Scan Rate Cyclic Voltammetry Research Articles

Role of Solvent Coordination in the Multi-electron Redox Cycle of Nickel Diethyldithiocarbamate.

Nickel(II) diethyldithiocarbamate, NiII(dtc)2, is known to undergo a 2e- ligand-coupled electron transfer (LCET) oxidation to form [NiIV(dtc)3]+. However, the thermodynamics and kinetics of this 2e- process can be greatly affected by solvent coordination. For low coordinating solvents like acetonitrile and acetone, 2e- oxidation is observed via cyclic voltammetry (CV) at a single potential while stronger coordinating solvents like methanol, N,N-dimethylformamide, dimethyl sulfoxide, and pyridine exhibit a 1e- oxidation wave by formation of [NiIII(dtc)2(sol)x]+ intermediates. The decay of these complexes to eventually yield [NiIV(dtc)3]+ was monitored as a function of CV scan rate and temperature to extract rate constants and activation parameters. A thorough analysis of activation parameters revealed that ΔHapp⧧ generally increased with solvent coordination ability, suggesting solvent dissociation was a key factor in the rate limiting step. However, ΔSapp⧧ was found to be negative for all solvents, suggesting an associative mechanism in line with dimer formation with NiII(dtc)2 to facilitate ligand exchange. Density function theory calculations supported the competitive nature of dissociative and associative steps. Using these calculations, we propose two paths for decay of [NiIII(dtc)2(sol)x]+ species based on the coordination strength of the solvent. These studies point to the ability of solvents to either aid or hinder multielectron LCET reactions.

Monitoring the Behavior of Na Ions and Solid Electrolyte Interphase Formation at an Aluminum/Ionic Liquid Electrode/Electrolyte Interface via Operando Electrochemical X-ray Photoelectron Spectroscopy.

In electrochemical energy storage devices, the interface between the electrode and the electrolyte plays a crucial role. A solid electrolyte interphase (SEI) is formed on the electrode surface due to spontaneous decomposition of the electrolyte, which in turn controls the dynamics of ion migration during charge and discharge cycles. However, the dynamic nature of the SEI means that its chemical structure evolves over time and as a function of the applied bias; thus, a true operando study is extremely valuable. X-ray photoelectron spectroscopy (XPS) is a widely used technique to understand the surface electronic and chemical properties, but the use of ultrahigh vacuum in standard instruments is a major hurdle for their utilization in measuring wet electrochemical processes. Herein, we introduce a 3-electrode electrochemical cell to probe the behavior of Na ions and the formation of SEI at the interface of an ionic liquid (IL) electrolyte and an aluminum electrode under operando conditions. A system containing 0.5 molar NaTFSI dissolved in the IL [BMIM][TFSI] was investigated using an Al working electrode and Pt counter and reference electrodes. By optimizing the scan rate of both XPS and cyclic voltammetry (CV) techniques, we captured the formation and evolution of SEI chemistry using real-time spectra acquisition techniques. A CV scan rate of 2 mVs-1 was coupled with XPS snapshot spectra collected at 10 s per core level. The technique demonstrated here provides a platform for the chemical analysis of materials beyond batteries.

Boosting Li-ion storage kinetics via constructing layered TiO2 anode

Due to the typical intercalation-deintercalation mechanism, TiO2 holds great promise as a sustainable anode for next-generation lithium-ion batteries (LIBs). However, commercial TiO2 (C–TiO2) is granular and shows slow ionic conductivity, which greatly hinders its development due to sluggish kinetics, leading to low reversible capacity and inferior rate capability. In this study, a two-dimensional layered TiO2 (L-TiO2) anode is prepared via a one-step calcination process, which can effectively shorten the lithium ions diffusion path and improve its lithium ions conductivity. We elucidated the enhanced electrochemical performance of L-TiO2 as an anode in LIBs through pseudocapacitive acceleration of lithium ions intercalation and deintercalation using various characterization techniques, including different scan rate cyclic voltammetry tests, in situ electrochemical impedance spectroscopy, in situ Raman spectroscopy, and in situ X-ray diffraction. In comparison to C–TiO2 material, L-TiO2 material showcases remarkable electrochemical performance, achieving a capacity of 166 mAh/g after 100 cycles at 0.1 C. Additionally, the lithium-ion diffusion coefficient calculated for the L-TiO2 is two orders of magnitude greater, underscoring its potential as a negative electrode material for LIBs.

