Reversible Electrochemical Process Research Articles

A Stable High-Capacity Lithium-Ion Battery Using a Biomass-Derived Sulfur-Carbon Cathode and Lithiated Silicon Anode.

A full lithium‐ion‐sulfur cell with a remarkable cycle life was achieved by combining an environmentally sustainable biomass‐derived sulfur‐carbon cathode and a pre‐lithiated silicon oxide anode. X‐ray diffraction, Raman spectroscopy, energy dispersive spectroscopy, and thermogravimetry of the cathode evidenced the disordered nature of the carbon matrix in which sulfur was uniformly distributed with a weight content as high as 75 %, while scanning and transmission electron microscopy revealed the micrometric morphology of the composite. The sulfur‐carbon electrode in the lithium half‐cell exhibited a maximum capacity higher than 1200 mAh gS −1, reversible electrochemical process, limited electrode/electrolyte interphase resistance, and a rate capability up to C/2. The material showed a capacity decay of about 40 % with respect to the steady‐state value over 100 cycles, likely due to the reaction with the lithium metal of dissolved polysulfides or impurities including P detected in the carbon precursor. Therefore, the replacement of the lithium metal with a less challenging anode was suggested, and the sulfur‐carbon composite was subsequently investigated in the full lithium‐ion‐sulfur battery employing a Li‐alloying silicon oxide anode. The full‐cell revealed an initial capacity as high as 1200 mAh gS −1, a retention increased to more than 79 % for 100 galvanostatic cycles, and 56 % over 500 cycles. The data reported herein well indicated the reliability of energy storage devices with extended cycle life employing high‐energy, green, and safe electrode materials.

Covalent Coupling-Stabilized Transition-Metal Sulfide/Carbon Nanotube Composites for Lithium/Sodium-Ion Batteries.

Transition-metal sulfides (TMSs) powered by conversion and/or alloying reactions are considered to be promising anode materials for advanced lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). However, the limited electronic conductivity and large volume expansion severely hinder their practical application. Herein, we report a covalent coupling strategy for TMS-based anode materials using amide linkages to bind TMSs and carbon nanotubes (CNTs). In the synthesis, the thiourea acts as not only the capping agent for morphology control but also the linking agent for the covalent coupling. As a proof of concept, the covalently coupled ZnS/CNT composite (CC-ZnS/CNT) has been prepared, with ZnS nanoparticles (∼10 nm) tightly anchored on CNT bundles. The compact ZnS-CNT heterojunctions are greatly beneficial to facilitating the electron/ion transfer and ensuring structural stability. Due to the strong coupling interaction between ZnS and CNTs, the composite presents prominent pseudocapacitive behavior and highly reversible electrochemical processes, thus leading to superior long-term stability and excellent rate capability, delivering reversible capacities of 333 mAh g-1 at 2 A g-1 over 4000 cycles for LIBs and 314 mAh g-1 at 5 A g-1 after 500 cycles for SIBs. Consequently, CC-ZnS/CNT exhibits great competence for applications in LIBs and SIBs, and the covalent coupling strategy is proposed as a promising approach for designing high-performance anode materials.

Synchronized ion and electron transfer in a blue T-Nb2O5-x with solid-solution-like process for fast and high volumetric charge storage

The practical application of supercapacitor is largely hindered by insufficient volumetric energy density. Herein, a pseudocapacitive material with high volumetric specific capacity is achieved by introducing oxygen deficiency into T-Nb2O5, which produces a blue T-Nb2O5-x material with simultaneously low barrier for ion and electron transfer. By carrying out over-discharge experiments combined with in-situ X-ray diffraction and transmission electron microscopy, we further revealed that a solid-solution like electrochemical process without substantial structural change and internal stress provides the structural foundation for the reversible electrochemical process. The blue T-Nb2O5-x could achieve a particle-level volumetric specific capacity of 907.9 mAh/cm3 at 10 mA/g, much higher than traditional pseudocapacitive materials that only work with their shallow surfaces. The intrinsic bulk lithium storage mechanism endows the material with an excellent electrode-level volumetric specific capacity of 141.0 mAh/cm3 within 1.2-minute discharge. An asymetric lithium-ion capacitor was assembled using active carbon as cathode to demonstrate its performance in practical device.

