Co-reporter:Yuan Zhang, Yougen Hu, Pengli Zhu, Fei Han, Yu Zhu, Rong Sun, and Ching-Ping Wong
ACS Applied Materials & Interfaces October 18, 2017 Volume 9(Issue 41) pp:35968-35968
Publication Date(Web):September 27, 2017
DOI:10.1021/acsami.7b09617
Flexible pressure sensors are one of the vital component units in the next generation of wearable electronics for monitoring human physiological signals. In order to improve the sensing properties of the sensors, we demonstrate flexible, tunably resistive pressure sensors based on elastic microstructured polydimethylsiloxane (PDMS) film via a simple, low-cost colloid self-assembly technology, which uses monodispersed polystyrene (PS) microspheres as monolayer and an ordered sacrificial template. The sensors exhibit high sensitivity of −15 kPa–1 under low pressure (<100 Pa), with fast response time (<100 ms), high stability over 1000 cycles of pressure loading/unloading, low-pressure detection limit of 4 Pa, and wide working pressure regime (<5 kPa) by optimizing the size of PS microspheres. Moreover, the multipixel arrays of the pressure sensor are fabricated to illustrate the sensing ability of space pressure distribution. The developed flexible pressure sensors are successfully used to detect human neck pulse, show great promise for monitoring human body motions, and have potential applications in wearable devices.Keywords: microdome-patterned films; polystyrene microspheres; resistive pressure sensors; self-assembly; tunable sensitivity;
Co-reporter:Xingtian Shuai, Pengli Zhu, Wenjin Zeng, Yougen Hu, Xianwen Liang, Yu Zhang, Rong Sun, and Ching-ping Wong
ACS Applied Materials & Interfaces August 9, 2017 Volume 9(Issue 31) pp:26314-26314
Publication Date(Web):July 28, 2017
DOI:10.1021/acsami.7b05753
Flexible pressure sensors have attracted increasing research interest because of their potential applications for wearable sensing devices. Herein, a highly sensitive flexible pressure sensor is exhibited based on the elastomeric electrodes and a microarray architecture. Polydimethylsiloxane (PDMS) substrate, coated with silver nanowires (AgNWs), is used as the top electrode, while polyvinylidene fluoride (PVDF) as the dielectric layer. Several transfer processes are applied on seeking facile strategy for the preparation of the bottom electrode via embedding AgNWs into the PDMS film of microarray structure. The flexible pressure sensor integrates the top electrode, dielectric layer, and microarray electrode in a sandwich structure. It is demonstrated that such sensors possess the superiorities of high sensitivity (2.94 kPa–1), low detection limit (<3 Pa), short response time (<50 ms), excellent flexibility, and long-term cycle stability. This simple process for preparing such sensors can also be easily scaled up to construct pressure sensor arrays for detecting the intensity and distribution of the loaded pressure. In addition, this flexible pressure sensor exhibits good performance even in a noncontact way, such as detecting voice vibrations and air flow. Due to its superior performance, this designed flexible pressure sensor demonstrates promising potential in the application of electronic skins, as well as wearable healthcare monitors.Keywords: capacitive pressure sensor; flexible; microarray electrode; PDMS; PVDF; silver nanowires;
Co-reporter:Lulu Lv;Liang Huang;Gang Li
Journal of Materials Science: Materials in Electronics 2017 Volume 28( Issue 18) pp:13521-13531
Publication Date(Web):24 May 2017
DOI:10.1007/s10854-017-7191-0
Polymer composites of polyvinylidene fluoride (PVDF) filled with SiO2–reduced graphene oxide (RGO) hybrids were fabricated and their dielectric properties and energy storage performance were systematically investigated. Hybrid SiO2–RGO with core-cell were prepared by using of SiO2 particles as rigid template and the thermal reduction of the electrostatic assembled SiO2–GO hybrids, in which the inside rigid particles could support the uniform dispersion of ultrathin RGO sheets in the PVDF matrix and thus leading to a much lower percolation threshold (0.141 vol% for RGO in composite) than those of most reported graphene/polymer composites. Only a small amount of RGO in composites lead to high dielectric permittivity (72.94) and low dielectric loss (0.059) which should be ascribed to the increase of interfacial polarization between filler and matrix. More importantly, the composites with high breakdown strength (2438 kV/cm), energy density (0.301 J/cm3) and charge–discharge efficiency (91.2%) can be achieved by incorporation of 10 wt% filler loading. This study provides a special pathway to ensure the dispersion and highly efficient usage of ultrathin graphene sheets in the polymer matrix and achieve graphene/polymer composite with excellent dielectric performance and energy storage density.
