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K. H. Kang

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Theoretical investigation on the liquid junction potential in a slit-like microchannel

                                                                                                                               

Kwan Hyoung Kang* and In Seok Kang¢Ó

Department of Mechanical Engineering* and Department of Chemical Engineering,¢Ó

Pohang University of Science and Technology, San 31, Hyoja-dong, Pohang 790-784,
Republic of Korea

(Submitted to the J. Electroanalytical Chemistry)

 

The liquid junction potential (LJP) is generated at the interface of the two electrolyte solutions of different ionic concentrations (see Fig. 1). It can be applied to generate electricity (Fig. 2) and it can also be applied to passive control of the trajectory of the charged micro- and nanoparticles in the micro total analysis systems.

In this work, an analytical model is provided to predict the LJP and the associated electrostatic field generated by the contacting two electrolyte layers in a slit-like channel, for the case of the simple 1:1 electrolyte system. The one-dimensional Nernst–Planck equation is analyzed to investigate the temporal evolution of the concentration distribution.

 

(a) isolated

(b) diffusion

(c) ion distribution

 

Fig. 1 Diffusivity difference of ionic species induces the concentration polarization.

 

 

 

 

(a) mFuel cell in a microchannel [1]

(b) Concentration fuel cell in a channel [2]

 

Fig. 2 Application of the LJP for the membraneless fuel cell

 

 

As a result, comprehensive analytical formulas for the LJP, the electric field, and the charge density are obtained. The LJP is obtained by introducing the concentrations at the boundary surfaces to the Planck¡¯s equation written for the finite domain. The analytical result for the LJP is compared with the existing experimental result of Lagger et al. [2], which shows a reasonable agreement as shown in Fig. 3.

Of particular interest is the influence of the initial concentration ratio and the thickness ratio of the two electrolyte layers. It is shown that there exist limiting profiles in the temporal evolution of the LJP, with respect to the variation of the concentration ratio and the thickness ratio, respectively. The implication of the electric field produced by the charge separation is discussed concerning the behavior of the charged particles in the micro total analysis systems.

 

Fig. 3. Validation of the theory. x and y-axes represents the non-dimensional time and the LJP. The experiment of Lagger et al. [2] is performed in a mini channel shown in Fig. 2(b). The lines indicate the theoretical prediction and the symbols represent the experimental results obtained for different concentrations and the location of the electrode in the channel.

 

References

[1] R. Ferrigno, A. D. Strook, T. D. Clark, M. Mayer, G. M. Whitesides ¡°Membraneless Vanadium Redox Fuel Cell Using Laminar Flow,¡± J. Am. Chem. Soc. 124 (2002) 12930.

[2] G. Lagger, H. Jensen, J. Josserand, H. H. Girault ¡°Hydro-voltaic cells. Part I. Concentration cells,¡± J. Electroanal. Chem. 545 (2003) 1.

Lastly Modified in October 13, 2003