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)     

A zinc-air cell employing a packed bed anode

A cell with a particulate zinc electrode and a monofunctional air electrode has been studied on a laboratory scale. The cell has the feature of relying on solutal natural convection, rather than a pump, for electrolyte circulation. Cells of 80 and 400 cm² (air electrode area) have been discharged at constant or stepped current. In two cases cell discharge was halted and restarted after many hours with little or no impact on cell voltage. Based on the laboratory data a preliminary design of a 32 kWh (115 MJ) battery was completed. The projected specific energy of this cell is 79.2 Wh kg^–1 (637 kJ kg^–1), while the peak specific power is 111 W kg^–1 (20% depth of discharge), meeting of the US Department of Energy targets for a battery for an electric van.     

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)     

Electrolytic recovery of metals from waste waters with the ‘Swiss-roll’ cell

The Swiss-roll cell has been used for the removal of copper from dilute synthetic waste waters. Batch experiments have shown that in acidic solutions the copper concentration may be taken down to a concentration under 1 ppm. Without N₂-sparging the current efficiency at a concentration of 22 ppm Cu was 30%. The cell was also used to separate metals from mixtures found in pickling baths. Thus 99·9% copper was removed from a Cu/Zn sulphate solution with no detectable change in the Zn concentration. The deposited metal may be leached out chemically or stripped out by anodic polarization.List of symbols a specific cell cost ($ m^–2s^–1) - A electrode area (m²) - b integration constant (M) - c concentration (M) - c _o initial concentration (M) - c steady state concentration (M) - d thickness of cathode spacer (m) - d _h hydraulic diameter (m) - D diffusion coefficient (m²s^–1) - f friction factor - k mass transfer coefficient (m s^–1) - K flow rate independent cost per unit time ($ s^–1) - K _cell cost associated with cell per unit time ($ s^–1) - K _pump cost associated with pumping per unit time($ s^–1) - K _tot total cost per unit time ($ s^–1) - l breadth of electrode perpendicular to flow (m) - L length flow path across electrode (m) - p specific pumping cost [$(W s)^–1] - P pressure drop across cell (N m^–2) - (Re) Reynolds number - (Sc) Schmidt number - (Sh) Sherwood number - t time (s) - v electrolyte flow velocity (m s^–1) - V volume of electrolyte in batch experiment (m³) - [Y effluent through-put (m³ s^–1) - Z volume flow rate through cell (m³ s^–1) - porosity of cathode spacer This paper was presented at the 27th ISE-Meeting Zurich, September 6–11, 1976.     

Polyaniline: characterization as a cathode active material in rechargeable batteries in aqueous electrolytes

An analytically pure form of chemically synthesized polyaniline having the emeraldine oxidation state has been used as a cathode active material together with a Zn anode in the fabrication of rechargeable cells in 1.0 M aqueous ZnCl₂ electrolyte (pH4). The experimental capacity and energy density based only on the weight of polymer employed in constructing the cell are 151.5 Ah kg^–1 and 159.1 Wh kg^–1 respectively at a constant discharge current of 0.75 mA cm^–2 (average discharge voltage 1.05V). The cell reactions in the charge and discharge processes have been determined. The modified capacity and energy density, when taking into account the calculated weights of Zn and HCl involved in the discharge reactions, are 109.3 Ah kg^–1 and 114.8 Wh kg^–1 respectively. The cell shows excellent recyclability and coulombic efficiency.     

Computer simulation of high-discharge-rate battery systems

Simulations were carried out for a proposed two-dimensional high-discharge-rate cell under load with an interelectrode gap of the order of 100 m. A finite difference program was written to solve the set of coupled, partial differential equations governing the behaviour of this system. Cell dimensions, cell loads, and kinetic parameters were varied to study the effects on voltage, current and specific energy. Trends in cell performance are noted, and suggestions are made for development of cells to meet specific design criteria. Modelling difficulties are discussed and suggestions are made for improvement.Nomenclature A surface area of unit cell (cm²) - A _k conductivity parameter (cm^{2 –1} mol^–1) - b Tafel slope (V) - c concentration (mol cm^–3) - c ₀ concentration of bulk electrolyte (mol cm^–3) - D diffusivity (cm² s^–1) - D _h lumped diffusion parameter (J s cm^–2 mol^–1) - D _s lumped diffusion coefficient (A cm² mol^–1) - E rest potential of electrode (V) - F Faraday constant (96 500 C mol^–1) - i current density (A cm^–2) - I total current for unit cell (A) - i ₀ exchange current density (A cm^–2) - N flux of charged species (mol cm² s^–1) - R gas constant (8.314 J mol^–1 K^–1) - R _ext resistance external to cell () - t time (s) - T temperature (K) - t ₀ transference number - u mobility (cm² mol J^–1 s^–1) - V volume of an element in the cell (cm³) - V _ext voltage external to cell (V) - z charge on an ion - _c concentration overpotential (V) - _s surface overpotential (V) - conductivity (^–1 cm^–1) - stoichiometric coefficient - electric potential in solution (V)     

