Linear Sweep Voltammograms Research Articles

Mechanochemical Synthesis of Nitrogen-Doped and Sulfur-Doped Multilayer Graphene for Use in Bifunctional Oxygen Electrodes

Nitrogen-doped and sulfur-doped mechanochemically synthesized multilayer graphene (N-doped and S-doped MSMG) were prepared by planetary ball-milling, and they were used in bifunctional gas diffusion electrodes (GDEs) for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Graphite, melamine, and elemental sulfur were used as raw materials. The surface area-normalized linear sweep voltammograms revealed that the N-doped and S-doped MSMG have higher intrinsic ORR/OER activity than the undoped MSMG. When the MSMG samples were used in GDEs, the N-doped and S-doped MSMG showed higher OER activity but lower ORR activity than the undoped MSMG. We analyzed the relationship between the specific surface area, intrinsic ORR/OER activity, and ORR/OER activity of GDEs and found that both the intrinsic ORR activity and surface area are important in the fabrication of GDEs with high ORR activity and that the intrinsic OER activity rather than the surface area is important in the fabrication of GDEs with high OER activity. The GDE fabricated from the S-doped MSMG showed the highest ORR/OER bifunctional activity among the MSMG-based GDEs, and its ORR/OER bifunctional activity was higher than the GDEs fabricated from other materials, such as reduced graphene oxide and electroconductive oxides.

Electro-Oxidation and Determination of Ciprofloxacin at f-MWCNT@Poly-Aniline Glassy Carbon Electrode

A simple and sensitive electrochemical sensor was developed to quantify ciprofloxacin by restricted electro-polymerization of aniline on GCE followed by drop coating functionalized MWCNTs. Electro-catalytic activity of modified electrodes was investigated by EIS and CV revealed decrease in electrode’s charge transfer resistance and increase in electron transfer kinetics. Effect of pH and scan rate suggests a mixed adsorption-diffusion process. Tafel slope (plot of ln∣j a ∣ or ln∣I a ∣ against E) with linear relationship of potential vs logarithm of current on the linear sweep voltammogram determined the electron transfer coefficient (α). Using the value of (α), number of electrons (n) involved in the rate determining step was obtained. Surface coverage of analyte molecules adsorbed, and diffusion coefficient of ciprofloxacin were estimated from the Laviron and Randles Sevcik equations respectively. Peak current obtained by LSV for various concentrations of ciprofloxacin exhibited two linear ranges, 0.1 μM to 1 μM and 1 μM to 20 μM, with limit of detection 0.08 μM (RSD = 2.4%, S/N = 3). Presence of species existing abundantly in the sample matrix do not affect the sensor signal. Proposed ciprofloxacin sensor demonstrated high reproducibility, long-term stability and fast reaction. The fabricated sensor successfully determined ciprofloxacin in pharmaceutical formulations with recoveries between 92 to 104%.

Tetraphenolphthalein Cobalt(II) Phthalocyanine Polymer Modified with Multiwalled Carbon Nanotubes as an Efficient Catalyst for the Oxygen Reduction Reaction.

Oxygen reduction reaction (ORR) is the main reaction at the cathode of a fuel cell that utilizes Pt/C as the benchmark catalyst. Due to sluggish activity, high cost, rare abundance, and durability issues, Pt/C must be replaced by nonprecious, stable, and easily synthesizable materials. This work involves the synthesis of novel, simple, low-cost, and environmentally friendly phenolphthalein-bearing cobalt(II) phthalocyanine polymer, poly(CoIITPpPc) dyad, as an efficient catalyst for ORR. The results of analytical characterizations reveal the formation of the poly(CoIITPpPc) polymer in the pure state. To further enhance the catalytic response of poly(CoIITPpPc), a hybrid composite is prepared using poly(CoIITPpPc) and multiwalled carbon nanotubes (MWCNTs) that increase the surface area and conductivity. The poly(CoIITPpPc) and hybrid composite are separately deposited on the electrode surfaces. The electron microscopy images confirm the uniform distribution of the poly(CoIITPpPc) molecules on the electrode surface and MWCNTs. The poly(CoIITPpPc) and hybrid composite electrodes are evaluated for ORR, and the hybrid composite exhibits better onset potential at 0.803 V versus reversible hydrogen reference electrode for ORR according to linear sweep voltammograms (LSVs). The obtained data are superior compared to those of other carbon-based redox-active materials reported previously and nearer to those of the benchmark catalyst (Pt/C). The rotating disc electrode measurement of the hybrid composite electrode confirms the total number of electrons involved in ORR to be four. Furthermore, the hybrid composite electrode exhibits an excellent stability for 100 LSV scans. The synergistic effect of poly(CoIITPpPc) and MWCNTs leads to the surprisingly high ORR activity due to the improved surface area, conductivity, and interfacial confined surface.

