In situ FTIR study of oxygen adsorption on nanostructured RuO2 thin-film electrode

In situ Fourier transform spectroscopy (FTIR) was used to study interactions of nanostructured ruthenium oxide (RuO₂) thin-film sensing electrode with O₂ at room temperature. RuO₂ nanostructures were pretreated at 1,000 °C for 1 h in order to obtain good crystallinity of amorphous RuO₂ nanoparticles. Morphology and properties of nanostructured RuO₂ were characterized by X-ray diffraction, thermo-gravimetric/differential thermal analysis, scanning electron microscopy, and FTIR. It was shown that pretreated RuO₂ is quite active for O₂ ⁻, O₂ ²⁻, and O²⁻ adsorption with clear 722 cm⁻¹ band for superoxide ions (O₂ ⁻) adsorption for the different oxygen concentrations. The results of in situ FTIR measurements revealed that the active sites for oxygen adsorption are not limited to the triple boundaries, but extended to surfaces of RuO₂ electrodes. Fundamental vibration frequencies of ruthenium–oxygen bond at a temperature of 23 °C as well as region above fundamental frequencies for the nanostructured RuO₂ were identified.     

Supercapacitive properties of activated carbon electrode in electrolyte solution with a lithium-modified silica nanosalt

In this work, lithium-modified silica nanosalt (Li202) is solution-synthesized and used as a gel-forming additive in 1.5 M tetraethylammonium tetrafluoroborate (TEABF₄)/acetonitrile (ACN) electrolyte solution for the supercapacitor with activated carbon electrode. The electrochemical properties of the supercapacitor adopting the Li202 (5 wt.%) are investigated using linear sweep voltammetry, cyclic voltammetry, and complex impedance spectroscopy. By the addition of the Li202, the electrochemical stability of the electrolyte is improved over 4.0 V (corresponding to the current density below 0.6 mA cm⁻²) and higher specific capacitances at the scan rates of 10–500 mV s⁻¹ are obtained. Thus, the Li202 can be considered as a promising electrolyte additive to enhance the supercapacitive properties of activated carbon electrode.     

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) gel electrolytes: a detailed investigation of their conductivity and characterization

Poly(ethylene glycol)/poly(2-acrylamido-2-methyl-1-propane sulfonic acid) (PEG/PAMPS) with a transparent appearance were prepared in the presence of ammonium persulfate (APS) as an initiator at 70 °C for 24 h. PEG/PAMPS-based polymer gel electrolytes in a motionless and uniform state were obtained by adding the required amount of liquid electrolytes to a dry PEG/PAMPS polymer. Liquid electrolytes include organic solvents with high boiling points (-1-methyl-2-pyrrolidone (NMP) and γ-butyrolactone (GBL)) and a redox couple (alkali metal iodide salt/iodine). The optimized conditions for PEG/PAMPS-based gel electrolytes based on the salt type, the concentration of alkali metal iodide salt/iodine, and solvent volume ratio were determined to be NaI, 0.4 M NaI/0.04 M I₂, and NMP:GBL (7:3, v/v), respectively. The highest ionic conductivity and the liquid electrolyte absorbency were 2.58 mS cm^?1 and 3.6 g g^?1 at 25 °C, respectively. The ion transport mechanism in both the polymer gel electrolytes and liquid electrolytes is investigated extensively, and their best fits with respect to the temperature dependence of the ionic conductivity are determined with the Arrhenius equation.     

A polymer electrolyte based on poly(vinylidene fluoride-hexafluoropylene)/hydroxypropyl methyl cellulose blending for lithium-ion battery

A polymer electrolyte based on the blending of poly(vinylidene fluoride-hexafluoropylene) (PVDF-HFP) and hydroxypropyl methyl cellulose (HPMC) was prepared for the first time. The structure and performance of the gel polymer electrolyte were characterized and measured by X-ray diffraction, Fourier transform infrared, thermogravimetric analysis, scanning electron microscopy, electrochemical impedance spectroscopy, linear sweep voltammetry, and by a charge/discharge test. The results show that the gel polymer electrolyte has the best performance when PVDF-HFP/HPMC ratio (w/w) is 4:1. At room temperature, the ionic conductivity can reach 0.38?×?10^?3 S cm^?1, the electrochemical stable window is up to 5.0 V (vs. Li/Li⁺), and the half cell of Li/GPE/LiMn₂O₄ shows high-discharge-specific capacity and good cycling performance.     

