Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures

Electrical properties of thin dielectric films at the solid‐liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co‐polymeric hydrogels of polyacrylic acid co‐sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co‐planar geometry. Silane‐modified glasses were characterized by the co‐planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger . The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint‐test cell versus this co‐planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (R_s) was a spectral feature seen only by the co‐planar hydrogel cell. Thus, it can be concluded that the use of such co‐planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.     

Impedance spectra analysis of thermoresponsive poly(acryloyl‐L‐proline methyl ester) gel membrane in LiCl solution

Impedance spectra analysis of a thermoresponsive poly(acryloyl‐L ‐proline methyl ester) (poly(A‐ProOMe)) hydrogel membranes in an aqueous solution of LiCl was carried out using a simple equivalent model. The hydrogel membrane was synthesized by γ‐radiation‐induced polymerization and crosslinking of A‐ProOMe monomer aqueous solution in a glass‐cast. By means of the impedance spectra analysis, a novel method for the calculation of the ionic conductivity of the hydrogel membranes in LiCl solution was proposed. The calculated ionic conductivity was in agreement with the determined value. In addition, effects of temperature and LiCl concentration on the impedance spectra and ionic conductivity of the gel membrane were analyzed. Results indicated that the impedance spectra analysis is a very useful tool for evaluating the electric properties of gel membranes in an electrolyte solution. The poly (A‐ProOMe) gel membrane in 1.0 M LiCl solution showed a high ionic conductivity of about 0.2 S/cm at 14 °C. The temperature‐dependence of the ionic conductivity was a complex nonlinear form due to the volume phase transition of the thermoresponsive poly(A‐ProOMe) gel membrane, and the volume phase transition temperature appeared to be decreased with the increase in the LiCl concentration. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2843–2851, 2005     

离子液体中吡咯的电化学聚合及性质研究

以1-丁基-3-甲基咪唑六氟磷酸盐离子液体作为溶剂和支持电解质,分别在铂电极和导电玻璃电极上电化学聚合得到了聚吡咯,聚合过程中发现,在离子液体中聚合的循环伏安图,其电流的变化和传统有机溶剂中的不同,通过交流阻抗技术研究了修饰电极的电化学性质,采用在线紫外、拉曼、红外谱对聚吡咯进行了光谱表征,得到了聚吡咯的特征峰,采用扫描电镜研究了聚合物的形貌。最后将修饰电极应用到了对对苯二酚的催化反应当中,显示了一定的催化作用。     

A Self‐Healing Integrated All‐in‐One Zinc‐Ion Battery

The self‐healing of zinc‐ion batteries (ZIBs) will not only significantly improve the durability and extend the lifetime of devices, but also decrease electronic waste and economic cost. A poly(vinyl alcohol)/zinc trifluoromethanesulfonate (PVA/Zn(CF₃SO₃)₂) hydrogel electrolyte was fabricated by a facile freeze/thaw strategy. PVA/Zn(CF₃SO₃)₂ hydrogels possess excellent ionic conductivity and stable electrochemical performance. Such hydrogel electrolytes can autonomously self‐heal by hydrogen bonding without any external stimulus. All‐in‐one integrated ZIBs can be assembled by incorporating the cathode, separator, and anode into hydrogel matrix since the fabrication of PVA/Zn(CF₃SO₃)₂ hydrogel is a process of converting the liquid to quasi‐solid state. The ZIBs show an outstanding self‐healing and can recover electrochemical performance completely even after several cutting/healing cycles.     

Miniaturized Reference Electrodes. II. Use in Corrosive,Biological, and Organic Media

In a recent paper [9] we reported the manufacturing and performance of miniaturized reference electrodes (MREs) with low sensitivity to chloride ions and pH. Here, we demonstrate the wide range applicability of a MRE based on an Ag/Ag₂S internal reference element (IRE), imbedded in a photopolymerized hydrogel of improved composition, which contains the supporting electrolyte. Exchange current density, temperature coefficient, impedance value, and the voltammetric and potentiometric use of the Ag/Ag₂S‐based MRE are discussed relative to the previously reported Ag/AgSCN, Ag/Ag₃PO₄, and Ag/AgCl‐based MREs. No special or extensive conditioning is required when moving these MREs from aqueous supporting electrolyte to an organic solution or from one organic medium to another, and the equilibration time in a new medium is very rapid (<6 min). The new Ag/Ag₂S MRE has a highly stable potential in various media, including aqueous solutions (salt buffers and 20 wt.% H₂SO₄), biological samples (bovine serum albumin), mixed aqueous‐organic, and organic supporting electrolytes (methanol, ethanol, acetonitrile, propylene carbonate, methylene chloride, and DMSO). This is particularly advantageous when in the course of the electrochemical analysis an organic solution is being added to an aqueous supporting electrolyte. Such MREs are suitable for analyses of μL sample volumes and for use in protein‐containing media.     