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)     

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)     

Determination of overall mass transport coefficients in gas diffusion electrodes

Gas diffusion electrodes are used for many purposes, for example in fuel cells, in synthesis and as anodes in electrodeposition processes. The behaviour of gas diffusion electrodes has been the subject of many studies. In this work the transport of gas in the gas diffusion electrode, characterized by the overall mass transport coefficient, has been investigated using hydrogen-nitrogen mixtures. A reactor model for the gas compartment of the gas diffusion electrode test cell is proposed to calculate the concentration of hydrogen in the gas compartment as a function of the input concentration of hydrogen and the total volumetric gas flow rate. The mass transport coefficient is found to be independent of variations in hydrogen concentration and volumetric gas flow rate. The temperature dependence of the mass transport coefficient has been determined. A maximum was found at 40°C.Notation Agd geometric electrode surface area (m²) - C _in concentration of reactive component at the inlet of the gas compartment (mol m^–3) - c _out concentration of reactive component at the outlet of the gas compartment (mol m^–3) - E potential (V) - E _e equilibrium potential (V) - E _t upper limit potential (V) - F _v volumetric flow rate (m^–3 s^–1) - F _v,H volumetric flow rate of hydrogen (m^–3 s^–1) - F _v,N volumetric flow rate of nitrogen (m^–3 s^–1) - F _vin volumetric flow rate at the inlet of the gas compartment (m^–3 s^–1) - F _v,out volumetric flow rate at the outlet of the gas compartment (in ^–3 s^–1) - F _v,reaction volumetric flow rate of reactive component into the gas diffusion electrode (m^–3 s^–1) - Faraday constant (A s mo^–1) - I _gd current for gas diffusion electrode (A) - i _gd current density for gas diffusion electrode (A m^–2) - I _gd,1 diffusion limited current for gas diffusion electrode (A) - i _gd,1 diffusion limited current density for gas diffusion electrode (A m^–2) - I _gd,1,calc calculated diffusion limited current for gas diffusion electrode (A) - i _gd,1,calc calculated diffusion limited current density for gas diffusion electrode (A m^–2) - I _hp current for hydrogen production (A) - k _s mass transport coefficient calculated from c _out (m s^–1) - n number of electrons involved in electrode reaction - T temperature (°C) - V _m molar volume of gas (m³ mol^–1) - overpotential (V)     

The effect of the gas void distribution on the ohmic resistance during water electrolytes