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF₄) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10⁻³ S cm⁻¹ at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm⁻² equivalent to single electrode specific capacitance of 61.7 F g⁻¹ have been observed for the optimized GPE film.

     

Morphology-controlled PANI nanowire electrode by using deposition scan rate in H<Subscript>2</Subscript>SO<Subscript>4</Subscript>/PVA polymer electrolyte for electrochemical capacitor

Polyaniline (PANI) nanowire electrode was successfully prepared using electrodeposition method. The morphology, thickness, and electrochemical performance of PANI electrode can be controlled by varying the deposition scan rates. Lower deposition scan rate results in compact and aggregates of PANI nanowire morphology. The uniform nanowire of PANI was obtained at the applied scan rate of 100 mV s^?1, and it was used as symmetric electrode coupled with H₂SO₄/polyvinyl alcohol (PVA) gel electrolyte. The different concentrations of H₂SO₄ acid in polymer electrolyte have influenced the electrochemical performance as well. The optimum specific capacitance and energy density of P100 PANI electrode in 3 M H₂SO₄/PVA gel polymer electrolyte was 377 F g^?1 and 95.4 Wh kg^?1 at the scan rate of 1 mV s^?1. The good stability of the electrode in this system is applicable to many wearable electronics applications.     

Charge storage performance of lithiated iron phosphate/activated carbon composite as symmetrical electrode for electrochemical capacitor

In this study, a symmetric electrochemical capacitor was fabricated by adopting a lithium iron phosphate (LiFePO₄)-activated carbon (AC) composite as the core electrode material in 1.0 M Na₂SO₃ and 1.0 M Li₂SO₄ aqueous electrolyte solutions. The composite electrodes were prepared via a facile mechanical mixing process. The structural properties of the nanocomposite electrodes were characterised by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) analysis. The electrochemical performances of the prepared composite electrode were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that a maximum specific capacitance of 112.41 F/g was obtained a 40 wt% LiFePO₄ loading on an AC electrode compared with that of a pure AC electrode (76.24 F/g) in 1 M Na₂SO₃. The improvement in the capacitive performance of the 40 wt% LiFePO₄–AC composite electrode is believed to be attributed to the contribution of the synergistic effect of the electric double layer capacitance (EDLC) of the AC electrode and pseudocapacitance via the intercalation/extraction of H⁺, OH⁻, Na⁺ and SO₃²⁻ and Li⁺ ions in LiFePO₄ lattices. In contrast, it appears that the incorporation of LiFePO₄ into AC electrodes does not increase the charge storage capability when Li₂SO₄ is used as the electrolyte. This behaviour can be explained by the fact that the electrolyte system containing SO₄²⁻ only exhibits EDLC in the Fe-based electrodes. Additionally, Li⁺ ions that have lower conductivity and mobility may lead to poorer charge storage capability compared to Na⁺ ions. Overall, the results reveal that the AC composite electrodes with 40 wt% LiFePO₄ loading on a Na₂SO₃ neutral electrolyte exhibit high cycling stability and reversibility and thus display great potential for electrochemical capacitor applications.     

Performance studies on composite gel polymer electrolytes for rechargeable magnesium battery application

Effect of micron-sized MgO particles dispersion on poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF–HFP) based magnesium-ion (Mg²⁺) conducting gel polymer electrolyte has been studied using various electrical and electrochemical techniques. The composite gel films are free-standing and flexible with enough mechanical strength. The optimized composition with 10 wt% MgO particles offers a maximum electrical conductivity of ∼6×10⁻³ S cm⁻¹ at room temperature (∼25°C). The Mg²⁺ ion conduction in gel film is confirmed from cyclic voltammetry, impedance spectroscopy and transport number measurements. The applicability of the composite gel electrolyte to a rechargeable battery system has been examined by fabricating a prototype cell consisting of Mg (or Mg–MWCNT composite) and V₂O₅ as negative and positive electrodes, respectively. The rechargeability of the cell has been improved, when Mg metal was substituted by Mg–MWCNT composite as negative electrode.     