Hydrothermal Self-assembly Synthesis of Mn3O4Reduced Graphene Oxide Hydrogel and Its High Electrochemical Performance for Supercapacitors

In the present work Mn3O4/reduced graphene oxide hydrogel （Mn3O4-rGOH） with three dimensional （3D） networks was fabricated by a hydrothermal self-assembly route. The morphology, composition, and microstructure of the as-obtained samples were characterized using powder X-ray diffraction （XRD）, X-ray photoelectron spectroscopy （XPS）, thermogravimetry analysis （TG）, atomic absorption spectrometry （AAS）, field emission scanning electron microscopy （FESEM） and transmission electron microscope （TEM）. Moreover, the electrochemical behaviors were evaluated by cyclic voltammogram （CV）, galvanostatic charge-discharge and electrochemical impedance spectroscopy （EIS）. The test results indicated that the hydrogel with 6.9% Mn3O4 achieved specific capacitance of 148 F.g^-1 at a specific current of 1 A.g^-1, and showed excellent cycling stabilily with no decay after 1200 cycles. In addition, its specific capacitance could retain 70% even at 20 A.g^- 1 in comparison with that at 1 A.g ^-1 and the operating window was up to 1.8 V in a neutral electrolyte.     

A 3D Nanostructured Hydrogel‐Framework‐Derived High‐Performance Composite Polymer Lithium‐Ion Electrolyte

Solid‐state electrolytes have emerged as a promising alternative to existing liquid electrolytes for next generation Li‐ion batteries for better safety and stability. Of various types of solid electrolytes, composite polymer electrolytes exhibit acceptable Li‐ion conductivity due to the interaction between nanofillers and polymer. Nevertheless, the agglomeration of nanofillers at high concentration has been a major obstacle for improving Li‐ion conductivity. In this study, we designed a three‐dimensional (3D) nanostructured hydrogel‐derived Li_0.35La_0.55TiO₃ (LLTO) framework, which was used as a 3D nanofiller for high‐performance composite polymer Li‐ion electrolyte. The systematic percolation study revealed that the pre‐percolating structure of LLTO framework improved Li‐ion conductivity to 8.8×10^?5 S cm^?1 at room temperature.     

Improved Efficiency and Stability of Flexible Dye Sensitized Solar Cells on ITO/PEN Substrates Using an Ionic Liquid Electrolyte

Flexible dye‐sensitized solar cells (DSSCs) built on plastic substrates have attracted great interest as they are lightweight and can be roll‐to‐roll printed to accelerate production and reduce cost. However, plastic substrates such as PEN and PET are permeable to water, oxygen and volatile electrolyte solvents, which is detrimental to the cell stability. Therefore, to address this problem, in this work, an ionic liquid (IL) electrolyte is used to replace the volatile solvent electrolyte. The initial IL‐based devices only achieved around 50% of the photovoltaic conversion efficiency of the cells using the solvent electrolyte. Current‐voltage and electrochemical impedance spectroscopy (EIS) analysis of the cells in the dark indicated that this lower efficiency mainly originated from (i) a lack of blocking layer to reduce recombination, and (ii) a lower charge collection efficiency. To combat these problems, cells were developed using a 12 nm thick blocking layer, produced by atomic layer deposition, and 1 μm thick P25 TiO₂ film sensitized with the hydrophobic MK‐2 dye. These flexible DSSCs utilizing an IL electrolyte exhibit significantly improved efficiencies and a <10% drop in performance after 1000 h aging at 60°C under continuous light illumination.     

A Long‐Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution

In this paper, we report an advanced long‐life lithium ion battery, employing a Pyr₁₄TFSI‐LiTFSI non‐flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn‐C) nanocomposite anode, and a layered LiNi_1/3Co_1/3Mn_1/3O₂ (NMC) cathode. The IL‐based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel–Tammann–Fulcher (VTF) trend. Lithium half‐cells employing the Sn‐C anode and NMC cathode in the Pyr₁₄TFSI‐LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn‐C electrodes are combined into a cathode‐limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g^?1 and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL‐based lithium ion cells are suitable batteries for application in electric vehicles.     

