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Compact solid‐state refrigeration systems that offer a high specific cooling power and a high coefficient of performance (COP) are desirable in a wide range of applications where efficient and localized heat transfer is required. Here, a double‐unit electrocaloric (EC) polymer‐based refrigeration device with high intrinsic thermodynamic efficiency is demonstrated using a flexible EC polymer film with improved performance by doping plasticizer and an electrostatic actuation mechanism. The double‐unit refrigeration device achieves a large temperature span of 4.8 K, which is 71% higher than that of the single‐unit device. A specific cooling power of 3.6 W g−1 and a maximum COP of 8.3 for the cooling device are produced. The surface temperature of a central processing unit (CPU) cooled by an active EC device is 22.4 K lower than that of the CPU cooled in air. The highly efficient and compact EC cooling device demonstrated here not only leapfrogs the performance of existing solid‐state cooling technologies, but also brings solid state cooling closer to reality for a variety of practical applications that require compact or mechanically flexible refrigeration. [ABSTRACT FROM AUTHOR]

While stretchable micro‐supercapacitors (MSCs) have been realized, they have suffered from limited areal electrochemical performance, thus greatly restricting their practical electronic application. Herein, a facile strategy of 3D printing and unidirectional freezing of a pseudoplastic nanocomposite gel composed of Ti3C2Tx MXene nanosheets, manganese dioxide nanowire, silver nanowires, and fullerene to construct intrinsically stretchable MSCs with thick and honeycomb‐like porous interdigitated electrodes is introduced. The unique architecture utilizes thick electrodes and a 3D porous conductive scaffold in conjunction with interacting material properties to achieve higher loading of active materials, larger interfacial area, and faster ion transport for significantly improved areal energy and power density. Moreover, the oriented cellular scaffold with fullerene‐induced slippage cell wall structure prompts the printed electrode to withstand large deformations without breaking or exhibiting obvious performance degradation. When imbued with a polymer gel electrolyte, the 3D‐printed MSC achieves an unprecedented areal capacitance of 216.2 mF cm−2 at a scan rate of 10 mV s−1, and remains stable when stretched up to 50% and after 1000 stretch/release cycles. This intrinsically stretchable MSC also exhibits high rate capability and outstanding areal energy density of 19.2 µWh cm−2 and power density of 58.3 mW cm−2, outperforming all reported stretchable MSCs. [ABSTRACT FROM AUTHOR]

The fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO2) nanoparticles on Ti3C2Tx MXene nanosheets. The resulting RuO2@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO2 nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO2@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm−3 at 1 mV s−1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm−3 at 2000 mV s−1), outstanding flexibility, remarkable energy (13.5 mWh cm−3) and power density (48.5 W cm−3). [ABSTRACT FROM AUTHOR]

The availability and the high-efficiency of the device for cooling the central processing unit provides a unique option for thermal management of microcircuits in the future. Electrocaloric effect, electrostatic actuating, high efficiencies, microelectronics cooling, solid-state cooling Keywords: electrocaloric effect; electrostatic actuating; high efficiencies; microelectronics cooling; solid-state cooling EN electrocaloric effect electrostatic actuating high efficiencies microelectronics cooling solid-state cooling 1 1 1 04/10/21 20210408 NES 210408 In article number 2003771, Rujun Ma and co-workers report a highly efficient double-unit solid-state refrigeration device based on two-layer modified electrocaloric polymer stacks actuated by electrostatic forces. [Extracted from the article]

Keywords: 3D printing; MXene; stretchable micro-supercapacitor; thick electrode; wearable electronics EN 3D printing MXene stretchable micro-supercapacitor thick electrode wearable electronics 1 1 1 04/16/20 20200414 NES 200414 In article number 1903794, Jiajie Liang and co-workers present a strategy for the 3D-printing and unidirectional freezing of a nanocomposite gel composed of MXene, MnO SB 2 sb nanowires (NWs), AgNWs, and C60 to construct intrinsically stretchable micro-supercapacitors (MSCs) with thick and honeycomb-like porous interdigitated electrodes. The 3D-printed MSC exhibits high areal capacitance of 216.2 mF cm SP -2 sp at 10 mV s SP -1 sp , and remains stable when stretched up to 50%. 3D printing, MXene, stretchable micro-supercapacitor, thick electrode, wearable electronics. [Extracted from the article]