Multiresponsive flexile sensors with strain, temperature, humidity, and other sensing abilities serving as real electronic skin (e‐skin) have manifested great application potential in flexible ...electronics, artificial intelligence (AI), and Internet of Things (IoT). Although numerous flexible sensors with sole sensing function have already been reported since the concept of e‐skin, that mimics the sensing features of human skin, was proposed about a decade ago, the ones with more sensing capacities as new emergences are urgently demanded. However, highly integrated and highly sensitive flexible sensors with multiresponsive functions are becoming a big thrust for the detection of human body motions, physiological signals (e.g., skin temperature, blood pressure, electrocardiograms (ECG), electromyograms (EMG), sweat, etc.) and environmental stimuli (e.g., light, magnetic field, volatile organic compounds (VOCs)), which are vital to real‐time and all‐round human health monitoring and management. Herein, this review summarizes the design, manufacturing, and application of multiresponsive flexible sensors and presents the future challenges of fabricating these sensors for the next‐generation e‐skin and wearable electronics.
Multiresponsive flexible sensors susceptible to various stimuli including strain, temperature, humidity, etc., have been rapidly emerging due to their great potential application in e‐skins. Thus, the recent progress of multiresponsive flexible sensors including the design strategies (the choices of sensing materials and mechanisms, and structure designs and fabrication methods), applications and prospects is reviewed to promote further development of e‐skins.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Ruthenium (Ru)‐based catalysts, with considerable performance and desirable cost, are becoming highly interesting candidates to replace platinum (Pt) in the alkaline hydrogen evolution reaction ...(HER). The hydrogen binding at Ru sites (Ru−H) is an important factor limiting the HER activity. Herein, density functional theory (DFT) simulations show that the essence of Ru−H binding energy is the strong interaction between the 4dz2
orbital of Ru and the 1s orbital of H. The charge transfer between Ru sites and substrates (Co and Ni) causes the appropriate downward shift of the 4dz2
‐band center of Ru, which results in a Gibbs free energy of 0.022 eV for H* in the RuCo system, much lower than the 0.133 eV in the pure Ru system. This theoretical prediction has been experimentally confirmed using RuCo alloy‐nanosheets (RuCo ANSs). They were prepared via a fast co‐precipitation method followed with a mild electrochemical reduction. Structure characterizations reveal that the Ru atoms are embedded into the Co substrate as isolated active sites with a planar symmetric and Z‐direction asymmetric coordination structure, obtaining an optimal 4dz2
modulated electronic structure. Hydrogen sensor and temperature program desorption (TPD) tests demonstrate the enhanced Ru−H interactions in RuCo ANSs compared to those in pure Ru nanoparticles. As a result, the RuCo ANSs reach an ultra‐low overpotential of 10 mV at 10 mA cm−2 and a Tafel slope of 20.6 mV dec−1 in 1 M KOH, outperforming that of the commercial Pt/C. This holistic work provides a new insight to promote alkaline HER by optimizing the metal‐H binding energy of active sites.
Optimizing Ru−H adsorption/desorption efficiency, via adjusting the Ru 4dz2
orbital in RuCo alloy‐nanosheets, enables highly promoted alkaline hydrogen evolution reaction. This optimized adsorption/desorption efficiency is demonstrated by the hydrogen sensor and temperature programmed desorption experiments. The RuCo alloy‐nanosheets possess a record low overpotential of 10 mV at 10 mA cm−2, superior to the commercial Pt/C and Ru/C.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Efficient utilization of abundant solar energy for steam generation is an attractive, renewable, and environment-friendly technology for seawater desalination and wastewater purification, enabling ...solutions to address the global long-standing water scarcity issues. However, the low energy efficiency, high cost and complex systems with multiple components of state-of-the-art technologies hindered their practical applications. Herein, we report the first example of three-dimensional (3D) MXene architecture (3DMA)-based solar steam generators
via
a facile two-step dip coating process without any annealing or high temperature carbonization. The 3DMAs prepared by a cost-effective, scalable, simple fabrication method show effective broadband solar absorption (∼98%) and excellent solar thermal conversion ability based on 2D to 3D morphological transformation of MXenes, making good use of intrinsic theoretical photothermal performance of MXenes. The particularly hydrophilic nature of MXenes and the macroporous structure of melamine foam allow continuous water supply to 3DMAs owing to their strong capillary effect. As a result, the 3DMAs achieve water evaporation rates of 1.41 and 7.49 kg m
−2
h
−1
under solar illumination of 1 sun and 5 sun with a superb solar steam efficiency of up to 88.7% and 94.2%, respectively. This scalable 3DMA can be used to produce clean water from both seawater and wastewater with rejections close to 100% for organic dyes and metal ions. This work creates a platform to develop novel composite materials for solar-driven seawater desalination and wastewater purification
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opening a new window for the utilization of MXenes as photothermal agents in practical applications.
