Polyvinyl Alcohol Gel Electrolyte Research Articles

A High Voltage Symmetric Supercapacitor Comprising Concentrated NaCl: PVA Electrolyte and Partially Reduced Graphene Oxide Electrodes

AbstractStrategies to improve energy density in supercapacitors are mainly based on utilizing electrodes providing larger effective surfaces and electrolytes allowing op eration in wider voltage windows. Here, a water‐based, binder‐free, environmentally friendly, high voltage, and quasi‐solid‐state symmetric supercapacitor is presented comprising partially reduced graphene oxide active electrodes and concentrated NaCl: polyvinyl alcohol gel electrolyte. It is shown that the ionic diffusion through the electrode‐electrolyte interface is augmented by the partial reduction of the graphene oxide electrodes up to an optimum level. The safe operation voltage window is 4 V; the high field endurance is attributed to the ion‐saturated hydrogel electrolyte used. At a scan rate of 25 mV/s, the provided capacitance and stored energy are 0.1 F.cm−2 and 5.6 e−5 W.h.cm−2, respectively. The optimized device retains ~90 % of its initial capacitance after 1000 charge‐discharge cycles; no meaningful sign of degradation is detected afterwards up to the 2000 cycles examined. These results place further emphasis on the potentials of the gel polymer electrolytes in the fabrication of environmentally friendly supercapacitors. Our findings are anticipated to accelerate improvements in the properties of the graphene‐based electrodes, particularly in conjunction with the proposed electrolyte.

Computational investigation of enhanced properties in functionalized carbon nanotube doped polyvinyl alcohol gel electrolyte systems.

Recently, functionalized carbon nanotubes (fCNTs) were shown to increase the mechanical strength, thermal stability, and ionic conductivity in polyvinyl alcohol (PVA) based gel electrolytes (GE) for Zn ion batteries. However, questions remain about the origin of the property enhancement and the interactions between components of GEs. In this work, we employ density functional theory calculations to analyze the interactions between fCNT, PVA, and Zn ions. CNTs with increasing numbers of carboxyl (-COOH) functional groups and PVA chains with varying lengths were studied. We found that increasing the number of -COOH on the CNTs enhanced the adsorption energies (Eads) of PVA, and Eads also increased as the number of monomers increased. We then modelled the coordination of a Zn ion in fCNT-PVA complexes. Our results suggest that strong fCNT-PVA interactions contribute to the enhanced mechanical strength, while the enhanced ionic conductivity is partly owing to weak Zn adsorption.

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High-Capacity and High-Rate Fiber-Shaped Zinc-Ion Batteries.

Aqueous Zn-ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α-MoO3 holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO3 cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al2 O3 coating and phosphating process, the constructed Zn//P-MoO3- x @Al2 O3 battery delivers impressive capacity of 257.7 mAh g-1 at 1 A g-1 and superior rate capability (57% capacity retention at 20 A g-1 ), dramatically surpassing the pristine Zn//MoO3 battery (115.8 mAh g-1 ; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm-3 ) as well as favorable energy density (14.4 mWh cm-3 ; 240 Wh kg-1 ) are both achieved by the fiber-shaped quasi-solid-state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high-performance ZIBs.

Enhanced capacitive performance of activated carbon paper electrode material

Abstract

Engineering the volumetric effect of Polypyrrole for auto-deformable supercapacitor

Polypyrrole (PPy) is one of the most extensively studied conducting polymers and it has promising application prospects in supercapacitors. However, PPy-based supercapacitors generally suffer from poor cycling stability due to the volumetric effect induced by ion doping/de-doping during the redox reactions. Therefore, the volumetric effect has usually been considered deleterious for supercapacitor applications. Herein, we demonstrate that the volumetric effect of PPy can be collected by synergy of flexible electrodes and solid-sate electrolytes. Furthermore, the accumulative volumetric effect is utilized in auto-deformable supercapacitors for the first time. The as-designed supercapacitor consists of flexible electrodes (PPy film, reduced graphene oxide (rGO) film) and a polyvinyl alcohol (PVA) gel electrolyte. When the redox reaction starts, the volumetric change of the PPy film induced by Na+ ion insertion is captured by the PVA gel electrolyte, resulting in mechanical deformation of the supercapacitor. As the accumulative volumetric effect drives greater deformation of the device, more electrochemically active sites are generated in the PPy film, leading to a higher energy storage capacity of the supercapacitor. Specifically, a certain correlation exists between the deformation degree and the energy storage capacity. As the deformation degree approaches 100% from 0%, the discharge capacity increases to 359 mF/cm3 from 101 mF/cm3. This auto-deformation characteristic endows the supercapacitor with subjective initiative, which establishes an important foundation for a smart energy storage device.

