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Recently, low‐temperature wearable strain sensors, referring to those working at sub‐zero temperatures, are attracting increasing attentions. However, the fabrication of low‐temperature strain sensors with large working ranges, high sensitivity, and good stability remains a major challenge. In this study, a novel low‐temperature wearable strain sensor is fabricated by depositing the silver nanoplates (Ag NPs)/carbon nanotubes (CNTs) composite onto a cured silicone (DS) substrate that is constructed by using a 3D printing technology. The synergistic effect of the Ag NPs with positive temperature coefficient of resistance (TCR) and the CNTs with negative TCR enable the Ag NPs/CNTs/DS strain sensor's TCR value (−1.16 × 10−5 K−1) to approach zero. The Ag NPs/CNTs/DS strain sensor demonstrates a high gauge factor over a large working range (0–100%) and fast response and recovery rates. Simultaneously, the Ag NPs/CNTs/DS strain sensor displays outstanding reproducibility and long‐term stability at −40 °C as well as excellent temperature cycling resistance under cyclic temperature of −40 to 60 °C. The Ag NPs/CNTs/DS strain sensor is further validated by incorporating into a wireless sensing system for remotely monitoring various human activities at −40 °C. This work provides wearable strain sensors for monitoring human‐machine interaction under low‐temperature condition. [ABSTRACT FROM AUTHOR]

The exploration of wearable strain sensors with new characteristics and functionalities could fuel the rapid development of Internet of Things (IoT) technology for the healthcare industry. Herein, we present a flexible, waterproof, and highly sensitive strain sensor that is fabricated by integrating graphene (G), carbon black (CB), and polydimethylsiloxane (PDMS) into the three-dimensional (3D) framework of commercial Ni sponge via a simple, cost-effective, and scalable drop-coating method. The G/CB/Ni strain sensor demonstrates good flexibility, high sensitivity (gauge factor of 138 at 16% strain), and long-term stability. The G/CB/Ni sensor could not only precisely monitor subtle human motions such as pulse, blinking, and swallowing, but it also shows potential in testing muscle strength. A wireless sensor system that consists of the G/CB/Ni strain sensor, an STM32 controller, a ZigBee module, and a portable power source is assembled, which enables remote transmission of data collected from the sensor to the computer wirelessly. The G/CB/Ni sensor also exhibits excellent waterproofness and can be safely used to monitor human motions under humid conditions and in water. The G/CB/Ni strain sensor featuring flexibility, high sensitivity, and waterproofness has great potential for applications in healthcare management, personal rehabilitation training, and outdoor motion monitoring. [ABSTRACT FROM AUTHOR]

Abstract: Hierarchical nanostructures with highly exposed active surfaces for high‐performance pseudocapacitors have attracted considerable attention. Herein, a one‐step growth of (Ni xCo1−x)9Se8 solid solution series in various conductive substrates as advanced electrodes for flexible, foldable supercapacitors is developed. The formation of (NixCo1−x)9Se8 solid solution is confirmed by Vegard's law. Interestingly, the as‐grown (NixCo1−x)9Se8 solid solution series spontaneously crystallized into nanodendrite arrays with hierarchical morphology and fractal feature. The optimized (Ni0.1Co0.9)9Se8 nanodendrites deliver a specific capacitance of 3762 F g−1 at a current density of 5 A g−1 and remains 94.8% of the initial capacitance after 5000 cycles, owing to the advantage from fractal feature with numerous exposed ( 01 1 ¯) surface as well as fast ion diffusion. The as‐assembled flexible (Ni0.1Co0.9)9Se8@carbon fiber cloth (CFC)//PVA/KOH//reduced graphene oxide@CFC device exhibits an ultrahigh energy density of 17.0 Wh kg−1@ 3.1 kW kg−1, outperforming recently reported pseudocapacitors based on nickel‐cobalt sulfide and selenide counterparts. This study provides rational guidance toward the design of fractal feature with superior electrochemical performances due to the significantly increased electrochemical active sites. The resulting device can be easily folded, pulled, and twisted, enabling potential applications in high‐performance wearable and gadget devices. [ABSTRACT FROM AUTHOR]