3D MXene architectures combining the high light absorption ability of MXenes and porous melamine foam exhibit efficient solar steam generation.
Hybrid graphene aerogels (HGA) consisting of graphene oxide (GO) and graphene nanoplatelets (GNP) were prepared and introduced into polyethylene glycol (PEG) via vacuum impregnation, aiming at ...obtaining composite phase change materials (PCMs) with high thermal conductivity, outstanding shape-stabilization, high energy storage density, commendable thermal repeatability and the ability to light-to-heat energy storage. GO nanosheets formed a three-dimensional supporting network to keep the shape of PEG stable during phase change and GNP dispersed uniformity along the network structure of GO and thus a thermal conductive pathway was constructed. The incorporation of HGA remarkably enhanced the thermal conductivity and shape-stabilization of the composite PCMs. The PEG/HGA composite PCM with only ca. 0.45 wt% GO and ca. 1.8 wt% GNP, showed an enhanced thermal conductivity of 1.43 W/mK from 0.31 W/mK of pure PEG and an improvement of 361%, much higher than the improvement that can be achieved by solution or melt blending. Moreover, an energy conversion from light to heat was realized with the composite PCMs. Thus, this work provides a simple, green and environmentally friendly way to achieve simultaneous enhancement of the thermal conductivity, energy storage density and shape-stabilization of PCMs and realize light-to-thermal energy conversion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
As a renewable and environment-friendly technology for seawater desalination and wastewater purification, solar energy triggered steam generation is attractive to address the long-standing global ...water scarcity issues. However, practical utilization of solar energy for steam generation is severely restricted by the complex synthesis, low energy conversion efficiency, insufficient solar spectrum absorption and water extraction capability of state-of-the-art technologies. Here, for the first time, we report a facile strategy to realize hydrogen bond induced self-assembly of a polydopamine (PDA)@MXene microsphere photothermal layer for synergistically achieving wide-spectrum and highly efficient solar absorption capability (≈ 96% in a wide solar spectrum range of 250–1,500 nm wavelength). Moreover, such a system renders fast water transport and vapor escaping due to the intrinsically hydrophilic nature of both MXene and PDA, as well as the interspacing between core-shell microspheres. The solar-to-vapor conversion efficiencies under the solar illumination of 1 sun and 4 sun are as high as 85.2% and 93.6%, respectively. Besides, the PDA@MXene photothermal layer renders the system durable mechanical properties, allowing producing clean water from seawater with the salt rejection rate beyond 99%. Furthermore, stable light absorption performance can be achieved and well maintained due to the formation of ternary TiO2/C/MXene complex caused by oxidative degradation of MXene. Therefore, this work proposes an attractive MXene-assisted strategy for fabricating high performance photothermal composites for advanced solar-driven seawater desalination applications.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The development of wearable healthcare electronics has created higher demands on both the sensitivity and stretchability of flexible sensors. As it is generally difficult to obtain a trade-off ...between sensitivity and stretchability, the fabrication of strain sensors with both a wide operating range (≥100%) and high sensitivity (GF ≥ 100) remains a great challenge. Here, we propose for the first time a strategy based on the consolidation of two basic but seemingly paradoxical sensing mechanisms,
i.e.
, slippage and crack propagation mechanisms, to greatly enhance the sensitivity of stretchable strain sensors. Based on stretchable polyurethane (PU) fibers, which can be easily woven into conventional fabrics to produce wearable devices, we present a multilayer sensing structured fiber sensor fabricated by layer-by-layer self-assembly of sliver nanowire (AgNW)/waterborne polyurethane (WPU) layers and MXene layers. The sensor simultaneously exhibits an ultrahigh sensitivity (GF = 1.6 × 10
7
) and a wide operating range (up to 100%), as well as great reliability and stability (1000 cycles) and fast response (344 ms) and relaxation (344 ms). Moreover, smart fabrics were fabricated by integrating fiber strain sensors into different clothes and a prototype body posture monitoring, analysis, and correction system was presented for healthcare applications. Our work not only breaks down the technological wall between high sensitivity and high stretchability of strain sensors, but also shows the great potential applications of wearable, comfortable, and non-intrusive electronics for real-time health monitoring.
Integrating slippage and crack propagation points in a new direction towards highly sensitive and stretchable sensors for wearable healthcare.
