Reversible Cyclic Voltammetry Research Articles

SYNTHESIZING AND INVESTIGATING THE ELECTRICAL PROPERTIES OF CARBONIZED METAL–ORGANIC FRAMEWORKS

The iron-based metal–organic frame (Fe-MOF), VNU-20, and its carbonized analogues were synthesized. Subsequently, this material was investigated for electrical properties in comparison with the carbonized samples from other MOFs and ZIFs (such as ZIF-8, ZIF-67, MOF-199, MIL-53). The experiments showed the results with the reversible cyclic voltammetry (CV) curve characterized by the redox oxidation reactions of Fe(II)/Fe(III). Furthermore, the electrode composed of carbonized VNU-20 shows a comparable capacitance with that of carbonized ZIF-67, the highest capacitance material recorded up to date for the same class of materials. While further experiments need to be carried out for the optimization, initial analyzes show the promising result for further investigation and use of carbonized VNU-20 as the electrode material for electro-catalysis and the supercapacitor.

The role of an intramolecular hydrogen bond in the redox properties of carboxylic acid naphthoquinones.

A bioinspired naphthoquinone model of the quinones in photosynthetic reaction centers but bearing an intramolecular hydrogen-bonded carboxylic acid has been synthesized and characterized electrochemically, spectroscopically, and computationally to provide mechanistic insight into the role of proton-coupled electron transfer (PCET) of quinone reduction in photosynthesis. The reduction potential of this construct is 370 mV more positive than the unsubstituted naphthoquinone. In addition to the reversible cyclic voltammetry, infrared spectroelectrochemistry confirms that the naphthoquinone/naphthoquinone radical anion couple is fully reversible. Calculated redox potentials agree with the experimental trends arising from the intramolecular hydrogen bond. Molecular electrostatic potentials illustrate the reversible proton transfer driving forces, and analysis of the computed vibrational spectra supports the possibility of a combination of electron transfer and PCET processes. The significance of PCET, reversibility, and redox potential management relevant to the design of artificial photosynthetic assemblies involving PCET processes is discussed.

Reversible Cyclic Voltammetry and Non-Unity Stoichiometry: The Ag/AgBr/Br- Redox Couple.

The voltammetry of electrochemically reversible couples in which a soluble reactant is converted into an insoluble product is investigated computationally via simulation and, in the context of the Ag/AgBr/Br-redox couple, experimentally. The voltammetric waveshape is characterized and, when analyzed via apparent transfer coefficient analysis, shown to give rise to apparent transfer coefficients very considerably in excess of unity, leading to the generic insight for the characterization of electrode reactions involving solution and solid phase reactants.

Preparation, characterization of mixed-valence antimony-tin phosphomolybdic polyoxometalates and application in the cyclohexanone oxidation in the presence of hydrogen peroxide

In this work, a series of polyoxometalates (POMs), as soluble salts of formula Sn1.5PMo12O40, SbPMo12O40 and H 3-x Sn x1 Sb x2 PMo 12 O 40 (x=2x 1 +3x 2 and x 1 , x 2 = 0–0.75) were synthesized using the cationic exchange method under stoichiometric conditions. They were characterized and tested in the oxidation of cyclohexanone using hydrogen peroxide in the absence of organic solvent, co-catalyst phase transfer compounds or surfactants. UV–Visible and X-ray photoelectron spectroscopic analyses showed a partially reduced state of POM with coexistence of the couples Mo(VI)/Mo(V), Sb(V)/Sb(III) and Sn(IV)/Sn(II), without affecting their structure, results confirmed by FT-IR and Raman spectroscopies. The reversible cyclic voltammetry analysis evidenced the valence change of the Mo species, Mo(VI)/Mo(V). The POMs are found to be active in the cyclohexanone oxidation reaction and among them the most efficient is H 0.75 Sb 0.75 PMo 12 O 40 with 49% of adipic acid yield.