Redox-active dinuclear oxorhenium(V) pyrazolate complexes

Four new structurally similar dinuclear oxorhenium(V) complexes, [{Re(O)X(PPh3)}2(μ-O)(μ-4-X′-pz)2], where pz = pyrazolate anion, X = X′ = Cl (1) and Br (4), X = Cl, X′ = Br (2), and X = Br, X′ = Cl (3), have been synthesized and characterized. Little variation in spectroscopic features – 1H NMR, IR, UV–Vis – exists among the four complexes. All complexes possess a bent Re-O-Re core as well as distorted octahedral coordination geometry around the rhenium centers. A reversible one-electron electrochemical process is observed at approximately 0.84 V vs. Fc+/Fc in all four complexes; however, changing the terminal halide from chloride to bromide slightly destabilizes the oxidized Re(VI) center.

Electrodeposition behaviour of copper from ore leachate and copper ammonium sulphate

The deposition behaviour of copper ammonia complexes from ore leachate and synthetic copper ammonium sulphate solutions was investigated using cyclic voltammetrywith platinumas counter electrode. The work is carried out to understand the deposition behaviour of the ore for hydrometallurgical and electro winning application. The chemical reduction and deposition of copper from both solutions consisted of two reversible electrochemical processes, each involving the transfer of a single electron. The Cu(NH3)4 2+ complex in the copper leachate is first reduced to Cu(NH3)4 + before being reduced to metallic copper. With synthetic copper ammonium sulphate (Cu(NH3)4SO4), the reduction to metallic copper is a ligand-coupled electron transfer reaction which proceeds as two sequential, single-electron transfer processes. The Cu/Cu(NH3)4 2+ redox reaction during deposition of copper from the leachate is fast compared to that of the Cu/Cu2+ redox reaction in the Cu(NH3)4SO4 synthetic solution. Investigation of the electrochemical kinetics shows that the linear relationship between the peak current and the square root of the scan rate is an indication that the Cu(NH3)4 + and Cu(NH3)4SO4 reduction to Cu proceeds through a diffusion-controlled process.
 Bangladesh J. Sci. Ind. Res.55(3), 229-236, 2020

Active Materials LiFeSi<sub>x</sub>P<sub>1-x</sub>O<sub>4</sub>/C as Lithium Ion Battery Cathode with Doping Variations Si Ions (0≤x≤0,06)

A cathode Lithium Ferro Phospate (LFP) composite material with variation doping ion Silicon (Si) with x = 0; 0,01; 0,03; 0.06 and carbon coating (LiFeSixP1-xO4/C) as lithium ion battery cathode were synthesized by a solid state reaction and wet milling methods. X-Ray Diffraction (XRD) pattern showed that the of olivine phase formed, and analysis characterization of Scanning Electron Microscopy (SEM) have shown average dimension particle of cathode in orde 1 micron. Analysis by Cyclic Voltammetry (CV) doping ion Si x = 0,03 have the best reversible electrochemical process than the other concentration, and have the highest charge and discharge capacity (78,745 mAh/g).

Nanomolar detection of chlorogenic acid at the cross-section surface of the pencil lead electrode

The detection of chlorogenic acid in clinic samples for metabolic kinetics study is quite a challenging task due to the low concentration and the lacking of sensitive quantitation methods. In this work, a porous pencil lead electrode (PLE) has been used to detect chlorogenic acid by square wave voltammetry (SWV) technique. The redox potential of chlorogenic acid is at ca. + 0.42V (pH = 3.0) versus saturated calomel electrode (SCE), and it’s a reversible thin layer electrochemical process with two-electrons and two-protons involved in this reaction. The sensitivity was significantly improved due to the enrichment of CGA at the porous structure of the electrode. Under the optimized conditions, the concentration of chlorogenic acid was linear in the range of 7.7 × 10―8 ∼ 7.7 × 10―6 M with detection limits down to 4.5 × 10―9 M (R2 = 0.9978, S/N = 3). The electrode was successfully used for the determination of chlorogenic acid in human urine with near 100 % recovery. Due to the advantages of simplicity of fabrication, high sensitivity, good reproducibility and easy renewability, we believe that the porous PLE is quite a promising candidate for determination of chlorogenic acid in clinic samples.

