Sharp Redox Peaks Research Articles

Tailored Electrolytes for New Redox-Active Polymers

Radical polymers are gaining increasing interest as active materials for batteries owing to their great potential for fast charging, and the fact that no critical elements are involved. PTMA [poly(2,2,6,6- tetramethylpiperidinyloxy-4-yl methacrylate)] is one of the best-investigated radical polymers for lithium batteries, providing high redox activity, fast kinetics and great reversibility during cycling.1 However, the electrochemically active nitroxyl radicals are embedded in a six-membered ring with four methyl groups attached to stabilize the radical, which limits its theoretical capacity due to the rather high molecular weight of the overall functional moiety. To increase the theoretical capacity, a decrease of the “unnecessary” mass is therefore desirable. Smaller redox-active molecules, however, commonly show a high solubility in liquid electrolytes, which prevents stable long-term cycling.Herein, we present a new redox-active polymer based on low molecular weight amides, for which the solubility issue has been overcome by proper design. We show that the electrolyte composition (salt concentration and the choice of solvents as well as their ratio) plays a decisive role for (i) the redox behavior and kinetics (broad vs. sharp redox peaks and the redox peak separation), (ii) the eventual redox potential, which is greater than for PTMA, and (iii) the long-term stable cycling at high dis-/charge rates. As a result, the rational optimization of the electrolyte composition enables achieving excellent electrochemical performance, rendering this new class of polymers highly promising for high-performance rechargeable batteries. Finally, we unveil the underlying phenomena by means of complementary ex situ and in situ characterization techniques to provide an in-depth understanding and, thus, allow for the tailored design of suitable electrolyte compositions for this new class of redox-active polymers and, potentially, polymer electrode materials in general.(1) Kim, J.-K.; Kim, Y.; Park, S.; Ko, H.; Kim, Y. Encapsulation of Organic Active Materials in Carbon Nanotubes for Application to High-Electrochemical-Performance Sodium Batteries. Energy Environ. Sci. 2016, 9 (4), 1264–1269. https://doi.org/10.1039/C5EE02806J.

Comparative of MIL101(Cr) and nano‐MIL101(Cr) Electrode as an Electrochemical Hydrogen Peroxide Sensor

AbstractHerein, an electrochemical sensor for the detection of H2O2 based on nafion glassy carbon electrode modified with MIL101(Cr) and nano‐MIL101(Cr) are developed and its electrochemical characterizations analyzed by CV and CA. In comparison with the NGCE, MIL101/NGCE and nano‐MIL101/NGCE, the nano‐MIL101/NGCE showed a sharp redox peak specific to H2O2 was obtained in the phosphate‐calibrated solution. nano‐MIL101/NGCE exhibited good linear response in terms of the relationship between peak currents and concentrations as from 0 to 650 μM (R2=0.99), with a low limit of detection 3.8 μM, high sensitivity 986 μA mM−1 cm−2 and nano‐MIL101/NGCE exhibited ideal repeatability, reproducibility, stability and the interference‐free perception of H2O2.

Investigation of Alkyl Amine Substituted Quinone Derivatives for the Redox Flow Battery Applications in Acidic Medium

2,5-bis((dimethylamino)methyl)benzene-1,4-diol (H2QDMA), a redox-active molecule and its derivatives are synthesised by a one-step chemical method using Mannich reaction has been explored as catholyte with vanadium (V2+/V3+) anolyte for aqueous redox flow battery applications. The solubility of H2QDMA was ∼ 0.75 M in 3 M H2SO4. H2QDMA showed one sharp redox peak at the formal potential 0.6 V ± vs Ag/AgCl, and it was stable for 100 continuous CV cycles without any appreciable change in colour. The battery delivered a discharge capacity of ∼ 2 Ah L−1, which faded with cycles. We have carried out a post cycle analysis of catholyte and anolyte to understand the origin of the capacity fading. Towards this, the oxidized form of H2QDMA, i.e., QDMA, was synthesized. The stability of QDMA in acidic solution was low, and the colour of the solution changed to intense brown with time. The UV–Visible spectrum and CV curves of the QDMA reflects the same behaviour as observed with the catholyte solution obtained post galvanostatic charge-discharge analysis. This study concluded that the QDMA undergoes faster chemical transformation, presumably through the Michael addition reaction process, compared to its participation in the desired electrochemical process.