Co-reporter:Qian Guo, Pengli Zhu, Gang Li, Junjie Wen, Tianyu Wang, Daoqiang (Daniel) Lu, Rong Sun, Chingping Wong
Composites Part B: Engineering 2017 Volume 116(Volume 116) pp:
Publication Date(Web):1 May 2017
DOI:10.1016/j.compositesb.2016.10.081
Three kinds of silica nanoparticles with different surface functional groups (amino groups, epoxide groups, and alkyl chain groups) were prepared and used as fillers in the amine-cured epoxy resin systems to investigate the relationship between the interfacial interaction and the rheological and thermal properties of silica nanoparticles reinforced epoxy nanocomposites. It has been found that attractive interfacial interaction significantly contributed to reduce the viscosity and dramatically enhance the viscosity stability as well as reinforce the thermal stability of epoxy nanocomposites. While repulsive interfacial interaction had considerable negative effects on both of the viscosity and viscosity stability. Glass transition temperature of epoxy nanocomposites is closely related to the effects of the interfacial interaction on the curing process of bulk epoxy. This study may also shed lights on the choice of an optimum surface functional group for other inorganic fillers to improve the rheological properties and meanwhile keep good comprehensive thermal properties for epoxy nanocomposites.Attractive and repulsive interfacial interactions of the silica nanofillers with the amine-epoxy matrix were constructed and their great effects on the viscosity and viscosity stability of epoxy nanocomposites were reported.Download high-res image (374KB)Download full-size image
Co-reporter:Haibo Su;Leicong Zhang;Fengrui Zhou;Xianwen liang;Tingxi Li;Qing Wang;Rong Sun;Chingping Wong
Sustainable Energy & Fuels (2017-Present) 2017 vol. 1(Issue 7) pp:1601-1610
Publication Date(Web):2017/08/22
DOI:10.1039/C7SE00214A
Direct printing techniques have generated significant research interest in fabricating flexible and scalable micro-supercapacitors (MSCs). In this study, we report a facile and cost-effective way to synthesize water soluble reduced graphene oxide (WSG) with a high concentration by decoration with aminobenzenesulfonic acid (ABS) and reduction with ascorbic acid. The WSG possesses excellent electrical conductivity (360 S m−1), good water dispersion stability as well as a high zeta potential value (−62 mV at pH 11), and the concentration of the as-prepared WSG could reach 5 mg mL−1, nearly as great as the highest value from previous reports. Then, using this high-concentration WSG dispersion directly as an electrochemically active ink material, micro-supercapacitor electrodes could be facilely fabricated via a direct printing technique on common printing paper, and the all-solid-state flexible MSCs could be further assembled. The results show that these flexible MSCs exhibit high area and volume specific capacitances of 2.67 mF cm−2 and 6.75 F cm−3, maintaining 94.8% of their initial specific capacitance after 5000 cycles at a scan rate of 50 mV s−1. More importantly, the capacitance and potential can be expanded by connecting a WSG-MSC device in parallel and in series, and the assembled devices are further demonstrated to be capable of lighting a liquid crystal display with three WSG-MSCs in series. These findings not only provide a simple way to synthesize WSG with a high concentration, but also facilitate its applications in printable and flexible MSCs with high performance.
