Revisiting the thermodynamic mechanisms of thermoelectric energy conversion

The efficiency improvement of thermoelectric power generation requires a comprehensive understanding concerning its intrinsic energy conversion mechanism. Existing optimization strategies mainly focus on microscopic aspect, while the thermodynamic principles governing energy conversion and cycling remain underexplored. In this study, within the framework of classical equilibrium thermodynamic theory, the nature of the thermal cycle of thermoelectric power generation is affirmed, the physical model of the thermoelectric heat engine (THE) is polished, and the ideal cycle is constructed. Furthermore, with the aid of temperature-entropy (T-s) and chemical potential-quantity of matter (μ-n) diagrams, heat (q) and work (w) exchanges are clarified. The pathways of heat energy to chemical work and then to electrical work conversion in the system is then revealed, and thermodynamic enthalpy is extended to carrier enthalpy (h∗), leading to a revised expression of the energy conservation equation in thermoelectricity. Finally, the working medium suitable for the ideal cycle is discussed, along with the conception of equations of state and process equations for the working medium. An in-depth understanding of the thermoelectric conversion process from the perspective of thermal cycle not only reveals the underlying nature of thermoelectric effect but also offers new insights for designing advanced thermoelectric materials.