Synthesis of mesoporous polythiophene/MnO2 nanocomposite and its enhanced pseudocapacitive properties

Mesoporous nanocomposite of polythiophene and MnO₂ has been synthesized by a modified interfacial method, aiming to develop electrode materials for supercapactitors with an enhanced cycle performance and high-rate capability. The N₂ adsorption/desorption isotherm test of the prepared hybrid indicates a high surface area and a typical mesoporous feature. A uniform hierarchical microstructure with submicron-spheres assembled from ultrathin nanosheet with diameters less than 10 nm has been confirmed by field-emission scanning electron microscopy and transmission electron microscopy. The employed interfacial synthesis is found to be advantageous to retard the overgrowth of nuclei. The retention of 97.3% of its initial capacitance after 1000 cycles at a charge/discharge rate of 2 A g⁻¹ indicates excellent cycle performance of the nanocomposite electrode. At a high-rate charge/discharge process of 10 A g⁻¹, the nanocomposite electrode retained 76.6% of its capacitance at 1 A g⁻¹, suggesting good high-power capability. The important roles of polythiophene in the as-prepared nanocomposite are highlighted in terms of their functions on enhancing the electrical conductivity and constraining the dissolution of manganese oxides during charge-discharge cycles.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Growth of polyaniline on rGO-Co3S4 nanocomposite for high-performance supercapacitor energy storage

Recently, since the supercapacitors have drawn considerable attention, a vast study have been triggered in order to develop efficient electrodes for responding to the increasing demand of supercapacitors. In this report, a possible approach have been used to prepare a ternary nanocomposite, polyaniline/reduced graphene oxide-cobalt sulfide (PANI/rGO-Co₃S₄). At first, a simple and inexpensive hydrothermal route has been used for the preparation of cobalt sulfide (Co₃S₄) on the surface of graphene oxide sheets (rGO-Co₃S₄). Then, the polyaniline nanorods have been flourished on the surface of rGO-Co₃S₄ sheets via in situ chemical polymerization of aniline which was synergistically adjoined to the graphene surface. Polyaniline has uniformly covered the surface of the rGO-Co₃S₄ due to the rational combination of two components. Combining of PANI with rGO-Co₃S₄ electrode material amplify its electrochemical efficiency in terms of a high specific capacitance of 767 F g^?1 at 1 A g^?1 and 81.7% of specific capacitance maintenance after 5000 cycles due to the creation of synergistic effect. Therefore, the ternary nanocomposite of PANI/rGO-Co₃S₄ provides a new promising pathway for the expanding of high-performance electrode materials for supercapacitors.     

Synthesis of Co(OH)2/graphene/Ni foam nano-electrodes with excellent pseudocapacitive behavior and high cycling stability for supercapacitors

Vertically aligned graphene nanosheets have been synthesized by radio-frequency plasma-enhanced chemical vapor deposition on nickel-foam current collectors and that have been used as substrates for cathodic electrodeposition of cobalt hydroxide nanosheets in Co(NO₃)₂ aqueous solution. Raman spectrum exhibits that high-quality graphene nanosheets have been synthesized. The composites have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, cyclic voltammetry and galvanostatic charge/discharge. It indicates that hexagonal Co(OH)₂ has a network microstructure, consisting of interlaced sheets with the thickness of 12 nm coated on the graphene nanosheets. The binder-free nano-electrode exhibits excellent pseudocapacitive behavior with pseudocapacitances of 693.8 and 506.2 Fg⁻¹ at current density of 2 and 32 Ag⁻¹, respectively, in a potential range of −0.1–0.45 V. The capacitance can retain about 91.9% after 3000 charge–discharge cycles at 40 Ag⁻¹, which is higher than that of Co(OH)₂/Ni foam (after 2000 cycles, 75.5% of initial capacitance remains). The introduction of graphene between Co(OH)₂ and Ni foam demonstrates an enhancement of electrochemical stability of the nano-electrodes.     