Co-reporter:Yu Zhu;Yougen Hu;Tao Zhao;Xianwen Liang;Rong Sun;Ching-ping Wong
New Journal of Chemistry (1998-Present) 2017 vol. 41(Issue 12) pp:4950-4958
Publication Date(Web):2017/06/12
DOI:10.1039/C7NJ00246G
Copper nanowires (CuNWs) are extremely prone to oxidation, which greatly limits their practical applications, even though they are inexpensive, abundant and have high electrical conductivity. Herein, a facile and novel method is developed to alleviate the oxidation of CuNWs by embedding CuNWs into water-dispersible modified graphene (WGP) sheets to form a uniform hybrid conductive film using a simple vacuum filtration process. The CuNWs and WGP films possess electrical conductivity of 3.19 × 103 S m−1 and 5.6 × 103 S m−1, respectively. With the addition of WGP to form a CuNWs–WGP hybrid film, the electrical conductivity of the CuNWs is further improved to 3.02 × 104 S m−1 due to the synergistic effects of the CuNWs and WGP. The CuNWs–WGP hybrid films show excellent antioxidative stability even after exposure in air for 8 weeks without any obvious oxidation. Then, using this conductive hybrid film, a sandwich structured PDMS/CuNWs–WGP/PDMS flexible strain sensor was fabricated. The strain sensor exhibits good flexibility and stretchability with only less than 15% loss of electrical conductivity over 450 times mechanical bending, and was successfully used to monitor human motion, such as finger bending, swallowing and voice recognition.
Co-reporter:Yougen Hu, Tao Zhao, Pengli Zhu, Yu Zhu, Xingtian Shuai, Xianwen Liang, Rong Sun, Daoqiang Daniel Lu and Ching-Ping Wong
Journal of Materials Chemistry A 2016 vol. 4(Issue 24) pp:5839-5848
Publication Date(Web):02 Jun 2016
DOI:10.1039/C6TC01340F
Printable elastic conductive composites with high conductivity and flexibility have exciting applications in burgeoning flexible electronics. However, the low-cost fabrication of flexible conductors is still a great challenge, especially they can be directly printed on various substrates even including the wearable woven textiles, and give perfect printed patterns. Herein, we report a facile and low-cost strategy to fabricate directly printable elastic conductive composites with a conductivity of 4.12 × 104 S m−1 at a low silver loading of 42.88 wt%. The elastic conductor is simply comprised of core–shell polystyrene/silver (PS@Ag) hybrid conductive particles with an average size of 5.86 μm and a viscous polydimethylsiloxane (PDMS) matrix. The viscous mixture pastes can be easily fabricated into conductive films or directly printed on various substrates to obtain elastic conductive circuits with arbitrary geometries and high resolution by the screen printing method. The fabricated elastic PS@Ag/PDMS conductor exhibits high electrical conductivity and good electrical stability under vigorous cycles of mechanical deformations, such as bending, crimping and stretching. These merits make it a competitive candidate for flexible circuits and wearable electronic devices.
Co-reporter:Leicong Zhang, Pengli Zhu, Fengrui Zhou, Wenjin Zeng, Haibo Su, Gang Li, Jihua Gao, Rong Sun, and Ching-ping Wong
ACS Nano 2016 Volume 10(Issue 1) pp:1273
Publication Date(Web):December 22, 2015
DOI:10.1021/acsnano.5b06648
In this study, a flexible asymmetrical all-solid-state supercapacitor with high electrochemical performance was fabricated with Ni/MnO2—filter paper (FP) as the positive electrode and Ni/active carbon (AC)—filter paper as negative electrode, separated with poly(vinyl alcohol) (PVA)–Na2SO4 electrolyte. A simple procedure, such as electroless plating, was introduced to prepare the Ni/MnO2–FP electrode on the conventional laboratory FP, combined with the subsequent step of electrodeposition. Electrochemical results show that the as-prepared electrodes display outstanding areal specific capacitance (1900 mF/cm2 at 5 mV/s) and excellent cycling performance (85.1% retention after 1000 cycles at 20 mA/cm2). Such a flexible supercapacitor assembled asymmetrically in the solid state exhibits a large volume energy density (0.78 mWh/cm3) and superior flexibility under different bending conditions. It has been demonstrated that the supercapacitors could be used as a power source to drive a 3 V light-emitting diode indicator. This study may provide an available method for designing and fabricating flexible supercapacitors with high performance in the application of wearable and portable electronics based on easily available materials.Keywords: electroless plating; filter paper; flexible supercapacitor; MnO2; polymer electrolyte;
Co-reporter:Yu Zhang, Pengli Zhu, Gang Li, Wenzhao Wang, Liang Chen, Daoqiang Daniel Lu, Rong Sun, Feng Zhou and Chingping Wong