Hierarchical nanostructures with highly exposed active surfaces for use in high-performance pseudocapacitors have attracted considerable attention. Herein, we developed a one-step method for the in situ growth of (NH4)2V10O25·8H2O urchin-like hierarchical structures on highly conductive nickel foam substrates for use as advanced electrodes for all-solid-state asymmetric supercapacitors. The in situ growth of (NH4)2V10O25·8H2O urchin-like hierarchical structures delivers a specific capacitance of 1530 F g−1 at a current density of 1.5 A g−1, and retains 95.1% of the initial capacitance after 10 000 cycles, owing to the advantages of the urchin-like hierarchical structure such as more active sites for electrochemical reactions, as well as a shortened diffusion length for the charge carriers due to a binder-free effect, which exceeds that of most recently reported vanadates and polyvanadates. The as-assembled all-solid-state (NH4)2V10O25·8H2O@Ni//PVA/KOH//RGO@Ni device exhibits a comparable capacity of 92.2 F g−1 at a current density of 0.4 A g−1 and excellent cycling performance through 5000 cycles. Our study provides rational guidance toward the design of novel hierarchical nanostructures of polyvanadate for solid-state supercapacitors with superior electrochemical performances in long-term cycling stability and high energy density. [ABSTRACT FROM AUTHOR]

Intrinsically p-type conductivity and a wide bandgap of ≈3.6 V endow inorganic delafossite CuGaO2 with great promise for fabricating high-performance UV photodetectors. Nevertheless, CuGaO2-based optoelectronic devices hindered because the intrinsic direct transitions are symmetry forbidden in CuGaO2. This study reports a large-area synthesis of 'CuGaO2 nanoplate/ZnS microsphere' heterostructure arrays using a facile solution-based strategy associated with an oil/water interfacial self-assembly approach. It is found that a large number of ZnS microspheres with a polycrystalline structure grow on the top surface of CuGaO2 hexagonal platelets through Ostwald ripening mechanism, forming high-density p-n heterojunctions. A parabolic dependence between the size of ZnS microsphere and the growth time is confirmed in this growth. The UV light adsorption of the heterostructure CuGaO2/ZnS thin film is two times higher than that of the pristine CuGaO2 thin film. Furthermore, the as-designed 'CuGaO2 nanoplate/ZnS microsphere' heterostructure arrays exhibit enhanced photoresponse properties. This work offers a new insight into the rational design of optoelectronic devices from the synergetic effect of p-type 2D nanoplates as well as n-type nanostructures such as ZnS, ZnO, CdS, and CdO. [ABSTRACT FROM AUTHOR]

A green route is designed to gain a clear idea of growth mechanism of complex VO2 (B) hierarchical microstructures, since this kind of metal oxide has various metastable phases due to their diverse valence states. Three-dimensional (3D) uniform flower-like VO2 (B) hierarchical microstructure has thus been assembled with the interleaving nanoplates, which are about 25 nm in thickness and well-crystallized in structure with {114} planes as the dominant surfaces. Results of the systemic control experiments revealed that formation of the flower-like VO2 (B) results from a fast nucleation-growth process, where ethylene glycol (EG) not only acts as a green solvent and reductive agent, but also plays a key role in self-assembly of the resulted VO2 (B) hierarchical microstructures. Hydroxyl amount on the solvent molecule is crucial in formation and shape control of VO2 (B) hierarchical microstructures. Result of this work would be helpful to understand the growth mechanism of complex three-dimensional hierarchical superstructures of different metal oxides, which is very important to material science and inorganic synthetic chemistry. [ABSTRACT FROM AUTHOR]

Layered niobium phosphates have been considered very promising energy storage materials because of their high theoretical operating voltage window and the rich oxidation states of niobium. However, their development has been stymied by the phase‐controlled synthesis due to the insolubility of niobium sources except in concentrated hydrofluoric (HF) acid systems. Herein, a new avenue is opened for layered acid niobium phosphate (2NbOPO4·H3PO4·H2O) synthesis in a mild oxalic acid system. Taking advantage of this strategy, in situ growth of sub‐5 nm 2NbOPO4·H3PO4·H2O nanosheet (NPene) arrays on conductive carbon fiber cloth (CFC) substrates is achieved as self‐standing electrodes for solid‐state supercapacitors. Interestingly, the NPene@CFC electrode exhibits a typical cation (H+ or Li+)‐intercalation kinetics with a wide potential window of 0–1.0 V in aqueous electrolytes. Given the wide potential window and highly exposed active surface, the solid‐state asymmetric supercapacitors constructed from such a NPenes@CFC electrode display a high working potential of 2.0 V, energy density of 122.2 W h kg−1 at a power density of 589.7 W kg−1, cycle stability with a capacitance retention of 94.2% after 10 000 cycles, and also outstanding flexible and wearable characteristics. [ABSTRACT FROM AUTHOR]