Impact of the 2Fe2P core geometry on the reduction chemistry of phosphido-bridged diiron hexacarbonyl compounds

The effect of core geometry constraints of hydrogenase H-cluster analogues on reduction chemistry have been explored by a combination of structural, electrochemical and IR spectroelectrochemical (IR-SEC) studies. A series of phosphido-bridged diiron hexacarbonyl complexes, Fe2(µ2-PPh2(CH2)xPPh2)(CO)6, x = 2 (2P) and 4 (4P) and previously reported with x = 3 (3P) and the unlinked bis-diphenylphosphido (DP) analogues were investigated. The X-ray structures of the neutral complexes demonstrate the effect of the linking group on the Fe2P2 core geometry with P–Fe–Fe–P torsion angles of 95 (2P), 101 (3P), 108 (4P) and 109° (DP) and a twisting of the Fe(CO)3 fragments from an eclipsed geometry (2P, 3P and DP) for 4P. For all four compounds the primary reduction process involves two close-spaced one-electron reactions (E1 and E2) with a systematic trend to more negative reduction potentials with a shorter link between the bridging phosphorus atoms. This reflects the greater constraint that the bridging group places on the adoption of a planar 2Fe2P geometry. The sensitivity of the core geometry is greater for E2 than E1 and this impacts the stability of the monoanion with respect to disproportion (Kdisp(298 K) = 0.02 (2P), 2.4 (3P) and 3540 (4P and DP)). 4P has a stable dianion and gives reversible cyclic voltammetry at 298 K and is quasi-reversible at 253 K, whereas the response of 2P is irreversible at 298 K, with two distinct daughter products, but becomes quasi-reversible at 253 K. IR-SEC measurements enabled elucidation of the spectra and time evolution of the reduction products. These results are consistent with a bimolecular reaction giving a distinct reduced product modelled as a dimeric, 4Fe species. The sensitivity of the reduction chemistry of the bridged diiron compounds underpins their utility as catalytic proton reduction catalysts and the systematic trends delineated in this investigation provide the framework for charting the path of their redox-coupled chemical reactions.

Facile synthesis of hierarchical porous Na3V2(PO4)3/C composites with high-performance Na storage properties

Porous Na3V2(PO4)3/C composites were prepared in situ via a simple solution method using various amounts of cetyltrimethylammonium bromide and glycine mixtures. Platelet particles with a thickness of ~150 nm were formed when 0.4 mmol cetyltrimethylammonium bromide and 0.4 mmol glycine were used, resulting in a high specific surface area (16 m2 g−1) and porosity (0.05 cm3 g−1) of the composites. In addition, the porous Na3V2(PO4)3/C composites presented good reversible cyclic voltammetry peaks with low hysteresis and delivered a high specific discharge capacity of 113 mA h g−1, which decreased to 99 mA h g−1 (capacity retention of 88.1%) after 200 cycles at the current rate of 1 C. The high rate capability (96 mA h g−1 at 10 C) of the composites was attributed to their unique foamy microstructure, plate-like particles, and high electronic conductivity.

Reversible voltammetry at cylindrical electrodes: Validity of a one-dimensional model

The cyclic voltammetry of a reversible one-electron-transfer electrochemical reaction is investigated using finite difference simulations at three electrode geometries: an ‘infinitely long cylinder’ electrode featuring a cylindrical electrode with an infinite length, an ‘annular band’ electrode, whose band-shape electrochemically active area is located around an infinitely long insulating cylinder, and a ‘full cylinder’ electrode which resembles the microwire electrodes widely used in electrochemical experiments with both side and end active. Following the simulation of the infinitely long cylindrical electrode, a polynomial equation is introduced to describe the forward peak potentials at different scan rates. Based on further simulations of the other two electrodes, we find if the lengths of the latter are greater than ~ 104 times the radius of the cylinders, the electrochemical reversible cyclic voltammetry of them can be well described by the infinitely long cylinder model with errors of less than 1%.

Voltammetric Measurement of Adsorption Isotherm for Ferrocene Derivatives on Highly Oriented Pyrolytic Graphite.