Nanoscale 2015 vol. 7(Issue 32) pp:13775-13783
Publication Date(Web):29 Jul 2015
DOI:10.1039/C5NR03414K
Highly stable monodispersed nano Cu hydrosols were facilely prepared by an aqueous chemical reduction method through selecting copper hydroxide (Cu(OH)2) as the copper precursor, poly(acrylic acid) (PAA) and ethanol amine (EA) as the complexing agents, and hydrazine hydrate as the reducing agent. The size of the obtained Cu colloidal nanoparticles was controlled from 0.96 to 26.26 nm by adjusting the dosage of the copper precursor. Moreover, the highly stable nano Cu hydrosols could be easily concentrated and re-dispersed in water meanwhile maintaining good dispersibility. A model catalytic reaction of reducing p-nitrophenol with NaBH4 in the presence of nano Cu hydrosols with different sizes was performed to set up the relationship between the apparent kinetic rate constant (kapp) and the particle size of Cu catalysts. The experimental results indicate that the corresponding kapp showed an obvious size-dependency. Calculations revealed that kapp was directly proportional to the surface area of Cu catalyst nanoparticles, and also proportional to the reciprocal of the particle size based on the same mass of Cu catalysts. This relationship might be a universal principle for predicting and assessing the catalytic efficiency of Cu nanoparticles. The activation energy (Ea) of this catalytic reaction when using 0.96 nm Cu hydrosol as a catalyst was calculated to be 9.37 kJ mol−1, which is considered an extremely low potential barrier. In addition, the synthesized nano Cu hydrosols showed size-dependent antibacterial activities against Pseudomonas aeruginosa (P. aeruginosa) and the minimal inhibitory concentration of the optimal sample was lower than 5.82 μg L−1.
Co-reporter:Qian Guo, Pengli Zhu, Gang Li, Liang Huang, Yu Zhang, Daoqiang Daniel Lu, Rong Sun and Chingping Wong
RSC Advances 2015 vol. 5(Issue 62) pp:50073-50081
Publication Date(Web):04 Jun 2015
DOI:10.1039/C5RA06914A
Due to the unique properties of nanoparticles, such as small size, large specific surface area and special optical performance, nanosilica is a promising candidate for replacing the conventional micron-sized silica to reinforce the performance of epoxy resins in microelectronic industries. But, its intensive inclination to form agglomerates in epoxy matrices, and its negative effects on the viscosity and glass transition temperature (Tg) of epoxy resins have limited its applications. In this work, a silica hybrid composed of sub-micron sized (500 ± 50 nm) and nano-sized (60 ± 10 nm) silica spheres was prepared and introduced into an epoxy polymer matrix. With this type of silica hybrid as a reinforcing filler, the dispersion quality of the nanosilica particles into the epoxy matrix was greatly improved due to the de-agglomeration effect of the large silica spheres. Also, the Tg of the epoxy composites was significantly enhanced while the viscosity of the liquid epoxy composites before curing remained lower at high filler loading as compared to the corresponding single-sized nanosilica filled epoxy nanocomposites.
Co-reporter:Yougen Hu, Tao Zhao, Pengli Zhu, Xianwen Liang, Rong Sun and Ching-Ping Wong
RSC Advances 2015 vol. 5(Issue 1) pp:58-67
Publication Date(Web):01 Dec 2014
DOI:10.1039/C4RA12475H
Utilizing a simple improved electroless plating method, ca. 6 μm sized monodisperse polystyrene/silver (PS/Ag) core–shell microspheres with a complete, homogeneous and compact coverage of Ag nanoparticles layer were successfully prepared. In this approach, modified lightly cross-linked PS (LCPS) microspheres with a uniform diameter of 5.6 μm were used as templates. After the LCPS cores were removed by dissolving with dimethyl formamide (DMF), the outer silver shells assembled by amounts of Ag nanoparticles maintain good hollow spherical structure. The size and coverage degree of Ag nanoparticles on the PS/Ag microspheres could be easily tuned by changing the concentration of [Ag(NH3)2]+ ions in aqueous media. The electrical conductivity of the obtained PS/Ag core–shell microspheres changes from 3.76 × 104 S m−1 to 3.33 × 105 S m−1 as increasing the coverage density of Ag nanoparticles. Moreover, the catalytic assays indicate that the resultant monodisperse PS/Ag core–shell microspheres show excellent catalytic activity for the reduction of methylene blue (MB) by NaBH4. In particular, the corresponding hollow Ag spheres exhibit more outstanding catalytic activity due to their stable hollow structure and higher specific surface area.