Electrochromic (EC) energy storage devices that possess characteristics of energy storage and electrochromism are highly desirable and have increasingly attracted research interests, whilst devices that can be stretched or are flexible have received very little attention. Herein, we report a flexible and rechargeable aluminium (Al) ion EC battery (ECB), which consists of a WO 3 film as positive electrode, PET/ITO as substrate, Al sheet as negative electrode, aluminum trichloride (AlCl 3) aqueous solution as electrolyte, and absorptive glass mat (AGM) as electrolyte carrier and separator. The ECB exhibits a high specific capacity of 142 mAhg−1, while demonstrating reversible color transitions between white (bleached state) and dark blue (colored state) during the cyclic charge/discharge processes. Furthermore, the ECB can work at bending angles of 0-80° with a capacity retention of 92.3% after 40 bending cycles. The flexibility of the ECB is ascribed to the flexible, porous, and highly stable features of the AGM as well as the deformability of the PET/ITO substrate. The potential widow of the ECB can be largely enhanced by connecting small-sized ECBs internally in series while maintaining the energy density unchanged. The present study demonstrates that the ECB using the AGM as the electrolyte carrier and separator may have great potentials for the construction of both flexible, portable electronics and smart windows. A flexible and rechargeable electrochromic battery that possesses characteristics of energy storage, electrochromism, and deformability is assembled by using absorptive glass mat (AGM) as the electrolyte carrier and separator. Image 1 • The WO 3 films were deposited on the PET/ITO substrate using a magnetron sputtering method. • A flexible and rechargeable ECB was assembled with AGM as electrolyte carrier and separator. • The ECB exhibited high specific capacity (142 mAhg−1) and can work at bending angles of 0-80°. [ABSTRACT FROM AUTHOR]

The accelerated evolution of the Internet of Things has brought new challenges to the gas sensors, which are required to work persistently under harsh conditions, like high humidity. However, currently, it is quite challenging to solve the hindrance of the trade-off between gas-sensing performance and anti-humidity ability of the chemiresistive gas sensors. Herein, hydrophobic inorganic CeO 2 /SnO 2 heterostructure films were prepared by depositing the CeO 2 layers with a thickness of a few nanometers onto the SnO 2 film via a magnetron sputtering method. The sensors based on the CeO 2 /SnO 2 heterostructure films demonstrated excellent gas-sensing performance toward trimethylamine (TEA) with high response, wide detection range (0.04-500 ppm), low record detection limit (0.04 ppm), ideal reproducibility, and long-term stability, while concurrently possessing promising anti-humidity ability. A portable, wireless TEA-sensing system containing the CeO 2 /SnO 2 sensor was constructed to realize the real-time monitoring of trace concentration of the volatiles released from a fish. This work provides a novel strategy to prepare advanced chemiresistive gas sensors for humidity-independent detection of harmful gases and vapors and will accelerate their commercialization process in the field of food safety and public health.

Rechargeable aqueous Zn-ion batteries (ZIBs) have recently attracted much attention due to their low cost and superior safety. Unfortunately, their low capacity and poor cycle life still hinder their practical application. Here, we have developed a general synthesis strategy for ultrasmall spinel oxide nanodots (Mn 3 O 4 , CoMn 2 O 4 , MnCo 2 O 4.5 , Co 3 O 4 , and ZnMn 2 O 4 ) with abundant oxygen vacancies and highly active surface. Among them, 6.0-nanometer-sized Mn 3 O 4 nanodots deliver the best Zn-ion storage ability with a high reversible capacity of 386.7 mA h g -1 at 0.1 A g -1 , excellent rate performance, and a long-term stability of 500 cycles at 0.5 A g -1 . Taking advantage of the highly activated surficial atoms, shortened transfer pathway, and introduction of numerous oxygen vacancies, an ultrahigh Zn 2+ diffusion coefficient of 2.4 × 10 -10 cm 2 s -1 has been detected during the discharge process. This value is more than 2 orders of magnitude higher than that of other spinel oxide nanostructures in previous reports and also the highest one in all of the as-reported ZIB cathode materials to date. Our finding offers promising opportunities for the development of ZIB cathode materials with high energy density, long-term cycling stability, excellent flexibility, and wearability.