Electrochemical redox supercapacitors using PVdF-HFP based gel electrolytes and polypyrrole as conducting polymer electrode

Electrochemical redox supercapacitors have been fabricated using polymeric gel electrolytes polyvinylidene fluoride co-hexafluoropropylene (PVdF-HFP)–ethylene carbonate (EC)–propylene carbonate (PC)–MClO₄: M = Li, Na, (C₂H₅)₄N and electrochemically deposited polypyrrole as conducting polymer electrode. The performance of the capacitors have been characterized using a.c impedance spectroscopy, cyclic linear sweep voltammetry and galvanostatic charge–discharge techniques. The capacitors shows larger values of overall capacitance of about 14–25 mF cm^− 2 (equivalent to a single electrode specific capacitance of 78–137 F g^− 1 of polypyrrole), which corresponds to the energy density of 11–19 W h kg^− 1 and power density of 0.22–0.44 kW kg^− 1. The values of capacitance have been found to be almost stable up to 5000 cycles and even more. A comparison indicates that the capacitive behaviour and the capacitance values are not much affected with the size of cations of the salts incorporated in gel electrolytes, rather predominant role of anions is possible at the electrode–electrolyte interfaces. Furthermore the coulombic efficiencies of all the cells were found to be nearly 100% that is comparable to the liquid electrolytes based capacitors.     

Low-temperature zirconia oxygen gauges based on RuO2 electrode

A low temperature oxygen gauge based on zirconia electrolyte has been developed. It makes use of RuO₂ as electrode material in place of platinum in conventional gauges. The low interfacial impedance of the RuO₂ electrode makes it possible to keep the cell resistance below 10⁶ ω even at low temperatures. Nernst's law tests indicate that this cell can give theoretical outputs down to 498 K campared to 923 K for gauges with platinum electrodes. Faraday's law tests confirm its good performance over a wide range of oxygen concentrations. High electronic conductivity, single oxide phase, slight non-stoichiometry and good adherence are responsible for the good performance of RuO₂ as electrode. An activation energy of 90.95 kJ/mole observed for the interface shows that the vacancy movement in the electrolyte is the rate controlling step. The evaporation of RuO₂ as RuO₄ gives rise to flow dependent output. This can be overcame by operating the cells at low temperatures though at the cost of speedy response. The low operating tempratures lead to a compact gauge with good stability.     

Electrochemical characterization on layered lithium ruthenate for electrochemical supercapacitors

Electrochemical characteristics of lithium ruthenate (Li_xRuO_2+0.5x·nH₂O) for electrochemical capacitors' electrode material were first examined in this paper by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Results show that Li_xRuO_2+0.5x·nH₂O has electrochemical capacitive characteristic within the potential range of − 0.2–0.9 V (vs. SCE) in 1 M Li₂SO₄ solution. The capacitance mainly arises from pseudo-capacitance caused by lithium ions' insertion/extraction into/out of the Li_xRuO_2+0.5x·nH₂O electrode. The specific capacitance of 391 F g^− 1 can be delivered at 1 mA charge–discharge current for Li_xRuO_2+0.5x·nH₂O electrode with an energy density of 65.7 W h kg^− 1. This material also exhibits an excellent cycling performance and there is no attenuation of capacitance over 600 cycles.     

Poly(dimethylsiloxane)-poly(ethylene oxide) based polyurethane networks used as electrolytes in lithium electrochemical solid state batteries

Ionic conductivity and redox stability domain of a new type of polymer electrolyte have been studied. The polymer electrolytes were prepared from a network of poly (dimethylsiloxane-grafted ethylene oxide) copolymer crosslinked by an aliphatic isocyanate (grafted PDMS) and containing 10 wt% LiClO₄. Ionic conductivities higher than 10^?5 ω^?1 cm^?1 are obtained above 30°C. The study of the electrochemical stability of the crosslinking agent suggests that the unreacted isocyanate groups are not stable. The electroactivity domain of the grafted PDMS-LiClO₄ 10 wt% electrolyte is larger than 3 V. The performances of a solid state battery using this electrolyte have been investigated. The first discharge and charge depths were 73%. The rechargeability behaviour have been compared with those of a Li/RuO₂ battery with a linear high molecular weight P(EO)₈-LiClO₄ as electrolyte.     

A preliminary study on a new LiBOB/acetamide solid phase transition electrolyte

New solid electrolytes containing acetamide and lithium bioxalato borate (LiBOB) with different molar ratios have been investigated. Their melting points (T_m) are around 42 °C. The ionic conductivities and activation energies vary drastically below and above T_m, indicating a typical feature of phase transition electrolyte. The ionic conductivity of the LiBOB/acetamide electrolyte with a molar ratio of 1:8 is 5 × 10^? 8 S cm^? 1 at 25 °C but increases to 4 × 10^? 3 S cm^? 1 at 60 °C. It was found that anode materials, such as graphite and Li₄Ti₅O₁₂, could not discharge and charge properly in this electrolyte at 60 °C due to the difficulty in forming a stable passivating layer on the anodes. However, a Li/LiFePO₄ cell with this electrolyte can be charged properly after heating to 60 °C, but cannot be charged at room temperature. Although the LiBOB/acetamide electrolytes are not suitable for Li-ion batteries due to poor electrode compatibility, the current results indicate that a solid electrolyte with a slightly higher phase transition temperature than room temperature may find potential application in stationary battery for energy storage where the electrolyte is at high conductive liquid state at elevated temperature and low conductive solid state at low temperature. The interaction between acetamide and LiBOB in the electrolyte is also studied by Raman and FTIR spectroscopy.     

