Quasi-reversible Electrochemical Reaction Research Articles

Sensitive electrochemical detection of dopamine using CuCo2O4/graphene quantum dots-modified carbon paste electrode

This research investigates the fabrication and electrochemical characterization of a modified graphene paste electrode (MCPE) incorporating CuCo2O4 bimetallic oxide and its composite with graphene quantum dots (GQDs) for dopamine detection. The CuCo2O4 was synthesized via a hydrothermal method. The oxidation–reduction behavior of dopamine on the GQD/CuCo2O4/CPE indicates a quasi-reversible electrochemical reaction with an absorption-controlled electron transfer process and the kinetics of the catalytic reaction followed pseudo first-order. The average value of the electron transfer rate constant for GQD/CuCo2O4 was observed to be 0.047 s−1. Characterization of the obtained materials was performed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Subsequently, under optimized conditions, cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were employed to evaluate the dopamine sensing performance of the MCPEs. The GQD/CuCo2O4 composite electrode exhibited a lower detection limit (0.004 μM) and quantification limit (0.013 μM) for DA compared to the CuCo2O4 electrode (0.0088 μM and 0.030 μM, respectively). The GQD/CuCo2O4 nanocomposite showed better sensitivity (33.0 mA/mM) than CuCo2O4 (17.9 mA/mM) due to the superior conducting nature of GQD. Finally, the applicability of the GQD/CuCo2O4-based MCPE was demonstrated by measuring DA in real samples.

Combining electron transfer, spin crossover, and redox properties in metal-organic frameworks

Hofmann coordination polymers (CPs) that couple the well-studied spin transition of the FeII central ion with electron-responsive ligands provide an innovative strategy toward multifunctional metal-organic frameworks (MOFs). Here, we developed a 2D planar network consisting of metal-cyanide-metal sheets in an unusual coordination mode, brought about by infinitely π-stacked redox-active bipyridinium derivatives as axial ligands. The obtained family of materials show vivid thermochromism attributed to electron transfer and/or electronic spin state change processes that can occur either independently or concomitantly. Importantly, the redox activity of the ligands within the structure leads to the quasi-reversible electrochemical reduction reaction on a spin-crossover complex at solid state. These observations have been confirmed via temperature-dependent single-crystal X-ray diffraction, magnetic measurements, Mössbauer, EPR, optical and vibrational spectroscopies as well as quantum chemical calculations.

Determination of the standard rate constant for soluble-soluble quasi-reversible electrochemical systems by linear sweep voltammetry: Application to the electrochemical oxidation on screen-printed graphite electrodes

Semi-analytical approach was used for modeling and establishing Linear Sweep Voltammetry (LSV) profiles in the case of quasi-reversible electrochemical reactions involving soluble species. The effects of charge transfer coefficient (α) and dimensionless kinetic rate constant (Λ) on the shape and position of voltammograms were investigated. The combined effect on the LSV responses, peak current, half peak width and peak potential was also analyzed qualitatively and quantitatively. Kinetic curves were constructed in the form of the change in the LSV characteristics as a function of (α, Λ) and then modeled by the interpolation functions. The obtained equations are an easy-to-use tool in order to calculate the heterogeneous kinetic rate constant for quasi-reversible charge transfer. Experimental-theory validation has been performed on ferrocyanide oxidation on screen-printed graphite electrodes.

Mesoporous nickel oxide nanostructures: influences of crystalline defects and morphological features on mediator-free electrochemical monosaccharide sensor application

Morphological and surface features are the key tools used to tune the catalytic performance of any metal oxide. In the present study, nickel oxide nanoparticles (NiO NPs) with three different morphologies were prepared using a simple hydrothermal method. The electrocatalytic performance of the prepared NiO NPs was evaluated with regard to the detection of monosaccharide glucose. The physicochemical properties of prepared NiO nanostructures were confirmed using different conventional characterization techniques. The flower-like morphological NiO NPs with nanosized petals have a high surface area and a more defective surface, resulting in improved heterogeneous catalytic activity compared to hexagonal and spherical morphological NiO NPs in glucose oxidation. The anionic and cationic vacancies on the mesoporous surface of NiO nanopetals endorsed an enhanced charge transfer efficiency compared to other NiO morphologies. The effect of scan rate, confirmed by cyclic voltammetry analysis, ensured the diffusion-controlled quasi-reversible electrochemical reaction between surface-modified electrodes and analyte. The NiO petals showed a wide linear detection range (100 nmol L−1–12 mmol L−1) and a lower detection limit of 57 nmol L−1. In addition, the anti-interference ability, repeatability, stability and real sample analysis further affirmed the enhanced catalytic features of NiO nanopetals. The results showed that defective surfaces and surface features of the NiO nanostructures could be used to tune their overall sensor performance in future applications.