Reversible and specific adsorption of redox-active molecules from the electrolyte solution to the electrode surface is an important process and is often diagnosed by cyclic voltammetry (CV). The entire voltammogram, however, is rarely analyzed quantitatively, thereby completely missing or incorrectly extracting inherent information about the adsorption isotherm. Herein, we report CV measurements of the adsorption isotherm for ferrocene derivatives on the basal plane of highly oriented pyrolytic graphite (HOPG) to quantitatively understand the thermodynamics of ferrocene-HOPG and ferrocene-ferrocene interactions at HOPG/water interfaces. Specifically, reversible CV of (ferrocenylmethyl)trimethylammonium, ferrocenemethanol, and 1,1'-ferrocenedimethanol is obtained at 0.05-10 V/s to confirm that only reduced forms of ferrocene derivatives are adsorbed on HOPG. Finite element analysis of the entire voltammogram yields the Frumkin isotherm to separately parametrize ferrocene-HOPG and ferrocene-ferrocene interactions. Adsorption of all ferrocene derivatives is driven by similarly weak ferrocene-HOPG interactions with free energy changes of approximately -20 kJ/mol. Adsorption of ferrocenemethanol is strengthened by intermolecular hydrogen bonding, which is quantitatively represented by a free energy change of -8 kJ/mol for surface saturation and is qualitatively characterized by a pair of sharp adsorption and desorption peaks following a pair of diffusional peaks. By contrast, adsorption of (ferrocenylmethyl)trimethylammonium and 1,1'-ferrocenedimethanol remains weak because of electrostatic repulsion and weak hydrogen bonding, respectively, which correspond to the respective free energy changes of +0.7 and -3 kJ/mol for surface saturation. The unfavorable or weakly favorable intermolecular interactions broaden or narrow a diffusional peak during the forward scan, respectively, without yielding a post peak.

A new theory and automatic computation of reversible cyclic voltammograms at an inlaid disk electrode

By generalising the recent theory of chronoamperometry [L. K. Bieniasz, Electrochim. Acta 199 (2016) 1], a new, semi-analytical description of reversible cyclic voltammetry at an inlaid disk electrode is obtained, assuming equal diffusion coefficients of the electroactive species. In contrast to some former modelling studies, the new theory does not involve simplified or low-accurate approximations to the chronoamperometric current or integral transformation kernel, but it is mathematically rigorous. An explicit expression for the voltammetric current function is derived, in the form of an inverse Laplace transform of an infinite series involving spheroidal wave functions. An equivalent formula involving convolution integrals, more suitable for calculations, is also obtained, as well as an integral equation for the current function. The voltammograms are calculated automatically with a prescribed accuracy, by using either the adaptive integrator INTDE based on double exponential formulas, or the adaptive Huber method for integral equations. INTDE is more efficient, allowing one to compute a current function value with a relative error as close to ±10−16 as is possible, in a computing time of ca. 1 ms on a contemporary laptop computer.

Electrochemical Behavior of Graphite Anode in LiF-NaF-KF Eutectic with YF3

The electrode reactions and electrolysis process of graphite anode were investigated in LiF-NaF-KF (FLiNaK, 46.5-11.5-42.0mol%) eutectic with YF3 at 823K. Two different types of reactions were observed on graphite anode. The graphite was oxidized to carbon mono- and dioxide in a potential range of 0–2V (vs. Ni2+/Ni, similarly hereinafter), and carbon fluorides were generated when the potential fell into 6–8V. In addition, some fluoride products could be reduced at about −0.22V during reverse cyclic voltammetry scan, which has never been reported. Anode potential fluctuation was found between 6 and 8V during galvanostatic electrolysis due to the formation of gaseous products as well as change of anode surface area and current density. Both Raman and X-ray photoelectron spectroscopy were employed to probe the chemical states of fluorination/oxidation products on graphite anode after electrolysis. The formation of fluorocarbon species is responsible for the disorder on graphite surface.

