Theories describing the electrochemical double layer have long presented challenges to researchers, yet remain important understanding electrochemical processes. Many of these challenges stem from the multiscale nature of electrochemical interfaces where excess carrier concentrations, whether ions in electrolytes or electrons/holes in semiconductors, can extend 10s of nanometers into the bulk. It is expensive and difficult to capture the full interface with atomistic methods whereas continuum-level mean field approaches often face issues with adequately capturing steric and other physiochemical aspects of the carriers. In both cases, there are issues with the definition of potentials which are experimentally relevant and self-consistent with the associated effects on the participating media [1].

Nevertheless, numerous physiochemical effects that include but are not limited to specific adsorption, dielectric decrement, specific adsorption, osmotic pressures, solvent mixing, and ionic correlations have been identified and described [1-3]. And corrections to mean field theories, such as through the perturbation for finite sized ions, have been put forth to improve predictability [4-6].

In this talk, a quasi-Fermi perspective on transport and space charge near interfaces will be presented. The approach put forward simplifies analysis for electrolytic solutions including for transport at dissimilar interfaces. A perspective on the potential scale and ties to absolute electrode potentials will be presented. The approach will be demonstrated with bipolar membrane electrolyte and photoelectrochemical conversion interfaces.

References

[1.] A. Baskin and D. Prendergast, Improving Continuum Models to Define Practical Limits for Molecular Models of Electrified Interfaces, J Electrochem Soc 164 (2017), E3438-E3447.

[2.] D. Ben-Yaakov, D. Andelman, D. Harries and R. Podgornik, Beyond standard Poisson-Boltzmann theory: ion-specific interactions in aqueous solutions, J Phys-Condens Mat 21 (2009).

[3.] D. Ben-Yaakov, D. Andelman and R. Podgornik, Dielectric decrement as a source of ion-specific effects, J Chem Phys 134 (2011).

[4.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. II. Modified Poisson-Nernst-Planck equations, Phys Rev E 75 (2007).

[5.] M. S. Kilic, M. Z. Bazant and A. Ajdari, Steric effects in the dynamics of electrolytes at large applied voltages. I. Double-layer charging, Phys Rev E 75 (2007).

[6.] M. Z. Bazant, Theory of Chemical Kinetics and Charge Transfer based on Nonequilibrium Thermodynamics, Accounts Chem Res 46 (2013), 1144-1160.