Reversibly tuning thermopower enabled by phase-change electrolytes for low-grade heat harvesting

Thermodiffusion-based thermoelectrochemical cells have become one of the promising candidates for self-power supply by efficiently harvesting low-grade heat. However, fulfilling continuous energy output is still challenging because of the non-reciprocating motion of cations and anions during diffusion by adopting a steady heat source. Herein, we propose a moderate-concentration phase-change electrolyte for tuning the thermodiffusion process and the thermopower. Interestingly, the dominant ion can be alternated between cations and anions only by operando regulation of the physical state of the as-designed electrolyte, enabling the reversible polarization of devices from the p-type to the n-type with a tunable thermopower from 3.2 to −2.1 mV K−1. Moreover, the correlation of phase transition behaviors, solvation structures, and thermoelectrochemical performances is investigated. As a proof-of-concept, a prototype module consisting of n-type and p-type units connected in series displays high sensitivity and stability for long-term power generation under light irradiation, demonstrating the potential of phase-change electrolytes in energy-related applications.