In-situ STM and AFM Studies on Electrochemical Interfaces in imidazolium-based ionic liquids

Voltammetric responses, adsorption behaviors and layered structures of 1-ethyl-2, 3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide (EMMITFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) at Au (111) have been investigated by cyclic voltammetry, in-situ STM and in-situ AFM force curve measurements, respectively. Cyclic voltammetry measurements pointed out that two pairs of sharp redox peaks are located at around 0.1 and 0.7 V in EMMITFSI, but not in EMITFSI. In-situ STM studies revealed no etching of the Au (111) surface in the investigated potential region in EMMITFSI, but an etched Au (111) surface was observed in EMITFSI in the same potential region, indicating that the interaction between EMITFSI and the Au (111) surface is much stronger than that between EMMITFSI and the Au (111) surface. In-situ AFM force curve measurements showed three layered structures at Au (111)/EMITFSI interface, but no force curves with saw-toothed feature can be obtained when the potential is higher than +0.5 V, which implies the disappearance of layered structures. In EMMITFSI, force curves with saw-toothed feature can be obtained even at +1.2 V. The fact that layered structures can form in a broader potential region indicates that a stronger interaction exists between the EMMI cation and the TFSI anion. It is inferred that the methylation of the hydrogen position provides a configuration for EMMI cations with an increased hydrophobic interaction, which maintains the layered structure in wider potential region. As a consequence, the electrode potential may induce structural transition of the layered structures, which is responsible for the origin of the voltammetric features.

Curcumin-quinone immobilised carbon black modified electrode prepared by in-situ electrochemical oxidation of curcumin-phytonutrient for mediated oxidation and flow injection analysis of sulfide

Curcumin, a natural pigment of the turmeric, has been widely used as a phytonutrient for various health benefits. There are several electrochemical reports relating to curcumin-metal complex modified electrodes for electroanalytical applications, and sensing of curcumin utilising the electrochemical behaviour of the phenolic site using different carbon-based chemically modified electrodes, in the literature. Herein, we report, a curcumin-quinone (Cur-Q) derivative immobilised carbon black (CB) modified glassy carbon electrode, designated as GCE/CB@Cur-Q, prepared by an in-situ electrochemical oxidation method, for efficient electrocatalytic oxidation and electrochemical sensing application of sulfide in pH2 KCl-HCl solution. The “as prepared” GCE/CB@Cur-Q showed a sharp redox peak at an apparent standard electrode potential, Eo′=0.55V vs. Ag/AgCl with surface excess and peak-to-peak potential values of 12.37×10−9molcm−2 and 19±5mV respectively. No such electrochemical behaviour was noticed when unmodified GCE was subjected to the electrochemical oxidation of curcumin. The existence of Cur-Q was confirmed by Liquid chromatography-mass spectrometer and in-situ electrochemical quartz crystal microbalance measurements. Amongst various carbon materials like CB, multiwalled carbon nanotube (MWCNT), single-walled carbon nanotube, oxygen functionalized MWCNT, graphite nanopowder, graphitised mesoporous carbon, carbon nanofiber, graphene oxide and activated charcoal investigated, CB was showed an excellent electrochemical reaction for the in-situ formation of Cur-Q. A highly sensitive electrocatalytic oxidation and sensing by amperometric i-t and flow injection analysis of sulfide at operating potential, 0.55V vs. Ag/AgCl with detection limit values (signal-to-noise ratio=3) of 2.4×10−6 and 7.12×10−6M respectively, without any interference from other biochemicals like uric acid, dopamine, nitrite, cysteine, NADH and H2O2, unlike the conventional chemically modified electrodes with serious interferences, have been demonstrated.

Effect of coating thickness of Al-doped Li4Ti5O12 (LTO) on the electrochemical performance of half cell battery

Effect of coating thickness of Al-doped Li4Ti5O12 (LTO) sheet on the electrochemical performance of battery cells is reported. A 0.025 mol Al-doped LTO powder was synthesized by solid state reaction method, for the anode sheet was made by the doctor blade method. The sheet manufacturing was carried out by varying the coating thickness from 100, 200, 300 and 400 μm to determine the effect on the electrochemical performance of the battery cell. The analysis of phase was conducted by X-ray diffraction (XRD); for electrochemical performances were conducted by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge discharge (CD) method. XRD analysis showed that there are two phases formed, i.e. LTO and rutile phases (TiO2) of 75.6% and 24.4%, respectively. EIS results showed that the thicker the coating layer, the conductivity of the sample become slower. Furthermore, the results indicate that the sample with thickness of 100, 200 and 300μm indicated sharp redox peak, and 400 μm showed wide redox peaks. The specific capacity and specific power of the half cell battery decreases with the increasing of coating thickness. The best cell capacity is obtained by sample with 100 μm thickness with specific discharge capacity of 134.3 mAh/g.