Step potential as a diagnostic tool in square-wave voltammetry of quasi-reversible electrochemical processes

By applying square-wave voltammetry (SWV) and through examining the most common electrochemical kinetic region, i.e. the quasi-reversible charge transfer process, the important role of the step potential (height, ΔE) was theoretically and practically studied considering both, the dissolved as well as the electrode surface confined redox species. It was found that the impact of the step potential is readily manifested through the scan rate (v) of an SWV experiment, the one being the product of the frequency of pulses (f) and the step potential (v = ΔE f). The presented studies evidently confirmed that the role of the step potential is very complex but that it significantly affects the morphology of both, the forward as well as the backward SWV current components, which applies for any degree of electrochemical reversibility. Furthermore, it was demonstrated that in case of quasi-reversible electrochemical reactions the degree of reversibility profoundly depends on the step potential applied. Moreover, it was proven that the degree of reversibility can be markedly improved by correspondingly decreasing ΔE. This has significant importance in the context of electrode kinetics as well as in analytical applications. Hence, this study clearly demonstrated that besides the frequency, the step potential can be an additional important tool for inspecting and improving the electrode kinetics in SWV. Finally, in order to test a practical example of a quasireversible electrode reaction of a dissolved redox couple, the SWV measurements of theFe3+(aq)/Fe2+(aq) redox couple were carried out using a basal plane pyrolytic graphite electrode and the resulting readings confirmed our theoretical predictions.

Double-pulse chronoamperometry using short times for the kinetic study of simple quasi-reversible electrochemical reactions at low overpotentials

This work presents a simple and fast way to determinate the standard heterogeneous rate constant (k0) of simple quasi-reversible electrochemical reactions based on the short time double-pulse chronoamperometry at low overpotentials. The value of k0 was determined for the faradaic reaction involving redox couples of iron complexes on a commercial glassy carbon electrode. The errors involved in this type of analysis were evaluated by finite difference numerical simulations, and accurate determinations of k0 values have proved to be possible at short times in the case where the charge transfer is considerably hindered in comparison to the mass-transfer of the electroactive species. A very good correspondence was observed between the experimental findings and the theoretical analysis involving the finite difference numerical simulation.

Silver nitrate nanosheet supported on porous carbon three-dimensional substrate as cathode material and its lithium storage mechanism

In this paper, we present the direct application of AgNO3 as a novel host material for lithium storage. Fabricated as cathode material, commercial AgNO3 particles show an initial charge capacity at 157.1 mAh g−1, and retain a capacity of only 11.5 mAh g−1 after 100 cycles. By preparing AgNO3 nanosheets supported on conductive carbon three-dimensional substrate, enhanced lithium storage performance can be achieved. As-prepared AgNO3 nanosheets exhibit the charge capacity at 141.7 mAh g−1 in the first cycle, and maintain at 82.0 mAh g−1 after 100 cycles. The three-dimensional carbon substrate with considerable strength and tenacity supporting AgNO3 nanosheets presents fast electron/ion transport, large electroactive surface area, and excellent structural stability. The reaction mechanism of AgNO3 with Li is also studied by ex situ and in situ techniques during the initial cycle. It can be concluded that lithium storage process of AgNO3 is associated with a quasi-reversible electrochemical conversion reaction. During the discharge process, the electrochemical reaction of AgNO3 with Li results in the formation of Ag and LiNO3. In the reverse charge process, AgNO3 can be re-generated by its conversion reaction. Therefore, it is anticipated that AgNO3 nanosheets can be a probable cathode candidate for lithium-ion batteries.