Synthesis of hydrothermally reduced graphene/MnO2 composites and their electrochemical properties as supercapacitors

Hydrothermally reduced graphene/MnO₂ (HRG/MnO₂) composites were synthesized by dipping HRG into the mixed aqueous solution of 0.1 M KMnO₄ and 0.1 M K₂SO₄ for different periods of time at room temperature. The morphology and microstructure of the as-prepared composites were characterized by field-emission scanning electron microscopy, X-ray diffraction, Raman microscope, and X-ray photoelectron spectroscopy. The characterizations indicate that MnO₂ successfully deposited on HRG surfaces and the morphology of the HRG/MnO₂ shows a three-dimensional porous structure with MnO₂ homogenously distributing on the HRG surfaces. Capacitive properties of the synthesized composite electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 1 M Na₂SO₄ aqueous solution as electrolyte. The main results of electrochemical tests are drawn as follows: the specific capacitance value of HRG/MnO₂-200 (HRG dipped into the mixed solution of 0.1 M KMnO₄ and 0.1 M K₂SO₄ for 200 min) electrode reached 211.5 F g⁻¹ at a potential scan rate of 2 mV s⁻¹; moreover, this electrode shows a good cyclic stability and capacity retention. It is anticipated that the synthesized HRG/MnO₂ composites will find promising applications in supercapacitors and other devices in virtue of their outstanding characters of good cycle stability, low cost and environmentally benign nature.     

One step synthesis of rGO-Ni3S2 nano-cubes composite for high-performance supercapacitor electrodes

In the last decade, supercapacitors possessing high power density and cyclic stability have attracted great interests in various applications. Graphene-based composite electrodes are known as a promising candidate for supercapacitors due to synergistic effects. For the first time, in this work, we develop a simple one-step hydrothermal synthesis of graphene wrapped Ni₃S₂ nanocubes (rGO-Ni₃S₂) composite for high-performance and low-cost supercapacitor electrodes. The rGO-Ni₃S₂ electrode exhibits an ultrahigh specific capacity of 616 C g^?1 at the current density of 1 A g^?1 with excellent cycling durability of 92.7% after 5000 cycles, which is much better when compared with the counterpart without graphene (pure Ni₃S₂). We attribute the remarkable performance of the rGO-Ni₃S₂ electrode to the synergistic effects of the graphene as the conductive support and Ni₃S₂ cubics as the pseudocapacitive material. This work constitutes a step forward towards the development of low-cost and high-performance supercapacitors for the next generation of portable electronics.     

Electrodeposited nickel nanocone/NiMoO4 nanocomposite designed as superior electrode materials for high performance supercapacitor

A nickel nanocone-modified NiMoO₄ hybrid (NiMoO₄/NNC) on Ni foam (NF) substrate is engineered to enhance the capacitance performance of NiMoO₄ via facile and convenient electrodeposition strategy, followed by hydrothermal method. The presence of nickel nanocone (NNC) increases the density of reaction active sites of NiMoO₄/NNC/NF, which can shorten the charge diffusion pathway and boost ionic/electronic conductivities. As expected, the NiMoO₄/NNC/NF, as a prospective electrode material, presents appreciable electrochemical properties. Remarkably, the NiMoO₄/NNC/NF electrode demonstrates a high specific capacitance of 2813 F g^?1 at 3 A g^?1 and manifests considerable cycling durability with a retention of 94% of the initial capacitance over consecutive 5000 cycles. Furthermore, a NiMoO₄/NNC/NF//AC/NF asymmetric supercapacitor displays a great electrochemical performance by delivering high energy density (43 Wh kg^?1) and power density (821 W kg^?1) as well as notable durableness (10% decay after 5000 cycles). The presented results suggest that NiMoO₄/NNC/NF can be considered as a binder-free electrode for highly stable supercapacitors.     

Comparative study on MoS2 and WS2 for electrocatalytic water splitting

Replacing Pt by earth abundant catalysts is one of the most important tasks toward potential large-scale HER applications. Among many potential candidates, low cost and earth abundant transition metal dichalcogenides such as MoS₂ and WS₂ have been promising as good H₂ evolution electrocatalysts when they are engineered into the structures with active sites. In this work, we have performed systematic studies on the catalytic reactivity of both MoS₂ and WS₂ materials produced by one-step and scalable thermolysis from (NH₄)₂WS₄ and (NH₄)₂MoS₄ precursors respectively. Structural analysis shows that these materials prepared at a higher thermolysis temperature exhibit higher crystallinity. The H₂ evolution electrocatalysts efficiency for the MoS₂ prepared at a lower temperature is higher than those at higher temperatures, where amorphous MoS₂ or S₂²⁻${{\text{S}}_2}^{2-}$ species instead of crystalline MoS₂ is the main active site. By contrast, crystalline WS₂ prepared at high temperature is identified to be the key reaction site. Both catalysts display excellent efficiency and durability as an electrocatalyst operating in acidic electrolytes. This work provides fundamental insights for further design and preparation of emergent metal dichalcogenide catalysts, beneficial for the development in clean energy.     