Facile fabrication of GCE/Nafion/Ni composite, a robust platform to detect hydrogen peroxide in basic medium via oxidation reaction.

Nickel particles alone can oxidize hydrogen peroxide but confronts extreme stability problem which imparts a barrier to act as sensor. The porous Nafion bed on glassy carbon electrode (GCE) surface provides the sureness of incorporating of Ni particles which was further exploited as an electrochemical sensor for H2O2 detection through oxidative degradation process. The simple electrochemical incorporation of Ni particles along the pores of Nafion improves the stability of the sensor significantly. The oxidative pathway of hydrogen peroxide on GCE/Nafion/Ni was probed by analyzing mass transfer dependent linear sweep voltammograms both in static and rotating modes along with chronoamperometry. An electron transfer step determines the overall reaction rate with k°= 2.72×10-4cms-1, which is supported by the values of transfer coefficient (β) in between (0.68-0.75). Sensing performance was evaluated by recording differential pulse voltammograms (DPVs) with the linear detection limit (LOD) of 1.8 μM and linear dynamic range (LDR) of 5-500 μM. Real samples from industrial sources were successfully quantified with excellent reproducibility mark GCE/Nafion/Ni electrode as an applicable sensor.

Enhanced catalytic efficiency of bimetallic Pt-Pd on PAMPs-modified graphene oxide for formic acid oxidation

A catalyst composed of 2-acrylamido-2-methyl-1-propane sulfonic acid (PAMPs) modified graphene oxide (GO) as the supporting material (PAMPs/GO) and electrodeposited monometallic and bimetallic catalysts (Pt and/or Pd) as the active catalytic component was fabricated to enhance the formic acid oxidation. The morphology of the prepared catalysts was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), while the chemical compositions were identified by energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Functional groups of the supporting materials and catalysts were identified by Fourier transform infrared (FT-IR) spectroscopy. The electrochemical measurements of the synthesized catalysts were evaluated by cyclic voltammetry (CV) and chronoamperometry (CA), respectively. The kinetics of formic acid oxidation on the synthesized catalysts were determined by Tafel extrapolation of linear sweep voltammograms. The CO tolerance of the electrocatalyst was examined by CO stripping measurements. The results showed that the catalysts with PAMPs exhibited much higher electrocatalytic activity and longer-term stability for formic oxidation than the catalyst without PAMPS. In addition, the 3Pt3Pd/10%PAMPs/GO catalyst showed the greatest catalytic activity, stability, and fastest charge transfer kinetics when compared to other bimetallic catalysts and monometallic catalysts. In conclusion, modifying the GO surface with PAMPs can improve the efficiency of the electrocatalyst activity of Pt/Pd catalysts. The 3Pt3Pd/10%PAMPs/GO catalyst is a promising electrocatalyst for the enhancement of formic acid oxidation.