Lithium storage mechanism in superior high capacity copper nitrate hydrate anode material

Copper nitrate hydrate (Cu(NO3)2·2.5H2O) exhibits superior high lithium storage capacity (2285 mAh g−1) as anode material for lithium-ion batteries. The structural transformation and lithium storage mechanism of Cu(NO3)2·2.5H2O are thoroughly studied by various advanced analytical techniques. It is found that the lithium storage process of Cu(NO3)2·2.5H2O is associated with a quasi-reversible electrochemical conversion reaction. During the discharge process, the electrochemical reaction of Cu(NO3)2·2.5H2O with lithium results in the formation of Cu, LiNO3, Li3N, Li2O and H2O. In the reverse charge process, Cu(NO3)2 can be generated by a conversion reaction. As a result, Cu(NO3)2·2.5H2O shows the reversible charge capacities of 1632.1 mAh g−1 in 0.0–3.4 V and 689.1 mAh g−1 in 1.0–3.4 V, respectively.

Electrochemical mechanism of rusticyanin (Rus.) isolated from A. ferrooxidans measured by Rus.-ZnS-QDs/L-Cys/Au electrode

Electrochimcal behaviors of rusticyanin (Rus.) isolated from Acidithiobacillus ferrooxidans were investigated through Rus.-ZnS-QDs/L-Cys/Au electrode. The cyclic voltammetric results indicate that rusticyanin immobilized on the surface of Rus.-ZnS-QDs/L-Cys/Au electrode can undergo a direct quasi-reversible electrochemical reaction. The immobilized rusticyanin is not denatured and still retains its activity in the temperature range of 19–43 °C. The reduction ability of the protein increases and its oxidation ability becomes weak with the increase of pH from 6.0 to 7.8. Fe2+ ions in the solution can promote the electron transfer kinetics of the immobilized rusticyanin and make its peak potentials (φp) markedly move negatively.

Synthesis and electrochemical performance of β-Co(OH) 2

A novel electro-active material was synthesized by precipitation under high levels of supersaturation. The compound was pure β-Co(OH) 2 with hexagonal crystal structure by XRD analysis, and it was flake-shaped, 50–200 nm in particle size and ∼20 nm in thickness by FE-SEM observation. The quasireversible electrochemical reaction between β-Co(OH) 2 and Co upon charging/discharging produced a maximum discharge capacity of 462 mAh g −1, and furthermore the discharge capacity retained 97.6% of the initial capacity at the 100th cycle. These findings highlight the potential for β-Co(OH) 2 compound in applications to negative electrode materials of alkaline rechargeable batteries.

A whisker-like carbon composite for the immobilization of laccase and its bioelectrochemistry

A novel mesoporous carbon/whisker-like carbon (MCWC) composite was used for the immobilization of laccase (Lac) and its bioelectrochemical behaviors were studied. It was confirmed by XPS that Lac was strongly adsorbed on the surface of the MCWC composite. The cyclic voltammetric results showed that the immobilized Lac underwent a direct quasi-reversible electrochemical reaction. The value of the electron transfer rate constant ks was estimated to be 0.770 s−1, indicating a reasonably fast electron transfer between the immobilized Lac and the underlying electrode. The surface concentration (Γ) of Lac was estimated to be 2.730 × 10−12 mol/cm2. Further experimental results showed that the immobilized Lac displayed an appreciable electrocatalytic activity to the electrochemical reduction of O2. These properties could be attributed to the particular structure of loosely packed nanometer-scale carbon whiskers and the existence of a large amount of oxygen-containing groups. The immobilization method and the novel carrier (MCWC) may find new applications in fabricating the biocatalysts for biofuel cells.

Immobilization and Direct Electrochemistry of Horseradish Peroxidase on Large Cage-Like Mesoporous Silica FDU-12

We report on a direct electron transfer and bioelectrocatalysis of horseradish peroxidase (HRP) immobilized in mesoporous silica FDU-12 with three-dimensional (3D) large cages and entrances. UV-Vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, and impedance spectroscopy were used to prove the interaction between HRP and FDU-12. Results from cyclic voltammetry show that immobilized HRP can undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E0′, is -0.325 V in a phosphate buffer solution (PBS, pH 6.9) and this is almost independent of the scan rate from 40 to 300 mV·s -1. The experimental results also demonstrate that the immobilized HRP retains its bioelectrocatalytic activity for the reduction of H2O2. Furthermore, the electrode can be stored at 4 °C for several weeks without any loss of enzyme activity. Thus, FDU-12 is a novel matrix for realizing a direct electron transfer of various proteins and enzymes and the preparation of electrodes for the third biosensors.

