Contribution of convective transport to thermoelectricity in confined electrolyte solutions

Thermoelectricity in electrolyte-filled slit channels is studied using analytical methods for solving the combined Stokes, Nernst-Planck, Poisson, and heat transport equations. Next to a temperature gradient, the scenario considered accounts for a pressure gradient and an electric field applied along the channel. Closed-form analytical expressions are derived for the thermoelectric current and the thermovoltage expressed by the Seebeck coefficient, which are compared to numerical results obtained using the finite-element method. A special focus is put on convective charge transport resulting from thermoosmotic flow, which is massively augmented when considering nanochannels with a Navier-slip condition at the channel walls. The corresponding convective transport has a negligible effect on thermoelectricity in the regime of strong electric double layer overlap. By contrast, when the Debye length is much smaller than the channel width, convection can yield a massive increase of the thermoelectric current and power. This occurs in the case of a nonvanishing slip length, where thermoelectricity in the absence of convection is taken as a reference. Generally, it can be concluded that boundaries with a nonvanishing slip length can induce a significant thermoelectric response via convective transport even in cases where the Debye length is much smaller than any length scale of the compartments or channels in which the liquid is contained.