Electrochemical analysis of butylated hydroxytoluene

Electrochemical analysis has carried out butylated hydroxytoluene (BHT) measurements. Cyclic voltammetry is used in this research as a qualitative-quantitative analysis of oxidation and reduction reaction processes, adsorption processes on electrode surfaces, and chemical electron transfer mechanisms. This research aims to determine the optimum deposition time and scan rate in cyclic voltammetry, the BHT standard equation, the limit of detection, and the recovery percentage. In this research, a deposition time of 25 seconds produces the highest current response of 3.89672 x 10-4 Ampere. The scan rate is 150 mV/second, producing the highest and optimum current response of 4.24561 x 10-4 Ampere. BHT standard equation y = (4.92784 x 10-6) x + (1.25207 x 10-4) is obtained with R2 = 0.99933. The limit of detection value is 2.69683 ppm, and the recovery percentage is 101.314%. Therefore, this cyclic voltammetry method is suitable for analyzing BHT because it has high sensitivity.

Electrochemical deposition of Ag nanoparticles on ITO-coated glass: effect of different cyclic voltammetry scan rates on Ag deposition

This work aims to investigate the effect of different cyclic voltammetry scan rates on silver nanoparticles deposition on ITO-coated glass aiming to obtain improve its optical and electrical properties. The deposition was evaluated using different physical, chemical and optical characterization techniques, such as SEM, XRD, FTIR, UV–visible and electrochemical tests. Cyclic voltammetry was used to measure the Ag deposition at two different scan rates (20 CV at 10 mV/s and 100 CV at 30 mV/s). The characterization results have confirmed the formation of a homogeneous crystal layer of silver on ITO, which exhibited high transmittance in the visible light region. According to the cyclic voltammetry measurements, the outer spheres of the Ag NPs associated with the redox reaction illustrate the typical reduction and oxidation waves of Ag in the range of (−100 to +700) mV. The quantification using Cyclic voltammetry measurements has shown that the Ag nanoparticles deposition on ITO thin films are inversely proportional to the scan rates; in other words, higher deposition is obtained at lower scan rates.

A highly explicit electrochemical biosensor for catechol detection in real samples based on copper-polypyrrole.

Catechol is a pollutant that can lead to serious health issues. Identification in aquatic environments is difficult. A highly specific, selective, and sensitive electrochemical biosensor based on a copper-polypyrrole composite and a glassy carbon electrode has been created for catechol detection. The novelty of this newly developed biosensor was tested using electrochemical techniques. The charge and mass transfer functions and partially reversible oxidation kinetics of catechol on the redesigned electrode surface were examined using electrochemical impedance spectroscopy and cyclic voltammetry scan rates. Using cyclic voltammetry, chronoamperometry, and differential pulse voltammetry, the characteristics of sensitivity (8.5699 μA cm-2), LOD (1.52 × 10-7 μM), LOQ (3.52 × 10-5 μM), linear range (0.02-2500 μM), specificity, interference, and real sample detection were investigated. The morphological, structural, and bonding characteristics were investigated using XRD, Raman, FTIR, and SEM. Using an oxidation-reduction technique, a suitable biosensor material was produced. In the presence of interfering compounds, it was shown that it was selective for catechol, like an enzyme.

Electrochemical response of surface-attached redox DNA governed by low activation energy electron transfer kinetics.

The mechanism responsible for electron transport within layers of redox DNA anchored to electrodes has been extensively studied over the last twenty years, but remains controversial. Herein, we thoroughly study the electrochemical behavior of a series of short, model, ferrocene (Fc) end-labeled dT oligonucleotides, terminally attached to gold electrodes, using high scan rate cyclic voltammetry complemented by molecular dynamics simulations. We evidence that the electrochemical response of both single-stranded and duplexed oligonucleotides is controlled by the electron transfer kinetics at the electrode, obeying Marcus theory, but with reorganization energies considerably lowered by the attachment of the ferrocene to the electrode via the DNA chain. This so far unreported effect, that we attribute to a slower relaxation of water around Fc, uniquely shapes the electrochemical response of Fc-DNA strands and, being markedly dissimilar for single-stranded and duplexed DNA, contributes to the signaling mechanism of E-DNA sensors.