The integration of high flexibility, high energy density and wide voltage window for solid-state supercapacitors remains a big challenge to date. Herein, ultrathin CoSeO3·H2O nanoribbons (thickness: ∼14 nm) with typical pseudocapacitive behavior were synthesized in a high yield by a solution-based refluxing process. Freestanding CoSeO3·H2O ribbon/hydroxylated multi-walled carbon nanotube (HWCNT) paper could be fabricated through a vacuum-assisted filtration strategy owing to its ultrathin nature, ribbon-like morphology and inherent flexibility. Unexpectedly, an asymmetric supercapacitor constructed from this as-prepared CoSeO3·H2O/HWCNT hybrid paper exhibits a high 2.4 V voltage window as well as excellent rate capability and cycle performance. The energy density of this device is 132.3 W h kg-1 at 960 W kg-1 with a stable cycling ability of up to 10 000 cycles, which is superior to those of almost all previously reported asymmetric supercapacitors based on freestanding paper. Furthermore, this supercapacitor shows outstanding bendability and mechanical stability at different bending degrees from 0° to 180° with no changes in capacitive behavior. Our work provides new opportunities for developing high-performance asymmetric supercapacitors with high energy density, wide voltage window, and high flexibility in a novel CoSeO3·H2O system for potential applications including flexible displays, collapsible mobile phones, and wearable equipment.

The realization of high-performance anode materials with high capacity at fast lithiation kinetics and excellent cycle stability remains a significant but critical challenge for high-power applications such as electric vehicles. Two-dimensional nanostructures have attracted considerable research interest in electrochemical energy storage devices owing to their intriguing surface effect and significantly decreased ion-diffusion pathway. Here we describe rationally designed metastable CoSeO 3 ·H 2 O nanosheets synthesized by a facile hydrothermal method for use as a Li ion battery anode. This crystalline nanosheet can be steadily converted into amorphous phase at the beginning of the first Li + discharge cycling, leading to ultrahigh reversible capacities of 1100 and 515 mAh g -1 after 1000 cycles at a high rate of 3 and 10 A g -1 , respectively. The as-obtained amorphous structure experiences an isotropic stress, which can significantly reduce the risk of fracture during electrochemical cycling. Our study offers a precious opportunity to reveal the ultrafast lithiation kinetics associated with the rapid amorphization mechanism in layered cobalt selenide nanosheets.

Two-dimensional (2D) hydroxide nanosheets can exhibit exceptional electrochemical performance owing to their shortened ion diffusion distances, abundant active sites, and various valence states. Herein, we report ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O nanosheets (thickness ∼30 nm) which crystallize in a layered structure and exhibit a high specific capacitance of 3946.5 F g -1 at 3 A g -1 for an electrochemical pseudocapacitor. ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O was synthesized by a homogeneous precipitation method and spontaneously crystallized into 2D nanosheets in well-defined hexagonal morphology with crystal structure revealed by synchrotron X-ray powder diffraction data analysis. In situ growth of ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O nanosheet arrays on conductive Ni foam substrate was successfully realized. Asymmetric supercapacitors based on ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O nanosheets @Ni foam// PVA, KOH//reduced graphene oxide exhibits a high energy density of 114.8 Wh kg -1 at an average power density of 643.8 W kg -1 , which surpasses most of the reported all-solid-state supercapacitors based on carbonaceous materials, transition metal oxides/hydroxides, and MXenes. Furthermore, a supercapacitor constructed from ZnCo 1.5 (OH) 4.5 Cl 0.5 ·0.45H 2 O nanosheets@PET substrate shows excellent flexibility and mechanical stability. This study provides layered bimetallic hydroxide nanosheets as promising electroactive materials for flexible, solid-state energy storage devices, presenting the best reported performance to date.

Two-dimensional LDH nanosheets recently have generated considerable interest in various promising applications because of their intriguing properties. Herein, we report a facile in situ nucleation strategy toward in situ decorating monodispersed Ni-Fe LDH ultrafine nanosheets (UNs) on graphene oxide template based on the precise control and manipulation of LDH UNs anchored, nucleated, grown, and crystallized. Anion-exchange behavior was observed in this Ni-Fe LDH UNs@rGO composite. The Ni-Fe LDH UNs@rGO electrodes displayed a significantly enhanced specific capacitance (2715F g -1 at 3 A g -1 ) and energy density (82.3 Wh kg -1 at 661 W kg -1 ), which exceeds the energy densities of most previously reported nickel iron oxide/hydroxides. Moreover, the asymmetric supercapacitor, with the Ni-Fe LDH UNs @rGO composite as the positive electrode material and reduced graphene oxide (rGO) as the negative electrode material, exhibited a high energy density (120 Wh kg -1 ) at an average power density of 1.3 kW kg -1 . A charge transfer from LDH layer to graphene layer, which means a built in electric field directed from LDH to graphene can be established by DFT calculations, which can significantly accelerate reaction kinetics and effectively optimize the capacitive energy storage performance.