Due to the presence of gas bubbles on the electrode surface and in the interelectrode gap during water electrolysis, the ohmic resistance in the cell increases. The main aim of this investigation is to obtain insight into the effect of the gas void distribution on the ohmic resistance in the electrolysis cell. The gas void distribution perpendicular to the electrode surface has been determined at various current densities, solution flow velocities and heights in the cell, taking high speed motion pictures. From these measurements it follows that two bubble layers can be distinguished. The current density distribution and the ohmic resistance in the electrolysis cell have been determined using a segmented nickel electrode. The current density decreases at increasing height in the cell. The effect is more pronounced at low solution flow velocities and high current densities. A new model to calculate the ohmic resistance in the cell is proposed.Nomenclature A _l electrolyte area (m²) - c constant (–) - d _wm distance between the working electrode and the diaphragm resp. the tip of the Luggin capillary (m) - E voltage of an operating cell (V) - f gas void fraction (–) - F Faraday constant (C/mol) - f ₀ gas void fraction at the electrode surface (–) - f _b gas void fraction in the bulk electrolyte (–) - h height from the bottom of the working electrode (m) - h _r reference height (= 1 cm) (m) - H total height of the electrode (m) - i current density (A m^–2) - i _av average current density (A m^–2) - i _r reference current density (= 1 kA m^–2) (A m^–2) - R resistance () - R specific resistance (_m) - R unit surface resistance (m²) - R ₁ resistance of the first bubble layer () - R ₂ resistance of the second bubble layer () - R _cell ohmic resistance in the cell () - R _b bubble radius (m) - s _l degree of screening by bubbles in the electrolyte (–) - _l liquid flow velocity (m s^–1) - _{1, r} reference liquid flow velocity (= l m s^–1) (m s^–1) - V _M molar gas volume (m³ mol^–1) - w width of the electrode (m) - x distance from the electrode surface (m) - thickness of the bubble layer adjacent to the electrode (m) - number of bubbles generated per unit surface area and unit time (m^–2 s^–1) Paper presented at the International Meeting on Electrolytic Bubbles organised by the Electrochemical Technology Group of the Society of Chemical Industry, and held at Imperial College, London, 13–14 September 1984.     

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)     

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 role of mass transfer in the kinetics of anodic dissolution of gas-evolving metallic surfaces

The rate of anodic dissolution of copper in phosphoric acid above the potential where oxygen evolution takes place was studied. Variables investigated were oxygen discharge rate, phosphoric acid concentration and electrode position. The mass transfer coefficient of the anodic dissolution of copper in phosphoric acid was related to the oxygen discharge rate and the physical properties of the solution by the equations for a vertical electrode:k=aV ^0.2(/u)^0.93 for a horizontal electrode:k=aV ^0.21(/u)^0.93 List of symbols k mass transfer coefficient (cm s^–1) - V oxygen discharge rate, (cm³cm^–2min^–1) - a constant - I current consumed in copper dissolution(A cm^–2) - Z number of electrons involved in the reaction - F Faraday's constant - C Solubility of copper phosphate in H₃PO₄,(mol cm^–3) - N rate of copper dissolution, (g-ion cm^–2s^–1) - diffusion layer thickness (cm) - r bubble radius (cm) - g acceleration of gravity (cm s^–2) - ¯V rise velocity of O₂ bubble (cm s^–1) - u viscosity (poise) - density (g cm^–3)     

Further studies of a zinc-air cell employing a packed bed anode part I: Discharge

The zinc-air cell employing a packed bed anode, described previously [2], has been the subject of further investigation. A 76 cm² (air electrode area) laboratory cell has been used to determine cell performance under a varying load corresponding to the Simplified Federal Urban Driving Schedule. The results were then used as a basis for the conceptual design of a 55 kW (peak power) battery. Projected specific energy of the battery was 110 Wh kg^–1 and projected specific power 97 W kg^–1 under SFUDS discharge. These values were increased to 228 Wh kg^–1 and 97 W kg^–1 when capacity is important and to 101 Wh kg^–1 and 150 W kg^–1 when power is important, based on the results of discharge experiments at 45°C. Preliminary experiments were carried out to determine the long term stability of the air electrode in this application, to measure self discharge of the zinc and to test the practicality of mechanically recharging the cell.T. Huh (deceased), was with the Department of Metallurgical Engineering, Pusan National University, Pusan, Korea.     

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)     

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)     

A new Zn|AlCl3|MnO2 galvanic cell suitable to water-activation

The Zn|3m AlCl₃ (aq)|MnO₂ galvanic cell gives an open circuit voltage (OCV) of 2.0V. When the cell is discharged at constant current (1.5 mA cm^–2 or 50 mAg^–1), its discharge curve shows a relatively flat portion in the region 2.0–1.6 V and the cell has an energy density of 550 Wh (kg of MnO₂)^–1 with a discharge capacity of 330 mA (kg of MnO₂)^–1, these values being about 2 times and 1.5 times, respectively, larger than those of the Zn|5m ZnCl₂|MnO₂ cell. The cell also shows good discharge behaviour at higher electric currents (for example 9.5 mAcm^–2 or 240 mAg^–1), and the advantages of the Zn|AlCl₃|MnO₂ cell over the Zn|ZnCl₂|MnO₂ are clear at the higher discharge currents. The high discharge voltage, energy density, and discharge capacity of the Zn|AlCl₃|MnO₂ cell are attributed to the strong buffering effect of AlCl₃ at pH3. Due to this buffering effect, the electrolytic solution causes gradual corrosion of the zinc and, consequently, the cell is suited to water-activation.     