CHARACTERIZATION OF REDUCED GRAPHENE OXIDE/ACTIVATED CARBON-BASED ELECTRODE CONTAINING MIXING CMC-SBR BINDER AND APPLICATION IN SUPERCAPACITOR

In this work, variation of mixing a combination of carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) as both used as the binder in the electrode has been studied. The purpose of using CMC-SBR as the binder in the electrode is to achieve a high supercapacitor performance. The electrode preparation has been carried out by mixing the reduced graphene oxide (rGO) and activated carbon (AC) in a blender. The binder preparation started by dissolving the CMC and SBR in the deionized water using a clean glass container. Then, rGO/AC has been stirred with the CMC-SBR for 60 minutes until a homogenous slurry formed. All electrodes have been characterized with Raman spectroscopy. The electrochemical tests such as cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) for all electrode compositions were performed. The electrode with 4:6 (in weight percentage) of CMC-SBR shows the highest specific capacitance (Csp) of 59.65 F g-1 (CV scan rate of 1 mV s-1) and 12.82 F g-1 from GCD test. This confirmed that the electrode containing 4 wt.% of CMC and 6 wt.% of SBR resulting in the best composition, which is reliable and practical for the supercapacitor application.

Understanding How Organosilicon Additives Delay Electrolyte Decomposition on LiNi0.8Mn0.1Co0.1O2 (NMC 811) Cathodes Using in Situ Techniques

Cathode materials such as LiNi0.8Mn0.1Co0.1O2 (NMC811) are of great interest for Li-ion battery (LIB) systems. By increasing the Ni content, the price decreases since Co is an expensive transition metal. In addition, NMC811 offers higher capacity and operating at high voltages, compared to other cathode materials (i.e., LCO, LMO, etc.). However, this cathode material suffers degradation from different sources. One of the main detrimental processes is oxygen loss from the lattice, which can cause decomposition of electrolyte components such as cyclic carbonates and further generate undesirable gassing in LIB systems. Several different organosilicon (OS) compounds have been reported to decrease gassing during storage with NMC622/Gr multi-layer pouch cells. Besides reducing gassing, OS compounds have been reported to increase the thermal stability of PF6 - and reduce HF, which is detrimental for LIB systems. Currently, the exact mechanism for how OS additives alleviate these undesired electrolyte degradation reactions is not well known. In this study we performed a mechanistic investigation on the effects of OS3 (organosilicon additive) during Li the intercalation/deintercalation processes on NMC811. First, we explored how OS3 affects the electron transfer kinetics by performing variable scan rate cyclic voltammetry. Second, we studied the mass accumulated on NMC811 surfaces during the first cycle as a function of applied potential using in situ electrochemical quartz crystal microbalance (EQCM). Finally, we analyzed the chemical composition of the cathode surface layer and how it evolves as a function of potential using in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) at stepwise points during the first cycle. Together, these techniques provide a comprehensive study of the reactions occurring at the NMC811 electrode surface during the first cycle, including lithium intercalation kinetics, mass deposition and dissolution, and the chemical composition of surface decomposition species as a function of potential, it was found that OS3 delays the onset of mass accumulation and therefore delays electrolyte degradation during the first cycle on NMC811 cathode materials as confirmed by the presence of new absorbance features on in situ ATR-FTIR. We successfully identified a potential mechanism of action of how organosilicon additives help to prevent the carbonate-based electrolyte to decompose on NMC811 surfaces. These studies further provide new insights into the mechanisms of performance enhancement observed with OS additives.

Durability Assessment of Transition Metal Oxygen Electroreduction Catalysts with on-Line Flow Cell Trace Elemental Analysis