Three-dimensional Ni(OH)2 nanoflakes/graphene/nickel foam electrode with high rate capability for supercapacitor applications

Supercapacitor, known as an important energy storage device, is also a critical component for next generation of hydrogen fuel cell vehicles. In this study, we report a novel route for synthesis of three-dimensional Ni(OH)₂/graphene/nickel foam electrode by electrochemical depositing Ni(OH)₂ nanoflakes on graphene network grown on nickel foam current collector and explore its applications in supercapacitors. The resulting binder-free Ni(OH)₂/graphene/nickel foam electrode exhibits excellent supercapacitor performance with a specific capacitance of 2161 F/g at a current density of 3 A/g. Even as the current density reaches up to 60 A/g, it still remains a high capacitance of 1520 F/g, which is much higher than that of Ni(OH)₂/nickel foam electrode. The enhanced rate capability performance of Ni(OH)₂/graphene/nickel foam electrode is closely related to the presence of highly conductive graphene layer on nickel foam, which can remarkably boost the charge-transfer process at electrolyte–electrode interface. The three-dimensional graphene/nickel foam substrate also significantly improves the electrochemical cycling stability of the electrodeposited Ni(OH)₂ film because of the strong adhesion between graphene film and electrodeposited Ni(OH)₂ nanoflakes. Results of this study provide an alternative pathway to improve the rate capability and cycling stability of Ni(OH)₂ nanostructure electrode and offer a great promise for its applications in supercapacitors.     

Enhancing the photoelectrochemical performance of p-silicon through TiO2 coating decorated with mesoporous MoS2

MoS₂ is a promising electrocatalyst for hydrogen evolution reaction and a good candidate for cocatalyst to enhance the photoelectrochemical (PEC) performance of Si-based photoelectrode in aqueous electrolytes. The main challenge lies in the optimization of the microstructure of MoS₂, to improve its catalytic activity and to construct a mechanically and chemically stable cocatalyst/Si photocathode. In this paper, a highly-ordered mesoporous MoS₂ was synthesized and decorated onto a TiO₂ protected p-silicon substrate. An additional TiO₂ necking was introduced to strengthen the bonding between the MoS₂ particles and the TiO₂ layer. This meso-MoS₂/TiO₂/p-Si hybrid photocathode exhibited significantly enhanced PEC performance, where an onset potential of +0.06 V (versus RHE) and a current density of −1.8 mA/cm² at 0 V (versus RHE) with a Faradaic efficiency close to 100% was achieved in 0.5 mol/L H₂SO₄. Additionally, this meso-MoS₂/TiO₂/p-Si photocathode showed an excellent PEC ability and durability in alkaline media. This paper provides a promising strategy to enhance and protect the photocathode through high-performance surface cocatalysts.     

Thermal evolution in air and argon of nanocrystalline MoS2 synthesized under hydrothermal conditions

Nanocrystalline molybdenum sulfide was synthesized between 150°C and 225°C under hydrothermal conditions starting from ammonium heptamolybdate and thiourea. Samples were characterized with X-ray powder diffraction, electron microscopy, nitrogen adsorption, thermoanalysis and infrared spectroscopy. The hydroxyls involved in the synthesis and adsorbed on crystals surface hindered crystallization and samples still recrystallized after the final dehydroxylation step above 300°C, just when hydroxyls were isolated from each other. This also promoted sulfur bond breaking that gave rise to partial transformation of the MoS₂ into MoO₂ when the annealing atmosphere was argon, and to the total transformation of the sulfide into MoO₃ when it was air. The initial MoS₂ crystals were bend; many of them were isolated, and others associated in bundles that formed worm-like grains interacting with each other to produce spherical grains aggregated in clusters. This morphology gave rise to samples with a low specific surface area.     