Mass transfer at the gas evolving inner electrode of a concentric cylindrical reactor

Mass transfer coefficients for an oxygen evolving vertical PbO₂ coated cylinder electrode were measured for the anodic oxidation of acidified ferrous sulphate above the limiting current. Variables studied included the ferrous sulphate concentration, the anode height, the oxygen discharge rate and the anode surface roughness. The mass transfer coefficient was found to increase with increasing O₂ discharge rate,V, and electrode height,h, according to the proportionality expressionK V ^0.34 h ^0.2. Surface roughness with a peak to valley height up to 2.6 mm was found to increase the rate of mass transfer by a modest amount which ranged from 33.3 to 50.8% depending on the degree of roughness and oxygen discharge rate. The present data, as well as previous data at vertical oxygen evolving electrodes where bubble coalescence is negligible, were correlated by the equationJ=7.63 (Re. Fr)^–0.12, whereJ is the mass transferJ factor (St. Sc ^0.66).Notation a ₁,a ₂ constants - A electrode area (cm²) - C concentration of Fe²⁺ (M) - d bubble diameter (cm) - D diffusivity (cm² s^–1) - e electrochemical equivalent (g C^–1) - F Faraday's constant - g acceleration due to gravity (cm s^–2) - h electrode height (cm) - I _Fe ²⁺ current consumed in Fe²⁺ oxidation A - I _{o 2} current consumed in O₂ evolution, A - K mass transfer coefficient (cm s^–1) - m amount of Fe²⁺ oxidized (g) - P gas pressure (atm) - p pitch of the threaded surface (cm) - Q volume of oxygen gas passing any point at the electrode surface (cm³ s^–1) - R gas constant (atm cm³ mol^–1 K^–1) - r peak-to-valley height of the threaded surface (cm) - t time of electrolysis (s) - T temperature (K) - solution viscosity (g cm^–1 s^–1) - V oxygen discharge velocity as defined by Equation 3 (cm s^–1) - Z number of electrons involved in the reaction - Sh Sherwood number (Kd/D) - Re Reynolds number (Vd/) - Sc Schmidt number (v/D) - J mass transferJ factor (St. Sc ^0.66) - St Stanton number (K/V) - Fr Froude number (V ²/dg) - Solution density, g cm^–3 - v Kinematic viscosity (cm² s^–1) - bubble geometrical parameter defined in [31] - fractional surface coverage - diffusion layer thickness (cm)     

Application of metallic foams in electrochemical reactors of the filter-press type: Part II Mass transfer performance

This paper focuses on mass transfer characteristics of classical filter-press electrochemical reactors without membranes. In the tested configuration, the working electrode consists of a lane plate with a sheet of foam and the counter-electrode consists of a plane plate with a turbulence promoter. The global mass transfer coefficients of the two electrodes have the same order of magnitude. Moreover, a comparison with literature data shows that their values remain in the range of those previously presented. Due to the high specific surface area of the foam used (A _ve, = 6400 m^–1), the ratio of the surface area of the working electrode to that of the counter electrode is 15. The electroreduction of ferricyanide has been carried out to test the performance of this configuration. The value of the final conversion has been compared to that calculated from mass transfer coefficients and surface areas of the electrodes.List of symbols A _ve dynamic specific surface area of the foam: surface area per volume of material (m^–1) - A_ve dynamic specific surface area of the electrode consisting of a plate and a sheet of foam: surface area per volume of electrode (m^–1) - A _vs static specific surface area (m^–1) - C _in ferricyanide concentration at the inlet of the cell (mol m^–3) - C _out ferricyanide concentration at the outlet of the cell (molm^–3) - D diffusion coefficient (m² s^–1) - d _h equivalent hydraulic diameter, dh = 2lh (l + h)^–1 (m) - F Faraday number (C mol^–1) - h channel thickness (m) - I limiting diffusion current (A) - I _{c a} final limiting diffusion current intensity at the anode (A) - I _cf final limiting diffusion current intensity at the cathode (A) - k _a mass transfer coefficient at the anode (m s^–1) - k _c mass transfer coefficient at the cathode (ms^–1) - k _d mass transfer coefficient (m s^–1) - l channel width (m) - n number of electrons in the electrochemical reaction - Q _v volumetric flow rate in the channel (m³ s^–1) - Re Reynolds number, Re = U ₀ d _h v ^–1 - S active surface area of the electrode (m²) - S _a surface area of the anode (m²) - S _c surface area of the cathode (m ²) - S _c Schmidt number, Sc = v D ^–1 - Sh Sherwood number, Sh = k _d D _h/D - U ₀ superficial velocity (m s^–1) - V volume offered to fluid flow in the volumic electrode (m³) - V volume of one tank reactor in the cascade (m³) - X conversion - X _f final conversion Greek letters porosity - v kinematic viscosity (m² s^–1) - density (kg s^–1) - residence time in a continuous stirred tank reactor = /Q _v (s)     