Proton exchange membrane hydrogen fuel cell (PEMFC) cathodes for commercial applications are typically based on platinum group materials that exhibit remarkable oxygen reduction reaction (ORR) activity and stability. Despite this performance, the high cost of such platinum electrodes prevents a more rapid transition to a more sustainable hydrogen economy involving PEMFCs. Platinum-free transition metal ORR catalysts have been identified and tested as high activity, low-cost alternatives with well-established protocols, though understanding the durability of these materials would require more experimental efforts. Techniques for measuring catalyst degradation typically involve activity loss measurements, surface-sensitive microscopy and spectroscopy, and liquid aliquot collection for metal loss quantification that are all performed post-catalysis for extended periods of time. Experiments using this approach provide valuable information about overall catalyst material degradation but usually cannot elucidate mechanistic or potential-dependent phenomena that may occur on shorter time scales. More rigorous experiments with synchrotron radiation have been utilized to investigate the degradation mechanisms of platinum-based fuel cell catalysts but studies on other transition metal materials are less widespread due to the high time requirements and limited accessibility of synchrotron beamlines for such experiments. In our work, we utilize an on-line electrochemical flow cell coupled with an in-house inductively coupled plasma-mass spectrometer (ICP-MS) for evaluation of fuel cell catalyst degradation in acidic electrolyte environments. Oxygen and nitrogen gas saturated electrolytes with a constant pH of 1 but differing chemical identity are flowed through the cell and across a working electrode composed of non-platinum transition metals. Dissolved metal ions are convectively transported to the ICP-MS where they are measured with up to part per trillion resolution with a time delay of ~4 seconds, enabling millisecond resolution of transient catalyst surface degradation. We evaluate the oxygen mass transport capabilities of our custom-machined flow cell against a commercial flow cell and compare to the much more established rotating disk electrode (RDE) technique for distinguishing ORR activity. Cyclic voltammetry measurements in oxygen-saturated electrolyte on various metal foils indicate potential dependent corrosion in agreement with what is expected from a Pourbaix (potential-pH) diagram of stability. In contrast, potential cycling these materials in the ORR-relevant range reveals degradation during ORR electrocatalysis that increases with ORR current to differing amounts as a function of the metal in a way that has not been previously characterized. Notably, degradation appears to be suppressed in the ORR potential range when saturating the electrolyte with nitrogen compared to oxygen, suggesting that surface-bound oxygen and ORR intermediates have a potential-dependent role in enabling degradation. Probing degradation during ORR conditions further with varied cyclic voltammetry scan rates and directions reveals more fundamental information about the timescales of catalytic corrosion processes and may inform the development of activation protocols that enhance the lifetime of ORR catalyst materials during operation. Through electrochemical flow cell testing in various pH 1 electrolytes, we make suggestions for electrolyte compositions and catalyst operation potential ranges that maintain activity and stability to advise fuel cell catalyst researchers in developing platinum-free PEMFC cathode materials. We are also developing additional flow cell configurations to allow testing of other non-precious ORR catalyst morphologies such as nanoparticle catalysts on carbon supports. The on-line ICP-MS flow cell architecture accelerates materials stability and degradation experiments for rapid assessment of platinum-free ORR electrocatalysts through in-house experiments and direct comparability to established electrochemical techniques.

Redox-Active Organic Molecules and Modified Graphene-Based Materials As Active Material Composites for Supercapacitor Applications

Green and sustainable energy demand has directed the modern world toward producing clean energy storage devices to cut down fossil fuel consumption. Supercapacitors are energy storage devices that have attracted much attention due to owning outstanding properties. Supercapacitors use two main mechanisms to storge charge: I) electrical double layer II) pseudocapacitance. Graphene-based materials have shown promising performance in supercapacitors due to their high surface area and proper electrical conductivity. One of the challenges of working with graphene is the restacking of the graphene sheets, leading to poor performance and lower capacitance. Studies have used doping graphene with different heteroatoms as one of the techniques to overcome the restacking and enhancement of its electrochemical performance. Moreover, redox-active organic molecules, including anthraquinones, phenols, and phenathrequinones, also can be employed to modify graphene.In this work we develop composite active material structures consisting of modified graphene-based materials and organic molecules containing redox active functional groups to provide pseudo-capacitance capabilities. By combining these materials, specific capacitance values above 600 F/g were obtained (at cyclic voltammetry scan rates of 50 mV/s) along with good capacitance retention following repeated electrochemical cycling. In this presentation we will discuss the influence of synthesis route and processing parameters and the resulting structures and performance of the active supercapacitor materials. By correlating these results, we provide insight into the energy storage mechanisms and durability considerations pertaining to these hybrid materials.