Efficient degradation of trimethoprim with ball-milled nitrogen-doped biochar catalyst via persulfate activation

This study explored a novel eco-friendly metal-free biochar catalyst for trimethoprim (TMP) degradation in an aqueous solution. The preparation of a ball-milled and N-doped mulberry biochar (BMNMB) for the activation of persulfate to degrade an antibiotic. BMNMB exhibits a large contact surface area and high colloidal stability compared to pristine biochar, ball-milled, and thermally treated biochar (BMMB). Surface analysis studies confirmed the heteroatom doping of the ball-milled biochar materials. The degradation efficiency of TMP in the BMNMB900/PS (>97%) was higher than those of the BMMB900/PS (73%) and pristine MB/PS (24%) systems. The TMP removal treads were further verified by the pseudo-first-order kinetic model (PFOKM). The effective degradation of TMP was obtained under neutral pH conditions. The heterogeneous catalytic reaction performance was examined using the Langmuir–Hinshelwood (L–H) kinetic model. The anions had a negative impact on the catalytic activation of BMNMB900 with PS. The chemical scavenger analysis was confirmed via both radical (HO• and SO4•−) and non-radical (1O2) reactive oxygen species (ROS) formed in the BMNMB900/PS system. Further, substantial evidence of 1O2 formation in the BMNMB900/PS system was observed in the electron spin resonance (ESR) analysis in the presence of D2O. Moreover, the linear sweep voltammogram also clearly demonstrated the electron transfer process in the BMNMB900/PS system. The TMP degradation mechanisms were proposed via the intermediate analysis using ultra-high-performance liquid chromatography with mass spectroscopy (UHPLC-MS/MS). The BMNMB900 catalyst with PS system successfully demonstrated the reusability of a catalyst in TMP degradation.

Synthesis, Characterization, and Hydrogen Evolution Activity of Metallo-meso-(4-fluoro-2,6-dimethylphenyl)porphyrin Derivatives.

Zn(II), Cu(II), and Ni(II) 5,10,15,20-tetrakis(4-fluoro-2,6-dimethylphenyl)porphyrins (TFPs) have been synthesized and characterized. The electronic spectroscopy and cyclic voltammetry of these compounds, along with the free-base macrocycle (2H-TFP), have been determined; 2H-TFP was also structurally characterized by X-ray crystallography. The Cu(II)TFP exhibits catalytic activity for the hydrogen evolution reaction (HER). The analysis of linear sweep voltammograms shows that the HER reaction of Cu(II)TFP with benzoic acid is first-order in proton concentration with an average apparent rate constant for HER catalysis of kapp = 5.79 ± 0.47 × 103 M–1 s–1.

Antimony-decorated graphite felt electrode of vanadium redox flow battery in mixed-acid electrolyte: Promoting electrocatalytic and gas-evolution inhibitory properties

• The shift of electrode gas-evolution potential by antimony. • Utilizing the electrocatalytic properties of antimony in stabilizing the electrode. • Improving vanadium redox flow battery efficiency by facilitating redox reactions. Facilitation of redox reactions and inhibition of gas evolution in the graphite felt electrode of vanadium redox flow battery (VRFB) is investigated by adding antimony ions to the electrolyte. The electrolyte is used as a mixture of sulfuric acid and hydrochloric acid to stabilize the vanadium ion. Antimony has quasi-reversible reactions prior to the electrochemical reactions of vanadium ion pairs. In general, as shown by the results of scanning electron microscopy, metallic antimony is decorated on the surface of graphite felt during charge–discharge cycles. The results of full-window cyclic voltammetry indicate an increase in the cyclic stability of samples containing antimony, especially at a concentration of 7.5 mM. This is due to the electrocatalytic properties of antimony and the facilitation of vanadium electrochemical reactions. Ease of reactions is also closely related to the improvement of vanadium ion diffusion coefficients in samples containing antimony. The reduction peak of V 3+ to V 2+ in the bare sample practically disappears after a few cycles, which is due to the superiority of hydrogen gas evolution. Linear sweep voltammograms confirm the effectiveness of antimony in shifting the potential position of hydrogen and oxygen evolution. Wettability and contact angle tests show more water adsorption by antimony-decorated graphite felts compared to the bare one which has a direct effect on improving the performance of the electrodes. Although antimony is added to anolyte in VRFB and has the most beneficial effect on the negative electrode, antimony cross-contamination does not have a bad effect on positive electrode performance and even it also stabilizes the reduction–oxidation currents ratio on positive electrode based on cyclic voltammetry results. In general, the presence of antimony increases all three types of coulombic, voltage, and energy efficiency in VRFB.

