Temperature adaptive self-regenerating ionic thermoelectric cycles for time domain thermal energy harvesting
Qikai Li, Yu Mao, Chunlin Pang, Xinya Wu, Shuai‐Hua Wang, Huan Li, Yupeng Wang, Weishu Liu, Shien‐Ping Feng
Abstract
The rising demand for sustainable energy solutions has promoted significant interest in ionic thermoelectric materials, which convert low-grade waste heat into electrical energy through spatial temperature gradients. However, diurnal temperature variations, which offer potential for location-independent time-domain thermal energy, remain largely unexplored. To overcome the challenges of harvesting spatially limited thermal energy, this study presents an ionic thermoelectric cycle (t-ITC) designed for time-domain thermal energy harvesting, incorporating two gels with contrasting temperature coefficients. A temperature-adaptive self-regeneration (TASR) strategy is proposed to set the critical regeneration temperature (TCR) at the midpoint of temperature fluctuations, facilitating long-term device operation. The regeneration criteria are defined as neutralization of the electrochemical potential difference between separated cells, and a method based on shared counter-ion self-balancing is introduced. Employing a polyacrylamide-polyvinylpyrrolidone (PAM-PVP) matrix with KI3/KI and K3Fe(CN)6/K4Fe(CN)6 redox couples, both utilizing the same counter-ion K+ for regeneration, the t-ITC device attains a peak energy density of 3.28 kJ m–2 per cycle and a relative Carnot efficiency of 8.39% with 70% heat recuperation, under cycling conditions between 60 °C and 10 °C. This work highlights the potential of t-ITC devices for global-scale time-domain thermal energy on a global scale, across diverse environments, such as hot deserts and cold plateaus. The authors present a PAM-PVP hydrogel ionic thermoelectric device using KI3/KI and K3Fe(CN)6/K4Fe(CN)6 redox couples to harvest time-domain thermal energy without external charging, reaching 4% relative Carnot efficiency from 60 °C to 10 °C.