High-rate metal-free MXene microsupercapacitors on paper substrates

MXene is a promising energy storage material for miniaturized microbatteries and microsupercapacitors(MSCs).Despite its superior electrochemical performance,only a few studies have reported MXene-based ultrahigh-rate(>1000 mV s^(−1))on-paper MSCs,mainly due to the reduced electrical conductance of MXene films deposited on paper.Herein,ultrahigh-rate metal-free on-paper MSCs based on heterogeneous MXene/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)(PEDOT:PSS)-stack electrodes are fabricated through the combination of direct ink writing and femtosecond laser scribing.With a footprint area of only 20 mm^(2),the on-paper MSCs exhibit excellent high-rate capacitive behavior with an areal capacitance of 5.7 mF cm^(−2)and long cycle life(>95%capacitance retention after 10,000 cycles)at a high scan rate of 1000 mV s^(−1),outperforming most of the present on-paper MSCs.Furthermore,the heterogeneous MXene/PEDOT:PSS electrodes can interconnect individual MSCs into metal-free on-paper MSC arrays,which can also be simultaneously charged/discharged at 1000 mV s^(−1),showing scalable capacitive performance.The heterogeneous MXene/PEDOT:PSS stacks are a promising electrode structure for on-paper MSCs to serve as ultrafast miniaturized energy storage components for emerging paper electronics.

CdTe-paper-based Visual Sensor for Detecting Methyl Viologen

This study developed a method on detecting methyl viologen(paraquat)using a CdTe-paper-based visual sensor.The CdTe Qdots were immobilized on the paper using glycerin.The volume percentages of CdTe in glycerin were optimized to be 50%.The sensing principle is that the methyl viologen quenches the fluorescence intensity of CdTe Qdots in a concentration dependent manner.The sensor is linearly response to the logarithm concentration of the methyl viologen in the range from 0.39μmol/L to 3.89 mmol/L with a detection limit of 0.16μmol/L and the corre-lation coefficient R^(2) of 0.99.Three parallel experiments at the methyl viologen concentration of 38.89μmol/L give a relative error of 2.45%,which indicates a good reproducibility.The sensor is not disturbed by other pestisides in-cluding omethoate,anilofos,machete and glyphosate isopropylamine salt.The advantages of this sensor are dis-posable,stable,convenient,and easy to operate.

Core-shell structure and domain engineering in Bi_(0.5)Na_(0.5)TiO_(3)-based ceramics with enhanced dielectric and energy storage performance

Coreeshell structured Bi_(0.5)Na_(0.5)TiO_(3)eKTaO_(3)þx%(in mass)Li_(2)CO_(3)ceramics were fabricated in this study.Increasing x from 0 to 2 leads to the decrease of sintering temperature from 1175℃to 1020℃.The limited diffusion of Ta5þresults in chemical heterogeneities and coreeshell microstructures.The Ta5þ-depleted cores show the nanodomains(~10 nm),while the Ta^(5+)-rich shells display the polar nanoregions(1e2 nm).From x¼0 to 1,the appearance of cores with nanodomains contributes to the increase of dielectric constant and maximum polarization,while the further addition of Li2CO3 suppresses the dielectric and polarization responses due to the reduced grain sizes and polarization coupling.The enhanced dielectric relaxation and existence of core-shell microstructure with different polarization levels help to optimize the dielectric temperature stability.The x¼2 ceramics exhibit a stable high dielectric constant~1400 over a wide temperature range of 20e520℃.More encouragingly,the ultrafine grain size and coreeshell microstructure in the x¼2 ceramics greatly benefit the improvement of breakdown strength.Combined with the delayed polarization saturation and high ergodicity,a high recoverable energy density of~5.07 J/cm3 is obtained under 44 kV/mm,with a high efficiency of~85.17%.

Template-free synthesis of inorganic hollow spheres at water/“water-brother”interfaces as Fenton-like reagents for water treatment

This paper reports a template-free method to synthesize a series of inorganic hollow spheres(IHSs)including Cu-1,Cu-2,Ni-1,Ni-2 based on mineralization reactions at water/"water-brother" interfaces. "Water-brother" was defined as a solvent which is miscible with water,such as ethanol and acetone. The water/"water-brother" interfaces are very different from water/oil interfaces. The "water-brother" solvent will usually form a homogenous phase with water. Interestingly,in our method,these interfaces can be formed,observed and utilized to synthesize hollow spheres. Utilizing the unique porous properties of the spheres,their potential application in water treatment was demonstrated by using Cu-1 IHSs as Fenton-like reagents for adsorption and decomposition of Congo Red from aqueous solution. The final adsorption equilibrium was achieved after 30 min with the maximum adsorption capacity of 86.1 mg/g,and 97.3% removal of the dye in 80 min after adsorption equilibrium. The IHSs can be reused as least 5 times after treatment by Na OH.This method is facile and suitable for large-scale production,and shows great potential for watertreatment.

Reversible conductivity recovery of highly sensitive flexible devices by water vapor

With decreasing size of integrated circuits in wearable electronic devices,the circuit is more susceptible to aging or fracture problem,subsequently decreasing the transmission efficiency of electricity.Micro-healing represents a good approach to solve this problem.Herein,we report a water vapor method to repair microfiber-based electrodes by precise positioning and rapid healing at their original fracture sites.To realize this micro-level conducting healing,we utilize a bimaterial composed of polymeric microfibers as healing agents and electrically conductive species on its surface.This composite electrode shows a high-performance conductivity,great transparency,and ultra-flexibility.The transmittance of our electrode could reach up to 88 and 90%with a sheet resistance of 1 and 2.8Ωsq^(−1),respectively,which might be the best performance among Au-based materials as we know.Moreover,after tensile failure,water vapor is introduced to mediate heat transfer for the healing process,and within seconds the network electrode could be healed along with recovering of its resistance.The recovering process could be attributed to the combination of adhesion force and capillary force at this bimaterial interface.Finally,this functional network is fabricated as a wearable pressure/strain sensing device.It shows excellent stretchability and mechanical durability upon 1000 cycles.