Symmetric Two-electrode System Research Articles

0D-3D Superstructure of Biocarbon with FeCl3-Assisted for Electrochemical Symmetrical Supercapacitor

Biomass materials exhibit a diversity of macrostructures that can be derived or developed into various 0D-3D nanoscale structural designs with various different dimensions such as spherical, nanofiber, tubular, nanosheet, hierarchical, nanosphere, and honeycomb structures, when converted into activated carbon. This research converts oil palm empty fruit bunch fiber biomass into supercapacitor carbon material by optimizing the chemical activation process by varying the activating reagent. The active carbon conversion process includes precarbonization stages, chemical activation (KOH, FeCl3, and ZnCl2), carbonization, and physical activation. The resulting electrode was confirmed to have a morphology with a 0D to 3D structure (nanosphere, nanofiber and nanopore) due to the FeCl3 activator, so the resulting surface area was high (517.998 m/g). Biomass was successfully converted into carbon which was confirmed through through the resulting physical and electrochemical properties. The electrochemical performance of the sample supercapacitor cell was analyzed in a symmetric two-electrode system in 1 M H2SO4 electrolyte solution. The FeCl3-activated samples shows the highest specific capacitance of 256 F/g at a scan rate of 1 mV/s. In addition, oil palm empty fruit bunch fiber biomass is a potential raw material, as a carbon material for supercapacitor cells with high performance.

B-site disorder driven Griffiths-like phase and electrochemical behavior in Y2NiCrO6 double perovskite

In this investigation, nanoparticles of B-site disordered Y2NiCrO6 (YNCO) double perovskite were synthesized by the facile sol–gel method to evaluate their magnetic and electrochemical properties. Their crystallographic structure is monoclinic and the average size of the particles is 79±16 nm. XPS analysis indicated a mixed oxidation states of B-site transition metals Ni2+/Ni3+ and Cr2+/Cr3+. The mixed valence states of Ni and Cr, along with the mixed magnetic phases of YNCO, constitute a signature of the B-site disorder. This antisite disorder contributed to the observation of a Griffiths-like phase arising from ferromagnetic short-range interactions above the magnetic transition up to the Griffiths temperature, T G = 137 K. The synthesized YNCO double perovskite demonstrated a promising behavior as an electrode material for electrochemical supercapacitors. In a three-electrode system, it displayed a specific capacitance of 270 F g−1 at a current density of 0.5 A g−1. In a symmetric two-electrode system, YNCO exhibited a specific capacitance of 180 F g−1 at 0.5 A g−1, alongside an energy density of 6.25 Wh kg−1 at 250 W kg−1 power density. In both cases, we employed a mild 0.5 M neutral aqueous Na2SO4 solution as the electrolyte, in contrast to the typically employed corrosive and concentrated alkaline aqueous solution. The fascinating magnetic and charge storage properties of the B-site disordered YNCO double perovskite indicate its potential for use in spintronic devices and as efficient electrodes in symmetric hybrid supercapacitors.

Crystalline Ni5P4/amorphous CePO4 core/shell heterostructure arrays for highly-efficient electrocatalytic overall water splitting

Exploring low-cost and highly efficient bifunctional electrocatalysts for overall water splitting has become a research focus recently. Crystalline/amorphous core/shell heterostructures have great potential for applications in the field of electrocatalytic overall water splitting. However, related research is still challenging. Herein, crystalline Ni5P4 nanosheets/amorphous CePO4 nanocrystals core/shell heterostructure arrays were developed for electrocatalytic overall water splitting. It is shown that the heterostructure array required competitive HER and OER overpotentials of 94 and 191 mV in alkaline environment (10 mA/cm2), respectively. Encouragingly, the symmetrical two-electrode system constructed with the heterostructure array only required an ultra-low cell voltage of 1.535 V to achieve a current density of 10 mA/cm2. This indicates the system has huge potential in overall water splitting. The electrocatalytic mechanism was studied systematically by combining theoretical calculation and experimental characterization. It was found that the surface coating of amorphous CePO4 could not only significantly increase the electrochemical active surface area and improve the charge transfer of crystalline Ni5P4 nanosheets, but could also regulate d-band center of Ni5P4 and optimize the adsorption towards reaction intermediates in water splitting. The results not only provide an excellent crystalline/amorphous core/shell heterostructure bifunctional electrocatalyst for overall water splitting but also greatly expand the application of rare earth metal phosphate CePO4.