Enhanced photocatalytic activities of three-dimensional graphene-based aerogel embedding TiO2 nanoparticles and loading MoS2 nanosheets as Co-catalyst

A novel graphene-based three-dimensional (3D) aerogel embedded with two types of functional nanomaterials had been prepared by a facile one-pot hydrothermal process. During the hydrothermal reaction, graphene, TiO₂ nanoparticles and MoS₂ nanosheets were self-assembled into the 3D interconnected networks aerogel, where the uniformly dispersed TiO₂ nanoparticles were densely anchored onto the graphene nanosheets and decorated with the ultrathin MoS₂ nanosheets. The UV–vis DRS and PL spectra measurement shows that the MoS₂/P25/graphene aerogel exhibits enhanced light absorption and efficient charge separation properties. As a new photocatalyst, the photocatalytic activity was evaluated by photoelectrochemical test and photodegradation methyl orange (MO) under UV irradiation, an improvement of photocurrent was observed, as 6 times higher for MoS₂/P25/graphene aerogel (37.45 mA/cm²) than pure P25 at +0.6 V, and the fastest photodegradation of MoS₂/P25/graphene aerogel was found within 15 min. The improved photocatalytic activity is attributed to the porous structure, good electrical conductivity and the maximization of accessible sites of the unique 3D graphene aerogel, the increasing active adsorption sites and photocatalytic reaction centers for the introduction of MoS₂ nanosheets, and the positive synergetic effect between the three components in this hybrid. This work demonstrates that the as-prepared MoS₂/P25/graphene aerogel may have a great potential application in photoelectrochemical hydrogen production and pollution removal.     

Carbon nanofibre/hydrous RuO2 nanocomposite electrodes for supercapacitors

Amorphous RuO₂·xH₂O and a VGCF/RuO₂·xH₂O nanocomposite (VGCF = vapour-grown carbon fibre) are prepared by thermal decomposition. The morphology of the materials is investigated by means of scanning electron microscopy. The electrochemical characteristics of the materials, such as specific capacitance and rate capability, are investigated by cyclic voltammetry over a voltage range of 0–1.0 V at various scan rates and with an electrolyte solution of 1.0 M H₂SO₄. The specific capacitance of RuO₂·xH₂O and VGCF/RuO₂·xH₂O nanocomposite electrodes at a scan rate of 10 mV s⁻¹ is 410 and 1017 F g⁻¹, respectively, and at 1000 mV s⁻¹ are 258 and 824 F g⁻¹, respectively. Measurements of ac impedance spectra are made on both the electrodes at various bias potentials to obtain a more detailed understanding of their electrochemical behaviour. Long-term cycle-life tests for 10⁴ cycles shows that the RuO₂·xH₂O and VGCF/RuO₂·xH₂O electrodes retain 90 and 97% capacity, respectively. These encouraging results warrant further development of these electrode materials towards practical application.     

Synthesis of hierarchical tube-like yolk-shell Co3O4@NiMoO4 for enhanced supercapacitor performance

Transition metal oxides with three-dimensional architectures have attracted great interest as high-performance supercapacitor electrodes. In this work, tube-like yolk-shell Co₃O₄@NiMoO₄ composite were prepared via a two-step synthesis for the first time. Ultrathin NiMoO₄ nanosheets arrayed randomly to form porous shell, which fully covered around Co₃O₄ fibers with interspaces between core and shell. Benefitting from unique structure and chemical composition, the Co₃O₄@NiMoO₄ composite as supercapacitor electrodes exhibited enhanced specific capacitance of 913.25 F g^?1 at high current density of 10 A g^?1 and large capacitance retention of 88% with current density increased from 0.5 to 20 A g^?1 as well as remarkable cycling stability. In addition, NiCo₂O₄@NiMoO₄ and NiFe₂O₄@NiMoO₄ composites with similar morphologies were obtained. Namely, this work exhibits a general approach to reasonable construct and preparation hierarchical structure for high performance supercapacitor electrodes.     

Synthesis of MoS2-carbon composites with different morphologies and their application in hydrogen evolution reaction

MoS₂-carbon composites which with different morphologies were synthesized by hydrothermal method and tested with respect to their application in hydrogen evolution reaction (HER). Their performances were compared to evaluate how the morphology influence HER. The obtained results showed that the composite containing amorphous MoS₂ showed higher activity than composite which contains crystalline MoS₂. The catalytic activity of composite was highly correlated to its active surface area which was controlled by the morphology. In addition, compared with composite which contains amorphous MoS₂, the composite containing crystalline MoS₂ showed higher durability in the long-term operation. However, in acidic and alkaline environments, the stability of composite containing amorphous MoS₂ is better than which containing crystalline MoS₂. The impedance measurements suggested that the high catalytic activity of the composite stems from the synergistic effect of MoS₂ and carbon materials. The enhanced understanding of these highly active hydrogen evolution catalysts can facilitate the development of economical electrochemical hydrogen production systems.     

