Efficient heat removal and recovery are two conflicting processes that are difficult to achieve simultaneously. Here, in this work, we pave a new way to achieve this through the use of a smart thermogalvanic hydrogel film, in which the ions and water undergo two separate thermodynamic cycles: thermogalvanic reaction and water-to-vapor phase transition. When the hydrogel is attached to a heat source, it can achieve efficient evaporative cooling while simultaneously converting a portion of the waste heat into electricity. Moreover, the hydrogel can absorb water from the surrounding air to regenerate its water content later on. This reversibility can be finely designed. As an applicative demonstration, the hydrogel film with a thickness of 2 mm was attached to a cell phone battery while operating. It successfully decreased the temperature of the battery by 20 °C and retrieved electricity of 5 μW at the discharging rate of 2.2 C.

of the temperature, quasi-Fermi levels of holes and electrons become closer to each other under some working conditions, [10,11] and the barrier height of the P-N junction decreases. [10] Moreover, the band gap of the P-N junction reduces and carrier transition from the valence band to conduction band becomes easier. [12,13] These effects bring adverse impacts on a variety of the energy conversion processes including photoelectric conversion, [14,15] electroluminescence, [16] voltage controlled tunneling, [10,17] and so on. Hence, efficiently dissipating the waste heat and maintaining the operation temperature at a low level is essentially important for the semiconductor devices to achieve efficient, reliable, and safe operations.A variety of heat dissipation approaches, including fin heat sink [18][19][20] and materials phase change, [21,22] have been applied to low down the operation temperature of the semiconductor devices. However, the low capacity of heat dissipation using these methods can hardly satisfy the requirements of high-energy-density devices. [23,24] Radiative cooling technology is promising and can passively dissipate heat from Earth into outer space, but it is only notable at night and the application is limited in outdoor situations. [25][26][27] Although active cooling devices such as forced air circulation [28,29] and hydro-cooling, [30,31] show high cooling performance, they have high energy consumptions and require complex auxiliary accessories (e.g., fans or water pumps). These limitations render them little adaptability in either large-scale or portable applications. Simply structured cooling technology with high capacity of heat dissipation remains a great challenge.Herein, we present a universal, simple, efficient, low-cost, and passive cooling strategy to adaptively low down the working temperature of the semiconductor devices. By using its evaporative cooling capability, a thin layer of lithium-and bromine enriched polyacrylamide (PAAm) hydrogel can efficiently dissipate the waste heat induced by nugatory carrier transport in the P-N junctions of a semiconductor device. When attaching the hydrogel onto the semiconductors, it will absorb the heat from the semiconductors, which results in the rising of the hydrogel temperature. And the water molecules will be released and quickly dissipate the waste heat into the ambient air due to the large latent heat of water. This can efficiently cool down the semiconductors for a better working efficiency. In the standby mode, the hydrogel can spontaneously harvest water from its High temperature brings adverse impacts on the energy efficiency, and even destroys a semiconductor device. Here, a novel and cost-effective strategy is proposed to boost the energy efficiency of semiconductor devices by using the self-adaptive evaporative cooling of a lithium-and bromine-enriched polyacrylamide hydrogel. Water inside the hydrogel can quickly evaporate to dissipate the waste heat generated by the nugatory carrier transport in the P-N junction. In dormancy,...

Coating metal-organic frameworks (MOFs) on metal substrates is an important research orientation in the applications of MOFs. However, the existing binder-based coating method needs repetitive operations and unavoidably plugs the pores of MOFs, resulting in a reduction of the adsorption capacity. Herein, a binder-free method is proposed to construct the MOF-on-metal structure. The well-intergrown polycrystalline Al-MOF layer on aluminum substrate is prepared by in situ synthesizing Al-based MOFs (MIL-96 and MIL-100) with aluminum ions from the dissolution of aluminum substrates. The morphology and chemical compositions of the MOF coating layer are systematically characterized, and a pH-controlled strategy is proposed to regulate the relative proportion of the hybrid MOFs. Importantly, the MOF-onmetal structure displays ultrahigh water adsorption capacity of 192.5 g m −2 , which is the highest of all reported desiccant-coated metal structures, and superior cycling stability. Further, the performance of a desiccant heat pump system utilizing MOF-on-metal structure is predicted, demonstrating that the operation period is 80% longer than a system with a binder-based silica gel coating, and the average dehumidification capacity can reach 8.36 g kg −1 dry air. In conclusion, the new method enables the formation of binder-free, low-cost, and high-performance MOF coating and has a broad prospect in energy-efficient adsorption-based applications.

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