Engineering of N, P co-doped hierarchical porous carbon from sugarcane bagasse for high-performance supercapacitors and sodium ion batteries

Porous carbon is one of the most promising electrode materials for energy conversion and storage devices due to its high specific surface area, low cost, sustainability, appropriate charging/discharging voltage platform and high interlayer spacing. However, the disadvantage of insufficient energy storage capacity frustrates its wide applications. Herein, a novel N, P co-doped porous carbon derived from sugarcane bagasse (SBNPk) was prepared by hydrothermal method combined with KOH activation and carbonization, and was applied to supercapacitors (SCs) and sodium-ion batteries (SIBs). The SBNPK possesses a special hierarchical porous structure, improved surface area, larger interlayer spacing, and moderate N, P doping level. Specifically, the SBNPk carbonization at 600 °C (SBNPk-600) exhibits the highest specific capacitance (356.4 F g−1 at 1 A g−1), good rate capability and excellent cycle stability (5% loss over 10,000 cycles) in a three-electrode system. Further assembled in a symmetrical two-electrode system, the SBNPK-600//SBNPK-600 can still provide a higher energy density of 6.5 Wh kg−1 at 251.9 W kg−1 and superior cycle performance (96.5% of capacitance retention at 2 A g−1 after 20,000 cycles). Surprisingly, the SBNPK-600 as an anode for SIBs also delivers a high reversible capacity of 304.1 mAh g−1 at 25 mA g−1 and excellent cycle performance (225.7 mAh g−1 after 1000 cycles at 500 mA g−1), indicating its superior sodium storage capability. This work provides a simple and new way to enhance the electrochemical performance of biomass waste-derived carbon by heteroatom doping, which is helpful to further boost its application in the field of energy storage.

3D host-guest material of {Ag(pz)} modified {BW12O40} with supercapacitor, photocatalytic dye degradation and H2O2 sensing performances

The synthesis and properties of inorganic-organic hybrids based on {BW12O40} are still the focus of polyoxometalates. Here, 3D host-guest material with the molecular formula [Ag5(pz)6(H2O)4][BW12O40] (pz ​= ​pyrazine) (1) was synthesized by the hydrothermal method. The single crystal analysis showed that the compound was composed of a [Ag3(pz)4]3+ fragment, a [Ag2(pz)2(H2O)4]2+ fragment, and a [BW12O40]5- anion. In the structure, Ag ions are connected into 1D wavy linear bridge chains by pz ligands to form {Ag-pz}n. Twelve Ag ions form a large loop via pz, and each loop forms a supramolecular 2D structure with two {BW12O40} and forms a 3D structure through supramolecular interaction. In the three-electrode system with compound 1 as the active substance and nickel foam as the collector, the specific capacitance is 245.6 ​F ​g−1 when the current density is 1 ​A ​g−1. Higher than those reported in the literature. Constitute a symmetric two-electrode system, with an energy density of 6.9 ​Wh kg−1, with a power density of 498.7 ​W ​kg−1. And after 5000 cycles, the specific capacitance remains at 92.5%. Besides, the photocatalytic degradation rates of methylene blue (MB), methyl orange (MO), and rhodamine B (RhB) were 93.2% and 90.0%, and 93.7%, respectively. Good sensing performance for H2O2, with a wide linear range (5 μ M-0.27 ​mM) and low detection limit (2.2 μ M).

