Temperature-adaptive self-regenerating ionic-thermoelectric cycles for time-domain thermal energy harvesting

This work develops a hydrogel-based ionic thermoelectric cycling device that harvest day-night temperature differences without external charging (t-ITC device). 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.