Impedance Analysis of Inherently Redox‐Active Ionic‐Liquid‐Based Photoelectrochemical Cells: Charge‐Transfer Mechanism in the Presence of an Additional Redox Couple

An intensive electrochemical impedance study was carried out to understand the charge‐transfer processes in photoelectrochemical (PEC) cells based on ionic liquid (IL) electrolytes. Three different electrolytes were utilized to understand the role of redox species as well as the medium on the charge‐transfer mechanism. The negligible diffusion resistance, despite the presence of two different redox species in the case of Fe(CN)₆^?4/?3 in IL, was explained on the basis of charge transfer between species of two different redox couples. Accordingly, the redox species are not required to travel through the bulk of the electrolyte for the removal of accumulated charges, as short‐range charge transfer between the IL and the Fe(CN)₆^?4/?3 species facilitates the removal of accumulated charges. It is also shown that PEC cells utilizing dual redox couples are highly stable with larger photoelectrochmeical windows, >3 V.     

A Liquid/Liquid Electrolyte Interface that Inhibits Corrosion and Dendrite Growth of Lithium in Lithium‐Metal Batteries

A proof‐of‐concept study on a liquid/liquid (L/L) two‐phase electrolyte interface is reported by using the polarity difference of solvent for the protection of Li‐metal anode with long‐term operation over 2000 h. The L/L electrolyte interface constructed by non‐polar fluorosilicane (PFTOS) and conventionally polar dimethyl sulfoxide solvents can block direct contact between conventional electrolyte and Li anode, and consequently their side reactions can be significantly eliminated. Moreover, the homogeneous Li‐ion flow and Li‐mass deposition can be realized by the formation of a thin and uniform solid‐electrolyte interphase (SEI) composed of LiF, Li_xC, Li_xSiO_y between PFTOS and Li anode, as well as the super‐wettability state of PFTOS to Li anode, resulting in the suppression of Li dendrite formation. The cycling stability in a lithium–oxygen battery as a model is improved 4 times with the L/L electrolyte interface.     

Electrochemical impedance characterization and photovoltaic performance of N719 dye‐sensitized solar cells using quaternized ammonium iodide containing polyfluorene electrolyte solutions

This study develops a series of titanium oxide electrode‐based N719 dye‐sensitized solar cells (DSSCs) using quaternized ammonium iodide containing main‐chain and star‐shaped polyfluorene (MPF‐E and SPF‐E) electrolyte solutions. The electrochemical impedance and photovoltaic properties of the polyfluorene electrolyte‐based DSSCs were studied and compared to those of the poly(ethylene oxide) (PEO) electrolyte‐based DSSCs. As with the PEO electrolyte‐based DSSCs, the recombination impedance increased with increase in the polymer content for the MPF‐E electrolyte‐based DSSCs, whereas the photovoltaic performance did otherwise. Nevertheless, the reduction in the photovoltaic properties was not significant for the SPF‐E electrolyte‐based DSSCs. The electrochemical impedance and photovoltaic properties of the different polymer‐based DSSCs are also discussed as a function of the polymer concentration. Copyright © 2010 John Wiley & Sons, Ltd.     

Electrochemical characterization of hydrogels for biomimetic applications

Hydrogels are increasingly being recognized as having potential in bio‐compatible applications. In previous work, we investigated the feasibility of poly(ethylene glycol)‐dimethacrylate (PEG‐1000‐DMA) and poly(ethylene glycol)‐diacrylate (PEG‐400‐DA) polymerized using either a chemical initiator (C) or a photoinitiator (P) to encapsulate and stabilize biomimetic membranes for novel separation technologies or biosensor applications. In this paper, we have investigated the electrochemical properties of the hydrogels used for membrane encapsulation. Specifically, we studied the crosslinked hydrogels by using electrochemical impedance spectroscopy (EIS), and we demonstrated that chemically crosslinked hydrogels had lower values for the effective electrical resistance and higher values for the electrical capacitance compared with hydrogels with photoinitiated crosslinking. Transport numbers were obtained using electromotive force measurements and demonstrated that at low salt concentrations, both PEG‐400‐DA‐C and PEG‐400‐DA‐P hydrogels presented an electropositive character whereas PEG‐1000‐DMA‐P was approximately neutral and PEG‐1000‐DMA‐C showed electronegative character. Sodium transport numbers approached the bulk NaCl electrolyte value at high salt concentrations for all hydrogels, indicating screening of fixed charges in the hydrogels. The average salt diffusional permeability 〈P_s〉 and water permeability 〈P_w〉 were found to correlate with EIS results. Both PEG‐1000‐DMA‐C and PEG‐400‐DA‐C had higher 〈P_s〉 and 〈P_w〉 values than PEG‐1000‐DMA‐P and PEG‐400‐DA‐P hydrogels. In conclusion, our results show that hydrogel electrochemical properties can be controlled by the choice of polymer and type of crosslinking used and that their water and salt permeability properties are congruent with the use of hydrogels for biomimetic membrane encapsulation. Copyright © 2011 John Wiley & Sons, Ltd.     