Effect of surface modification by KOH activation on the electrochemical performance of Co3O4 nanoparticles

In this work, the effects of different Co3O4:KOH mass ratios on the microstructure, chemical state, and surface properties of Co3O4 nanoparticles were investigated and discussed. The different KOH contents in the activation process affecting the electrochemical properties of the samples were determined in a three-electrode configuration. The results showed that the sample with a Co3O4:KOH mass ratio of 1:0.5 (Co@0.5KOH) exhibited the highest specific capacitance of 204.0 F/g at a current density of 1 A/g. The excellent capacitance retention of 97.7% was observed after a 5000 cycle galvanostatic charge/discharge test. A symmetrical two-electrode system was set up, and the results showed that the Co@0.5KOH sample had a superior energy density of 3.5 Wh/kg and a power density of 276.0 W/kg at a current density of 1 A/g. The KOH activation method was effective and could be extended to other metal oxides to obtain better electrode materials for supercapacitors.

Synthesis of hierarchical ZnO/NiO nanocomposite Wurtz hexagonal nanorods via hydrothermal for high-performance symmetric supercapacitor application

This paper describes a simple and well-controlled hydrothermal synthesis of transition metal hydroxide (TMH) based on Nickel Oxide-Zinc Oxide (NZ) nanocomposite to construct free-standing and stable hybrid Wurtz Hexagonal Nanorods (HN) via a hydrothermal technique. The NZ nanocomposite was characterized and analyzed utilizing a variety of techniques, including XRD, FTIR, FESEM, HRTEM, XPS, and Raman Spectroscopy. The fabrication of the symmetrical two-electrode system results in the NZ-15 nanocomposite. It had a high specific capacitance (Csp) of 933.2 Fg−1 at a current density (CD) of 1 Ag−1. And also obtain long-term cycle stability of capacitance retention of 79.64 % and the coulombic efficiency of 97.24 %, even after 5000 cycles. It had a maximum energy density (ED) of 23.7 Whkg−1 and a power density (PD) of 214.1 Wkg−1 as well. The electrode's practical use was tested by lighting them up with a commercial blue LED linked in series, which flashes for nearly 1 to 2 min with intermittent voltage drops. The high electrochemical performance and other results could be evidence that the development of innovative new electrode materials hybrid Wurtz HNs structure is a prominent candidate for high-energy-density supercapacitor applications (SCs).

Synthesis of {P2W18}-based coated structured nano materials with supercapacitors and H2O2 sensing

The combination of metal-organic frameworks (MOFs) with large specific surface area and high stability and Dawson-type polyoxometalates (POMs) with excellent electron transfer ability to build a new inorganic-organic hybrid as energy storage materials can give full play to the advantages of both. Therefore, the inorganic organic hybrid nano material {Ag4K2P2W18O62}@[Ag3(μ-Hbtc)(μ-H2btc)]n (which became {Ag4K2P2W18O62}@Ag-BTC, where BTC = 1,3,5-benzenetricarboxylic acid) was synthesized by liquid-assisted grinding. The XRD, SEM, TEM characterization show that {Ag4K2P2W18O62}@Ag-BTC is a coating structure. The specific capacitance is 378.9 F g−1 at a current density of 1 A g−1, with a retention rate of 93.5 % for 5000 cycles. An energy density of 7.8 Wh kg−1 and the power density of 500.0 W kg−1 are obtained in water-based symmetric two-electrode supercapacitor system. In addition, when used as an H2O2 sensor, it has a broad detection range of 1.5 μM to 1.5 mM and the small detection limit of 0.206 μM, also offers excellent interference immunity and stability. Moreover, by applying this nano material to the detection of H2O2 in human serum, results are acceptable. The above result shows that the composite material synthesized by the liquid-assisted grinding method adequately combines properties of both parent materials is a viable strategy for achieving performance enhancement.