Ion-transfer electrochemistry at arrays of nanoscale interfaces between two immiscible electrolyte solutions arranged in hexagonal format

• Nanoscale interfaces between two immiscible electrolyte solutions were studied. • Arrays of pores were formed by focused ion beam milling. • Hexagonal array format was characterised by ion transfer voltammetry. • Comparison of experiment and numerical simulation was undertaken with good agreement. • nanoITIES arrays in hexagonal format reach independent diffusion at large separations. The electrochemical behaviour of hexagonally arranged nanopore arrays was studied by simple ion transfer across the interface between two immiscible electrolyte solutions (ITIES) formed between water and 1,2-dichloroethane. The hexagonal nanoITIES arrays were supported at nanopores fabricated by focused ion beam milling into 50 nm thick silicon nitride films. Six arrays with different pore centre-to-centre distance ( r c ) to radius ( r a ) ratios were prepared. Within these arrays, the diffusion-limited steady-state currents ( i ss ) of tetrapropylammonium cation (TPrA + ) ion transfer increased concomitantly with increasing r c / r a ratio, reaching a plateau at r c / r a ≥ 96, which is greater than that previously reported for square-patterned nanoITIES arrays ( r c / r a ≥ 56). The diffusion regime and i ss associated with simple ion transfer across a nanopore array was also examined using numerical simulations, via COMSOL Multiphysics software, incorporating a 3-dimensional geometry and employing finite element analysis. Simulated linear sweep voltammograms of TPrA + transfer demonstrated a unique diffusional behaviour dependent on hexagonal nanopore spacing and the r c / r a ratio, analogous to the experimental voltammograms. Overlay of simulated and experimental voltammograms for each r c / r a ratios showed good agreement. These results indicate that a new design criterion is required to achieve independent diffusion at hexagonal nanointerface arrays, in order to maximize nanodevice performance in electrochemical sensor technologies.

Voltammetric Determination of Isoniazid in the Presence of Acetaminophen Utilizing MoS2-Nanosheet-Modified Screen-Printed Electrode.

We used MoS2 nanosheets (MoS2 NSs) for surface modification of screen-printed electrode (MoS2NSs-SPE) aimed at detecting isoniazid (INZ) in the presence of acetaminophen (AC). According to analysis, an impressive catalytic performance was found for INZ and AC electro-oxidation, resulting in an appreciable peak resolution (~320 mV) for both analytes. Chronoamperometry, differential pulse voltammetry (DPV), linear sweep voltammogram (LSV), and cyclic voltammetry (CV) were employed to characterize the electrochemical behaviors of the modified electrode for the INZ detection. Under the optimal circumstances, there was a linear relationship between the peak current of oxidation and the various levels of INZ (0.035–390.0 µM), with a narrow limit of detection (10.0 nM). The applicability of the as-developed sensor was confirmed by determining the INZ and AC in tablets and urine specimens, with acceptable recoveries.

Ultrasensitive electrochemical detection for nanomolarity Acyclovir at ferrous molybdate nanorods and graphene oxide composited glassy carbon electrode

An electrochemical sensor based on ferrous molybdate (FeMoO4) loaded graphene oxide composites was prepared and used for the ultrasensitive detection of Acyclovir in nanomolar concentrations. FeMoO4 nanorods were prepared by hydrothermal method, and loaded with graphene oxide by ultrasonication. The materials were characterized by Scanning Electron Microscopy, X-ray diffractometer and Energy Dispersive Spectroscopy. The electrochemical sensor was fabricated by drop-coating method for the determination of Acyclovir. The sensing performance was investigated by cyclicvoltammetry, electrochemical impedance and linear sweep voltammogram. The results showed that the optimal signals appeared on the electrode. Furthermore, the oxidation peak current was linearly related to the Acyclovir concentration in the range of 0.1–10 μM and 10–100 mM. The limit of detection was 20 nM (S/N = 3). The sensor was used to analyze in process and in situ Acyclovir drug samples with good recoveries of 95.0–100.0% and excellent accuracy in nanomolarity.