Characterization of Electrode/Electrolyte Interface of ECIS Devices

Electric cell‐substrate impedance sensing requires low electrode/electrolyte interface impedance for effective biomedical and biophysical applications. Thus a complete understanding of physical processes involved in the formation of an electric double layer is required to design a low interface impedance device. This paper presents the numerical simulation of the impedance for the electrode/electrolyte interface of three‐electrode devices along with the practical realization for the effective workout of impedance sensing devices. The three‐electrode based impedance sensing devices along with phosphate buffered saline as electrolyte is simulated using COMSOL Multiphysics to evaluate the impedance of the electrode/electrolyte interface. Microfabrication technology is used to realize three‐electrode impedance sensing devices with diverse configuration which are used to measure the electrode/electrolyte interface impedance. The measured impedance data were then compared with the COMSOL simulated results and it is found that both the data sets fitted well with less than 5 % RSE. The results obtained from simulation and experiments indicate that the impedance due to double layer diffusion dominates in the low frequency region up to few kHz whereas electrolytic bulk resistance plays a major role in the higher frequency range. The experimental impedance data were further interpreted by electrochemical impedance spectroscopy analysis software to model the equivalent circuit of the electrochemical system.     

A Full Flexible NH4+ Ion Battery Based on the Concentrated Hydrogel Electrolyte for Enhanced Performance

Non-metal ammonium ( ) ions have recently been explored as effective charge carriers in battery systems due to their abundancy, light weight, small hydration shells in water. The research concerning the use of redox chemistry in batteries, particularly in flexible batteries, is still in its infancy. For the first time, we report a flexible full ion battery (AIB) composed of a concentrated hydrogel electrolyte sandwiched between NH₄V₃O₈ ⋅ 2.9H₂O nanobelts cathode and polyaniline (PANI) anode, for enhanced performance. The hydrogel electrolyte is simply synthesized by using ammonium sulfate, xanthan gum and water. As a reference, the AIB based on the liquid aqueous electrolyte is prepared first, which exhibits a capacity of 121 mAh g⁻¹ and a capacity retention of 95 % after 400 cycles at a specific current of 0.1 A g⁻¹. On the other hand, the simple synthesis of the hydrogel electrolyte allows us to facilely tune and optimize the salt contents in the electrolyte, to maximize the ionic conductivity, transport kinetics, mechanical characteristics, and consequently the battery performance. It is found that the flexible battery based on the hydrogel electrolyte prepared from 3 M ammonium sulfate solution shows the best electrochemical performance, i. e., a capacity of 60 mAh g⁻¹ while maintaining a capacity retention of 88 % after 250 cycles at a specific current of 0.1 A g⁻¹. Moreover, the flexible AIB retains excellent electrochemical performance when bent at different angles, demonstrating remarkable mechanical strength and flexibility. Therefore, this study sheds new light on the utilization of concentrated hydrogel electrolyte in the AIB chemistry, for developments of novel electrochemical energy storage technology with high safety and low cost.     

Salt‐Based Organic–Inorganic Nanocomposites: Towards A Stable Lithium Metal/Li10GeP2S12 Solid Electrolyte Interface

Solid‐state Li metal battery technology is attractive, owing to the high energy density, long lifespans, and better safety. A key obstacle in this technology is the unstable Li/solid‐state electrolyte (SSE) interface involving electrolyte reduction by Li. Herein we report a novel approach based on the use of a nanocomposite consisting of organic elastomeric salts (LiO‐(CH₂O)_n‐Li) and inorganic nanoparticle salts (LiF, ‐NSO₂‐Li, Li₂O), which serve as an interphase to protect Li₁₀GeP₂S₁₂ (LGPS), a highly conductive but reducible SSE. The nanocomposite is formed in situ on Li via the electrochemical decomposition of a liquid electrolyte, thus having excellent chemical and electrochemical stability, affinity for Li and LGPS, and limited interfacial resistance. XPS depth profiling and SEM show that the nanocomposite effectively restrained the reduction of LGPS. Stable Li electrodeposition over 3000 h and a 200 cycle life for a full cell were achieved.     