Li Ion Transport and Electrochemical Decomposition of Garnet Li7-XLa3Zr2-XTaxO12 Solid Electrolytes

Ionic conductivity and chemical stability are two properties that are critical for the successful deployment of solid electrolytes in next-generation Li ion batteries. Among reported candidate materials up to date, garnet Li7-xLa3Zr2-xTaxO12 (LLZrTaO) has been viewed as one of the most promising oxides for solid electrolyte use, capable of reaching conductivity levels that come very close to conventional liquid/polymer electrolytes (~10-3 S/cm). It is also known to possess good stability at the reductive potential regime, technically enabling the use of Li metal anode for high energy density. However, understanding of the Li ion transport and the electrochemical stability at the oxidative potential regime for doped garnet oxides is still limited. In this work, we present our first-principles density functional theory (DFT) calculations and experimental results on LLZrTaO, focusing on two main points: i) the atomistic-level analysis of Li ion transport and ii) investigation of reactivity during battery charge process at the electrolyte-cathode/interphase region. DFT optimizations of doped garnet model cells suggest a trend following Vegard’s law, i.e., a decreasing lattice parameter with an increasing Ta content which is in good agreement with experimental data. By molecular dynamics, bulk Li ionic conductivities for compositional end members LLZrO and LLTaO were estimated to be 1.06 x 10-4 (0.33 eV) and 1.63 x 10-3 S / cm (0.26 eV), respectively. The former agrees well with those in experiments while a difference is noted for the latter, in which the experimental value is lower by three orders of magnitude than our prediction. Possible reasons that could explain for the difference are as follows: i) an ion transport process at high temperatures that differs from that in the low temperature region ii) an unaccounted effect from intentional/unintentional Al doping and Li+/H+ exchange reactions in experiments, and/or ii) finite model size effects inherent in the calculation which prevent the phase-space sampling for superstructures.We analyzed the observed capacity fading during the charge process of an air-isolated Li ion battery with an LLZrTaO solid electrolyte (at x = 0.375 doping level), Li metal anode, and LiFePO4+carbon (LFP+C) active cathode material. Cyclic voltammetry (CV) measurements of assembled Li/LLZrTaO/(LLZrTaO+C) and Li/LLZrTaO/Al cells showed an increase and an absence of oxidation current, respectively. No reduction current is noted in the reverse CV sweep direction which means that the reaction is irreversible. These CV profiles indicate that the garnet solid electrolyte may have been decomposed via a reaction with carbon, forming a defective garnet and carbon-containing oxide products. XRD data for the post-charge solid electrolyte showed no detectable impurity phases which is consistent with the formation of decomposition product(s) that is (are) made up of light elements. Meanwhile, DFT calculations showed an interesting trend in the operating stability of garnet compounds, i.e., the smaller is the relative electronegativity of the framework octahedral cation, the more thermodynamically stable the base garnet compound becomes against carbon reaction; the order of increasing stability is Nb ≈ Ti < Ta < Zr < Hf.

The Electrochemical Study of Vanillin in Acetonitrile

A detailed electrochemical study of vanillin was performed in acetonitrile using a platinum electrode. At low scan rates≤1Vs−1, vanillin displayed an anodic peak at ca. 1.12 vs. (Fc/Fc+)/V, and a cathodic peak at ca. 0.09 vs. (Fc/Fc+)/V (on the reverse cyclic voltammetry (CV) scan after the initial oxidation) due to the reduction of a secondary reaction product. Both redox processes were found to involve a transfer of two electrons via controlled-potential electrolysis experiments, and it is surmised that vanillin first undergoes a −2e−/-H+ oxidation, followed by a hydrolysis reaction and the loss of its methoxy substituent to generate a corresponding 1,2-benzoquinone that can subsequently be reduced via +2e−/+2H+. When higher scan rates ≥2Vs−1 were employed, however, the aforementioned homogeneous reactions were partially outrun; leading to the detection of an additional cathodic peak at ca. −0.28 vs. (Fc/Fc+)/V which is ascribed to the reduction of the transient hemiketal intermediate that is formed immediately after the reaction of the phenoxonium cation with trace water. A similar trend to the fast scan rate CVs was likewise recorded at lowered temperatures (≤−10°C). Digital simulations were used to model the cyclic voltammetry data which enabled an estimation of the electrochemical and kinetic parameters associated with the electrode reactions. Independently, vanillin can also be electrochemically reduced at ca. −1.58 vs. (Fc/Fc+)/V, which is proposed to involve the formation of molecular hydrogen.

