Temperature-gradient effects on electric double layer screening in electrolytes

Abstract

Temperature gradients drive asymmetric ion distributions via thermodiffusion (the Soret effect), leading to deviations from the classical Debye–Hückel potential. We introduce the Eastman entropy of transfer, S^±=α±kB for cations and anions, respectively, where kB is the Boltzmann constant, and analyze non-isothermal electric double layers in terms of the dimensionless Soret coefficients α±. Analytical solutions of the generalized Debye–Hückel equation show that, for α+=α−, the potential is exactly described by a modified Bessel function, while the marginal case α±=1 exhibits algebraic decay. An effective screening length, λeff, characterizes the near-electrode potential and increases with temperature, resulting in weaker screening on the hot side and stronger screening on the cold side for α±>−1. The differential capacitance is controlled by α± via λeff, with its minimum coinciding with the potential of zero charge (PZC) even in the presence of a temperature gradient. These findings highlight the fundamental coupling between electrostatics and thermodiffusion in non-isothermal electrolytes.