Co-reporter:Yu Zhang, Pengli Zhu, Liang Chen, Gang Li, Fengrui Zhou, Daoqiang (Daniel) Lu, Rong Sun, Feng Zhou and Ching-ping Wong
Journal of Materials Chemistry A 2014 vol. 2(Issue 30) pp:11966-11973
Publication Date(Web):24 Jun 2014
DOI:10.1039/C4TA01920B
Novel hierarchical architectures of porous copper (Cu) microspheres assembled with nanoparticles have been successfully synthesized by ingeniously selecting the precursor and complexant through a facile wet chemical reduction method. The resultant porous Cu microspheres have a size distribution of 700 ± 50 nm and have excellent monodispersity. The synergistic effect between the precursor of slightly soluble copper hydroxide and the complexants of polyacrylic acid and ethanol amine exactly induces the generation of unique porous hierarchical architectures. The obtained porous Cu microspheres were applied to reduce and degrade different organic dyes with high concentrations (4-nitrophenol, methylene blue, and rhodamine B) in the presence of NaBH4. Compared with solid Cu particles that have the same size, these porous Cu microspheres exhibit more excellent catalytic activity due to their hierarchical structures. Moreover, the catalyst with universal applicability could be easily separated from the catalytic system and sustainedly possess high stability in recycled reactions.
Co-reporter:Liang Huang, Pengli Zhu, Gang Li, Daoqiang (Daniel) Lu, Rong Sun and Chingping Wong
Journal of Materials Chemistry A 2014 vol. 2(Issue 43) pp:18246-18255
Publication Date(Web):05 Sep 2014
DOI:10.1039/C4TA03702B
Reduced graphene oxide (RGO)-encapsulated SiO2 hybrids (SiO2@RGO) were fabricated from the thermal reduction of electrostatically assembled SiO2@GO hybrids. Then, epoxy composites, filled with SiO2, SiO2@GO and SiO2@RGO hybrids, were prepared by a solvent-free curing process, and their thermal, dielectric and thermo-mechanical properties were investigated and compared. In the SiO2@RGO/epoxy composites, the mono-dispersed SiO2 nanoparticles are firmly embedded in the thin layer of RGO nanosheets, forming unique core–shell nanostructures that effectively prevent the aggregation of RGO nanosheets in the polymer matrix, construct conductive pathways at the particle–polymer interface and afford the epoxy composites with outstanding thermo-mechanical properties. The dielectric properties of the SiO2@RGO/epoxy composites exhibit a typical percolation transition near 0.174 vol% for RGO (20 wt% of SiO2@RGO hybrids), where the dielectric constant could reach 77.23 at 1 kHz, which is 22 times that of the neat epoxy resin. Upon further increase of the loading content, the gradual contact of the filler particles leads to the formation of interfacial continuous conductive networks, and both the thermal conductivity and dielectric constant of the composites show a dramatic increase. With a filler loading of 40 wt% SiO2@RGO (0.373 vol% for RGO), a thermal conductivity of 0.452 W m−1 K−1 is obtained, which is two times larger than that of neat epoxy. In addition, SiO2@RGO/epoxy composites reveal significantly decreased coefficient of thermal expansion (CTE) and increased glass transition temperature (Tg). We believe this special core–shell SiO2@RGO structure, with its inner mechanically enhanced inorganic particles and outer interfacial conductive phase, could make full use of the enhancement effect of different components and thus endow the polymer composites with outstanding properties overall.