Half-Cell Electrochemical Performance and Cost-Benefit Analysis of Utilizing Hybrid Ionic Liquids in Zinc/Bromine Flow Batteries

Ionic liquids (ILs) are typically employed as bromine sequestration agents (BSAs) in zinc/bromine (Zn/Br) flow batteries to facilitate charge/discharge operations. The present work builds upon previous investigations into alternative BSAs, and explores the hybrid utilization of 1-ethyl-3-methylimidazolium bromide ([C2MIm]Br) and the conventionally employed 1-ethyl-1-methylpyrrolidinium bromide ([C2MPyrr]Br) ILs in 5 different molar proportions (1:0, 3:1, 1:1, 1:3 and 0:1, respectively) within the Zn/Br electrolyte. The electrochemical performance and behavior of each solution in the zinc and bromine half-cells was studied via cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Preliminary results from electrochemical investigations and a normalized cost-benefit analysis are presented, together with a discussion on the feasibility of using hybrid IL solutions in Zn/Br systems. On the basis of charge and current densities during forward and reverse CV scans (i.e. charging and discharging phases) for a system utilizing glassy carbon electrodes, pure [C2MPyrr]Br and [C2MIm]Br offer the best performance, including efficiencies, for Br and Zn half-cells, respectively. This trend is generally maintained during cost analysis for each half-cell. EIS showed that low charge-transfer resistance is a primary reason for good performance in both half-cells. Furthermore, lower double-layer capacitance and Warburg diffusion limitations are potentially linked to better performance in the Zn and Br half-cells, respectively. Hybrid IL mixtures generally produced higher impedances compared to solutions containing a single type of IL. Interestingly, a preliminary whole-system analysis suggests that pure [C2MPyrr]Br is most cost-effective during charging while pure [C2MIm]Br offers the best cost-benefit during discharge. The 1:1 mixture generally gave the worst electrochemical performance and lowest cost-benefit in both half-cells, suggesting that non-equimolar mixtures of these ILs might be better suited for Zn/Br systems. These findings warrant further investigation of the behavior and influence of hybrid IL formulations for BSA applications in the bulk electrolyte and at the electrode-electrolyte interface, as well as full-cell charge/discharge cycle testing. While this work focuses on Zn/Br batteries, the methods and findings presented are also potentially applicable to other types of RFBs which utilize pure or hybrid ILs for bromine sequestration.

Electrochemistry and electrocatalysis of myoglobin immobilized in sulfonated graphene oxide and Nafion films

In this study, sulfonated graphene oxide (SGO) was synthesized and characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). It was used to make Mb–SGO–Nafion composite films by coating myoglobin (Mb) on the glassy carbon electrodes (GCE). Positions of the Soret absorption bands suggested that Mb retained its native conformation in the films. Mb–SGO–Nafion film modified electrode showed a pair of well-defined and nearly reversible cyclic voltammetry peaks at around −0.39 V versus saturated calomel electrode (SCE) in pH 7.0 buffers, characteristic of heme Fe(III)/Fe(II) redox couples. Electrochemical parameters such as electron transfer rate constant (ks) and formal potential (Eo′) were estimated by fitting the data of square-wave voltammetry with nonlinear regression analysis. Experimental data demonstrated that the electron transfer between Mb and electrode was greatly facilitated and showed good electrocatalytic properties toward various substrates, such as H2O2 and NaNO2, with significant lowering of reduction overpotential.

A new theory, and automatic computation of reversible cyclic voltammograms at a microband electrode

By generalising the recent theory of chronoamperometry [L. K. Bieniasz, Electrochim. Acta 178 (2015) 25], a new, semi-analytical description of reversible cyclic voltammetry at a microband electrode is obtained, assuming equal diffusion coefficients of the species involved in a redox reaction. In contrast to the formerly proposed model [K. Aoki, K. Tokuda, J. Electroanal. Chem. 237 (1987) 163], the new theory does not involve any heuristic approximations. It is based on the formalism of Mathieu equations and functions, and provides rigorous and complete expressions for the voltammetric current, in the form of either a convolution integral or an integral equation. The voltammograms are calculated automatically with a prescribed accuracy, by using either the adaptive integrator dqags from the QUADPACK package, or the adaptive Huber method for integral equations. The two methods are compared, and dqags is found to be more efficient. A highly accurate (relative error about 10−16) procedure for calculating the kernel function of the integral equation, and its moment integrals, is also described.