Pumping effect due to gas evolution in flow-through electrolysers

In electrolysers with recirculation where a gas is evolved, the pumping of electrolyte from a lower to a higher level can be effected by the air-lift effect due to the difference between the densities of the inlet electrolyte and the gaseous dispersion at the outlet. A balance equation for calculation of the rate of flow of the pumped liquid is derived. An equation for the calculation of the mean volume fraction of bubbles in the space between the electrodes is proposed and verified experimentally on a pilot electrolyser. The pumping efficiency of the air-lift effect is determined.Nomenclature a_A,a_C constants of linearized Tafel Equation 7 (V) - b electrode width (m) - b_A,b_C constants of linearized Tafel Equation 7 (V m^–2 A^–1) - c _pE specific heat of electrolyte (J kg^–1 K^–1) - d interelectrode distance (m) - d _E equivalent diameter of interelectrode space (m) - d _T diameter of tubing (m) - E _A,E _C potential of anode and cathode (V) - f correction term, see Equation 11 - F Faraday's constant (96 484 C mol^–1) - g acceleration of gravity (9.81 m s^–2) - H function defined by Equation 16 - I _T total current flowing through electrolyser (A) - l local current density (A m^–2) - j mean current density (A m^–2) - j reduced local current density - K ₁,K _2B criteria defined by Equations 12 and 13 - K ₃ criterion defined by Equation 9 - l pumping height equal tol _E–l _T (m) - l _E electrode height (m) - l _H length of tubing above electrolyser (m) - l _T level height in reservoir (m) - l _v,l _s length of tubing, see Fig. 1 (m) - n _O2,n _H2 number of electrons transferred per molecule of O₂ or H₂ - N _B,N _E pumping power, pumping extrapower, Equations 28, 31 (W) - N _T total power input for electrolysis (W) - p _M, p _p pressure losses in the interelectrode - p _z space, in the inlet tubing and in elbows (N m^–2) - P pressure at the upper edge of the electrode (N m^–2) - R gas constant (J K^–1 mol^–1) - Re, Re _M Reynolds criterion for the electrolyte and for gas dispersion - S _A,S _C thickness of anode and cathode (m) - T temperature (K) - T ₀,T _T temperatures at the inlet and outlet (K) - T temperature difference, T_T–T₀ (K) - U terminal voltage of electrolyser (V) - U increase of the mean voltage drop in the interelectrode space due to presence of bubbles (V) - v _E,v _M velocities of electrolyte and of gas dispersion between electrodes (m s^–1) - v _p velocity of electrolyte in inlet channel (m s^–1) - v _R rising velocity of bubbles (m s^–1) - V_E volume rate of flow of electrolyte (m³ s^–1) - V_G(x) volume rate of flow of gas at heightx (m³ s^–1) - V_GT volume rate of flow of gas at upper electrode edge (m³ s^–1) - x distance from lower electrode edge (m) - (x) volume fraction of bubbles at heightx between electrodes, and its mean value (Equations 5a, 22a) - friction coefficient of electrolyte in a tube - reduced height coordinate,x/l _E - E _pot volume-specific potential energy difference of electrolyte (J m^–3) - E _kin volume-specific kinetic energy difference of electrolyte (J m^–3) - E _dis volume-specific dissipated energy of electrolyte (J m^–3)