Design of Thin‐Gap Channel Flow Cells

An algebraic model for a parallel plate, zinc/bromine flow cell is presented and used to predict various performance quantities, which are compared to those predicted by using previously published differential equation models. The results presented compare well with previous work. The model is based on the concept of using well‐mixed zones and linear concentration and potential profiles for the diffusion layers and the separator. The Butler‐Volmer equation is used for the electrochemical reactions, and the homogeneous reaction between bromine and bromide is included.

Section: Model Solutionmentioning

confidence: 99%

“…The fundamentals of this technique are presented by Newman (10) and others (11,12). The model presented herein is an algebraic simplification of the second approach.…”

mentioning

confidence: 99%

An Algebraic Model for a Zinc/Bromine Flow Cell

Simpson

White

1989

“…Reactions 1 through 5 occur at the cathode, and the following oxygen evolution reaction is the main reaction at the anode U e (V vs. SHE) 4 OH---+ O2(g) + 2H2Oa) + 4e 0.401 [6] Due to assumption 12, reactions 2 through 5 are ignored at the anode but reaction 1 is considered by including the transport of nitrites through the separator. The reactions can be written in the following general format 9 sijM z: ~ nje [7] i In this format, the stoichiometric coefficient, Slj, is positive for products and negative for reactants when the reaction is written as a reduction.…”

Section: Model Developmentmentioning

confidence: 99%

A Boundary‐Layer Model of a Parallel‐Plate Electrochemical Reactor for the Destruction of Nitrates and Nitrites in Alkaline Waste Solutions

Prasad

Weidner

Farell

1995

so that a plot of Q vs. ~q yields a straight line with the intercept of in (io). This plot is the so-called Allen-Hickling plot. This procedure has been used extensively to determine the exchange current density from potential step data. The potential step data were collected with positive voltage feedback so that the voltage loss due to electrolyte resistance was compensated properly. The double-layer charging current is significant only in the initial time period. The kinetic current was obtained by square root extrapolation of the current between 0.6 and 1.0 ms to time zero. At least three measurements were taken at each potential. Sufficient time was allowed between measurements (usually 15 min). The activation polarization curve for the high-Btu gas is shown in Fig. 3. The corresponding Allen-Hickling plot is presented in Fig. 4. The exchange current density calculated according to the above procedure is 1.49 mA/cm 2, which is more than an order of magnitude lower than that of copper (26.3 mA/cm 2) or nickel (48.3 mA/cm2). The electrocatalytic activity of lithium letrite is significantly lower than that of nickel or copper. The Allen-Hickling plots for medium and low-Btu gases are shown in Fig. 5 and 6. A complete comparison of the three materials is listed in Table II. SummaryAn experimental approach was conducted to study the electrochemical properties of lithium ferrite as an alternative anode material in MCFC. Some unique characteristics were observed: (i) the open-circuit potential was shifted in the positive direction for lithium ferrite. The measured OCP is a mixed potential; (it) the steady state current is about 60 % lower than that of nickel under the same conditions; (iii) two waves were found in the cyclic voltammograms: the first wave is attributed to hydrogen oxidation and the second wave is related to oxidation of Fe 2 § to Fe 3 § in the structure; (iv) the exchange current density of hydrogen oxidation on lithium ferrite is an order of magnitude lower than that on copper or nickel; (v) kinetically speaking, lithium ferrite is not a favorable anode material, despite its having better sulfur tolerance and sintering resistance than nickel.

“…to predict current and potential distributions in chlorine cells (6,7), electroplating cells (8-10), and corrosion processes (11,12). Morris and Smyrl (12) did use three spatial coordinates in some of their work, but they did not consider the spatial dependence of the specific conductivities, as done here.…”

Section: Technical Notesmentioning

confidence: 99%

A Simple Model for a Zinc/Bromine Flow Cell and Associated Storage Tanks

Simpson

White

1990

A simple model for a parallel plate, zinc/bromine flow cell and associated storage tanks is presented and used to make time-dependent predictions for various quantities in the system. The model is based on a previously published algebraic model of the cell at steady-state and time-dependent, first-order differential equations for the storage tanks. The Butler-Volmer equation is used for the electrochemical reactions, and the homogeneous reaction between bromine and bromide is included. The model predictions indicate that the charging operation of a zinc/bromine battery can be significantly improved by using a storage tank with a larger residence time for the bromine side of the system. * Electrochemical Society Student Member. ** Electrochemical Society Active Member.