Reduced graphene oxide/hierarchal spinel nickel cobaltite nanoflowers composites for supercapacitor electrodes with ultrahigh capacitive and excellent rate performance

Researchers are extensively investigating transition metal oxides due to their unique porous architectural structure and remarkable electrochemical properties, which are suitable to boost the energy storage capabilities. In present work, facile chemical route was used to synthesize hierarchal spinel nickel cobaltite nanoflowers anchored reduced graphene oxide (NiCo₂O₄-rGO) as high performance electrode material. NiCo₂O₄ anchored rGO demonstrated specific capacitance of 2695 Fg^-1 at 1 Ag^-1, which is greater than pristine NiCo₂O₄ nanoflowers specific capacitance. NiCo₂O₄-rGO showed excellent stability and retention capability of 96% after 2500 cycles at 5 Ag^-1. Furthermore, NiCo₂O₄–rGO exhibited maximum energy density of 93.57 WhKg^?1 at power density of 250 WKg^-1. We have achieved specific capacitance and retention capability which is higher than previously reported results. This enhancement is mainly attributed to the spinel structure of NiCo₂O₄ and its robust structural affinity with rGO. Moreover, rGO possesses extended surface area provided ample of active sites and exceptional synergetic effect which helped to enhance the induction and consequently transportation of e^?/h⁺. More importantly due to its special morphological effects, in future NiCo₂O₄ anchored rGO nanoflowers may open new avenue in research but also used as an efficient electrode material for the construction of high performance supercapacitors.     

Design and synthesis of NiCo2O4/NiCoO2/graphene hybrid nanoarrays with enhanced capacitive performance

NiCo₂O₄/NiCoO₂/graphene hybrid nanoarrays on Ni foam have been designed and synthesized through a hydrothermal method and post-annealing treatment. Highly conductive graphene sheets were embedded into or coated onto the NiCo₂O₄/NiCoO₂ arrays, which strongly affect influence the morphology and electrochemical performance of hybrid nanoarrays. Under the effect of graphene, the architecture of the NiCo₂O₄/NiCoO₂ consists of cluster-like arrays that are self-assembled from numerous nanoneedles and provides more electroactive sites for the redox reaction. However, without the assistance of graphene, the pure NiCo₂O₄/NiCoO₂ exhibits the morphology of flake-like arrays on the Ni foam. The NiCo₂O₄/NiCoO₂/graphene arrays show an ultrahigh capacity of 1439 C g^-1 at a current density of 1 mA cm^-2, which is far larger than that of the pure NiCo₂O₄/NiCoO₂ flake-arrays (695 C g^-1). Furthermore, even at a high current density of 60 mA cm^-2, the NiCo₂O₄/NiCoO₂/graphene arrays maintain a high gravimetric capacity of 1172 C g^-1 (capacity retention: 81.4%), which indicates an excellent rate capability. Further, the hybrid capacitor shows a maximum energy density of 34.3 Wh kg^-1. The present study suggests that the NiCo₂O₄/NiCoO₂/graphene hybrid arrays have great application potential as a positive electrode for hybrid supercapacitors.     

Ag2CO3@PVDF/氧化石墨烯超滤膜及其分离性能

以聚偏氟乙烯（PVDF）为聚合物,氧化石墨烯（GO）为添加剂,聚乙烯吡咯烷酮（PVP-K30）为致孔剂,N,N-二甲基乙酰胺（DMAc）为溶剂配制铸膜液,借助相转化法制备了PVDF/GO膜（PGM）,并通过原位共沉反应在PGM表面沉积Ag₂CO₃得到Ag₂CO₃@PVDF/GO复合膜（AgC-PGM）;使用扫描电镜（SEM）、傅里叶红外光谱（FTIR）、水接触角、纯水通量、BSA截留率和三维荧光光谱（3D-EEM）考察了膜材料的形貌、亲水性、水通量和分离性。结果表明,当添加GO为0.4%（质量）,AgNO₃（5.0 mmol·L^-1）与Na₂CO₃（2.5 mmol·L^-1）共沉反应3次得到AgC-PGM;与PVDF膜（132.8 L·m^-2·h^-1）相比,AgC-PGM呈现出较高的亲水性和纯水通量（237.4 L·m^-2·h^-1）,其纯水通量提高了78.8%,对BSA截留率稳定在75%以上;在过滤校区湖水时,AgC-PGM不仅凸显去除蛋白质污染的能力,且出水COD和UV₂₅₄达到自然水体一级标准。     