2D hexagonal SnS2 nanoplates as novel co-reaction accelerator for construction of ultrasensitive g-C3N4-based electrochemiluminescent biosensor

In this work, a highly luminous efficiency methotrexate (MTX) biosensor was successfully prepared with the introduced of SnS2 nanoplates as novel co-reaction accelerator towards amplification electrochemiluminescence (ECL) signal of graphite-like carbon nitride/peroxidisulfate (g-C3N4/K2S2O8) system. Specifically, the SnS2 nanoplates, as an electrochemically regenerable co-reaction accelerator, could accelerate the reduction of S2O82− to produce abundant of sulfate-free radical (SO4·−), evidently enhancing the ECL emitting of g-C3N4. Owing to the reversible electrochemical process of Sn2+ and Sn4+, the regenerable of Sn4+ reactive sites could occur at the surface of electrode, significantly improving the efficiency of co-reaction accelerator. Based upon the excellent quenching effect of MTX towards g-C3N4/K2S2O8 system, the fabricated ECL biosensor manifested high sensitivity with a detection limit of 0.27 pM in the concentration of MTX from 1 pM to 10 μM. More importantly, the constructed biosensor was successfully applied to quantitation of MTX in human serum with favorable results. Consequently, the proposed strategy provided a new sight in the trace determination of MTX in bioanalysis fields.

Enhancing Catalytic Activity and Selectivity by Plasmon-Induced Hot Carriers.

SummaryPlasmon-assisted chemical transformation holds great potential for solar energy conversion. However, simultaneous enhancement of reactivity and selectivity is still challenging and the mechanism remains mysterious. Herein, we elucidate the localized surface plasmon resonance (LSPR)-induced principles underlying the enhanced activity (∼70%) and selectivity of photoelectrocatalytic redox of nitrobenzene (NB) on Au nanoparticles. Hot carriers selectively accelerate the conversion rate from NB to phenylhydroxylamine (PHA) by ∼14% but suppress the transformation rate from PHA to nitrosobenzene (NSB) by ∼13%. By adding an electron accepter, the as-observed suppression ratio is substantially enlarged up to 43%. Our experiments, supported by in situ surface-enhanced Raman spectroscopy and density functional theory simulations, reveal such particular hot-carrier-induced selectivity is conjointly contributed by the accelerated hot electron transfer and the corresponding residual hot holes. This work will help expand the applications of renewable sunlight in the directional production of value-added chemicals under mild conditions.

Charge-transfer materials for electrochemical water desalination, ion separation and the recovery of elements

Reversible electrochemical processes are a promising technology for energy-efficient water treatment. Electrochemical desalination is based on the compensation of electric charge by ionic species, through which the ions are immobilized and, thereby, removed from a feed-water stream flowing through a desalination cell. For decades, electrochemical desalination has focused on the use of carbon electrodes, but their salt-removal ability is limited by the mechanism of ion electrosorption at low molar concentrations and low charge-storage capacity. Recently, charge-transfer materials, often found in batteries, have demonstrated much larger charge-storage capacities and energy-efficient desalination at both low and high molar strengths. In this Review, we assess electrochemical-desalination mechanisms and materials, including ion electrosorption and charge-transfer processes, namely, ion binding with redox-active polymers, ion insertion, conversion reactions and redox-active electrolytes. Furthermore, we discuss performance metrics and cell architectures, which we decouple from the nature of the electrode material and the underlying mechanism to show the versatility of cell-design concepts. These charge-transfer processes enable a wealth of environmental applications, ranging from potable-water generation and industrial-water remediation to lithium recovery and heavy-metal-ion removal. Electrochemical processes enable energy-efficient desalination of water and the separation and recovery of elements. In this Review, we discuss the mechanisms and materials of this emerging generation of water-remediation technology.

