Highly Antifreezing Thermogalvanic Hydrogels for Human Heat Harvesting in Ultralow Temperature Environments.

Thermogalvanic hydrogels have been quickly developed and are widely used in thermal energy harvesting. However, the freezing behaviors of thermogalvanic hydrogels at subzero temperatures greatly limit their practical applications. Herein, we design an antifreezing thermogalvanic hydrogel based on [Fe(CN)6]3-/4- ions for thermoelectric power generation in ultralow temperature environments. The antifreezing thermogalvanic hydrogels show excellent flexibility at -80 °C owing to the hydrogen bonding between ethylene glycol and water molecules. Even after 500 cyclic tensile strains, the thermogalvanic hydrogels can still maintain excellent mechanical stability, and the Seebeck coefficient is as high as 1.43 mV/K, corresponding to a large retention rate of ∼95%. Moreover, we demonstrate a wearable thermoelectric shoe based on antifreezing thermogalvanic hydrogels for harvesting human thermal energy in a simulated winter environment of -30 °C, and the electricity can drive a green LED. This work provides important guidance for the design and optimization of antifreezing thermogalvanic hydrogels.

Multifunctional Superelastic Graphene-Based Thermoelectric Sponges for Wearable and Thermal Management Devices.

Power generation through harvesting human thermal energy provides an ideal strategy for self-powered wearable design. However, existing thermoelectric fibers, films, and blocks have small power generation capacity and poor flexibility, which hinders the development of self-powered wearable electronics. Here, we report a multifunctional superelastic graphene-based thermoelectric (TE) sponge for wearable electronics and thermal management. The sponge has a high Seebeck coefficient of 49.2 µV/K and a large compressive strain of 98%. After 10 000 cyclic compressions at 30% strain, the sponge shows excellent mechanical and TE stability. A wearable sponge array TE device was designed to drive medical equipment for monitoring physiological signals by harvesting human thermal energy. Furthermore, a 4 × 4 array TE device placed on the surface of a normal working Central Processing Unit (CPU) can generate a stable voltage and reduce the CPU temperature by 8 K, providing a feasible strategy for simultaneous power generation and thermal management.

Giant Room-Temperature Electrocaloric Effect of Polymer-Ceramic Composites with Orientated BaSrTiO3 Nanofibers.

Cooling based on the electrocaloric effect (ECE) is a promising solution to environmental and energy efficiency problems of vapor-compression refrigeration. Ferroelectric polymer-ceramics nanocomposites, integrating high electric breakdown of organic ferroelectrics and large EC strength of ceramics, are attractive EC materials. Here, we tuned the orientation of Ba0.67Sr0.33TiO3 nanofibers (BST nfs) in the P(VDF-TrFE-CFE) polymer. When the nfs were aligned parallel to the field, a ΔT of 11.3 K with an EC strength of 0.16 K·m/MV was achieved in the blends. The EC strength not only surpasses advanced nanocomposites but also is comparable to ferroelectric ceramics. The simulation indicates that a significantly higher electric field is concentrated in polymer regions around the ends of the orientated nfs, contributing to easier flipping of polymer chains for large ECE. This work provides a new method to obtain large ECE in composites for next-generation refrigeration.

High-Performance Coaxial Asymmetry Fibrous Supercapacitors with a Poly(vinyl alcohol)-Montmorillonite Separator.

Fibrous supercapacitors have garnered great interest from researchers because of their large electrode/electrolyte interface area, short ion transport path, and high flexibility. However, obtaining a thin gel electrolyte interlayer with a high ion transport rate and uniform thickness is still challenging. Here, we proposed an efficient wet-spinning technique to fabricate uniform polyvinyl-montmorillonite tubular layers for the preparation of a high-performance coaxial asymmetry fibrous supercapacitor (AFSC). The coaxial AFSC shows ultrahigh energy densities in the range of 2.86-4.04 µW h cm-2 at power densities of 0.16-1.61 mW cm-2 while maintaining a long cycling life (94% retention even after 20 000 cycles). After charging at a constant voltage of 2.4 V for 30 s, the flexible watchband which is composed of three series-connected AFSCs could power a commercial electronic watch for more than 2 min. This work provides a universal strategy to fabricate high-performance and wearable energy storage devices.

Electronic cooling and energy harvesting using ferroelectric polymer composites.