Heat generation in all-solid-state supercapacitors with graphene electrodes and gel electrolytes

This study aims to investigate time-dependent heat generation in all-solid-state supercapacitors. Supercapacitors were fabricated by assembling two identical electrodes made of graphene petal arrays grown on buckypaper by microwave plasma chemical vapor deposition. The electrodes were separated by either (i) a conventional phosphoric acid in polyvinyl alcohol (PVA) gel electrolyte or (ii) a redox-active potassium ferricyanide/ferrocyanide in PVA gel electrolyte. The devices with redox-active gel electrolyte exhibited about three times larger capacitance due to additional charge storage by reversible redox reactions. However, their internal resistance was about six times greater than devices with conventional gel electrolyte due to the lower electrolyte ionic conductivity. The heat generation rate measured under constant-current cycling was the sum of irreversible and reversible contributions. The irreversible heat generation rate in all supercapacitors was caused by resistive losses, i.e., Joule heating. The reversible heat generation rate was different at the positive and negative electrodes and was affected by electric double layer (EDL) formation, reversible redox reactions, and/or the presence of negatively charged functional groups at the electrode surface. The results of this study can be used to gain insight into the charging mechanism and also to develop thermal management solution for all-solid-state supercapacitors.

Electrochemical cycling stability of nickel (II) coordinated polyaniline

The nickel (II) coordinated polyaniline (PANI-Ni) was designed as active electrode material to improve electrochemical cycling stability of conductive polymer-based supercapacitors. The conductive coordination polymer of PANI-Ni was formed to grow on the substrate of carbon paper through the hydrothermal coordination reaction between Ni(Ac)2 and PANI. PANI-Ni with intrachain and interchain coordination structure could reinforce the polymer molecule chain strength to overcome volumetric swelling and shrinking during charge/discharge process. The specific capacitance was obviously improved from 234.5 F g−1 for bare PANI to 417 F g−1 for PANI-Ni in 1 M H2SO4 electrolyte at a current density of 1 A g−1 and a potential window of 0.8 V. PANI-Ni electrode shows the cycling capacitance retention of 93% after 1000 cycles at 5 A g−1. It also showed low capacitance loss of only 12% when the current density increased from 1 to 5 A g−1, presenting high rate capability. The symmetric PANI-Ni supercapacitor was constructed using PANI-Ni electrode and H2SO4 involved polyvinyl alcohol gel electrolyte. PANI-Ni supercapacitor showed the cycling capacitance retention of 83% after 1000 cycles at an output voltage of 1.7 V and a current density of 5 A g−1. PANI-Ni conductive coordination polymer presents the promising application prospect of supercapacitor.

Electrochemical capacitance of titanium nitride modified lithium titanate nanotube array

Titanium nitride modified lithium titanate nanotube array (TiN-Li4Ti5O12 NTA) was designed as the electrode material of lithium-ion supercapacitor for electrochemical energy storage. Li4Ti5O12 NTA was prepared through lithiation treatment of anodic TiO2 NTA and then annealing treatment in argon. TiN-Li4Ti5O12 NTA was formed through coating TiO2 sol on the surface of Li4Ti5O12 NTA and then full nitridation treatment in ammonia. Partially nitridized Li4Ti5O12 (N-Li4Ti5O12) NTA was also prepared through a controlled nitridation treatment of Li4Ti5O12 NTA in ammonia. TiN-Li4Ti5O12 NTA with full TiN coating layer exhibited higher conductivity than N-Li4Ti5O12 NTA with partially incorporated TiN. The capacitance accordingly increased from 79.58 F g−1 for N-Li4Ti5O12 to 143.83 F g−1 for TiN-Li4Ti5O12 at 0.5 A g−1 in 0.5 M Li2SO4. The capacitance retention ratio also increased from 72.95% to 82.41% after 1000 cycles at 3.0 A g−1. The all-solid-state supercapacitor was constructed using TiN-Li4Ti5O12 NTA electrode and polyvinyl alcohol gel electrolyte containing Li2SO4, showing high capacitance of 40.45 F g−1, energy density of 32.36 Wh kg−1 and power density of 0.6 kW kg−1 at the high output voltage of 2.4 V and current density of 0.5 A g−1. Therefore, TiN-Li4Ti5O12 NTA could act as a feasible electrode material of lithium-ion supercapacitor.