Porous NiO/Ag composite film for electrochemical capacitor application

A highly porous NiO/Ag composite film is prepared by the combination of chemical bath deposition and silver mirror reaction. The as-prepared NiO/Ag composite film has an interconnecting reticular morphology made up of NiO flakes with highly dispersed Ag nanoparticles of about 6 nm. The pseudocapacitive behavior of the NiO/Ag composite film is investigated by cyclic voltammograms (CV) and galvanostatic charge–discharge tests in 1 M KOH. The NiO/Ag composite film exhibits weaker polarization, higher specific capacitance and better cycling performance as compared to the unmodified porous NiO film. The specific capacitance of the porous NiO/Ag composite film is 330 F g⁻¹ at 2 A g⁻¹ and 281 F g⁻¹ at 40 A g⁻¹, respectively, much higher than that of the unmodified porous NiO film (261 F g⁻¹ at 2 A g⁻¹ and 191 F g⁻¹ at 40 A g⁻¹). The enhancement of pseudocapacitive properties is due to highly dispersed Ag nanoparticles in the composite film, which improves the electric conductivity of the film electrode.     

Significantly enhanced the properties of PE/GO composites with segregated structures via two-step compound

Conductive polymer composites (CPCs) have generated significant academic and industrial interest due to the wide applications in anti-static materials, electromagnetic interface, sensor, and conductors. Nonetheless, the CPCs fabricated by conventional melt-mixing applied to the scalable production generally have a very high percolation threshold, which always suffer from the various draw backs such as, high melt viscosities, low economic affordability, inferior mechanical properties, and solution compounding by reducing the viscosity improves the uniformity of nano-particles. This work aims at building a segregated structure in polyethylene to enhance mechanical properties and electrical conductivity, by taking advantage of the solution compounding and melt-blending methods. Based on the segregated structure, the composites showed the enhanced mechanical properties, thermal stabilities and antistatic properties with a low percolation threshold. In addition, the composite mechanism between graphene oxide and polyethylene and the structure-performance relationship of the CPCs were elucidated and explored by SEM, TEM, and FTIR.     

High dispersion and electrochemical capacitive performance of NiO on benzenesulfonic functionalized carbon nanotubes

This work describes an effective method to synthesize structurally uniform composite of nickel oxide/benzenesulfonic functionalized multiwalled carbon nanotubes composite (NiO/f-MWCNTs) using benzenesulfonic MWCNTs as the substrate. Benzenesulfonic group here is bifunctional both for solubilizing MWCNTs into aqueous solution and for tethering Ni²⁺ precursor onto MWCNTs surfaces to facilitate the follow-up chemical deposition of NiO by supplying surface binding and anchoring groups. The composite has a uniform surface dispersion and large coverage of NiO onto f-MWCNTs, which is characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscope, cyclic voltammetry and galvanostatic charge/discharge measurements. The NiO/f-MWCNTs composite improved the utilization of electrochemical capacitive materials and delivered capacity of 384 F/g at the constant current of 0.20 A/g due to f-MWCNTs as substrate.     

聚酰亚胺/氧化石墨烯复合材料的制备及其性能

以自制的氧化石墨烯(GO)为改性填料,通过原位聚合法制备了聚酰亚胺(PI)/GO复合材料,并对其形貌、结构和性能进行了表征和测试。结果表明:GO的引入未对PI结构产生破坏作用,且有效提高了PI的力学性能、热稳定性和介电性能,降低了吸水率;当GO质量分数为1.5%时,PI/GO复合材料的拉伸强度达126.9 MPa,较PI提高了55.7%;吸水率由3.65%降至0.92%,质量损失5%时的温度较PI提高了5.8℃;当GO质量分数为2.0%时,介电常数(0.1 MHz)较PI提高了83.1%。     

聚乙烯醇/氧化石墨烯分离膜的结构与性能

成膜材料聚乙烯醇（PVA）易溶胀,稳定性差,氧化石墨烯（GO）具有很好的化学稳定性,以PVA为主要原料,GO为添加剂,聚乙二醇为造孔剂,采用共混法制备了GO含量不同的PVA/GO分离膜,并用光学接触角测量仪、超滤杯等考察了分离膜的亲水性和耐污染性;采用SEM、IR、TGA等表征了分离膜的微观形貌、热学及力学性能。结果表明：GO的加入改善了分离膜的内部孔道、亲水性、纯水通量和耐污染能力,膜的热稳定性和力学性能均得到提高,当GO含量为2%时,分离膜的综合性能达到最优。     

Preparation and gas-sensing performance of GO/SnO2/NiO gas-sensitive composite materials