Co-reporter:Yu Zhang, Pengli Zhu, Gang Li, Tao Zhao, Xianzhu Fu, Rong Sun, Feng Zhou, and Ching-ping Wong
ACS Applied Materials & Interfaces 2014 Volume 6(Issue 1) pp:560
Publication Date(Web):December 13, 2013
DOI:10.1021/am404620y
Monodisperse copper nanoparticles with high purity and antioxidation properties are synthesized quickly (only 5 min) on a large scale (multigram amounts) by a modified polyol process using slightly soluble Cu(OH)2 as the precursor, l-ascorbic acid as the reductant, and PEG-2000 as the protectant. The resulting copper nanoparticles have a size distribution of 135 ± 30 nm and do not suffer significant oxidation even after being stored for 30 days under ambient conditions. The copper nanoparticles can be well-dispersed in an oil-based ink, which can be silk-screen printed onto flexible substrates and then converted into conductive patterns after heat treatment. An optimal electrical resistivity of 15.8 μΩ cm is achieved, which is only 10 times larger than that of bulk copper. The synthesized copper nanoparticles could be considered as a cheap and effective material for printed electronics.Keywords: antioxidative; copper nanoparticles; flexible conductors; large scale; monodisperse;
Co-reporter:Pengli Zhu, Qi Zheng, Rong Sun, Wenjie Zhang, Jihua Gao, Chingping Wong
Journal of Alloys and Compounds 2014 Volume 614() pp:289-296
Publication Date(Web):25 November 2014
DOI:10.1016/j.jallcom.2014.06.065
•BT coated by NZFO (BNCP) has been successfully prepared.•The outer BT phase could inhibit the grain growth of NZFO in the composites.•This structure is help to get the uniform ferromagnetic-ferroelectric composites.•BNCP composites with NZFO:BT (1.5:1) shows the best comprehensive performance.In this paper, we report the preparation of BaTiO3(BT)/Ni0.5Zn0.5Fe2O4(NZFO) ceramics which own the microstructure of BT coated by NZFO through the co-precipitation procedure (BNCP). X-ray diffraction measurements are used to demonstrate the phase change with different molar ratio of NZFO:BT, and their dielectric and magnetic properties of the composite has been investigated by a RF Impedance/Material Analyzer and M–H loop measurement. The results indicate that the BNCP composite ceramics with NZFO:BT molar ratio at 1.5:1 owns the largest Q (the quality factor) and product of μi × Q and shows nice comprehensive performance in multiferroic field. In addition, this inner BT phase endow the ceramic composites higher cut-off frequency fr and broaden the frequency scope of the composites with higher permeability which could greatly benefit its application.
Co-reporter:Songling Li;Tao Zhao;Rong Sun
Journal of Sol-Gel Science and Technology 2014 Volume 70( Issue 3) pp:366-370
Publication Date(Web):2014 June
DOI:10.1007/s10971-014-3291-y
Antimony doped tin dioxide (ATO) nanoparticles with different Sb doping contents were prepared by freeze-drying the precursor gel and then calcined procedure. The obtained ATO nanoparticles were characterized by X-ray diffraction, scanning electron microscope, optical and electrical techniques. Results indicated that ATO with 10 mol% Sb doping is optimal, with which had the lowest resistivity and highest transmittance in visible region as well as narrow particle size distribution. Thermal insulation properties of ATO/waterborne polyurethane (WPU) films coating on the glass substrates with different thickness were studied on a DIY heat insulating measurement box and showed that the glass coated with ATO/WPU films possessed better heat-insulating effect than empty glass
.
Co-reporter:Ruiqiang Chen;Dr. Pengli Zhu;Libo Deng;Tao Zhao; Rong Sun; Chingping Wong
ChemPlusChem 2014 Volume 79( Issue 5) pp:743-750
Publication Date(Web):
DOI:10.1002/cplu.201300398
Abstract
Aluminum-doped zinc oxide (AZO) nanorods were successfully prepared by a convenient solvothermal route. The crystal structure and morphology of AZO were characterized by XRD, SEM, and high-resolution TEM. The length and diameter of AZO nanorods decreased with increasing Al content. The optical and electrical properties of AZO were studied by UV/Vis spectroscopy and a four-point probe. The optical band gap of AZO increased initially because of the Burstein–Moss effect and then decreased as the Al content increased owing to the defects of AZO. The electrical resistivity of AZO nanorods varied conversely because of the change of electron and defect concentration (native and impurity defects). The native defect types, which were singly charged zinc and oxygen vacancies, were confirmed by photoluminescence spectroscopy. Moreover, not only the properties but also the growth mechanisms of AZO nanorods were affected by the defect concentrations of singly charged zinc vacancies and substituted Al, which were caused by increasing Al content. Finally, the AZO exhibited the smallest electrical resistivity with 1.5 at. % Al doping content, which was four orders of magnitude smaller than that of ZnO.