Enhanced electrochemical performance of carbon quantum dots-polyaniline hybrid

Abstract Carbon quantum dots-polyaniline (CQDs-PANI) hybrid was developed as supercapacitor electorde material by incorporating CQDs into PANI. PANI nanowires were grown vertically on carbon fiber substrate to form an interconnected network structure. Meanwhile, CQDs were uniformly distributed in the interior and on the surface of well-established net-like PANI nanowires. High specific capacitance of 738.3 F g−1 at 1.0 A g−1 was obtained for CQDs-PANI compared to that of 432.5 F g−1 for pure PANI. The capacitance retention after 1000 cycles of CQDs-PANI and PANI is 78.0% and 68.0% at 5.0 A g−1, respectively. The high capacitance and reasonable cycle stability were ascribed to the incorporation of CQDs into PANI, which improved the conductivity and alleviated the volume change of the CQDs-PANI electrode during the charge/discharge process. In addition, a flexible solid-state CQDs-PANI supercapacitor was constructed using carbon paper as current collector and polyvinyl alcohol gel electrolyte, exhibiting the stable capacitive performance at planar and bending state. The specific capacitance, energy and power density were determined to be 169.2 mF cm−2, 33.8 μWh cm−2 and 0.3 mW cm−2 at a potential window of 1.2 V and a current density of 1.0 mA cm−2. CQDs-PANI presented the promising application in flexible energy-related device.

Supercapacitance performance of polypyrrole/titanium nitride/polyaniline coaxial nanotube hybrid

The polypyrrole/titanium nitride/polyaniline (PPy/TiN/PANI) coaxial nanotube hybrid has been prepared as supercapacitor electrode material by stepwise loading of PPy and PANI into TiN nanotube array through normal pulse voltammetry and cyclic voltammetry electrodeposition process. P-type doping PPy and N-type doping PANI could be well incorporated into an integrated composite to act as an electroactive material. TiN nanotube array with highly ordered nanostructure and good electrical conductivity promoted the charge transfer capability of conducting polymers of PPy and PANI. PPy/TiN/PANI coaxial nanotube hybrid with P/N type doping properties exhibited high specific capacitance of 1471.9 F g−1 at a current density of 0.5 A g−1 and a potential window of 0.8 V in 1.0 M H2SO4 solution. It could keep the capacitance of 1077.4 F g−1 at high current density of 10 A g−1 and capacitance retention of 78.0% after 200 cycles, presenting good rate capability and reasonable cycling stability. All-solid-state flexible supercapacitor was constructed using PPy/TiN/PANI electrode and H2SO4-included polyvinylalcohol gel electrolyte. It offered superior energy storage capacity with respect to specific capacitance of 288.4 F g−1 and energy density of 129.8 Wh kg−1 at high potential window of 1.8 V and current density of 1.0 A g−1. PPy/TiN/PANI coaxial nanotube hybrid accordingly presented the promising application as supercapacitor electrode material for energy storage.

A graphene oxide incorporated TiO2 photoanode for high efficiency quasi solid state dye sensitized solar cells based on a poly-vinyl alcohol gel electrolyte

An effective self assembly method was used to synthesize hybrid nanocomposites of TiO2 nanoparticles on graphene oxide (GO) sheets for application in Dye Sensitized Solar Cells (DSSCs).

Porous poly(3,4-ethylenedioxythiophene) nanoarray used for flexible supercapacitor

Porous poly(3,4-ethylenedioxythiophene) (PEDOT) nanoarray used for flexible supercapacitor has been prepared to investigate its electrochemical capacitance performance. Well-aligned titania (TiO2) and titanium nitride (TiN) nanotube array was fabricated by an anodization, crystallization, nitridation processes. PEDOT-TiO2 and PEDOT-TiN nanoarray hybrid was fabricated by coating PEDOT on nanotube walls of TiO2 and TiN through a pulse voltammetry electrodeposition process. PEDOT nanopore array was fabricated through HF corrosion of TiN from PEDOT-TiN. The morphology and microstructure of PEDOT-TiO2, PEDOT-TiN and PEDOT were characterized by scanning electron microscopy and Raman spectroscopy. The electrochemical capacitance was investigated by cyclic voltammetry and galvanostatic charge–discharge measurements. PEDOT-TiO2 and PEDOT-TiN showed heterogeneous coaxial nanotube structure. PEDOT exhibited free-standing nanopore array structure. The specific capacitance of PEDOT-TiN nanoarray hybrid was determined to be 393.1Fg−1 at a current density of 1.0mAcm−2, presenting much higher capacitance than PEDOT-TiO2 nanoarray hybrid (128.7Fg−1) and PEDOT nanopore array (109.3Fg−1). All-solid-state flexible supercapacitor was constructed using supple electrode of PEDOT-TiN nanoarray hybrid and polyvinyl alcohol gel electrolyte of sulphuric acid. The volume specific capacitance, energy and power density were determined to be 4.08Fcm−3, 2.26mWhcm−3 and 250mWcm−3 at a high output voltage of 2.0V and a current density of 10mAcm−2. PEDOT-TiN nanoarray hybrid exhibited the effective energy storage in flexible supercapacitor application.