Facile synthesis of nitrogen-doped interconnected porous carbons derived from reed and chlorella for high-performance supercapacitors

Three-dimensionally (3D) nitrogen (N)-doped interconnected porous carbons (IPC) derived from cost-effective biomasses were facilely prepared by one-step method and utilized as electrochemical double layer capacitor (EDLC) electrodes. The reed and chlorella derived interconnected porous carbons (denoted as IPC-R and IPC-C) through carbonization with chemical activation both exhibited typical capacitive behaviors; importantly, by introducing N-rich chlorella into N-free reed by interactive‑carbonization, the resultant N-doped interconnected porous carbons (IPC-RC) positively demonstrated a high N content, a large specific surface area and pore volume as well as a high graphitization, which are crucial for fast ion diffusion and thus enhancing the electrochemical properties of supercapacitor. In the three-electrode system, the IPC-RC1.2 showed a superb specific capacitance of 340.4 F/g at a current density of 1 A/g, one of the highest capacitances for biomass derived‑carbon electrodes reported so far. Even at 20 A/g, the capacitance could achieve 265.5 F/g, revealing the superb rate capability. In the symmetric two-electrode system, the maximum power density and energy density reached up to 23.6 Wh/kg and 15,000 W/kg, respectively. Besides, an outstanding cycling stability was observed after 10,000 cycles.

Coral reef structured cobalt-doped vanadate oxometalate nanoparticle for a high-performance electrocatalyst in water splitting

Facing the energy crisis in the whole world, it is important to decompose water to obtain high-clean hydrogen energy. However, water splitting by electrocatalysis is suffering from high voltage and poor stability. Herein, we synthesize Co3V2O8 coral reef-like nanoparticles in a facile way, showing a low oxygen evolution reaction (OER) overpotential of 318 mV coupled with good stability, which is superior to commercial RuO2. Besides, the Co3V2O8 shows fast kinetics for hydrogen evolution reaction (HER) and small impedance. Furthermore, the Co3V2O8 nanoparticles are assembled in symmetric two-electrode system, which has a very low overall water splitting voltage of 1.50 V at 10 mA cm−2, this value surpasses the benchmark RuO2//Pt/C assembling and most of the other oxometalate-based electrocatalysts. This work provides a novel and facile way of preparing oxometalates nanomaterial electrocatalyst for hydrogen energy.

POTENSI DAUN JAHE MERAH SEBAGAI BAHAN DASAR PEMBUATAN ELEKTRODA SUPERKAPASITOR

Red ginger leaf waste (Zingiber Officinale Var Rubrum) has been successfully processed as an active carbon base material for supercapacitor electrodes. The process of making carbon electrodes starts from the preparation of the original material, drying, refining, chemical activation, integrated pyrolysis and neutralization. The focus of this research is on the chemical activator ZnCl2 which is used with different concentrations of (0.1 and 0.5) M. Activated carbon powder is printed using a press to produce carbon in the form of solid coins of uniform size. The optimization of the carbon element in the sample is carried out through a pyrolysis process at high temperature with a one-stage integrated technique. Where, carbonization in the N2 gas environment is carried out starting from room temperature 30°C up to 600°C followed by physical activation until the high temperature reaches 800°C in CO2 gas environment. Characterization of activated carbon samples from red ginger leaves begins with determining the amount of shrinkage that occurs in the pyrolysis process by measuring the mass, diameter and thickness of the carbon coins. Furthermore, the electrochemical properties were tested using two methods, namely cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) in a symmetrical two-electrode system. The electrochemical characterization was carried out under the influence of an aqueous electrolyte of 1M KOH and 1M Na2SO4 at a low potential window of 0-1 V. The optimum conditions of electrochemical properties were found in the red ginger leaf activated carbon sample with a ZnCl2 activator concentration of 0.5M for the electrolyte. KOH with a specific capacitance value of 115.9 F/g. while for electrolyte Na2SO4 found in ZnCl2 activator 0.1M with a value of 72 F/g. Through these results, red ginger leaves are known to have great potential as a base material for activated carbon electrodes to improve the performance of supercapacitors.