Effect of Nickle Substitution on the Performance of Lithium Ion Battery Material LiMnTiO$lt;inf$gt;4$lt;/inf$gt;

Spinel LiMn1-xNixTiO4(x=0, 0.1, 0.2, 0.3) cathode materials were prepared by Sol-Gel method. The surface morphology and phase structure of LiMn1-xNixTiO4 (x=0, 0.1, 0.2, 0.3) were characterized by FESEM and XRD. FESEM analysis indicated all the samples consisted of irregular particles and XRD patterns showed that all the materi- als had impurity TiO2, but there were no impurities related to Ni element. Electrochemical studies of doped and un- doped spinels were carried out by cyclic voltammetry (CV) and constant current charge-discharge. CV results showed that LiMnTiO4 had two couples of sharp redox peaks corresponding to Mn

Enhancing electro-codeposition and electrocatalytic properties of poly(neutral red) and FAD to determine NADH and H2O2 using amino-functionalized multi-walled carbon nanotubes

A bifunctional biosensor of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H2O2) has been successfully fabricated using amino-functionalized multi-walled carbon nanotubes (amino-MWCNT) as a template to immobilize neutral red (NR), poly(neutral red) (PNR), and flavin adenine dinucleotide (FAD). Sharp redox peaks indicate that the use of amino-MWCNT can improve the electro-codeposition of NR, PNR and FAD on the electrode surface. The hybrid composite can effectively lower the overpotential to 0.05 V and −0.1 V (vs. Ag/AgCl) for NADH and H2O2, respectively. The kinetic constant (kkin) of 1.6 × 104 M−1 s−1 and 2 × 105 M−1 s−1 is evaluated for NADH and H2O2, respectively. It shows linear concentration range of 1.3–933.3 μM and 1–2555 μM, sensitivity of 457.2 μA mM−1 cm−2 and 10.1 μA mM−1 cm−2, and a detection limit of 1.3 μM and 0.1 μM (S/N = 3), for NADH and H2O2, respectively. Recovery of 96.5–102% and relative standard deviation (R.S.D.) of <5% was obtained in bovine calf serum samples. It shows good selectivity avoiding interference of AA, DA, UA, glucose, galactose, fructose, and sucrose. It allows fabricating an active bifunctional biosensor of NADH and H2O2 due to simplicity, multifunction, low cost, low overpotential, high sensitivity, and high selectivity.

Photophysical Properties of the Newly Synthesized Triad Based on [70]Fullerene Studies with Laser Flash Photolysis

N,N-Dimethylaniline-pyrazolinoC70-ferrocene has been prepared with the 1,3-dipolar cycloaddition reaction of a nitrile imine with C70. Although three regioisomers regarding the position of the pyrazolino group on the C70 were identified in the reaction products, molecular orbital calculations indicate that the stabilities and electronic properties of the three isomers are almost the same, which was confirmed by the sharp redox peaks. The photophysical properties of the triads have been investigated by measuring the time-resolved emission and transient absorption spectra showing that charge separation takes place efficiently via the photoexcited singlet state of the C70 moiety with accepting an electron from the donor moieties. It was found that the pyrazolino ring mediates a charge separation between the donor moieties and the photoexcited C70 moiety.

Fabrication of all solid-state rechargeable lithium battery and its electrochemical properties

An all solid-state rechargeable lithium battery was successfully fabricated using a ceramic electrolyte and a thin film technique. A polymer-modified sol–gel method was applied in order to prepare the electrode-coated ceramic electrolyte. Li 4Ti 5O 12 known for its outstanding electrochemical performances and the partially crystallized glass ceramics, LiTi 2(PO 4) 3–AlPO 4 were adopted as electrode and electrolyte materials, respectively. The all solid-state battery cell constructed with lithium metal, PMMA buffer, and electrode-coated ceramic electrolyte was electrochemically evaluated with ac impedance, cyclic voltammetry, and discharge–charge test. The impedance of the interface between Li 4Ti 5O 12 film and the solid electrolyte showed a relatively low resistance of ∼110 Ω cm −2 at 1.60 V. Highly reversible sharp redox peaks were observed at around 1.55 V from cyclic voltammograms, and these were still clear even at a high scan rate of 3 mV s −1, indicating a fast electrochemical response. A charge–discharge experiment showed an excellent reversibility of the cell but a relatively smaller discharge capacity of 100.49 mAh g −1 at C/5 than theoretical one of 175 mAh g −1. This may be due to formation of an interlayer at the interface, which may be caused by chemical reaction between Li 4Ti 5O 12 and the ceramic electrolyte during a firing step during preparation. In spite of the undesirable side-reaction, the ceramic electrolyte was successfully applied to the solid-state rechargeable lithium battery by means of a thin film technique using the polymer-modified sol–gel method, through increasing the interfacial contact area, i.e. reducing the interfacial resistance.