Co-reporter:Ruiqiang Chen, ;Tao Zhao;Xianzhu Fu;Fengrui Zhou ;Rong Sun
European Journal of Inorganic Chemistry 2013 Volume 2013( Issue 20) pp:3491-3496
Publication Date(Web):
DOI:10.1002/ejic.201300156
Abstract
Hierarchical nanostructured Al-doped ZnO (AZO) powders were successfully prepared through a mild solution route. The crystal structure and morphology of AZO were determined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The morphology of the samples changed from random flower-like nanostructures to uniform flower-like hierarchical nanostructures with different Al doping contents. The optical and electrical properties of AZO were studied by UV/Vis spectroscopy and four-point probe. The optical band gap of AZO increased initially but then decreased as the Al content was increased owing to the Burstein–Mass effect and the many-body effect. Conversely, the electrical resistivity of the AZO powders first decreased and then increased with the Al doping content increasing because of changes in the electron and dopant concentrations. AZO exhibited the smallest electrical resistivity with an Al doping content of 1.0 at-%, which is two orders of magnitude smaller than the electrical resistivity of ZnO.
Co-reporter:Haibo Su, Pengli Zhu, Leicong Zhang, Fengrui Zhou, Gang Li, Tingxi Li, Qing Wang, Rong Sun, Chingping Wong
Journal of Electroanalytical Chemistry (1 February 2017) Volume 786() pp:
Publication Date(Web):1 February 2017
DOI:10.1016/j.jelechem.2017.01.002
•A low cost, sustainable and flexible substrate is fabricated with the modified office waste paper fibers.•Hybrid electrode with high electrochemical performance can be generated by introducing the RGO and MnO2.•The assembled supercapacitor shows excellent mechanical stability and great electrochemical cyclic stability.In order to develop a low cost, sustainable, and eco-friendly energy storage device, we demonstrated an all solid state symmetric flexible supercapacitor based on the office waste paper fibers-reduced graphene oxide-manganese dioxide (PF-RGO-MnO2) which acts as both the positive and negative electrodes. With the assistance of facile solution phase assembly and vacuum filtration method, the flexible PF-RGO-MnO2 electrodes with high physical flexibility and excellent mechanical strength were fabricated directly without any binder agents. Furthermore, owing to the advantages of the lager surface area and microfibers of the each single paper fiber, the PF-based hybrid flexible electrodes show high specific capacitance of 410 F g− 1 at 0.8 A g− 1 and retain 93% capacitance over 5000 cycles, indicating outstanding electrochemical performance. In addition, the assembled solid-state symmetric supercapacitors exhibit high energy density (19.6 Wh kg− 1 at 400 W kg− 1) and excellent cycling stability of 85.3% retention even after 2000 folding and bending cycles. These results propose a renewable way to turn “waste” into wealth, and provide a new method to fabricate the sustainable and freestanding paper-based supercapacitor for application in the flexible energy storage devices.A low cost, sustainable and flexible symmetrical supercapacitor was prepared based on office waste paper electrodes.