Novel synthesis of Zn2GeO4/graphene nanocomposite for enhanced electrochemical hydrogen storage performance

For the first time, a novel technique of preparing Zn₂GeO₄ nanostructures has been developed by using chemical precipitation method of GeCl₄ as a Ge precursor and acacen as a capping agent. Uniform and fine Zn₂GeO₄ nanoparticle was synthesized. The optimized Zn₂GeO₄ nanostructures anchored onto graphene sheets and Zn₂GeO₄/graphene nanocomposite synthesized through pre-graphenization, successfully. Hydrogen storage capacities of Zn₂GeO₄ nanoparticle and Zn₂GeO₄/graphene nanocomposite were compared, for the first time. Obtained results represent that Zn₂GeO₄/graphene nanocomposites have higher electrochemical hydrogen storage capacity than Zn₂GeO₄ nanoparticles. It was found that the synergistic effect between Zn₂GeO₄ nanoparticles and graphene sheets can improve the electrochemical performance of this hybrid composite electrode. After 29 cycles, the discharging capacities of the electrode reached to 2695 mAh/g. These results indicate that the Zn₂GeO₄/graphene nanocomposite can be potentially applied for electrochemical hydrogen storage.     

Synthesis and electrochemical performance of multi-walled carbon nanotube/polyaniline/MnO2 ternary coaxial nanostructures for supercapacitors

Multi-walled carbon nanotube (MWCNT)/polyaniline (PANI)/MnO₂ (MPM) ternary coaxial structures are fabricated as supercapacitor electrodes via a simple wet chemical method. The electrostatic interaction between negative poly(4-styrenesulfonic acid) (PSS) molecules and positive Mn²⁺ ions causes the generation of MnO₂ nanostructures on MWCNT surfaces while the introduction of PANI layers with appropriate thickness on MWCNT surfaces facilitates the formation of MWCNT/PANI/MnO₂ ternary coaxial structures. The thickness of PANI coatings is controlled by tuning the aniline/MWCNT ratio. The effect of PANI thickness on the subsequent MnO₂ nanoflakes attachment onto MWCNTs, and the MPM structures is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and field-emission scanning electron microscopy (FESEM). The results suggest that appropriate thickness of PANI layers is important for building MPM ternary coaxial structures without the agglomeration of MnO₂ nanoflakes. The MPM ternary coaxial structures provide large interaction area between the MnO₂ nanoflakes and electrolyte, and improve the electrochemical utilization of the hydrous MnO₂, and decrease the contact resistance between MnO₂ and PANI layer coated MWCNTs, leading to intriguing electrochemical properties for the applications in supercapacitors such as a specific capacitance of 330 Fg⁻¹ and good cycle stability.     

High electrochemical performance of PANI/CdO nanocomposite based on graphene oxide as a hybrid electrode materials for supercapacitor application

In the last decade, the production of clean and sustainable energy sources for energy storage purposes have grown dramatically due to the population growth and increasing demand for energy in the world. In this regard, supercapacitors have proved to be promising candidates in energy storage applications. Therefore, in this study, polyaniline/cadmium oxide/graphene oxide (PANI/CdO/GO) nanocomposite was prepared by co-precipitation method to evaluate the electrochemical performance. The structural and surface properties, morphology and particle size distribution were analyzed by XRD diffraction spectroscopy (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), N₂ adsorption-desorption, and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the synthesized nanocomposite was applied as an active electrode material and its performance was investigated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) in terms of energy storage. The results of these tests confirmed that PANI/CdO/GO nanocomposite provides great electrochemical behavior, including specific capacity of 647 F g^?1, energy density of 116.6 W h kg^?1, power density of 388 W kg^?1 compared to the other electrode. According to the stability test, the initial capacity maintenance was about 82% after 500 charge-discharge cycles, which indicated relatively good electrochemical stability. Moreover, the impedance spectroscopy studies showed that the nanocomposite possessed much lower internal strength and charge transfer reaction resistance in comparison to the other synthesized materials. Based on these results, it was found that the prepared nanocomposite has a good performance in the field of energy storage.