Electropolymerization of thiazole derivatives bearing thiophene and selenophene and the potential application in capacitors

• Three thiazole derivatives bearing thiophene and selenophene were used as monomers for electropolymerization. • Pseudocapacitor performance of deposited polymer layers was investigated on macroelectrode and ultramicroelectrode. • Pseudocapacitor behavior is related to the anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. • The approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion were analyzed. Three thiazole derivatives bearing thiophene and selenophene are synthesized and used as monomers for electropolymerization. The electropolymerization process is studied using cyclic voltammetry (CV) and electrochemical quartz crystal microbalance (EQCM) techniques. Deep understanding is obtained regarding the pseudocapacitor performance of deposited polymer layers by subjecting the macroelectrode and ultramicroelectrode to CV and galvanostatic charging–discharging experiments in three kinds of electrolytes. Notably, the highest specific capacitance is observed in the derivative bearing selenopheno[3,4- d ]thiazole and selenophene in a solution of tetrabutylammonium tetrafluoroborate. Furthermore, the electropolymerization rate is influenced by the kind of chalcogenophene and the CV scan rate. A spectroelectrochemistry experiment reveals the optical and electrochromic behavior of the deposited polymer layers. From these results, the pseudocapacitor performance of the deposited polymer layers is related to anion intercalation/deintercalation processes by faradaic reactions of oligomer chains. The EQCM experiments also reveal these processes during electropolymerization and anion intercalation/deintercalation into the deposited polymer layers. Finally, the approximate molecular weight of the solvated anion and the number of solvent molecules surrounding a solvated anion are analyzed using the EQCM data.

Mechanistic insights into homogeneous electrocatalytic reaction for energy storage using finite element simulation

• Electrocatalytic reactions for energy storage is studied by finite element modelling. • Reaction rate constant of HMF and L-cysteine is determined by SWV. • Increase of potential frequency and increment weakens the split current peaks in SWV. • Potential amplitude increase results in conspicuous current protuberance in SWV. The application of homogeneous electrocatalytic reactions in energy storage and conversion has driven surging interests of researchers in exploring the reaction mechanisms of molecular catalysts. In this paper, homogeneous electrocatalytic reaction between hydroxymethylferrocene (HMF) and L-cysteine is intensively investigated by cyclic voltammetry and square wave voltammetry for which, the second-order rate constant ( k ec ) of the chemical reaction between HMF + and L-cysteine is determined via a 1D homogeneous electrocatalytic reaction model based on finite element simulation. The corresponding k ec (1.1 (mol·m −3 ) −1 ·s −1 ) is further verified by linear sweep voltammograms under the same model. Square wave voltammetry parameters including potential frequency ( f ), increment ( E step ) and amplitude ( E SW ) have been comprehensively investigated in terms of the voltammetric waveform transition of homogeneous electrocatalytic reaction. Specifically, the effect of potential frequency and increment is in accordance with the potential scan rate in cyclic voltammetry and the increase of pulsed potential amplitude results in a conspicuous split oxidative peaks phenomenon. Moreover, the proposed methodology of k ec prediction is examined by hydroxyethylferrocene (HEF) and L-cysteine. The present work facilitates the understanding of homogeneous electrocatalytic reaction for energy storage purpose, especially in terms of electrochemical kinetics extraction and flow battery design.

MgMoO4 as an anode material for lithium ion batteries and its multi-electron reaction mechanism.

Single-phase magnesium molybdate, MgMoO4, is successfully synthesized by a facile sol-gel method. Attributed to the multielectron reaction and the synergistic effect of the elements molybdenum (Mo) and magnesium (Mg), the MgMoO4 electrode exhibits excellent electrochemical properties. After activation, benefiting from the decrease in particle size and the uniform nanosphere morphology, the MgMoO4 electrodes can deliver a stable high specific capacity of about 1060 mA h g-1 at a current density of 100 mA g-1 after 600 cycles. Based on the important role of the activation process, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and scan rate cyclic voltammetry (CV) measurement methods were employed to reveal the effect of the activation process on the electrochemical behavior of the electrode material. Furthermore, by combining the in situ X-ray diffraction (XRD) and ex situ X-ray photoelectron spectroscopy (XPS) results, we illustrate the lithium storage mechanism of the MgMoO4 electrode in detail.

Alginate NiFe2O4 Nanoparticles Cryogel for Electrochemical Glucose Biosensor Development.

Glucose biosensors based on porous material of alginate cryogel has been developed, and the cryogel provides a large surface area for enzyme immobilization. The alginate cryogel has been supplemented with NiFe2O4 nanoparticles to improve the electron transfer for electrochemical detection. The fabrication parameters and operational conditions for the biosensor have also been optimized. The results showed that the optimum addition of NiFe2O4 nanoparticles to the alginate solution was 0.03 g/mL. The optimum operational conditions for the electrochemical detection were a cyclic voltammetry scan rate of 0.11 V/s, buffer pH of 7.0, and buffer concentration of 150 mM. The fabricated alginate NiFe2O4 nanoparticles cryogel-based glucose biosensor showed a linear response for glucose determination with a regression line of y = 18.18x + 455.28 and R² = 0.98. Furthermore, the calculated detection limit was 0.32 mM and the limit of quantification was 1.06 mM.

