Metal Deposition‐Dissolution in Molten Halides: On the Question of Measurability of Very Fast Electrode Reaction Rates

Abstract

Metal deposition-dissolution reactions in molten salts are very fast and difficult to investigate, as evidenced by large discrepancies in the reported exchange current densities. An error analysis of the dc relaxation techniques was carried out, and it was determined that the measurement of the exchange current density can have a systematic error if the surface reaction rate is much faster than the diffusion rate. This systematic error will result in measured exchange current densities approximately equal to the largest exchange current density measurable under the given conditions. This systematic error can also result in fortuitously linear log io vs. log C and log io vs. lIT plots, even when the results are grossly ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.233.239.86 Downloaded on 2015-03-14 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.233.239.86 Downloaded on 2015-03-14 to IP Vol. 132, No. 7 ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.233.239.86ABSTRACT A traveling, dual-beam laser interferometer has been used to investigate mass-transfer boundary layers on planar electrodes in turbulent channel flow. The effect of secondary flows induced near the electrode/electrolyte interface by small flow obstacles in laminar bulk flow is compared to the effect of turbulent bulk flow produced by high electrolyte flow rates in an obstacle-free flow channel. It is shown that mass-transfer enhancement can be attained more efficiently by the use of small flow obstacles than by the use of high flow velocities.

Evaluation of the Electrochemical Behavior of CeCl3 in Molten LiCl-KCl Eutectic Utilizing Metallic Ce as an Anode

“…The order of magnitude of these results is similar to the lowest exchange current densities reported for mono and divalent elements in molten LiCl-KCl. [8][9][10][11][12] The reversibility at only the slowest scan rates and low activity coefficient of CeCl 3 supports a conclusion that significant molecular complexation occurs, and this may explain the observation of a low exchange current density.…”

“…RT F lnX agCl [11] Based on extrapolation of the data of Yang and Hudson 15 to the reference electrode concentration used in this work (0.0039 mole fraction AgCl), the potential of the reference electrode versus Cl À /Cl 2 is given by the expression E AgCl ¼ À0:9716 À 3:499 Â 10 À4 TðVÞ [12] Table III summarizes the experimental data obtained from open circuit potentiometry of a cerium rod or cerium deposited on a tungsten wire. Figure 10 shows the standard potentials computed from the experimental data of Table III, as well as literature data from several other studies.…”

“…Moreover, much of the data that has been published for other metals in LiCl-KCl is highly inconsistent, with data varying by 3 orders of magnitude between investigators, with the discrepancy appearing to be largely dependent upon the analysis technique. [8][9][10][11] This was largely explained by Settle and Nagy, 12 who reviewed the data of the literature and performed a comparative error analysis showing that classic techniques must be used for the fast molten salt reactions only with great care, lest grossly-erroneous measurements result. They found that a systematic error can occur if the reaction rate is much faster than the diffusion rate.…”

Mathematical Modeling of the Sodium/Iron Chloride Battery

“…where CTR is the total concentration in the reservoir. By using the relation that CTR = (CT)r=rL = 2/(Ye)r=r L, the above equation can be rewritten as a function of (XA)r=rL-The change of XA at r = r L with time is by i0.NF i = ~IN [23] RT In the matrix phase, the potential gradient is il = -%V4)1 [24] where i~ and 4~ are the current density and the potential in the solid matrix.…”

Thermodynamics and Kinetics Properties of Lanthanides (La, Ce, Pr, Nd) on Liquid Bismuth Electrode in LiCl-KCl Molten Salt

“…The dependency of the exchange current density on temperature can have linear form. 47 The results can provide data to model electrowinning at the liquid Bi electrode.…”