  When two electrolyte-immersed electrodes have different temperatures, a
voltage $\Delta \psi$ can be measured between them. This electrolyte Seebeck
effect is usually explained by cations and anions flowing differently in
thermal gradients. However, our molecular dynamics simulations of aqueous
electrolytes reveal a large temperature-dependent potential drop $\chi$ near
blocking electrodes caused by water layering and orientation. The difference in
surface potentials at hot and cold electrodes is more important to the Seebeck
effect than ionic thermodiffusion, $\Delta \psi \sim \chi_{\rm hot}-\chi_{\rm
cold}$.