Li Storage of Calcium Niobates for Lithium Ion Batteries

New types of niobates negative electrode were studied for using in lithium-ion batteries in order to alternate metallic lithium anodes. The potassium intercalated compound KCa2Nb3O10 and proton intercalated compound HCa2Nb3O10 were studied, and the electrochemical results showed a reversible cyclic voltammetry profile with acceptable discharge capacity. The as-prepared KCa2Nb3O10 negative electrode had a low discharge capacity caused by high overpotential, but the reversible intercalation and deintercalation reaction of lithium ions was activated after exchanging H+ ions for intercalated K+ ions. The initial discharge capacity of HCa2Nb3O10 was 54.2 mAh/g with 92.1% of coulombic efficiency, compared with 10.4 mAh/g with 70.2% of coulombic efficiency for KCa2Nb3O10 at 1 C rate. The improved electrochemical performance of the HCa2Nb3O10 was related to the lower bonding energy between proton cation and perovskite layer, which facilitate Li+ ions intercalating into the cation site, unlike potassium cation and perovskite layer. Also, this negative material can be easily exfoliated to Ca2Nb3O10 layer by using cation exchange process. Then, obtained two-dimensional nanosheets layer, which recently expected to be an advanced electrode material because of its flexibility, chemical stable, and thin film fabricable, can allow Li+ ions to diffuse between the each perovskite layer. Therefore, this new type layered perovskite niobates can be used not only bulk-type lithium ion batteries but also thin film batteries as a negative material.

Sol–gel derived silica/chitosan/Fe3O4 nanocomposite for direct electrochemistry and hydrogen peroxide biosensing

A novel strategy to fabricate hydrogen peroxide third generation biosensor has been developed from sol–gel of silica/chitosan (SC) organic–inorganic hybrid material assimilated with iron oxide magnetic nanoparticles (Fe3O4). The large surface area of Fe3O4 and porous morphology of the SC composite facilitates a high loading of horseradish peroxidase (HRP). Moreover, the entrapped enzyme preserves its conformation and biofunctionality. The fabrication of hydrogen peroxide biosensor has been carried out by drop casting of the SC/F/HRP nanocomposite on glassy carbon electrode (GCE) for study of direct electrochemistry. The x-ray diffraction (XRD) pattern and transmission electron microscopy (TEM) confirms the phase purity and particle size of as-synthesized Fe3O4 nanoparticles, respectively. The nanocomposite was characterized by UV–vis spectroscopy, fluorescence spectroscopy and Fourier transform infrared (FTIR) for the characteristic structure and conformation of enzyme. The surface topographies of the nanocomposite thin films were investigated by scanning electron microscopy (SEM). Dynamic light scattering (DLS) was used to determine the particle size distribution. The electrostatic interactions of the SC composite with Fe3O4 nanoparticles were studied by the zeta potential measurement. Electrochemical impedance spectroscopy (EIS) of the SC/F/HRP/GCE electrode displays Fe3O4 nanoparticles as an excellent candidate for electron transfer. The SC/F/HRP/GCE exhibited a pair of well-defined quasi reversible cyclic voltammetry peaks due to the redox couple of HRP-heme Fe (III)/Fe (II) in pH 7.0 potassium phosphate buffer. The biosensor was employed to detect H2O2 with linear range of 5 μM to 40 μM and detection limit of 5 μM. The sensor displays excellent selectivity, sensitivity, good reproducibility and long term stability.