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.

Computational modeling and experimental verification of cathode catalyst layer on PEM fuel cells

Fuel cell systems are environmentally friendly energy converters that directly transform the chemical energy of the fuel to electricity. The proton exchange membrane (PEM) fuel cells are one of the most common type of fuel cells since they deliver high power density and are lighter and smaller when compared to the other cells. However, commercialization of the PEM fuel cells is challenging due to the high cost of its components. In addition to high catalyst costs, the problem of poor water management is also a vital issue that needs to be overcome. While the gas diffusion layer of a fuel cell is essential for removing the by-product water, the Nafion solution contained in the catalyst layer has hydrophobic properties and is crucial for both preventing the water accumulation and increasing the effectiveness of the fuel cell. In this study, the effects of Carbon:Nafion ratio on the reduction potential was investigated. The cyclic voltammograms (CV) was produced for each ratio, and it was shown that the CVs exhibit characteristics of hydrogen adsorption/desorption peaks. All the linear sweep voltammogram (LSV) curves revealed well distinguished regions of kinetic, mixed and diffusion limited reaction rate. As a result, it was observed that the ratio of 1:5 resulted higher reduction potential compared to 1:3 and 1:7. Finally, a mathematical model was purposed, in which related the rotation rate and platinum coating with the current density, in order to gain insight about the responses of the fuel cell system. The constructed model is tested and validated experimentally for various parameters that are present in the system, and it may be utilized to determine oxygen reaction activities of the catalysts without performing any unnecessary electrochemical tests.

Derivative voltammetry: a simple tool to probe reaction selectivity in photoelectrochemical cells

We demonstrate the use of a derivative voltammogram method to predict the selectivity of the photo-driven oxidation of 5-hydroxymethylfurfural (HMF) on a WO3 photoanode using only information obtained from the linear sweep voltammogram (LSV).

MCR-ALS for Investigating the Effect of Adsorption on the Charging Current; Application for the Voltammetric Determination of Mefenamic Acid on a Glassy Carbon Electrode Modified with MWCNT and Poly L-Proline

This study represents the application of MCR-ALS for the separation of the different sources of variation in a series of the linear sweep voltammograms obtained from the oxidation of the Mefenamic acid as a model analyte on a poly L-proline and MWCNT-modified GCE. Two types of faradaic currents including adsorption and diffusion were separated successfully and the effects of the accumulation time and the concentration of Mefenamic acid were investigated on the variation of the charging current. The results showed that the contribution of the charging current on the measured signal decreases upon increasing the adsorption as a result of the blockage of the electrode active sites with the adsorbed species which is in agreement with the previous studies. The proposed methodology was employed for voltammetric determination of Mefenamic acid with enhanced figures of merit in real serum samples by removing the contribution of the charging current from the measured signal. The obtained results indicate the lower detection limit as 90 nM, wider linear range and higher sensitivity compared to the unprocessed and background-subtracted data.

Fundamentals on kinetics of electrochemical reduction of CO2 at a bismuth electrode

Electrochemical reduction of CO2 into renewable carbon–neutral fuels has been extensively studied. Current attentions mainly focus on the development of high-performance materials and molecular dynamics, fundamentals on kinetics of electrochemical reduction of CO2 are still unclear. Herein, we design a simplified electrochemical process, CO2-saturated K2SO4 solution at bismuth electrodes, to elucidate the electrochemical reaction kinetics of CO2 reduction reaction. A totally irreversible process for CO2 reduction reaction occurs and this reaction can be described as CO2 + H2O + 2e− → HCOO− + OH−. It is firstly reported that the reduction of CO2 at bismuth electrodes is of a diffusion-controlled process, and the diffusion coefficient of CO2 is (1.98 ± 0.22) × 10−5 cm2·s−1. From the well-defined linear sweep voltammograms, electron transfer coefficient is obtained as 0.18 ± 0.01. Combining with the half-wave potential (−1.503 ± 0.002 V vs. Ag/AgCl (sat. KCl)) from differential pulse voltametric results, the standard heterogeneous rate constant is estimated to be (3.4 ± 0.2) × 10−3 cm·s−1. These new findings may identify electrochemical reaction kinetic questions and be helpful to understanding the electrochemical conversion between CO2 and carbon–neutral renewable energy.

