Fig. 1. Schematic images of an open-circuit thermocell containing redox molecules (e.g., Fc⁺(ferrocenium)/Fc (ferrocene)) and charged nanoparticles. Left panel: Initial state immediately after the application of a temperature gradient where NP concentration is still homogeneous. Right panel: Steady state established after the completion of thermodiffusive movements of all charged species. Note that in the open-circuit configuration, there is no electric current flowing into and from the thermocell. Therefore both reduction and oxidation reactions occur at the hot and cold electrodes. In this example, the charged NPs move toward the cold region of the fluid, corresponding to a positive S_T. See the text for more explanation.