cylindrical battery which uses carbon fibres with high specific surface area as electrodes and a porous silica glass with high chemical stability as membrane has been fabricated. The results obtained from electrolysis of 0.5 M K₃Fe(CN)₆–0.5 M KCl and of 85 mM V(IV)–1 M H₂SO₄ indicate that the cell possesses excellent electrolytic efficiency. As a redox flow battery (RFB) its performance was investigated by employing all-vanadium sulfate electrolytes. The results of the cyclic voltammetry measurements indicate that at a glassy carbon electrode the electrochemical window for 2 M H₂SO₄ solution could reach 2.0 2.4 V. Constant current charging–discharging tests indicate that the batteries could deliver a specific energy of 24 Wh L^–1 at a current density of 55 mA cm^–2. The open-circuit cell voltage, after full charging, remained constant at about 1.51 V for over 72 h, while the coulombic efficiency was over 91%, showing that there was negligible self-discharge due to active ions diffusion through the membrane during this period.     

A mathematical model for platinum/ PTFE/porous nickel fuel cell oxygen diffusion electrodes

This paper describes the cylindrical agglomerate model for oxygen/alkali gas diffusion electrodes fabricated from platinum, PTFE and porous nickel. Corrections for the increase in hydroxyl ion concentration with increasing current density have been made to the original model of Brown and Horve. Changes in performance by variation of the bulk structural parameters, e.g. agglomerate radius, porosity and tortuosity, have been studied. Theoretical modes of electrode decay have been explored.List of symbols Transfer coefficient - C Concentration of O₂ in elec trolyte mol cm^–3 - C _i Concentration of O₂ atr = R mol cm^–3 - C _o Concentration of O₂ in electrolyte atr = mol cm^–3 - Diffusion coefficient of O₂ in KOH cm² sec^–1 - Film thickness cm - E Overpotential of the electrode V - F Faraday's constant - i Electrode current density A cm^–2 - i _a Current per agglomerate A - I ₁(Z) First order Bessel function - I ₀(Z) Zero order Bessel function - j Local current density A cm^–2 - j _o Exchange current density A cm^–2 - L Agglomerate length (catalyst thickness) cm - N Number of electrons in rate determining step - N _a Number of agglomerates per cm² of electrode - Potential drop along ag glomerate V - _L Potential drop at L_a V - r Radial direction - R Radius of agglomerate cm - R _o Gas constant - Density of platinum g cm^–3 - S _g Surface area per gram cm² g^–1 - Solubility coefficient of O₂ mol cm^–3 - _m Electrolyte conductivity (ohm cm)^–1 - T Absolute temperature °K - _a Axial tortuosity - Porosity of platinum in the agglomerate - _r Aadial tortuosity of the agglomerate - W Catalyst loading g cm^–2 - x Axial direction     

Mass transfer at rotating cone electrodes

Upright and inverted rotating cone electrodes (apex half angle 52°) have been studied using electrodeposition of copper from an acid electrolyte (Sc=1770) by means of limiting current mass transport techniques. The behaviour suggests that it is appropriate to regard these electrodes as modified disc electrodes. The upright rotating cone electrode exhibits a flow transition atRe=1×10⁵. In laminar flowSh=4.5Re ^0.48 and in turbulent flowSh=0.04Re ^0.95. The inverted rotating cone electrode exhibits a flow transition atRe=6×10⁴. In laminar flowSh=4.5Re ^0.45 and in turbulent flowSh=0.04Re ^0.88. The data have been interpreted in terms of a coating thickness affected by throwing power effects and the use of a conical cathode cell for control of high speed electrodeposition processes is indicated.Nomenclature A electrode area (cm²) - C _b concentration (of bulk solution) (mol cm^–3) - c concentration difference (mol cm^–3) - D diffusion coefficient (cm² s^–1) - f/2 friction factor - F Faraday's constant (96485 A s mol^–1) - i _L limiting current density (A cm^–2) - J mass transfer flux (mol s^–1 cm^–2) - K _L mass transfer coefficient (cm s^–1) - l slant height of the cone (cm) - U peripheral velocity (cm s^–1) - x local condition coordinate (cm) - z no. of electrons - apex half-angle of cone - angular velocity (rad s^–1) - wall shear stress (dyn cm^–2) - kinematic viscosity (cm² s^–1) - Re Reynolds number=Ud/v - Sc Schmidt number=v/D - Sh Sherwood number=K _L d/D     

Secondary aluminium-iron (III) chloride batteries with a low temperature molten salt electrolyte

Secondary aluminium-iron (III) chloride batteries using a low temperature molten salt electrolyte were constructed and tested. Discharge current densities were in the range 5 to 100 mA ( 1 to 20 mA cm^–2; C/4 to 5C); charging currents were 5mA (C/4 toC/2). Utilization of the positive electrode reactant was low due to the discharge rates and loading procedure. The mode for self discharge was dissolution of the positive electrode reactant and transport to the aluminium negative electrode where it reacted.     

Laser initiation of PETN

We studied experimentally the initiation ofPETN with a dispersity of 3700–22,000cm ²/kg and a density of 0.6–1.3g/cm ₃ by a laser (=1.06 µm and =40nsec). Data processing was based on dimensional analysis of the process and study of the phenomena accompanying initiation (crater formation and sudden change in optical characteristics). This made it possible to describe empirically the complex dependence of the threshold initiation energy ofPETN on its density and dispersity, the irradiation-zone diameter, and the acoustic impedance of a transparent base plate. The mechanism of laser initiation ofPETN is considered.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 4, pp. 113–119, July–August, 1996.     

An electrochemical hydrocyclone cell for the treatment of dilute solutions: approximate plug-flow model for electrodeposition kinetics

The mass transfer conditions in a hydrocyclone cell have been analysed and an approximate plug-flow model has been developed to describe metal ion depletion during batch recycle operation. The resulting concentration-time relationship and reaction rate equation has been shown to describe satisfactorily the experimental data obtained for the electrodeposition of copper and silver from dilute solutions. Moreover, these relationships have enabled the evaluation of mass transfer coefficients in the hydrocyclone cell.List of symbols a ₁,a ₂,b numerical exponents - C concentration (mol dm^–3) - C _o initial bath concentration (mol dm^–3) - C(0) cell inlet concentration (mol dm^–3) - C(L) cell outlet concentration (mol dm^–3) - k rate constant (h^–1) - K mass transfer coefficient (ms^–1) - K _L volumetric mass transfer coefficient = 2RLK (m³ s^–1) - L active length of the cylindrical cathode (m) - Q volumetric flow rate (m³ s^–1) - r inside radius of the conical part of the cell - r _A reaction rate of component A (mol dm^–3 h^–1) - R inside radius of the cylindrical part of the cell (m) - t time - u vertical (axial) velocity in the annulus - U cell voltage (V) - _t horizontal (tangential) velocity in the annulus - V _B volume of the reservoir/bath - V _R volume of the cell/reactor - _B residence of time of the reservoir