Electrochemical Behavior of Ti(III) Ions in Molten LiF–LiCl: Comparison with the Behavior in Molten KF–KCl

Ti(III) ions has been prepared by the addition of 0.50 mol% of Li2TiF6 and 0.33 mol% of Ti sponge to LiF–LiCl melt, and their electrochemical behavior has been investigated using cyclic voltammetry and square wave voltammetry at 923 K. The reduction of Ti(III) ions to metallic Ti is observed around 1.2 V vs Li+/Li, whereas the oxidation to Ti(IV) ions is observed at 2.78 V as a reversible electrochemical process. The diffusion coefficient of Ti(III) ions is determined to be 3.2 × 10−5 cm2 s−1. The electrochemical behavior of Ti(III) ions in LiF–LiCl melt is compared to that in KF–KCl melt. The potentials for Ti(IV)/Ti(III) and Ti(III)/Ti(0) couples based on the F2/F− potential in LiF–LiCl melt are more positive than those in KF–KCl melt by 0.41 V and 0.31 V, respectively. Such differences in potential are explained by the difference in interactions between Li+–F− and K+–F−.

Direct Water‐Writing/Electroerasing Pattern on PEDOT Inverse Opals

AbstractThis work presents a reversible direct water‐writing/electroerasing pattern on poly(3,4‐ethylene dioxythiophene) inverse opals (PEDOT‐IOs). The PEDOT‐IO‐0 is fabricated by potentiostatic polymerization of EDOT such that PEDOT infiltrates the interstices of a photonic crystal (PC) template, and the template is subsequently removed. The PEDOT‐IO‐I is obtained by reducing PEDOT‐IO‐0. There are four states and three different switches of PEDOT‐IOs: the first switch is the irreversible reduction of PEDOT‐IO‐0 to PEDOT‐IO‐I (neutral state). The second switch is the reversible electrochemical process between neutral and oxidized PEDOT‐IO‐I accompanied by a reversible stopband shift owing to ionic doping/dedoping. The third switch is the water treatment process of PEDOT‐IO‐I (oxidation state) to form PEDOT‐IO‐II, which induces a blueshift in the stopband owing to water‐induced removal of ions and shrinkage of the periodic structure. Combining the switches of PEDOT‐IO‐I and PEDOT‐IO‐II, a reversible water‐writing/electroerasing procedure is realized in the full‐solid state, producing multicolor patterns by water (a friendly ink) writing at different times. The as‐prepared PC pattern could be erased electrochemically. Reversible e‐paper can be successfully achieved based on the switches of PEDOT‐IOs, providing a novel method for the fabrication of functional optic materials.

Potassium nickel hexacyanoferrate as cathode for high voltage and ultralong life potassium-ion batteries

Potassium-ion batteries (KIBs) are considered as one of the most promising energy storage devices owing to the close redox potential to lithium, rich abundance and low cost potassium resource, promoting the exploration on cathode materials for K-ions storage. This paper reports a detailed experimental study on potassium nickel hexacyanoferrate, K1.81Ni[Fe(CN)6]0.97·0.086H2O (KNHCF), cathode for KIBs. KNHCF synthesized possesses few [Fe(CN)6]4- vacancies and coordinated water molecules, and high specific surface area along with developed microporous/mesoporous structures, which collectively induce highly reversible electrochemical intercalation process and fast kinetics. The resultant KNHCF cathode demonstrates reversible capacity of 57.0 mAh·g−1, high operating voltage of 3.74 V, outstanding voltage stability with no decay, good cycling stability (87.34%) after 1000 cycles and long-term lifetime over 8000 cycles with capacity fading rate of 0.0052% per cycle. A solid solution mechanism with zero-strain, where one-electron shuttle relied on C-coordinated FeⅡ/FeⅢ couple, plays an important role for K-ions intercalation/deintercalation. A 3.34 V full cell assembled with graphite anode delivers a high energy density of 142.6 Wh·kg−1 with the cpacity retention of 88.5% after 100 cycles, and ultra-long life-span over 5000 cycles can be achieved.

Improving the Electropolymerization Properties of Fluorene-Bridged Dicarbazole Monomers through Polyfluoroalkyl Side Chains.