Direct electrochemistry and enhanced electrocatalysis of horseradish peroxidase based on flowerlike ZnO–gold nanoparticle–Nafion nanocomposite

We developed a new flowerlike ZnO–gold nanoparticles (GNPs)–Nafion nanocomposite which can promote the direct electron transfer of horseradish peroxidase (HRP) immobilized in the film effectively. The cyclic voltammetric results show that HRP entrapped in the composite could undergo a direct quasi-reversible electrochemical reaction with a formal potential ( E 0′) of −0.32 V (versus Ag/AgCl) in phosphate buffer solution (PBS). The flowerlike ZnO and GNPs show synergistic effect and the ZnO–GNPs–Nafion–HRP modified GC electrode gives an enhanced electrocatalytic activity towards the reduction of hydrogen peroxide (H 2O 2). The calculated apparent Michaelis–Menten constant ( K m app ) is 1.76 mM, which is much lower than that reported, indicating a high catalytic activity of HRP. The catalysis currents increase linearly to the H 2O 2 concentration in a wide range of 1.5 × 10 −5 to 1.1 × 10 −3 M, with a correlation coefficient of 0.998. The detection limit is 9.0 × 10 −6 M (at the ratio of signal to noise, S/N = 3), demonstrating that the formed film provides a favorable microenvironment for the enzyme to retain its activity. Moreover, the modified electrode displays rapid response to H 2O 2 and possesses good stability and reproducibility.

Hemoglobin immobilized on whisker-like carbon composites and its direct electrochemistry

We developed a novel mesoporous carbon/whisker-like carbon (MCWC) composite which can promote the direct electron transfer of hemoglobin (Hb) immobilized on its surface. The cyclic voltammetric results showed that Hb immobilized on the surface of the MCWC composite could undergo a direct quasi-reversible electrochemical reaction. Its formal redox potential, E 0′ is −0.313 V in the phosphate buffer solution (pH 6.9) at a scan rate of 200 mV/s and is almost independent of the scan rate in the range of 100–600 mV/s. The dependence of E 0′ on the pH of phosphate buffer solution indicated that the redox reaction of Hb includes a one-electron-transfer reaction process coupled with one-proton-transfer. The experiment obtained larger value of electron transfer rate constant, k s, than that of Hb immobilized on other carriers reported previously due to its special structure of loosely packed nanometer-scale carbon whiskers and thus formed “V-type” nano-pores. Furthermore, Hb immobilized on the surface of the MCWC composite can retain the stable bioelectrocatalytic activity for the reduction of H 2O 2.

Direct electrochemistry behavior of Cytochrome c on silicon dioxide nanoparticles-modified electrode

A newfangled direct electrochemistry behavior of Cytochrome c (Cyt c) was found on glassy carbon (GC) electrode modified with the silicon dioxide (SiO2) nanoparticles by physical adsorption. A pair of stable and well-defined redox peaks of Cyt c′ quasi-reversible electrochemical reaction were obtained with a heterogeneous electron transfer rate constant of 1.66×10−3 cm/s and a formal potential of 0.069 V (vs. Ag/AgCl) (0.263 V versus NHE) in 0.1 mol/L pH 6.8 PBS. Both the size and the amount of SiO2 nanoparticles could influence the electron transfer between Cyt c and the electrode. Electrostatic interaction which is between the negative nanoparticle surface and positively charged amino acid residues on the Cyt c surface is of importance for the stability and reproducibility toward the direct electron transfer of Cyt c. It is suggested that the modification of SiO2 nanoparticles proposes a novel approach to realize the direct electrochemistry of proteins.

Copper and cadmium phosphonates based on 2-quinolinephosphonate

Hydrothermal reactions of 2-quinolinephosphonic acid ( 1) and CuSO 4 or CdSO 4 result in two new compounds with formula Cu(2-C 9H 6NPO 3) ( 2) and Cd(2-C 9H 6NPO 3)(H 2O) ( 3). Compound 2 has a layer structure in which dimers of edge-sharing {CuO 4N} square-pyramids are linked by {CPO 3} tetrahedra through corner sharing. Compound 3 shows a new type of layer structure where chains of corner sharing {CdO 5N} octahedra are connected by {CPO 3} tetrahedra into an inorganic layer. The quinoline groups fill in the inter-layer spaces in both cases. Crystal data for 1: monoclinic, space group P2 1/ c, a = 10.270(2) Å, b = 13.566(3) Å, c = 6.9818(16) Å, β = 101.916(4)°, V = 951.8(4) Å 3, Z = 4. For 2: monoclinic, space group P2 1/ c, a = 13.976(3) Å, b = 7.9398(18) Å, c = 7.8687(18) Å, β = 101.150(5)°, V = 856.7(3) Å 3, Z = 4. For 3: monoclinic, space group P2 1/c, a = 17.164(4) Å, b = 5.4870(12) Å, c = 10.850(2) Å, β = 101.557(4)°, V = 1001.1(4) Å 3, Z = 4. The magnetic measurement on 2 reveals a dominant antiferromagnetic exchange coupling between the Cu(II) centers. A quasi-reversible electrochemical reaction is observed for complex 2 immobilized on the surface of GC electrode, corresponding to the redox couple Cu 2+/Cu +. The fluorescent properties of 1– 3 are also investigated.