Preparation,properties, and Li-ion battery application of EC + PC-modified PVdF-HFP gel polymer electrolyte films

Based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and lithium tetrafluoroborate (LiBF₄) salt along with blending plasticizers, ethylene carbonate (EC) and propylene carbonate (PC), high Li-ion-conducting gel polymer electrolyte films are developed. Their properties are characterized by various techniques. The ambient temperature ionic conductivity of the 85PVdF-HFP:15LiBF₄ + 150(EC + PC) electrolyte film has a high value of 8.1 × 10^?4 S cm^?1. Its crystallinity, melting point, and electrochemical stability window are 9.5%, 115 °C, and 4.6 V, respectively. The mechanical testing shows that the Young’s modulus, yield strength, and breaking strain of this electrolyte film are 36.8 MPa, 3.4 MPa, and 320%, respectively. Lithium-ion batteries based on the gel polymer electrolyte film exhibit remarkable charge–discharge and cycling performances. The initial discharge capacity of this battery is as high as 165.1 mAh g^?1 at 0.1 C and just shows a small capacity fading of 4.8% after 120 cycles, indicating that the 85PVdF-HFP:15LiBF₄ + 150(EC + PC) system is an excellent electrolyte candidate for lithium-ion battery applications. The charge–discharge performance of the Li-ion cell fabricated with this gel polymer electrolyte film is apparently better than that of the previously reported Li-ion cells fabricated with other PVdF-HFP-based gel polymer electrolyte films.     

The growth mechanism and supercapacitor study of anodically deposited amorphous ruthenium oxide films

In the present study, ruthenium oxide (RuO₂) thin films were deposited on the stainless steel (s.s.) substrates by anodic deposition. The nucleation and growth mechanism of electrodeposited RuO₂ film has been studied by cyclic voltammetry (CV) and chronoamperometry (CA). The deposited films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive analysis by X-rays (EDAX) for structural, morphological, and compositional studies. The electrochemical supercapacitor study of ruthenium oxide thin films have been carried out for different film thicknesses in 0.5 M H₂SO₄ electrolyte. The highest specific capacitance was found to be 1190 F/g for 0.376 mg/cm² film thickness.     

MnO2-polypyrrole conducting polymer composite electrodes for electrochemical redox supercapacitors

Redox supercapacitors using electrochemically synthesised MnO₂-polypyrrole composite electrodes have been fabricated with different electrolytes, namely polymer electrolyte film (polyvinyl alcohol, PVA-H₃PO₄ aqueous blend), aprotic liquid electrolyte (LiClO₄-propylene carbonate, PC) and polymeric gel electrolyte [poly methyl methacrylate, (PMMA)-Ethylene carbonate (EC)-Propylene carbonate (PC)-NaClO₄]. The capacitors have been characterised using galvanostatic charge-discharge methods. The cell with aqueous PVA-H₃PO₄ shows non-capacitive behaviour owing to some reversible chemical reaction of MnO₂ with water while the MnO₂-polypyrrole composite is found to be a suitable electrode material for redox supercapacitors with aprotic (non-aqueous) electrolytes. The solid state supercapacitor based on MnO₂-polypyrrole composite electrodes with gel electrolyte gives stable values of capacitance of 10.0–18.0 mF cm⁻² for different discharge current densities.     

Fabrication of a nanoparticle TiO<Subscript>2</Subscript> photoelectrochemical cell utilizing a solid polymeric electrolyte of PAN–PC–LiClO<Subscript>4</Subscript>