Epoxy coated melamine-foam used to synthesize nitrogen-doped microporous carbon for super-capacitive energy storage

The epoxy is cured on the high nitrogen-containing melamine foam to construct a composite of epoxy@melamine-foam. Nitrogen doped porous carbon is synthesized by using the composite as a precursor. The atomic content of nitrogen of the resulting amorphous carbon is determined to be 3.6 at.%. The carbon has a typical microporous structure with a specific surface area of 1675 m2 g−1 and a pore volume of 0.81 cm3 g−1. In a three-electrode system in the basic aqueous electrolyte, a specific capacitance of 292.3 F g−1 is achieved from the electrode loaded with the nitrogen-doped electroactive carbon at a current density of 1 A g−1. In a symmetrical two-electrode system in the same electrolyte, a single electrode displays a specific capacitance of 265.3 F g−1 at 0.5 A g−1. For a simulated supercapacitor device, a specific energy of 8.5 W h kg−1 is obtained at the specific power of 103.3 W kg−1. Findings demonstrate the nitrogen doped microporous carbon can be used as a promising electrode material for supercapacitors.

Carbon nanofibers derived from cellulose via molten-salt method as supercapacitor electrode

Carbon nanofibers (CNFs) have been paid much attention as supercapacitor electrode due to outstanding chemical stability, high electron transfer rate and large specific surface area. However, the preparation process of CNFs is always stalemated in electrospinning, heat stabilization and carbonization. The problems of solvent pollution in the electrospinning process, complex process and high energy consumption in conventional carbonization process can't be solved. Herein, CNFs have been innovatively prepared from nanofibrillated cellulose by the molten-salt method (NaCl/NaOH). Molten salt penetrates between the fibers, separates and activates the fibers. The obtained carbon nanofibers remain developed branching structures and have a large specific surface area (899 m2 g−1). The electrical properties are tested in a symmetrical two-electrode system. The specific capacitance is 150 F g−1 at the current density of 1 A g−1. Low equivalent series resistance (1.13 Ω) indicates that it has high electrode conductivity. This study has taken into account energy conservation, environmental protection, recyclability and simplified preparation process, which has a very far-reaching significance for the industrial production of CNFs.

Facile synthesis of graphene oxide-polyaniline-copper cobaltite (GO/PANI/CuCo2O4) hybrid nanocomposite for supercapacitor applications

A novel type ternary GO/PANI/CuCo2O4 composite for electrode material was successfully synthesized and ensured by different characterizations such as XRD (X-ray diffraction), FTIR (Fourier transform infrared spectroscopy), FE-SEM (Field emission scanning electron microscopy), and EDS (Energy-dispersive X-ray spectroscopy). The interconnected morphology of ternary GO/PANI/CuCo2O4 indicates superior electrochemical performance. Ternary GO/PANI/CuCo2O4 displayed the maximum specific capacitance of 741.39 F/g at 1 mV/s scan rate and 312.72 F/g at 1 A/g current density using three-electrode and symmetric two-electrode system, respectively. The ternary GO/PANI/CuCo2O4 electrode based symmetric device had specific energy of 62.54 Wh/kg at 1 A/g current density and specific power of 5997.61 W/kg at 20 A/g. The systems have a wide potential window of 1.2 V, which is beneficial for the energy density. The ternary material electrode also has the lowest value of charge transfer resistance (Rct) as 12.23 Ω and relatively good specific capacitance of 84.25% after 5000 cycles. The excellent electrochemical nature of ternary GO/PANI/CuCo2O4 is mainly because of the synergistic effect which has brought this material to the spotlight for the supercapacitor application.

Facile synthesis of Veitchia merilli coir-based porous carbon using combined chemical and physical activation routes as electrode material for energy storage

