Electrochemical Transport

Collaborators: Martin Z. Bazant

Concentration field
Diffusion currents
Steady electrochemical transport around a polarizable sphere immersed in an electrolyte solution when a large, uniform electric field is applied: concentration profile of neutral salt (top) and diffusion currents (bottom). In these two images, the electric field is aligned with the z-axis.
Graphical representation of surface conservation laws
Graphical representation of surface conservation laws.

Novel electrochemical devices being explored for microfluidic and micro/nano-power source applications often electrochemical systems into operating regimes that test the limits of traditional macroscopic theories in electrochemistry. We study electrochemical transport in these extreme operating regimes by analyzing the classical Poisson-Nernst-Planck equations using asymptotic analysis and numerical simulations (Bazant et al., 2005; Chu & Bazant, 2005; Chu & Bazant, 2006).

One of the main conclusions of our work is that for weak electrolytes, large concentration gradients develop even at relatively small applied electric fields/voltages. These concentration gradients imply that the common approach of modeling electrochemical transport using linear circuit models is questionable for systems driven by strong electric fields/voltages.

Using novel asymptotic analysis techniques, we have also formally derived effective nonlinear electrochemical transport equations in the thin double-layer limit, which generalize linear circuit models (Chu & Z., 2007). The foundation for this work is a novel formulation of surface conservation laws which allows us to derive effective boundary conditions that capture the physics of the double layer without requiring linearization of the concentration and potential fields.

References

  1. Bazant, M. Z., Chu, K. T., & Bayly, B. J. (2005). Current-voltage relations for electrochemical thin films. SIAM Journal on Applied Mathematics, 65(5), 1463–1484. https://doi.org/10.1137/040609938 [pdf]
  2. Chu, K. T., & Bazant, M. Z. (2005). Electrochemical thin films at and above the classical limiting current. SIAM Journal on Applied Mathematics, 65(5), 1485–1505. https://doi.org/10.1137/040609926 [pdf]
  3. Chu, K. T., & Bazant, M. Z. (2006). Nonlinear electrochemical relaxation around conductors. Phys. Rev. E, 74(1), 011501. https://doi.org/10.1103/PhysRevE.74.011501 [pdf]
  4. Chu, K. T., & Z., B. M. (2007). Surface Conservation Laws at Microscopically Diffuse Interfaces. Journal of Colloid and Interface Science, 315(1), 319–329. https://doi.org/10.1016/j.jcis.2007.06.024 [pdf]