Investigation on Electrochemical Interface between Li4Ti5O12 and Li1 + xAlxTi2 − x ( PO4 ) 3 NASICON-Type Solid Electrolyte

An interface consisting of film electrode and -based NASICON (sodium superionic conductor)-type solid electrolyte (LTP) was prepared by a sol-gel coating method. The prepared solid-solid electrochemical interface was evaluated by cyclic voltammetry, galvanostatic discharge-charge test, and ac impedance method. The measured impedance of the interface between and LTP was about , and compressed semicircles were observed at all electrode potentials, indicating a presence of potential distribution at the electrochemical interface due to poor solid-solid contact between and LTP. In cyclic voltammograms of this electrochemical interface, a highly reversible sharp redox peak was observed at around . From discharge-charge tests, thin-film electrode on LTP showed high reversibility during discharge and charge cycles, and it exhibited discharge capacities of at rate and at rate, respectively.

Electrochemical oxidation and ex-situ STM observations of bis(4-dimethylamino-2-dihydroxyphenyl)squaraine dye layers on HOPG electrodes

Electrochemical oxidation of insoluble highly ordered bis(4-dimethylamino-2-dihydroxyphenyl)squaraine (1-1OHSQ) dye layers adsorbed on highly oriented pyrolytic graphite (HOPG) electrodes was studied in aqueous electrolytes. Staircase cyclic voltammetry obtained in chloride electrolytes revealed hysteresis characterized by large peak separations (100–200 mV) and sharp redox peaks (full width at half maximum (fwhm) 10–60 mV) the shape and potentials of which depended on electrolyte concentrations. Small stochastic reduction peaks were observed at more negative potentials that are associated with the reduction of small domains of the oxidized 1-1OHSQ layers. Peak potentials and peak shapes were also dependent on the identity of the electrolyte anion species. The results support a reaction scheme where electrolyte anions are incorporated into surface confined one-electron oxidized dye molecular layers. From the results of peak potential shifts, the preference for ion-pairing is estimated to be in the order of: I−>Br−>Cl−>SO42−≈ClO4−≈F−. Ex-situ STM observations were performed to reveal structural changes upon electrochemical oxidation of 1-1OHSQ layers in LiCl electrolytes. Two polymorphs with different angles of the long-axis of molecules to the directions of the molecular row were observed for the oxidized samples. Both polymorphs had larger packing densities compared to the reduced form of the dye.

Electrochemical and EQCM studies on the assembly of asymmetric viologen on bare and alkanethiol-coated Au electrodes

Abstract Cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques have been used to study the influence of anions and the alkyl chain length of thiol on the redox behavior of asymmetric viologen, N -ethyl- N ′-octadecyl viologen (C 18 EV 2+ ) on bare and alkanethiol (CH 3 (CH 2 ) n SH, n =3, 5, 7, 11, 17)-coated electrodes. The grazing angle reflectance FTIR spectral and cyclic voltammetric blocking experiments suggested that the alkyl chains of the n -octadecanethiol ( n -ODT) monolayers were disordered greatly in the C 18 EV 2+ inserted n -ODT monolayers when compared to pure n -ODT monolayers. On the other hand, the assembly of C 18 EV 2+ was more highly ordered on n -ODT monolayers than on a bare Au electrode. The assembly of C 18 EV 2+ on bare and alkanethiol-coated Au electrodes showed a single redox wave for the first reduction of C 18 EV 2+ in 0.1 M of KCl and Na 2 SO 4 . A sharp redox peak was observed for the assembly of C 18 EV 2+ on bare and short alkyl chain thiol ( n =3, 5, 7)-coated electrodes whereas a broad redox wave was observed on long alkyl chain thiol ( n =11, 17)-coated electrodes in 0.1 M NaClO 4 . On the other hand, a multiple redox peak was observed for the first reduction of C 18 EV 2+ on a bare Au electrode in 0.1 M NH 4 PF 6 . In the case of alkanethiol-coated electrodes, no redox response was observed for the assembly of C 18 EV 2+ on long chain alkanethiol-coated electrodes ( n =11, 17) while a single redox peak was observed on short chain alkanethiol ( n =3, 5, 7)-coated electrodes in 0.1 M NH 4 PF 6 . The observed lack of a redox response of C 18 EV 2+ on the long chain alkanethiol-coated electrodes has been explained by the non-entry of water molecules in the presence of very weakly hydrated PF 6 − anions. In these electrodes, the PF 6 − ions precipitate the assembly of C 18 EV 2+ in the absence of water molecules and it is inactive electrochemically. When the same electrode was transferred into the supporting electrolytes of KCl, Na 2 SO 4 or NaClO 4 , the PF 6 − ions were exchanged readily with these anions and the assembly became electroactive. EQCM data indicate that the ingress of water molecules into the assembly of C 18 EV 2+ increases as its assembly is bound to the electrodes coated with alkanethiols of shorter alkyl chain length. The ingress of water molecules also depends on the anions present in the solution. The ingress of water molecules into the assembly of C 18 EV 2+ on bare and alkanethiol-coated Au electrodes increases in the order of PF 6 − 4 − − 4 2− .