Thermal management emerges as a grand challenge of next-generation electronics. Efforts to develop compact, solid-state cooling devices have led to the exploration of the electrocaloric effect of ferroelectric polymers. Despite recent advances, the applications of electrocaloric polymers on electronics operating at elevated temperatures remain essentially unexplored. Here, we report that the ferroelectric polymer composite composed of highly-polarized barium strontium titanate nanofibers and electron-accepting [6,6] phenyl-C61-butyric acid methyl ester retains fast electrocaloric responses and stable cyclability at elevated temperatures. We demonstrate the effectiveness of electrocaloric cooling in a polymer composite for a pyroelectric energy harvesting device. The device utilizes a simulated central processing unit (CPU) as the heat source. Our results show that the device remains operational even when the CPU is overheated. Furthermore, we show that the composite functions simultaneously as a pyroelectric energy converter to harvest thermal energy from an overheated chip into electricity in the electrocaloric process. This work suggests a distinct approach for overheating protection and recycling waste heat of microelectronics.

An Active Pixel-Matrix Electrocaloric Device for Targeted and Differential Thermal Management.

More than 55% of electronic failures are caused by damage from localized overheating. Up to now, there is still no efficient method for targeted temperature control against localized overheating. Although some existing thermal management devices handle this issue by full coverage cooling, it generates a lot of useless energy consumption. Here, a highly efficient pixel-matrix electrocaloric (EC) cooling device is reported, which can realize a targeted and differential thermal management. The modified poly(vinylidene fluoride-tertrifluoroethylene-chlorofluoroethylene) reaches a large adiabatic temperature change of 7.8 K and is more suitable for thermal transfer and electrostatic actuation at high frequencies. All active pixels in the EC cooling device exhibit a stable temperature span of 4.6 K and a heat flux of 62 mW cm-2 , which is more than twice that of the one-layer EC device. Each refrigeration pixel can be independently controlled and effectively cooled down the localized overheating site(s) in situ. The surface temperature of the simulated central processing unit decreases by 33.2 K at 120 s after applying this EC device. Such a compact, embeddable, low cost, and active solid-state pixel-matrix cooling device has great potential for localized overheating protection in microelectronics.

Strong Tough Thermogalvanic Hydrogel Thermocell With Extraordinarily High Thermoelectric Performance.

Thermocells can continuously convert heat into electricity, and they are widely used to power wearable electronic devices. However, they have a risk of leakage and poor mechanical properties. Although quasi-solid ionic thermocells can overcome the issue of electrolyte leakage, the trade-off between their excellent mechanical properties and high thermopower remains a major challenge. In this study, stretching-induced crystallization and the thermoelectric effect are combined to propose a high-strength quasi-solid stretchable polyvinyl alcohol thermogalvanic thermocell (SPTC) with a large tensile strength of 19 MPa and high thermopower of 6.5 mV K-1 . The SPTC exhibits a high stretchability of 1300%, ultrahigh toughness of 163.4 MJ m-3 , and high specific output power density of 1969 µW m-2  K-2 . These comprehensive properties are superior to those of previously reported quasi-solid stretchable thermogalvanic thermocells. The use of SPTC-based systems in wearable devices for energy-autonomous strain sensors and health monitoring is demonstrated. This can facilitate the rapid implementation of sustainable wearable electronics in the Internet of Things era.

Self-sustaining personal all-day thermoregulatory clothing using only sunlight.

The human body must stay within a certain temperature range for comfort and safety. However, challenges for thermoregulatory clothing exist for harsh application scenarios, such as full day/night cycles, frigid polar regions, and space travel. We developed a flexible and sustainable personal thermoregulatory clothing system by integrating a flexible organic photovoltaic (OPV) module to directly acquire energy from sunlight and bidirectional electrocaloric (EC) devices. The flexible OPV-EC thermoregulatory clothing (OETC) can extend the human thermal comfort zone from 22°-28°C to 12.5°-37.6°C with a fast thermoregulation rate. The low energy consumption and high efficiency of the EC device allows for 24 hours of controllable and dual-mode thermoregulation with 12 hours of sunlight energy input. This self-powered wearable thermoregulatory platform has a simple structure, compact design, high efficiency, and strong self-adaptability with sunlight as the sole energy source.