In this study, a SnO₂/NiO composite material was prepared via a co-precipitation method. After calcination at 400 °C for 2 h, a binary composite material (SnO₂/NiO) with good crystallization was obtained. Then, a graphene oxide (GO)/SnO₂/NiO ternary composite material was prepared using a hydrothermal method, in which SnO₂/NiO performed secondary growth on the GO surface. The XRD results showed that SnO₂/NiO exhibited good crystallinity and proved the existence of a chemical bond, Sn–O–C, which was due to the formation of a chemical bond between GO and SnO₂/NiO. Lastly, GO/SnO₂/NiO was successfully prepared and coated on the surface of a gold electrode for gas sensitivity test. A good response to acetone gas in the concentration range of 10–500 ppm at 350 °C was determined. Compared with SnO₂/NiO, GO/SnO₂/NiO showed remarkable improvements in response time, recovery time, and sensitivity. At 350 °C, the sensitivity of acetone with a concentration of 50 ppm was 21.11, the response time was only 5 s, and the recovery time was 150 s. GO/SnO₂/NiO comprised two structures, chemical bond and p-n junction, which exerted a synergistic effect. GO/SnO₂/NiO indicated an excellent application prospect in acetone gas detection.     

Plasma surface modification of graphene oxide nanosheets for the synthesis of GO/PES nanocomposite ultrafiltration membrane for enhanced oily separation

In this study, two different monomers, namely hexafluorobutyl acrylate (HFBA) and diethylaminoethyl methacrylate (DEAEMA) were individually used to modify graphene oxide (GO) nanosheets via environmentally friendly plasma enhanced chemical vapor deposition (PECVD) method. The results from instrumental analyses confirmed the successful deposition of respective functional material onto the nanomaterials. Modified GOs were used as the nano-fillers to develop composite polyethersulfone (PES) ultrafiltration (UF) membrane with improved surface properties for oily solution treatment. All the developed membranes were characterized with a series of analytical instruments to support the findings of membrane filtration performance. The results indicated that the membrane incorporated with DEAEMA-GOs (coated with hydrophilic polymer) could achieve better results in terms of oil rejection, antifouling resistance and water recovery rate than the membrane incorporated with HFBA-GOs (coated with hydrophobic polymer). This is due to the reduced agglomeration between modified GOs as well as better interaction of hydrophilic-coated GOs with polymer membrane. Compared to the pure water flux of the membrane incorporated with unmodified GO, the membrane incorporated with DEAEMA-GO achieve approximately 85% higher value with oil removal rate remained almost unchanged (98.94% rejection).     

Ag nanoparticles anchored on MIL-100/nickel foam nanosheets as an electrocatalyst for efficient oxygen evolution reaction performance

Metal-organic frameworks (MOFs) exhibit excellent application potential in the field of electrocatalysis.In this study,we first prepare MIL-100 nanosheets on nickel foam (MIL-100/NF) and then successfully anchor Ag nanoparticles (NPs) on the nanosheets (Ag@MIL-100/NF) for oxygen evolution reaction(OER) catalysis.This strategy dramatically improves the conductivity of MIL-100 and the Ag NPs are uni-formly dispersed on the nanosheets.The Ag@MIL-100/NF catalyst has excellent electrocatalytic perfor-mance and long-term corrosion resistance,with a low overpotential of 207 mV and a long-term stability of at least 100 h at a current density of 50 mA·cm-2.The experimental results demonstrate that this high OER catalytic performance is due to the improved charge transfer after loading Ag NPs,the com-bination of nanosheets and highly dispersed Ag NPs that expose more active sites and the adjusted chem-ical valence states of Fe and Ni in MIL-100.This work provides a surface decoration approach for the preparation of excellent catalysts directly used in the OER.     

Fabrication of ZnO:Ag/GO composite thin films for enhanced photocatalytic activity

Zinc Oxide (ZnO), ZnO/GO (Graphene Oxide) and ZnO:Ag/GO nanocomposite thin films were deposited on glass substrates using a simple cost-effective automated jet nebulizer spray pyrolysis technique for photocatalytic degradation of organic dyes. The ZnO:Ag/GO film exhibits superior photocatalytic activity when compared with ZnO and ZnO/GO films. The degradation rate constant values of pristine ZnO and ZnO/GO films are found to be 0.0143 and 0.0176 min⁻¹, respectively whereas that of ZnO:Ag/GO is 0.0567 min⁻¹. The possible mechanism involved in the enhanced photocatalytic activity of ZnO:Ag/GO films for the degradation of Methylene Blue dye is proposed with the help of structural, optical and photoluminescence studies. The powder XRD profile confirms the hexagonal wurtzite structure of the synthesized catalysts. The results of Raman, XPS and EDX studies confirm the presence of GO in the ZnO/GO and GO and Ag in the ZnO:Ag/GO films.     