The facile functionalization of the fluorene scaffold at the 2,7-positions was utilized to provide access to two soluble carbazole-π-carbazole derivatives CFC-H1 and CFC-F1 featuring fully hydrogenated and polyfluorinated alkyl chains at the 9-position of the fluorene π-bridging unit, respectively. The optical and electrochemical properties of the new dicarbazoles were investigated. Their electrochemical polymerization over Pt and indium tin oxide electrodes allowed the generation of electroactive polymeric films, whose physicochemical characteristics were strongly dependent on the kind of alkyl chain present on the fluorene bridge. In particular, the electropolymerization of the polyfluorinated monomer allowed the fabrication of thin films with good electrical conductivity, reversible electrochemical processes, good electrochromic properties, and enhanced water repellency with respect to its nonfluorinated analogue.

Sulfur Loaded by Nanometric Tin as a New Electrode for High‐Performance Lithium/Sulfur Batteries

Herein, a composite material formed by coating sulfur on nanometric tin is investigated as the cathode for high‐performance lithium/sulfur (Li/S) batteries. The study includes structural and morphological characterization performed by X‐ray diffraction and electron microscopy, as well as electrochemical investigation by means of voltammetry, electrochemical impedance spectroscopy, and galvanostatic cycling in lithium cell. The data show an electrode reflecting the crystalline structure of S8 and Sn, with a suitable morphology that consists of micrometric sulfur particles surrounding a metallic core of nanometric tin. This particular configuration leads to optimal behavior in the lithium cell, with a highly reversible electrochemical process evolving between 1.9 and 2.8 V versus Li+/Li and low polarization. The S‐Sn composite shows a favorable electrode/electrolyte interphase having a resistance limited to few ohms after the first activation charge/discharge cycle in the Li/S cell, which allows suitable operation with excellent rate capability and limited capacity fading. Indeed, the cell shows an efficiency approaching 100% upon the first cycle, a maximum specific capacity of about 1200 mAh g−1 at C/10 rate, and still a relevant capacity value of about 700 mAh g−1 at the relatively high C‐rate of 2 C, with suitable retention upon 100 charge/discharge cycles.

Bis(N,N′-substituted oxamate) Zincate(II) complexes: Synthesis, spectroscopy, solid state structure and DFT calculations

Treatment of two equivalents of N,N′-bis(X-phenyl)oxamides (1) with one equivalent of [Zn(OAc)2(H2O)2] (2) in the presence of four equivalents of [nBu4N]OH produce the corresponding bis(N,N′-substituted oxamate) zincate(II) complexes with the general formula (nBu4N)2[Zn(X-phenyloxamide)2] (3) (a, X = 3-NO2; b, X = 4-NO2; c, X = 2,6 CH3; d, X = 3,4-CH3; e, X = 2-Br; f, X = 4-Br; g, X = 2-F; h, X = 4-F; i, X = 2-Cl; j, X = H). Complexes 3a–j have been characterized by elemental analysis, NMR (1H, 13C{1H}) and IR spectroscopy. In addition, 3a and 3f have been characterized by single crystal X-ray crystallography. The zinc (II) ion in the later complexes is four-coordinate with two ethanediamide-nitrogen atoms from two bidentate N,N′-disubstituted oxamate ligands at each metal center. In addition, the calculated electrostatic potentials of 3f rationalize the formation of chain structures via the Br…Br interaction. Complexes 3a–j showed a characteristic LLCT (π → π*) band in the UV-Vis spectra, which was confirmed by TD-DFT calculations. DFT calculations show that the Zn(II) orbitals are neither contributing to the HOMO nor to the LUMO, i.e. the HOMO and LUMO are mainly located on the ligands. The emission spectra analyses for Zn(II) complexes 3a–j show enhanced intensity and blue shifted emission compared to ligands 1a−j. The cyclic voltammetry measurements of complexes 3a–j showed reversible electrochemical processes for the (N,N′-substituted oxamate−2/−3) between −1.52 and −1.77 V using [NnBu4][B(C6F5)4] as the supporting electrolyte. It was found that the 3-nitro- (3a) and 4-nitro-functionalized (3b) derivatives resulted in a significantly higher Fc/Fc+ redox potential (E0′) compared to the more electron-rich 3, 4-dimethyl (3c) and 2,6-dimethyl (3d) derivatives.