Co-reporter:Liang Huang, Pengli Zhu, Gang Li, Daoqiang (Daniel) Lu, Rong Sun and Chingping Wong
Journal of Materials Chemistry A 2014 - vol. 2(Issue 43) pp:NaN18255-18255
Publication Date(Web):2014/09/05
DOI:10.1039/C4TA03702B
Reduced graphene oxide (RGO)-encapsulated SiO2 hybrids (SiO2@RGO) were fabricated from the thermal reduction of electrostatically assembled SiO2@GO hybrids. Then, epoxy composites, filled with SiO2, SiO2@GO and SiO2@RGO hybrids, were prepared by a solvent-free curing process, and their thermal, dielectric and thermo-mechanical properties were investigated and compared. In the SiO2@RGO/epoxy composites, the mono-dispersed SiO2 nanoparticles are firmly embedded in the thin layer of RGO nanosheets, forming unique core–shell nanostructures that effectively prevent the aggregation of RGO nanosheets in the polymer matrix, construct conductive pathways at the particle–polymer interface and afford the epoxy composites with outstanding thermo-mechanical properties. The dielectric properties of the SiO2@RGO/epoxy composites exhibit a typical percolation transition near 0.174 vol% for RGO (20 wt% of SiO2@RGO hybrids), where the dielectric constant could reach 77.23 at 1 kHz, which is 22 times that of the neat epoxy resin. Upon further increase of the loading content, the gradual contact of the filler particles leads to the formation of interfacial continuous conductive networks, and both the thermal conductivity and dielectric constant of the composites show a dramatic increase. With a filler loading of 40 wt% SiO2@RGO (0.373 vol% for RGO), a thermal conductivity of 0.452 W m−1 K−1 is obtained, which is two times larger than that of neat epoxy. In addition, SiO2@RGO/epoxy composites reveal significantly decreased coefficient of thermal expansion (CTE) and increased glass transition temperature (Tg). We believe this special core–shell SiO2@RGO structure, with its inner mechanically enhanced inorganic particles and outer interfacial conductive phase, could make full use of the enhancement effect of different components and thus endow the polymer composites with outstanding properties overall.
Co-reporter:Yougen Hu, Tao Zhao, Pengli Zhu, Yu Zhu, Xingtian Shuai, Xianwen Liang, Rong Sun, Daoqiang Daniel Lu and Ching-Ping Wong
Journal of Materials Chemistry A 2016 - vol. 4(Issue 24) pp:NaN5848-5848
Publication Date(Web):2016/06/02
DOI:10.1039/C6TC01340F
Printable elastic conductive composites with high conductivity and flexibility have exciting applications in burgeoning flexible electronics. However, the low-cost fabrication of flexible conductors is still a great challenge, especially they can be directly printed on various substrates even including the wearable woven textiles, and give perfect printed patterns. Herein, we report a facile and low-cost strategy to fabricate directly printable elastic conductive composites with a conductivity of 4.12 × 104 S m−1 at a low silver loading of 42.88 wt%. The elastic conductor is simply comprised of core–shell polystyrene/silver (PS@Ag) hybrid conductive particles with an average size of 5.86 μm and a viscous polydimethylsiloxane (PDMS) matrix. The viscous mixture pastes can be easily fabricated into conductive films or directly printed on various substrates to obtain elastic conductive circuits with arbitrary geometries and high resolution by the screen printing method. The fabricated elastic PS@Ag/PDMS conductor exhibits high electrical conductivity and good electrical stability under vigorous cycles of mechanical deformations, such as bending, crimping and stretching. These merits make it a competitive candidate for flexible circuits and wearable electronic devices.
Co-reporter:Yu Zhang, Pengli Zhu, Liang Chen, Gang Li, Fengrui Zhou, Daoqiang (Daniel) Lu, Rong Sun, Feng Zhou and Ching-ping Wong
Journal of Materials Chemistry A 2014 - vol. 2(Issue 30) pp:NaN11973-11973
Publication Date(Web):2014/06/24
DOI:10.1039/C4TA01920B
Novel hierarchical architectures of porous copper (Cu) microspheres assembled with nanoparticles have been successfully synthesized by ingeniously selecting the precursor and complexant through a facile wet chemical reduction method. The resultant porous Cu microspheres have a size distribution of 700 ± 50 nm and have excellent monodispersity. The synergistic effect between the precursor of slightly soluble copper hydroxide and the complexants of polyacrylic acid and ethanol amine exactly induces the generation of unique porous hierarchical architectures. The obtained porous Cu microspheres were applied to reduce and degrade different organic dyes with high concentrations (4-nitrophenol, methylene blue, and rhodamine B) in the presence of NaBH4. Compared with solid Cu particles that have the same size, these porous Cu microspheres exhibit more excellent catalytic activity due to their hierarchical structures. Moreover, the catalyst with universal applicability could be easily separated from the catalytic system and sustainedly possess high stability in recycled reactions.
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