On the influence of tin and bismuth UPD on Pt(111) and Pt(332) on the oxidation of CO

Deposition of Sn on a Pt(111) electrode gives rise to a sharp redox peak which is not due to the adsorption/desorption of Sn. The catalytic effect of this Sn-UPD on the oxidation of adsorbed CO is negligible. UPD of Sn on Pt(332) and Pt(755) on the other hand, has a remarkable catalytic effect; the onset of CO oxidation is shifted down to 0.25 V. Comparative experiments are presented for Bi deposition on these surfaces. Even when the bismuth coverage is high enough to block H-adsorption completely, CO is coadsorbed. Impedance measurements show that the rate of hydrogen adsorption is decreased by Sn UPD on Pt(111).

Electrochemically prepared poly(o-phenylenediamine) — Prussian blue composite film for a three-colour expressible ECD material

Both Prussian blue (PB) and poly(o-phenylenediamine) (PoPD) were easily electrodeposited as stable films onto a transparent indium tin oxide (ITO) electrode. The voltammogram of the PB film showed a reversible sharp redox peak current at about 0.25 V. Although the colour change was caused by altering the applied potentials, no colour change was seen after about 104 repetitions. The PoPD film also showed a reversible redox peak current at about −0.05 V. The redox reaction was accompanied by a readily observable colour change between nearly red (vermilion) and colourless. The PoPD film was electrodeposited onto the PB coated electrode to obtain a PB/PoPD composite film. The voltammogram of the film was comprised of the two redox waves of the individual components. The film retained the electrochromic properties of each component and there was no undesirable interference. By changing the potentials, the film exhibited a continuous variety of colours: colourless (-0.2 V), vermilion (0.1 V) and emerald green (0.6 V). The switching time of the colour change was found to be <600 ms. Compared with the PB film, the composite film lasted longer. About 60% of the colouration remained after 105 repetitions since the PoPD worked as a binder which enhanced the adhesion of PB to the electrode surface.

Transformation of cyclic voltammograms of polyparaphenylene (PPP) filmsprepared by adding strong acid to SO 2: correlation between redox behavior and microstructure of polymer chains

Polyparaphenylene (PPP) films were prepared by electrochemical oxidation of benzene in liquid SO 2 + CF 3SO 3H at low temperatures. Characteristic cyclic voltammograms (CVs) with sharp well-separated redox peaks were observed by scanning in H 2SO 4 (95%). Upon potential scanning between −0.1 V and +0.7 V versus a saturated calomel electrode (SCE) in H 2SO 4 (95%) at room temperature for several hours, the peaks decreased progressively and finally disappeared, being replaced by broad redox peaks. According to IR and X-ray photoelectron spectroscopy studies, the transfomation of the CV was accompanied by dopant exchange and cross-linking. The sharp reduction peak was attributed to the difficult removal of the CF 3SO 3 − anion which was introduced into the PPP film during electrochemical polymerization. When a high potential of +1.2 V/SCE was applied, the sharp redox peaks immediately became broad and ill defined, whereas their intensity decreased gradually without any shift when the potential scan was limited to +0.5 V/SCE.

Electropolymerization of benzene in a two-phase strong proton acid-benzene system

Anodic polymerization of benzene can be carried out under two-phase conditions if the electrode is immersed in the interfacial layer between benzene and acids of different strength, such as methanesulfonic, sulfuric, 20% fuming sulfuric, fluorosulfonic and trifluoromethanesulfonic acids. In all these cases the benzene oxidation is in the vicinity of 1 V/SCE. For films grown in usual acid media cyclic voltammetries are characterized by wide, ill-defined redox peaks. By contrast, in the superacids another state of the film with sharp redox peaks is observed. It is supposed that linear structure, with narrow distribution of the chain length, is realized in the latter case.