Multilayer Electrode Strategy Shorten Thermal Charging Time and Boost Energy Output in Gelatin‐Based i‐TE Cells

Abstract Gel‐based ionic thermoelectric (i‐TE) cells provide alternative thermal energy harvesting from the environment, showing obvious advantages in voltage matching for self‐powered Internet‐of‐Things (IoT) sensors. However, the gel‐based i‐TE cells always suffer a long thermal charging time and poor output power performance. Herein, a multilayer electrode engineering strategy is proposed from the device‐design level, aiming to decrease the ions' diffusion distance, increase the electrode surface area, and facilitate the ions' reaction and recovery process. The thermal charging time is shortened from 27 to 8 min as the electrode layers increase from 2 to 8. An ultrahigh instantaneous power density of 15.8 mW m −2 K −2 and 2 h output energy density ( E 2h ) of 403 J m −2 are achieved in an 8‐layer electrode i‐TE cell. Finally, A flexible and wearable i‐TE device with 20 units is demonstrated to generate a remarkable voltage of 3.8 V and output power of 282 µW by harvesting the human body heat. This work provides a feasible and effective route to design the i‐TE device, hopefully promoting its practical power generation application.