Electrochemical flexible supercapacitor based on manganese dioxide-titanium nitride nanotube hybrid

The manganese dioxide-titanium nitride (MnO2-TiN) nanotube hybrid has been designed to improve its electroactivity and conductivity for a supercapacitor application. Titanium nitride (TiN) nanotube array was prepared by an anodization process of titanium in ethylene glycol (EG) solution containing ammonium fluoride, subsequent calcination process in an air atmosphere, and final nitridation process in an ammonia atmosphere. Electroactive MnO2 was then loaded into well-aligned TiN nanotubes to form MnO2-TiN nanotube hybrid with well-designed shell layer of MnO2 through a controlled cyclic voltammetry electrodeposition process, which was directly supported on ultra thin and supple titanium foil to establish a bendable electrode. The morphology and microstructure of MnO2-TiN nanotube hybrid were characterized by scanning electron microscopy and X-ray diffraction. The electrochemical capacitance was investigated by cyclic voltammetry and galvanostatic charge/discharge measurements. The villiform MnO2 thin shell layer was fully covered on TiN nanotube walls to form a coaxial heterogeneous structure. Superior electrical conductivity and accessible nanochannels of TiN contributed to a high capacitance performance of MnO2. The specific capacitance of MnO2-TiN was determined to be 853.3Fg−1 (or 213.2mFcm−2) at a current density of 1.0Ag−1 (or 0.25mAcm−2). All-solid-state flexible supercapacitor was constructed using two symmetric film electrodes of MnO2-TiN nanotube hybrid and a polyvinyl alcohol gel electrolyte of KOH-KI-EG. The volume specific capacitance, energy and power density were determined to be 4.01Fcm−3, 1.81mWhcm−3 and 32.8mWcm−3 at a high potential window of 1.8V and a current density of 2.0mAcm−2. Such MnO2-TiN nanotube hybrid electrode material exhibited effective energy storage in flexible supercapacitor application.

Solution-based binder-free synthetic approach of RuO2 thin films for all solid state supercapacitors

In this rising field of portable electronics, all solid state thin film supercapacitors (ASSTFSs) have received tremendous courtesies due to their flexibility and high safety, which are considered as competitive candidates for energy power sources in flexible electronics. In present investigation, we demonstrate the first successful application of pseudocapacitive RuO2 in ASSTFS, exhibiting high capacitance, remarkable high-rate capability and long-term cycling stability. Nanocrystalline RuO2 thin films are developed on mesh like stainless steel substrate by facile chemical bath deposition (CBD) method at three different deposition temperatures. ASSTFSs were fabricated by simple process using two slightly separated RuO2 thin films well solidified in the H2SO4–polyvinyl alcohol gel electrolyte. Electrochemical studies of ASSTFS device was characterized by cyclic voltammetry, charge–discharge and impedance techniques. The highest specific capacitance of 234, 203 and 167Fg−1 for three RuO2 nanostructures was obtained. Further the device shows good stability after 1000 cycles. The non-ideal behavior of the supercapacitor was analyzed by impedance analysis. Additionally, the all-solid-state nature combined with superior electrochemical performance makes RuO2-based device an excellent candidate for power sources in portable electronics.

All-solid-state flexible thin film supercapacitor based on Mn3O4 stacked nanosheets with gel electrolyte

Recently, much effort has been devoted to accomplish thin, lightweight and flexible energy-storage devices for wearable electronics. Here, we demonstrate a novel kind of thin all-solid-state supercapacitor configuration with an extremely simple process using two slightly separated stacked nanosheets-like Mn3O4 electrodes well solidified in the H2SO4–polyvinyl alcohol gel electrolyte. This integrate device shows a high specific capacitance of 127 F g−1 for the electrode materials with good power and energy density values. These flexible and all-solid-state Mn3O4 supercapacitors bring new design opportunities of device configuration for future energy-storage devices. Present investigation first time reported that Mn3O4 is one of the most promising materials for the fabrication of all solid state thin film supercapacitors (ASSTFSs).

Structural Investigation of Polyvinyl Alcohol Gel Electrolyte by Small Angle X-ray Scattering

Polyvinyl alcohol based organogel electrolytes are a promising class of materials for lithium batteries and electrochemical supercapacitors. Amongst various classes of polymer electrolytes polymer based gel electrolytes have proven to be a materials for safer battery assembly with fast ion carrying capacity and better mechanical strength. Internal structure of gel is responsible for its ion conduction mechanism. This paper presents small angle X-ray scattering(SAXS) results for polyvinyl alcohol during its gelation in an organic solvent and salt system. Structural changes are observed during and after gelation for samples with varying polymer and lithium salt concentration and has been well documented by the SAXS results.