A nanoparticle TiO₂ solid-state photoelectrochemical cell utilizing as a solid electrolyte of poly(acrylonitrile)–propylene–carbonate–lithium perchlorate (PAN–PC–LiClO₄) has been fabricated. The performance of the device has been tested in the dark and under illumination of 100-mW cm⁻² light. A nanoparticle TiO₂ film was deposited onto indium tin oxide-covered glass substrate by controlled hydrolysis technique assisted with spin-coating technique. The average grain size for the TiO₂ film is 76 nm. LiClO₄ salt was used as a redox couple. The room temperature conductivity of the electrolyte is 4.2 × 10⁻⁴ S cm⁻¹. A graphite electrode was prepared onto a glass slide by electron beam evaporation technique. The device shows the rectification property in the dark and shows the photovoltaic effect under illumination. The best J _sc and V _oc of the device were 2.82 μA cm⁻² and V _oc of 0.58 V, respectively, obtained at the conductivity of 4.2 × 10⁻⁴ S cm⁻¹ and intensity of 100 mW cm⁻². The J _sc was improved by about three times by introducing nanoparticle TiO₂ and by using a solid electrolyte of PAN–PC–LiClO₄ replacing PVC–PC–LiClO₄ in the device. The current transport mechanism of the cell is also presented in this paper.     

Potentiometric DO detection in water by ceramic sensor based on sub-micron RuO2 sensing electrode

An alumina sensor using sub-micron RuO₂ sensing electrode (SE) was fabricated and examined for potentiometric dissolved oxygen (DO) detection in water at a temperature range of 9–35 °C. The electromotive force (emf) response at these temperatures was linear to the logarithm of DO concentration in the range from 0.6 to 8.0 ppm (log[O₂], −4.71 to −3.59). RuO₂-SE displays a Nernstian slope of −41 mV per decade at pH 8.0. It was also found that the response/recovery time to DO changes were sluggish as the water temperature cools down. Response time T ₉₀ to DO changes increased from 8 min at a temperature of 23 °C to about 30 min at a temperature of 9 °C. The proton conductivity of hydrous RuO₂ appears to be due to the dissociative adsorption of water and the formation of acidic OH groups in Ru (III,IV) cluster ions. In strong alkaline solutions, the sensor’s emf exhibited a mixed potential of fast and slow electrochemical reactions involving DO, RuO₄ ²⁻ and OH⁻ ions. The results also revealed that as pH of the solution increases to pH 10.0–13.0, the response/recovery rate becomes faster, stabilizing more or less quickly depending upon the solution alkalinity. Scanning electron microscopy, energy dispersive X-ray-analysis and impedance spectroscopy techniques were used to examine respectively the morphology, crystalline structure and electrochemical behaviour of sub-micron RuO₂ oxides.     

Preparation and characterization of biodegradable poly(ε-caprolactone)-based gel polymer electrolyte films

Biodegradable polymer electrolyte films based on poly(ε-caprolactone) (PCL) in conjunction with lithium tetrafluoroborate (LiBF₄) salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid were prepared by solution cast technique. The structural, morphological, thermal, and electrical properties of these films were examined using X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), and impedance spectroscopy. The XRD and OM results reveal that the pure PCL possesses a semi-crystalline nature and its degree of crystallinity decreases with the addition of LiBF₄ salt and EMIMBF₄ ionic liquid. DSC analysis indicates that the melting temperature and enthalpy are apparently lower for the 40 wt% EMIMBF₄ gel polymer electrolyte as compared with the others. The ambient temperature electrical conductivity increases with increasing EMIMBF₄ concentration and reaches a high value of ～2.83?×?10^?4 S cm^?1 for the 85 PCL:15 LiBF₄ + 40 wt% EMIMBF₄ gel polymer electrolyte. The dielectric constant and ionic conductivity follow the same trend with increasing EMIMBF₄ concentration. The dominant conducting species in the 40 wt% EMIMBF₄ gel polymer electrolyte determined by Wagner’s polarization technique are ions. The ionic conductivity of this polymer electrolyte (～2.83?×?10^?4 S cm^?1) should be high enough for practical applications.     

Self-Supported Graphite/Graphene/NiFe-LDH Electrodes for High Performance Oxygen Evolution Reaction

Reducing energy consumption and improving energy utilization efficiency has become the focus of research in the 21^st century. Electrocatalytic water splitting is one of the promising strategies for producing hydrogen energy. In this study, the non-noble nickel-iron layered double hydroxide (NiFe-LDH) catalyst is deposited on the electrochemically intercalated graphite/graphene (G/GE) substrate and directly used as the self-supported and binder-free electrode for electrocatalytic water oxidation. The Ni₂Fe₁-LDH@G/GE catalyst shows a low overpotential of 194 mV at a current density of 10 mA cm^–2, which is better than the noble metal catalyst IrO₂ (314 mV) and RuO₂ (330 mV) and many other related works. This research provides a facile way to directly prepare the catalyst electrode with high performance and low cost.