Direct electrochemistry and bioelectrocatalysis of hemoglobin immobilized on carbon black

It is reported for the first time that hemoglobin (Hb) was immobilized on the surface of carbon black powders modified at the surface of a glassy carbon electrode. The cyclic voltammetric results showed that the immobilized Hb could undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E 0, is − 0.330 V in phosphate buffer solution (pH 6.9) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 40–200 mV/s. The dependence of E 0, on the pH of the buffer solution indicated that the conversion of Hb–Fe(III)/Hb–Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized Hb retained its bioelectrocatalytic activity for the reduction of H 2O 2. Furthermore, the immobilized Hb can be stored at 4 °C for several weeks without any loss of the enzyme activity. Thus, the immobilized Hb may be used as a biocathodic catalyst in biofuel cells.

Direct Electrochemistry and Immobilization of Glucose Oxidase on Carbon Black

The IR spectroscopic and electrochemical measurements demonstrated that glucose oxidase(GOx)could be immobilized on the surface of carbon black(CB)using a simple adsorption method.The electrochemical measurements indicated that GOx immobilized on CB could undergo the quasi-reversible and direct electrochemical reaction and keep the bioelectrocatalytic activity for the glucose oxidation.Even after conservation for two weeks,its electrocatalytic activity decreased only 5%,illustrating the good stability of GOx immobilized on CB.

Biosensing Properties of TitanateNanotube Films: Selective Detection of Dopamine in the Presence of Ascorbate and Uric Acid

AbstractA novel strategy based on titanate nanotubes (TNTs) for developing an electrochemical biosensor is proposed. Stable TNT films are fabricated on glassy carbon (GC) electrodes by a casting technique. Cyclic voltammetry, electrochemical impedance spectrometry, and linear‐sweep voltammetry are used to characterize the TNT membrane‐covered GC electrodes (TNT/GCs). The TNT film is shown to demonstrate selectivity by charge exclusion. The TNT film is also shown to be capable of improving the mass transport to the electrode surface and electron transfer between dopamine (DA) and the electrode. Therefore, DA exhibits a quasireversible electrochemical reaction at the TNT/GC electrode. The voltammetric signal of DA is well resolved from those of ascorbate (AA) and uric acid (UA) at the TNT/GC electrode; therefore, DA can be selectively detected in the presence of a large excess of AA and UA at physiological pH. The linear calibration curve for DA is obtained over the concentration range 0.1–30 μM in a physiological solution that contains 0.1 mM AA and 0.3 mM UA.

Direct electrochemistry and bioelectrocatalysis of horseradish peroxidase immobilized on active carbon

For the first time horseradish peroxidase (HRP) immobilized on the surface of active carbon powder modified at the surface of a glassy carbon electrode has been shown to undergo a direct quasi-reversible electrochemical reaction. Its formal potential, E 0′, is −0.363 V in phosphate buffer solution (pH 6.8) at a scan rate of 100 mV/s and is almost independent of the scan rate in the range of 50–700 mV/s. The dependence of E 0′ on the pH of the buffer solution indicated that the conversion of HRP–Fe(III)/HRP–Fe(II) is a one-electron-transfer reaction process coupled with one-proton-transfer. The experimental results also demonstrated that the immobilized HRP retained its bioelectrocatalytic activity to the reduction of H 2O 2. Furthermore, the HRP adsorbed on the surface of the active carbon powder can be stored at 4 °C for several months without any loss of the enzyme activity. The method presented for immobilizing HRP can be easily extended to immobilize and obtain the direct electrochemistry of other enzymes.