(Invited) Spectroelectrochemical Sensors: The Quest for Selectivity

Introduction Exceptional selectivity is needed for sensors to accurately measure analytes in complex samples such as nuclear waste and natural water that contain many potentially interfering substances. Spectroelectrochemistry offers a unique means for providing selectivity by electrochemically modulating the optical signal used for quantitation. The modulated signal can be distinguished from the constant signals of potential interferences. An additional level of selectivity can be provided by adding a very thin film to the transparent electrode to first preconcentrated the analyte while rejecting interferences. Sensors using both visible absorption and fluorescence modes of detection have been developed for detection of organic and inorganic species including ferrocyanide [1] and technetium [2] complexes in nuclear waste and natural water. We have recently extended this research to the spectroelectrochemical investigation of molten salt systems, [3] including lanthanide and actinide measurements related to pyroprocessing [4] and molten salt reactor applications. Thin layer fluorescence-based spectroelectrochemical sensor A planar optically transparent electrode chip was fabricated and characterized for multimode sensing of target species. The chip was comprised of an indium tin oxide (ITO) working electrode, a platinum auxiliary electrode, and a Ag/AgCl reference electrode. Fluorescence was used for detection because limits of detection are typically several magnitudes lower than for absorption spectroscopy and selectivity improved by having adjustable wavelengths for both excitation and emission. A fluorescence spectroelectrochemical measurement using this chip incorporated into an optically transparent thin layer electrochemical (OTTLE) cell was demonstrated using the modulated emission of [Ru(bpy)3]2+. Molten salt absorbance-based spectroelectrochemistry Molten salt systems are of growing interest for a variety of applications, including meeting future energy needs such as molten salt reactors (MSRs). These reactors are of interest for several factors, including the ability to be operated at atmospheric pressures even at extremely high temperatures. The molten salts serve several functions, including heat transfer fluid, reactor coolant, and ability to contain high concentrations of dissolved fuel (plutonium, uranium, thorium). While the benefits of molten salt reactors have been identified, the chemistry of the molten salts is still not understood. Spectroelectrochemistry can provide the tools to characterize, monitor, and control the chemical behavior of fuel species (U, Pu), fission, and corrosion products throughout the molten salt reactor loop. Several of these species are electroactive and have a unique spectroscopic fingerprint that can be optically detected and modulated using electrochemistry. Spectroelectrochemical characterization can provide fundamental information such as concentration, oxidation state, and speciation at any point in the molten salt reactor system. The absorbance-based spectroelectrochemical modulation of uranium was demonstrated in the molten LiCl-KCl eutectic. The unique spectroscopic signatures for U(III) and U(IV) were identified and monitored as it was electrochemically modulated between the U(III)/U(IV) redox states. Based on variable scan-rate cyclic voltammetry, the diffusion coefficients of U(III) and U(IV) were measured.

Enhanced performance of ultra-thin polyaniline supercapacitor via aniline blue-WS SAMs with rich nucleation site

We report the ultrathin supercapacitor’s superior performance via the vertically aligned one-dimensional polyaniline structure (1D PANI) growth on the fluorine-doped tin oxide (FTO) substrate. FTO electrodes were treated by the molecular-self assembly, and the effects of different self assembled monolayers (SAMs) on both the evolution of PANI and electrochemical performance were examined. We obtained 809.09 F g−1 specific capacitance from ∼120 nm thick PANI (at 20 mV s−1 scan rate of cyclic voltammetry) via aniline blue water soluble SAMs modification. The supercapacitor’s internal dynamics were clarified by a new equivalent circuit model developed from the Graham model. Through the new model, accurate information about double-layer capacitance, percolation capacitance, and bulk capacitance, which composes the electrode’s capacitive performance, could be obtained. This work provided novel knowledge to develop PANI deposition and hence to achieve greater capacitances.