Conductive elastomeric materials of multi-walled carbon nanotube (MWCNT) filled thermoplastic vulcanizate (TPV) based on polypropylene (PP)/ethylene-propylene-diene rubber (EPDM) blends were ...fabricated via different processing procedures, i.e., one-step and two-step methods, to control strain sensitivity aiming at applications from strain sensors to stretchable conductors. The phase size of cross-linked EPDM could be effectively tuned and the average diameter of EPDM particles was 550 nm for one-step TPV and 230 μm for two-step TPV. Uniform dispersion of MWCNTs in two-step TPV and serious aggregations of MWCNTs in one-step TPV were observed. Both TPVs showed excellent strain-resistance repeatability for 50 tensile and recovery cycles. The one-step-TPV showed a potential to be used as strain sensor due to a high gauge factor (GF) of 1004 at a strain of 100%, while the resistance for the two-step TPV composite was independent with strain even at a strain of 200%, resulting in a stretchable conductor with excellent resistance memory effect. The different strain sensitivity can be explained by the orientation of PP matrix. Moreover, the two-step TPV showed much lower electrical conductivity percolation threshold, 0.65 wt.%. This work provided a simple route to tune the strain sensitivity of MWCNTs filled TPVs based on PP/EPDM blends for applications from strain sensors to highly stretchable conductor through different processing procedures to control the morphologies and MWCNT dispersion.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The crystallinity of semicrystalline polymers and molecular orientation of polymer have long been considered to be significant influencing factors on the thermal conductivity of polymer materials, ...but more clear-cut understanding on their impact on the thermal conductivity is still needed. In this work, poly-
l
-lactide (PLLA), whose crystallinity and orientation can be adjusted in a wide range, is selected to discuss the effect of degree of crystallinity and orientation on the thermal conductivity of PLLA. Meanwhile, the influence of temperature on the thermal conductivity is also discussed. PLLA compression-molded samples were heat-treated at 120 °C to tune the crystallinity of the samples, while the degrees of orientation were tuned by stretching the amorphous PLLA bars at 60 °C to different strains. It is found that environmental temperature of application affects the thermal conductivity obviously and the glass transition temperature of polymers shows a strong influence on the thermal conductivity of PLLA. Below
T
g
, the thermal conductivity of PLLA with different crystallinity increases with temperature and when the temperature is higher than
T
g
, the thermal conductivity of PLLA with different crystallinity decreases remarkably. It is also demonstrated that the thermal conductivity of PLLA increases with the increase in crystallinity, and the tensile strain linearly increases the thermal conductivity in the direction of molecular orientation and decreases the thermal conductivity in the perpendicular direction, which are in agreement with other semicrystalline polymers that has been reported.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Interfacial solar steam generation has been proved to be effective for desalination and water purification applications and a large number of smartly designed structures have been reported to reduce ...the heat conduction loss into bulk water by introducing thermally insulating porous foams. Actually, directly using air as the thermal insulation layer should be one of the most efficient ways to reduce the heat loss into bulk water. To this end, we present a bridge-arched hollow and self-floating integrative solar absorber/water evaporator prepared by a one-step hydrothermal reaction. The fully integrative water evaporator can achieve ∼92.9% water evaporation efficiency and 1.476 kg m
−2
h
−1
water evaporation rate under just 1 sun illumination. Such a high efficiency is caused by the unique bridge-arched raised upper surface, hollow interior, and tailored bilayer structure consisting of hydrophilic porous melamine foam for water transportation and a reduced graphene oxide layer for photothermal conversion. These features not only provide broadband solar absorption (∼95%), efficient light-to-heat conversion and a high water evaporation rate, but also suppress the heat loss at the same time. Owing to the simplicity of fabrication and recyclability, this novel composite structure is an ideal material for commercial, portable solar thermal conversion applications to obtain clean water
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seawater desalination and wastewater purification.
A bridge-arched integrated evaporator that introduces air as the thermal insulation layer exhibits high-efficiency solar steam generation.
An ice-templating self-assembly strategy and a vacuum impregnation method were used to fabricate polyethylene glycol (PEG)/hierarchical porous scaffold composite phase change materials (PCMs). ...Hierarchically interconnected porous scaffolds of boron nitride (BN), with the aid of a small amount of graphene oxide (GO), endow the composite PCMs with high thermal conductivity, excellent shape-stability and efficient solar-to-electric energy conversion. The formation of a three-dimensional (3D) thermally conductive pathway in the composites contributes to improving the thermal conductivity up to 2.36 W m
K
at a relatively low content of BN (ca. 23 wt%). This work provides a route for thermally conductive and shape-stabilized composite PCMs used as energy storage materials.
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