Improved Ionic Thermoelectric Performance of Adhesive and Self‐Healing Cationic High‐Entropy Gel Thermocell

Abstract Gel thermocell can directly convert heat into electricity by ions as energy carriers, capable of low‐grade heat harvesting. However, ionic thermoelectric performance, including ionic thermopower, output power density, and energy density, needs to be significantly improved to meet practical applications. To date, it still lacks an effective strategy to focus on gels to achieve the overall high performance. Herein, an adhesive and self‐healing cationic high‐entropy gel (CHEG) G‐FeCN 4−/3− ‐K + ‐Na + ‐Li + ‐Gdm + ‐Cs + in a multi‐ion cooperative chemical environment has been designed by the interaction between multications and anions, improving the entropy change of redox reaction, exchange current density, and ionic conductivity, thereby achieving an overall high ionic thermoelectric performance. The CHEG thermocell using the synergy of thermogalvanic and thermodiffusion effects showed a total ionic thermopower of 41 mV K −1 with 2.3 mV K −1 for the former, and delivered a maximum output power density of 14.3 mW m −2 K −2 and an energy density of 4.5 J m −2 K −2 . In addition, an ultrahigh maximum output power density of 4.13 mW m −2 K −2 was obtained in the CHEG device that was assembled by connecting four thermocells in series, which could realize electrocatalytic degradation of rhodamine B. This work demonstrates a feasible way to design high‐performance ionic thermoelectric gels and provides a new application in water pollution treatments.