Aryl ferrocenylmethylesters: Synthesis, solid-state structure and electrochemical investigations

The reaction of [Fe(η5-C5H4CH2OH)2] (1) with 2 equiv of ClC(O)R (2) (a, R = C6H5; b, R = 2-CH3-C6H4; c, R = 3-CH3-C6H4, d, R = 4-CH3-C6H4) produced the corresponding ferrocenyl carboxylates [Fe(η5-C5H4CH2OC(O)R)2] (3a–d). Treatment of [FcCH2OLi] (4-Li) (Fc = Fe(η5-C5H5)(η5-C5H4)) with (ClC(O))2C6H4 (5) (a, 1,2-((ClC(O))2-C6H4; b, 1,3-((ClC(O))2-C6H4; c, 1,4-((ClC(O))2-C6H4) in a 2:1 M ratio gave (FcCH2OC(O))2-C6H4 (6a–c), while with 1,3,5-(ClC(O))3-C6H3 (7) in a 3:1 M ratio produced 1,3,5-(FcCH2OC(O))3-C6H3 (8). All compounds were characterized by NMR (1H, 13C{1H}) and IR spectroscopy, ESI-TOF mass spectrometry and elemental analysis. The molecular structures of 3a–d and 6b in the solid state were determined by single crystal X-ray structure analysis, showing anti-periplanar orientations of the 1,1′-positioned substituents at ferrocene (3a–d). In the cyclic voltammograms of 3a–d, 6a–d and 8 reversible electrochemical redox processes (Fc/Fc+) were observed, ranging between 146 and 164 mV for 3a–d, ca. 100 mV for 6a–d and at 113 mV for 8 using [NnBu4][B(C6F5)4] as the supporting electrolyte. The molecular electronic structure of 3, 6 and 8 was calculated by DFT methods in order to obtain the HOMO and LUMO absolute and relative energies in addition to electron density and distribution within the molecular arrangements. It was found that different degrees of HOMO-LUMO energy gaps within the series, due to a lowering in the LUMO energy depending on the positions of the carboxylic ester substituents on the aryl rings, are in agreement with the electrochemical results obtained.

What Are the Radical Intermediates in Oxidative N-Heterocyclic Carbene Organocatalysis?

The oxidation of the Breslow intermediate resulting from the addition of an N-heterocyclic carbene (NHC) to benzaldehyde triggers a fast deprotonation, followed by a second electron transfer, directly affording the corresponding acylium at E > -0.8 V (versus Fc/Fc+). Similarly, the oxidation of the cinnamaldehyde analogue occurs at an even higher potential and is not a reversible electrochemical process. As a whole, and contrary to previous beliefs, it is demonstrated that Breslow intermediates, which are the key intermediates in NHC-catalyzed transformations of aldehydes, cannot undergo a single electron transfer (SET) with mild oxidants ( E < -1.0 V). Moreover, the corresponding enol radical cations are ruled out as relevant intermediates. It is proposed that oxidative NHC-catalyzed radical transformations of enals proceed either through SET from the corresponding electron-rich enolate or through coupled electron-proton transfer from the enol, in any case generating neutral capto-dative radicals. Relevant electrochemical surrogates of these paramagnetic species have been isolated.

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.

Electrochemical Impedance Spectroscopy as a Tool for Electrochemical Rate Constant Estimation.

Electrochemical impedance spectroscopy (EIS) was used for advanced characterization of organic electroactive compounds along with cyclic voltammetry (CV). In the case of fast reversible electrochemical processes, current is predominantly affected by the rate of diffusion, which is the slowest and limiting stage. EIS is a powerful technique that allows separate analysis of stages of charge transfer that have different AC frequency response. The capability of the method was used to extract the value of charge transfer resistance, which characterizes the rate of charge exchange on the electrode-solution interface. The application of this technique is broad, from biochemistry up to organic electronics. In this work, we are presenting the method of analysis of organic compounds for optoelectronic applications.