fig4

Figure 4. Working mechanism of TE, TGC and TDC. (A) A p-type TE with continuous hole flow driven by a temperature gradient. α is the thermopower, ΔV and ΔT are the potential difference and temperature difference between the hot and cold electrodes, respectively. V(T_H), V(T_L), T_H and T_L represent the potential and temperature at the hot and cold electrodes, respectively. (B) A p-type TGC with a redox reaction Ox + ne^- ↔ Red, producing a continuous current with electrochemical reactions occurring at the hot and cold electrodes. n is the number of electrons transferred in the reaction, F is the faradic constant, S_ox and S_red are the molar entropy of the redox species. (C) A p-type TDC with cations diffusing with higher mobility over anions, producing an intermittent current through the thermal charging and electrical discharging cycle. $$\hat{S}$$ is the Eastman entropy and D is ion diffusion coefficient. Note that the equation used to estimate the thermopower of TDCs is a theoretical example, which is derived from the simple system, e.g., a KCl aqueous electrolyte at ideal conditions.