Harnessing widely available low-grade thermal energy, such as industrial waste heat, geothermal sources, and daily temperature variations, is crucial for sustainable energy development. However, traditional thermoelectric conversion relies on spatial temperature gradients, making it challenging to utilize time-varying sources like diurnal temperature cycles.

Professor Weishu Liu’s research team from the Department of Materials Science and Engineering at the Southern University of Science and Technology (SUSTech), in collaboration with Professor Shien-Ping Feng from the City University of Hong Kong (CityUHK), has developed a novel quasi-solid-state ionic thermoelectric (i-TE) cyclic system for harvesting time-domain thermal energy.

Their findings have been published in the prestigious journal Nature Communications, under the title “Temperature-Adaptive Self-Regenerating Ionic-Thermoelectric Cycles for Time-Domain Thermal Energy Harvesting.”

The team’s innovative t-ITC system overcomes the limitation of conventional thermoelectric devices that rely on fixed spatial temperature gradients by employing two gel electrolytes with opposite temperature coefficients, enabling efficient and continuous energy harvesting under cyclic temperature conditions. In addition, they proposed a temperature-adaptive self-regeneration (TASR) strategy that that allows the operation time-domain temperature range to adapt to changing environmental conditions (Figure 1).

The system uses a polyacrylamide–polyvinylpyrrolidone (PAM–PVP) double-network hydrogel loaded with KI₃/KI and K₃Fe(CN)₆/K₄Fe(CN)₆ redox couples, sharing K⁺ as a common counterion. By precisely tuning the critical regeneration temperature between daily high and low extremes, the device automatically resets its voltage each cycle, ensuring long-term operational stability.

Figure 1. The operation mechanism of the TASR strategy in the T-ITC system

Under a temperature cycle between 60°C and 10°C, the t-ITC achieved a high energy density of 3.28 kJ m^-2 per cycle and a relative Carnot efficiency of 8.39% (assuming 70% heat recovery). The device retained over 90% of its energy output after 300 cycles, demonstrating excellent cyclic stability and environmental adaptability (Figure 2).

Figure 2. The performance of time-domain temperature difference harvesting and energy conversion efficiency of t-ITC device

The team further developed a flexible 5×5 integrated module, which successfully powered LED arrays and digital thermohygrometers under simulated extreme environments, such as deserts and plateaus, confirming its potential for global time-domain thermal energy harvesting (Figure 3).

Figure 3. The practical demonstration of power generation of the integrated t-ITC module in various environments such as deserts and plateaus

Postdoctoral fellow Qikai Li at CityUHK (formerly a Ph.D. graduate of SUSTech and HKU) and Ph.D. student Yu Mao from SUSTech are co-first authors of the paper. Professor Weishu Liu and Professor Shien-Ping Feng are the corresponding authors.

Paper link: https://doi.org/10.1038/s41467-025-63645-2

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