This study aimed to prepare Veitchia merilli coir (VMC) through pre-carbonisation process, followed by chemical activation using potassium hydroxide as an activating agent. The experiment was conducted under different pyrolytic physical activation temperatures of 650, 700, and 750 °C with the code VMS-650, VMS-700, and VMS-750 for each sample. Physical activation methods develop or modify the pore structure, specific surface area, and microstructure of activated carbon. Furthermore, the prepared VMCs were characterised using X-ray diffraction, Fourier transform infrared, scanning electron microscope, energy dispersive X-ray, and cyclic voltammetry with a symmetrical two-electrode system in 1 M H2SO4 solution. The microstructure analysis showed that the VMC carbon electrode has an amorphous structure with two broad peaks at 2θ angles around 26° and 44° corresponding to the (002) and (100) planes, with the L c VMS-700 having a value of 16.007 nm. The VMC electrode has a C≡C carbon bond as a functional group, which extends in bands from 2311.79 to 2373.51 cm−1. Meanwhile, the VMS-700 electrode shows a combined surface morphology of nanofibers as well as mesopores, and the energy dispersive X-ray results showed carbon content of 92.83%. The electrochemical properties of supercapacitor cells indicated this electrode had the highest specific capacitance value of 264.2 F g−1. From the obtained results, the respective physical and electrochemical properties of the carbon electrodes and supercapacitor cells showed that the activated VMC-700 at 700 °C is the optimum temperature to produce the best performance compared to 650 and 750 °C.

Highly Mesoporous Cobalt-Hybridized 2D Cu3P Nanosheet Arrays as Boosting Janus Electrocatalysts for Water Splitting.

Recently, developing economical electrocatalysts with high performance in water decomposition has become a research hotspot. Herein, two kinds of cobalt-hybridized Cu3P nanostructure array electrocatalysts (including highly mesoporous 2D nanosheets and sugar gourd-like 1D nanowires) were controllably grown on a nickel foam substrate through a simple hydrothermal method combined with a subsequent phosphating treatment method. An electrocatalytic test indicated that the as-prepared 2D nanosheet array exhibited excellent activity and stability toward hydrogen evolution reaction under alkaline conditions, which offered a low overpotential of 99 mV at 10 mA/cm2 and a small Tafel slope of 70.4 mV/dec, whereas a competitive overpotential of 272 mV was required for oxygen evolution reaction. In addition, the 2D nanosheet array delivered a low cell voltage of 1.66 V at 10 mA/cm2 in a symmetric two-electrode system, implying its huge potential in overall water decomposition. The electrocatalytic performance is superior to the as-prepared 1D nanowire array and most of the Cu3P-related electrocatalysts previously reported. Experimental measurements and first-principles calculations show that the excellent performance of the 2D nanosheet array can be attributed to its unique 2D mesoporous structure and hybridization of cobalt, which not only provide a large electrochemically active surface and fast electrocatalytic reaction kinetics but also weaken the binding strength of electrocatalytic reaction intermediates. The present study provides a simple and controllable approach to synthesize Cu3P-based bimetallic phosphide nanostructures, which can be used as boosting Janus electrocatalysts for water decomposition.

A novel ternary Fe3O4@Fc-GO/PANI nanocomposite for outstanding supercapacitor performance

This work introduced a novel ternary electrode material (Fe3O4@Fc1-GO/PANI2:1) for battery-type supercapacitor applications. This high performance electrode material was designed and synthesized via simple processes that involves a simple co-precipitation of magnetic nanoparticles (MNPs), surface modification of MNPs with ferrocene (Fc) moieties through hydrogen-bonded interaction, and preparation of nanohybrids and nanocomposites via physical mixing strategy. Different appropriate structural analyses were then applied for characterization of the synthesized materials. The supercapacitor properties of the materials were investigated by means of cyclic voltammetry (CV),galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS), tests. After electrochemical evaluations, the Fe3O4@Fc1-GO/PANI2:1nanocomposite was selected as optimal combination. This nanocomposite shows a 640mAh g−1 at 1 A g−1. Also, the selected nanocomposite was exhibited 86.68 % retention of initial capacity after 5000 CV cycles. Finally, this ternary nanocomposite was adopted for symmetric two-electrode system fabrication. The Fe3O4@Fc1-GO/PANI2:1-based symmetric cell delivered a high energy density of 106.2 Wh Kg−1 and a high power density of 6657 W Kg−1. These excellent electrochemical performances can be described to the synergistic effects between nanocomposite components.