One-step electrosynthesis of MnO2/rGO nanocomposite and its enhanced electrochemical performance

We present a facile one-step electrochemical approach to generate MnO₂/rGO nanocomposite from a mixture of Mn₃O₄ and graphene oxide (GO). The electrochemical conversion of Mn₃O₄ into MnO₂ through potential cycling is expedited in the presence of GO while the GO is reduced into reduced graphene oxide (rGO). The MnO₂ nanoparticles are evenly distributed on the rGO nanosheets and act as the spacer to prevent rGO nanosheets from restacking. This unique structure provides high electroactive surface area (1173?m² g^?1) that improves ions diffusion within the MnO₂/rGO structure. As a result, the MnO₂/rGO nanocomposite exhibits high specific capacitance of 473?F?g^?1 at 0.25?A?g^?1, which is remarkably higher (3 times) than the Mn₃O₄/GO prior conversion. In addition, the electrosynthesized nanocomposite shows higher conductivity and excellent potential cycling stability of 95% at 2000 cycles.     

Hierarchical Co3O4@ZnWO4 core/shell nanostructures on nickel foam: Synthesis and electrochemical performance for supercapacitors

To improve the electrochemical properties of Co₃O₄ for supercapacitors application, a hierarchical Co₃O₄@ZnWO₄ core/shell nanowire arrays (NWAs) material is designed and synthesized successfully via a facile two-step hydrothermal method followed by the heat treatment. Co₃O₄@ZnWO₄ NWAs exhibits excellent electrochemical performances with areal capacitance of 4.1 F cm⁻² (1020.1 F g⁻¹) at a current density of 2 mA cm⁻² and extremely good cycling stability (99.7% of the initial capacitance remained even after 3000 cycles). Compared with pure Co₃O₄ electrodes, the results prove that this unique hierarchical hybrid nanostructure and reasonable assembling of two electrochemical pseudocapacitor materials are more advantageous to enhance the electrochemical performance. Considering these remarkable capacitive behaviors, the hierarchical Co₃O₄@ZnWO₄ core/shell NWAs nanostructure electrode can be revealed promising for high-performance supercapacitors.     

Silver nanoparticles synthesized from mesoporous Ag/SBA-15 composites

Silver nanoparticles were prepared by removing silica from mesoporous Ag/SBA-15 composites. The results of nitrogen adsorption–desorption isotherms, X-ray diffraction, transmission electron microscopy and UV–vis spectroscopy indicated that Ag nanoparticles existed in the pore channels of SBA-15. Ag nanoparticles with diameters in the range of 2.5–5.5 nm and a narrow size distribution were confirmed by atomic force microscope images and energy-dispersive X-ray spectroscopy. UV–vis spectroscopy showed a broad emission peak of Ag nanoparticles centered at ca. 438 nm.     

High performance NiO/Ag/NiO transparent conducting electrodes for p-Si/n-ZnO heterojunction photodiodes

A NiO/Ag/NiO (NAN) transparent conducting electrode (TCE) was fabricated using a magnetron-sputtering system, and the NAN TCE was applied to p-Si/n-ZnO heterojunction photodiodes (HPDs). The NAN TCE exhibits a 50% higher transmittance than the Al electrode (less than 1%). However, a very low sheet resistance of 0.27 Ω/sq is obtained in Al electrode than in NAN TCE (6.5 Ω/sq). The NAN TCE could effectively enhance the photo response of p-Si/n-ZnO HPDs for both ultraviolet (UV) and visible bands as compared to the p-Si/n-ZnO HPDs with the traditional Al electrode. Compared to the traditional p-Si/n-ZnO HPDs using the Al electrode, for the p-Si/n-ZnO HPDs using NAN TCE, the 500 nm photo response is increased by approximately 10 times and the 280 nm photo response is significantly enhanced by approximately 100 times at a reverse-bias voltage of 1 V. The dark current of p-Si/n-ZnO HPDs with NAN TCE is two orders of magnitude lower than that of p-Si/n-ZnO HPDs with an Al electrode. The improved performance enhances the photo (500 nm) to dark current ratio from 2 for the p-Si/n-ZnO HPDs with Al electrode to 1.4 × 10³ for the one with NAN TCE. The photo (280 nm) to dark current ratio is enhanced from 8.5 × 10² to 6.8 × 10⁵. The mechanism results from the high transmittance in the NAN TCE and Ni diffusion in ZnO. The Ni diffusion in ZnO suppresses its defects and hence decreases electron scattering from crystallites/grains, thereby increasing carrier mobility.     