Properties of electrochemically copolymerized aniline and melamine on functionalized multiwalled‐carbon nanotube film electrodes

AbstractThe electrochemical properties of polymerized aniline (PANI) and polymerized melamine (PMEL) that were electrochemical copolymerized (PANIMEL) on a glassy carbon electrode (GCE) that had been coated with functionalized multiwalled carbon nanotubes (fMWCNT) to form a PANIMEL/fMWCNT/GCE film electrode were studied, with an aim toward electrochemical energy storage (EES). A number of factors, such as the choice of working electrode, electrolyte, switching potential, applied scan rate, and type of fMWCNTs, were initially investigated and evaluated during the individual electrochemical polymerization of aniline and melamine via successive potential cycling. The electrochemical copolymerisation of aniline and melamine was then studied with an ideal monomeric ratio of 1:3 that gave an optimal ratio of the voltammetric peak current heights with distinguishable redox peak potentials. Variable scan rate cyclic voltammetry (CV) of the electrosynthesized copolymer film electrode confirmed the dominance of the surface‐confined electron transfer process at the electrode. The electrochemical stability of the copolymer film electrode was also assessed and revealed a limited cyclability of the daughter polymeric melamine, which was hypothesized to be due to an excessive nitrogen content combined with a low porosity that led to a poor ion intercalation‐deintercalation mechanism. Electrochemical impedance spectroscopy (EIS) was performed to evaluate the electrochemical performance of the copolymerized film electrode with other control electrodes. The corresponding EIS results suggested that the copolymerized film electrode was electrochemically superior to the PMEL/fMWCNT/GCE film electrode but was inferior to the PANI/fMWCNT/GCE film electrode.

Equivalent Impedance Models for Electrochemical Nanosensor-Based Integrated System Design.

Models of electrochemical sensors play a critical role for electronic engineers in designing electrochemical nanosensor-based integrated systems and are also widely used in analyzing chemical reactions to model the current, electrical potential, and impedance occurring at the surface of an electrode. However, the use of jargon and the different perspectives of scientists and electronic engineers often result in different viewpoints on principles of electrochemical models, which can impede the effective development of sensor technology. This paper is aimed to fill the knowledge gap between electronic engineers and scientists by providing a review and an analysis of electrochemical models. First, a brief review of the electrochemical sensor mechanism from a scientist’s perspective is presented. Then a general model, which reflects a more realistic situation of nanosensors is proposed from an electronic engineer point of view and a comparison between the Randles Model is given with its application in electrochemical impedance spectroscopy and general sensor design. Finally, with the help of the proposed equivalent model, a cohesive explanation of the scan rate of cyclic voltammetry is discussed. The information of this paper can contribute to enriching the knowledge of electrochemical sensor models for scientists and is also able to guide the electronic engineer on designing next-generation sensor layouts.

Preparation and electrochemical performance of sodium manganese oxides as cathode materials for aqueous Mg-ion batteries

In recent years, the cathode materials of magnesium ion batteries have become a hot point of research, and the improvement of high-rate performance and cycle stability has become the main research goal. In this paper, sodium manganese oxide (Na<sub>0.55</sub>Mn<sub>2</sub>O<sub>4</sub>·1.5H<sub>2</sub>O) nanomaterial with a blended structure of nanowires and nanosheets is prepared by the hydrothermal method. The structure and morphology of the material are analyzed by X-ray diffraction and scanning electron microscopy. The variable rate charge-discharge curves and variable scan rate cyclic voltammetry curves are obtained by a battery tester and electrochemical workstation, respectively. The results show that the hydrothermal reaction time has significant effects on phase structure and morphology composition of the material. The nanosheets and nanowires in the sample form a closely blend by 72-h hydrothermal reaction (NMO-72), and the nanosheets effectively fill into the intersecting space of the nanowires. In this way, the tap density of the material is improved. More importantly, NMO-72 has higher discharge specific capacity and rate cycling performance. At a current density of 50 mA·g<sup>–1</sup>, the discharge specific capacity of NMO-72 reaches 229.1 mAh·g<sup>–1</sup>. At a current density of 1000 mA·g<sup>–1</sup>, the discharge specific capacity of the NMO-72 stabilizes at 81 mAh·g<sup>–1</sup>. When the current density returns to 50 mA·g<sup>–1</sup> again, the discharge specific capacity remains stable at 164.7 mAh·g<sup>–1</sup>. Besides, the cyclic voltammetry test shows that the NMO-72 material has more excellent magnesium ion diffusion kinetic performance than other materials. Therefore, the NMO-72 material has more excellent reversible specific capacity, high rate performance and cycling stability.