A dual‐activation strategy to tailor the hierarchical porous structure of biomass‐derived carbon for ultrahigh rate supercapacitor

Suffering from the competitive relationship between the abundant electrochemically active sites and the fast ion transfer channel, it still faces tremendous challenges in simultaneously designing and preparing biomass-derived carbons with excellent capacitive and rate performance. Herein, a dual-activation strategy of KOH and KMnO4 is used to prepare cotton stalks-derived porous carbon with large specific surface area (SSA) (1634 m2 g−1), interconnected network structure, as well as rational mesopores and micropore ratio. Consequently, the obtained sample exhibits an ultrahigh specific capacitance of 318 F g−1 at 1 A g−1, 71% capacitance retention at current density up to 50 A g−1, and only 2% capacitance dissipation in a two-electrode system in 6 M KOH after 10 000 cycles. Importantly, the obtained sample also shows a high areal capacitance of 3.8 F cm−2 under a high mass loading of 16 mg cm−2. Moreover, the obtained sample also delivers a high energy density of 19.9 Wh kg−1 at 397 W kg−1 in the symmetric two-electrode system using 1 M Na2SO4 aqueous electrolyte. This work provides an alternative avenue for the facile and scaled-up conversion of earth-abundant agricultural wastes into advanced carbon materials for supercapacitors application.

PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li+ and Zn2+ storage properties

Low-cost, high safety and environment-friendly aqueous energy storage systems (ESSs) are huge potential for grid-level energy storage, but the (de)intercalation of metal ions in the electrode materials (e.g. vanadium oxides) to obtain superior long-term cycling stability is a significant challenge. Herein, we demonstrate that polyvinyl alcohol (PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide (V2O5∙nH2O/rGO/PVA, denoted as the VGP) films enable long cycle stability and high capacity for the Li+ and Zn2+ storages in both the VGP//LiCl (aq)//VGP and the VGP//ZnSO4 (aq)//Zn cells. The binder-free VGP films are synthesized by a one-step hydrothermal method combination with the filtration. The extensive hydrogen bonds are formed among PVA, GO and H2O, and they act as structural pillars and connect the adjacent layers as glue, which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li+ and Zn2+ storage properties. As for Li+ storage, the binder-free VGP4 film (4 mg PVA) electrode achieves the highest specific capacitance up to 1381 F g−1 at 1.0 A g−1 in the three-electrode system and 962 F g−1 at 1.0 A g−1 in the symmetric two-electrode system. It also behaves the outstanding cyclic performance with the capacitance retention of 96.5 % after 15000 cycles in the three-electrode system and 99.7 % after 25000 cycles in the symmetric two-electrode system. As for Zn2+ storage, the binder-free VGP4 film electrode exhibits the high specific capacity of 184 mA h g−1 at 0.5 A g−1 in the VGP4//ZnSO4 (aq)//Zn cell and the superb cycle performance of 98.5 % after 25000 cycles. This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties, but also extends to construct other potential electrode materials for metal ion storage cells.

Single-step hydrothermal synthesis of nitrogen-doped ZnO nanostructures and an insight into its electrochemical properties

Zinc oxide (ZnO) nanostructures have been extensively used as electrochemical sensing material for the development of biosensors and bioimplantable devices. It is important to evaluate their electrochemical performance while developing materials with rapid response time and higher sensitivity. Herein, we present a novel one-step low-temperature hydrothermal technique for simultaneous nitrogen doping and growth of ZnO (N-ZnO) nanostructures. Nitrogen addition is expected to enhance the electron mobility and hence the electrical conductivity of ZnO. The nanostructures were characterized by X-ray diffraction, UV–Vis spectroscopy and field emission scanning electron microscopy. The electrochemical properties were studied by electrochemical impedance spectroscopy and cyclic voltammetry using an N-ZnO/Ag/Glass symmetric two-electrode system. The nitrogen addition to ZnO lattice is suggested by XRD peak shift, changing lattice parameters and dislocation density as compared to pristine ZnO. A substantial increase in the electrochemical response and conductivity can be attributed to nitrogen incorporation into ZnO lattice.