氧化镍/碳纳米管构筑准固态不对称超级电容器及电化学性能

以Ni(NO₃)₂为原料、NaOH为沉淀剂和羟基化碳纳米管（CNT）为基质首先制备了Ni(OH)₂/CNT复合材料, 然后将其于一定温度下煅烧,使其转变为NiO/CNT复合材料。用X射线粉末衍射仪（XRD）、场发射电子显微镜（FESEM）和透射电子显微镜（TEM）表征了样品的晶相与形貌,结果表明NiO纳米粒子紧密锚附在碳纳米管表面。复合材料可能的形成机理被提出。采用循环伏安法（CV）、单电极充放电和电化学阻抗研究了反应条件对其电化学性能的影响,确定最佳制备条件。将复合材料正极、活性炭负极和PVA-KOH电解质膜组装成准固态不对称超级电容器,电化学性能测试结果表明,在充放电电流密度11.2mA/cm²下,其比电容达到868.0F/g并保持稳定循环3700圈。7500次循环后,其比电容值仍有564.2F/g,显示出高的比电容和长的循环稳定性。     

Sol-gel fabrication of NiO and NiO/WO3 based electrochromic device on ITO and flexible substrate

Electrochromic devices (ECDs) with reversible transmittance change represent a promising alternative to smart windows. However, the low−cost facile fabrication of ECDs, particularly flexible devices, remains challenging. In this study, novel NiO is synthesized by a solid state method, and the as−prepared NiO is introduced as an electrochromic anodic layer and fabricated onto a transparent conductive electrode (indium tin oxide, ITO or flexible silver nanowires, AgNW) by a sol–gel spin coating and low temperature annealing (80 °C-150 °C). The solvent, thickness of NiO, and annealing temperature are evaluated to obtain higher ECD performance. NiO/ITO ECDs exhibit very high transmittance variation (ΔT = ~84%) at 700 nm with applied potentials of −3.0 and 0 V. The stability and transmittance variation of NiO/ITO are significantly improved in the presence of a WO₃ cathodic electrode at lower applied voltages of 1.5 to 0 V. The low processing temperature of 80 °C demonstrates the potential of the flexible ECDs. The flexible NiO–WO₃ device achieves a transmittance variation of ~38% at 700 nm with applied potential of 2.0 and 0 V, and retains the ECD performance. The application of low−cost solution−processed NiO and NiO/WO₃−based ECDs in flexible transparent conductive electrodes provides a new pathway for the fabrication of optical devices and printed electronics.     

Hybrid CuO-Co3O4 nanosphere/RGO sandwiched composites as anode materials for lithium-ion batteries

Hybrid CuO-Co₃O₄ nanosphere building blocks have been embedded between the layered nanosheets of reduced graphene oxides with a three dimensional (3D) hybrid architecture (CuO-Co₃O₄-RGO), which are successfully applied as enhanced anodes for lithium-ion batteries (LIBs). The CuO-Co₃O₄-RGO sandwiched nanostructures exhibit a reversible capacity of~847 mA·h·g^-1 after 200 cycles' cycling at 100 mA·g^-1 with a capacity retention of 79%. The CuO-Co₃O₄-RGO compounds show superior electrochemical properties than the comparative CuO-Co₃O₄, Co₃O₄ and CuO anodes, which may be ascribed to the following reasons:the hybridizing multicomponent can probably give the complementary advantages; the mutual benefit of uniformly distributing nanospheres across the layered RGO nanosheets can avoid the agglomeration of both the RGO nanosheets and the CuO-Co₃O₄ nanospheres; the 3D storage structure as well as the graphene wrapped composite could enhance the electrical conductivity and reduce volume expansion effect associated with the discharge-charge process.     

Carbon nanotube/graphene composite for enhanced capacitive deionization performance

In this study, single-walled carbon nanotubes were combined with graphene oxide nanosheets in aqueous dispersion and then chemically reduced to form the carbon nanotube/graphene (CNT/G) composite as electrodes for capacitive deionization (CDI). The structure of the CNT/G composite was highly porous, with single-walled carbon nanotubes (SWCNTs) sandwiched between graphene sheets that functioned as spacers and provided diffusion paths for smooth and rapid ion conduction. The associated increase in the electrical double-layer capacitance enhanced capacitive deionization performance. The CNT/G composite achieved a specific capacitance of 220 F/g and an electrosorption capacity of 26.42 mg/g with 100% regeneration, showing great potential as a high performance electrode material in CDI applications.