A simple strategy for the immobilization of catalase on multi-walled carbon nanotube/poly (l-lysine) biocomposite for the detection of H2O2 and iodate

Herein, we report a novel third-generation H2O2 and IO3− biosensor, which was fabricated by loading catalase (CAT) onto l-lysine/multiwalled carbon nanotube (PLL/f-MWCNT) film modified glassy carbon electrode (GCE). The UV–visible (UV–vis) and Fourier-transform infrared (FTIR) spectra show that the catalase encapsulated in the PLL/f-MWCNT film can effectively retain its bioactivity. The immobilized CAT retained its bioactivity with a high protein loading of 4.072×10−10molcm−2, thus exhibiting a surface-controlled reversible redox reaction, with a fast heterogeneous electron transfer rate of 5.48s−1. The immobilized CAT shows a couple of reversible and well-defined cyclic voltammetry peaks with a formal potential (E0) of −0.471V (vs. Ag/AgCl) in a pH 6.5 phosphate buffer solution (PBS). Moreover, the modified film exhibited high electrocatalytic activity for the reduction of hydrogen peroxide (H2O2). It exhibited a wide linear response to H2O2 in the concentration range of 1×10−6–3.6×10−3, with higher sensitivity (392mAcm−2M−1) and a lower Michaelis–Menten constant (0.224mM). It provided high-catalytic activity towards H2O2 in a shorter time (5s), with a detection limit of 8nM. These results indicate great improvement in the electrochemical and electrocatalytic properties of the CAT/PLL/f-MWCNT biosensor, offering a new idea for the design of third-generation electrochemical biosensors.

Electrochemical and Spectroscopic Characterization of LiCoO2 Thin-Film as Model Electrode

LiCoO2 thin-films deposited on various platinum substrates, i.e. single crystals of Pt(100), Pt(110) and Pt(111), and polycrystals (Pt-poly), are characterized by cyclic voltammetry (CV), X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) to discuss appropriateness of thin-film modeling of composite electrodes from the electrochemical and spectroscopic viewpoints. Structural characterization indicates (001) orientation of LiCoO2/Pt(100) and LiCoO2/Pt(111) thin-films, and (104) orientation of LiCoO2/Pt(110). LiCoO2/Pt-poly thin-film is polycrystalline with a broad distribution of tilt angle of LiCoO2 c-axis. The LiCoO2/Pt(100) and LiCoO2/Pt-poly thin-films exhibit reversible CV behavior, while the other two show irreversible behavior. The structural and electrochemical characterization suggests that the c-axis tilt angle is not the predominant factor for reversible electrochemical behavior of the LiCoO2 electrodes. Instead, polycrystalline structure with weak orientation seems to be preferable for high reversibility. Orientation dependence of XAS also indicates that the LiCoO2/Pt-poly thin-film shows similar spectrum to LiCoO2 powder. Thin-films having strong orientation lead to strong dependence of XAS spectra, and this can result in lack of spectroscopic information. From both the electrochemical and XAS viewpoints, the LiCoO2/Pt-poly thin-film having the polycrystalline structure with the broad distribution of the c-axis tilt angle is the most suitable for the thin-film modeling of the composite electrodes.

The electrochemical studies of cytochrome c incorporated in 3D porous calcium alginate films on glassy carbon electrodes

In this work, the cytochrome c (Cyt c) was incorporated in three-dimension (3D) porous calcium alginate (CA) films prepared by using sodium alginate, calcium chloride and polyethylene glycol, and formed the electroactive porous Cyt c–CA composite films. The stable composite films were characterized by means of scanning electron microscopy (SEM), UV-vis absorption, cyclic voltammetry (CV) and square-wave voltammetry (SWV) techniques. UV-vis experiments demonstrated that Cyt c assembled in the 3D porous CA films retains its near native conformation at medium pH. The Cyt c–CA films modified on glassy carbon electrodes showed a pair of well-defined and nearly reversible cyclic voltammetry peaks at about −0.352 V vs. SCE in protein-free buffer, which originated from heme FeIII/II redox couples within Cyt c. The electrochemical parameters such as apparent heterogeneous electron transfer rate constant (ks) and formal potential (Eo’) were estimated by fitting the data of SWV with nonlinear regression analysis. The Cyt c–CA films showed the electrocatalytic activity toward dioxygen, hydrogen peroxide, nitrite and trichloroacetic acid with significant decreases in the electrode potential required. Experimental data demonstrated that the porous film can provide a favorable microenvironment for the protein to directly transfer electrons with the underlying electrode and possess good stability and reproducibility, showing the possible future application of the films for biosensors and biocatalysis.