Effect of single-wall carbon nanotubes on the properties of polymeric gel electrolyte dye-sensitized solar cells

A hybrid of polymer/dispersed single-wall carbon nanotubes was utilized in networking a novel composition of gel electrolyte in dye-sensitized solar cells. The gel is composed of polyethylene glycol, polyvinyl pyrrolidone, single-wall carbon nanotubes, and I^?/I₃ ^? as electrolyte. Formation of the less conductive polyiodide species in electrolyte was prohibited by the addition of single-wall carbon nanotubes leading to the excellent photovoltaic behavior of the cell under simulated standard illumination of the fabricated device owing to the increased open circuit voltage (0.47 V). Electrochemical impedance spectroscopy was employed to quantify the charge transport resistance and the electron lifetime at the TiO₂ conduction band. Charge transport resistances at the TiO₂/dye/electrolyte interface were determined for the cells consisting of the non-gel reference and our new gel electrolytes, and it was indicated that the charge recombination between injected electrons and electron acceptors (I₃ ^?) in the redox electrolyte was remarkably retarded. Electrochemical parameters obtained by the fitting showed all of the resistances increased as compared to liquid electrolyte dye-sensitized solar cells that can be related to the increase in viscosity of the gel, which hinders the ionic transportation through the electrolyte. These results were also confirmed by the electron lifetime analyses. The characteristic peak shifted to a lower frequency in the Bode phase plot for the cell containing gel electrolyte which is an indication of a longer electron lifetime in comparison with that of the cell containing very conventional liquid electrolyte.     

Electrochemistry Investigation on the Graphene/Electrolyte Interface

In this study, the graphene/electrolyte interface was investigated in detail by the electrochemical method. The total interface capacitance was calculated from the electrochemical impedance spectroscopy (EIS) results, and its responses to different concentrations and pHs were also investigated. The minimum point of the capacitance was found to shift to right (vs. Ag/AgCl) as the concentration increased, and to left with increasing pH. As a comparison, gold/electrolyte interface was investigated in the same way, but didn’t show the similar behavior. To further explore the interface capacitance, proper models were proposed to fit the EIS results. Two constant‐phase elements (CPE) were used in the graphene‐electrolyte interface model to represent the double‐layer capacitance (CPE_dl) and the quantum capacitance (CPE_q), respectively. The CPE_q exhibited its sensitivity to concentration and pH, while CPE_dl did not. This study gives a new aspect to detect concentration and pH, and may provide a reference for the graphene‐based supercapacitor research.     

Electrodes and hydrogel electrolytes based on cellulose: fabrication and characterization as EDLC components

In the present work, the cellulose-based materials were manufactured and used as components of electrochemical double layer capacitors (EDLCs). The preparation method of cellulose membranes as well as composite electrodes containing cellulose as a binder was presented. These materials were prepared using for the first time ionic liquid/dimethyl sulfoxide (IL/DMSO) mixture solvent. Obtained components displayed a uniform structure, thermal stability, and good electrochemical properties. The electrochemical performances of these materials were studied in 2-electrode EDLC cells by common electrochemical techniques as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). The composite electrodes were investigated in three types of electrolytes: aqueous, organic, and ionic liquids. The cellulose membranes were, however, soaked in an aqueous electrolyte and tested as hydrogel polymer electrolytes. All investigated materials show high efficiency in terms of specific capacity. The studied cellulose-based capacitors exhibited specific capacitance values in the range of 20–22 F g^?1, depending on the type of applied electrolyte.     

A High‐Energy‐Density Potassium Battery with a Polymer‐Gel Electrolyte and a Polyaniline Cathode

A safe, rechargeable potassium battery of high energy density and excellent cycling stability has been developed. The anion component of the electrolyte salt is inserted into a polyaniline cathode upon charging and extracted from it during discharging while the K⁺ ion of the KPF₆ salt is plated/stripped on the potassium‐metal anode. The use of a p‐type polymer cathode increases the cell voltage. By replacing the organic‐liquid electrolyte in a glass‐fiber separator with a polymer‐gel electrolyte of cross‐linked poly(methyl methacrylate), a dendrite‐free potassium anode can be plated/stripped, and the electrode/electrolyte interface is stabilized. The potassium anode wets the polymer, and the cross‐linked architecture provides small pores of adjustable sizes to stabilize a solid‐electrolyte interphase formed at the anode/electrolyte interface. This alternative electrolyte/cathode strategy offers a promising new approach to low‐cost potassium batteries for the stationary storage of electric power.