High‐performance p‐n Thermocells by Interface Optimization Based on Liquid Metal for Powering Wearable Devices

Abstract Using body heat as a sustainable energy source through the thermoelectric effect to power wearable electronics is promising. Ionic thermoelectric materials based on the thermogalvanic effect can generate stable voltage under low‐temperature differences, but their low thermopower and poor contact interface with electrodes hinder practical use. In this study, strong chaotropic salts are utilized to modify the solvation shells of ions, increasing the thermopower of the p‐type redox couple [Fe(CN)₆]³⁻/[Fe(CN)₆]⁴⁻ to 3.98 mV K⁻¹. Additionally, Arrhenius acid is introduced to inhibit the deprotonation of the n‐type redox couple Fe³⁺/Fe²⁺, enhancing the thermopower to −2.29 mV K⁻¹. Liquid metal electrodes, with excellent deformability and hydrogen bonding with hydrogel surfaces, effectively reduce the resistance of thermocells. Thus, a pair of p‐n thermocells achieve a voltage output of 118 mV and a current density of 4.5 A m⁻², with a maximum power density of 0.11 W m⁻² (ΔT = 5 K). A wearable device integrated with 18 p‐n pairs can generate a voltage of 2.2 V from body heat and continuously power portable electronic devices. This work demonstrates the promising potential of wearable self‐powered devices for practical daily applications.