Hydrogen production from methanol-water mixture over NiO/TiO2 nanorods structure photocatalysts

In this work, efficient NiO nanoparticles/TiO2 nanorods p-n heterojunction structure photocatalyst is constructed by reasonable design of two-step calcination technology and examined for hydrogen production activity from methanol-water mixture. In the NiO/TiO2 heterojunction structure small NiO nanoparticles are evenly distributed on the surface of TiO2 and tightly connected together with TiO2, as it was determined by microscope characterization techniques, which conducive to the interface transport of photogenerated carriers. The novelty of this paper is the detailed characterization of NiO/TiO2 photocatalysts by electrochemical technics as Transient photocurrent response, Mott-Schottky plots, linear sweep voltammograms and Electrochemical impedance spectroscopy and their correlation with photoactivity. The rationally designed NiO/TiO2 p-n heterojunction promotes the transfer of photogenerated electrons and inhibits carrier recombination. The highest hydrogen production was exhibited in the presence of the 2-NiO/TiO2 composite during 3 h of UV irradiation (701 μmol/gcat.), which exceeded the activity of pure TiO2 by more than 1.3 times. The loss of photocatalytic hydrogen yield is negligible after repeating cycle reactions. Finally, a possible p-n heterojunction photocatalytic reduction mechanism has been discussed and apparent quantum yield was calculated.

MoS2 supported on Er-MOF as efficient electrocatalysts for hydrogen evolution reaction

The key to synthesis highly efficient MoS2 based electrocatalyst for hydrogen evolution reaction (HER) is to construct a reasonable composite system structure to improve the stability, reduce the aggregation and improve the intrinsic poor conductivity. In this paper, MoS₂ composite of erbium-based metal-organic framework (noted as Er-MOF/MoS2) were synthesized by hydrothermal method. The morphology and structure of the synthesized samples were characterized by powder X-ray diffraction (XRD), field emission electron microscopy (FESEM), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and the electrocatalytic performances were tested by linear sweep voltammograms (LSV), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), i-t. On the basis of the experiment, Er-MOF/MoS2 shows improved conductivity and more exposed active sites, exhibiting excellent HER activity in acidic media, with only 234 mV overpotential to achieve 10 mA cm−2, and a Tafel slope of 54.3 mV dec−1. This strategy of porous structure of MoS2 composite rare earth metal organic framework materials provides a novel and effective solution for preparing high performance MoS2 based electrocatalyst.

Kinetics of V5+/V4+ Redox Reaction—Butler-Volmer and Marcus Models

Kinetics of the V5+/V4+ redox reaction on Vulcan XC-72 modified glassy carbon disk electrode is investigated in a three-electrode configuration. Cyclic voltammograms of V5+/V4+ redox couple suggest that the overpotential range for the kinetic analysis is limited to ±300 mV, after excluding V4+/V3+ redox reaction at the negative overpotential and the oxygen evolution reaction at the positive overpotential. The linear sweep-voltammograms (LSVs) are corrected for potential drop due to solution resistance (iR s ), mass-transfer resistance, and most importantly, for the back reaction current. These corrections are imperative to estimate the Tafel slope in the limited range of overpotential for V5+/V4+ redox reaction. The charge-transfer coefficient (α) estimated from the Tafel slope deviates significantly from the expected value of 0.5 for the single electron-transfer reaction. Moreover, the instantaneous slope of the Tafel plot suggests that the α is overpotential dependent. Therefore, Marcus theory of electrochemical kinetics is applied to estimate the α. The reorganization energy (λ) calculated from the Arrhenius plots is in the range of values reported in the literature for the other redox couples.

(Invited) Demystifying Mathematical Modeling of Electrochemical Systems

One of the unique advantages of electrochemistry is that the relationship between thermodynamics and kinetics is quantitative, which is the basis of voltammetry. Mathematical models of electrochemical systems take advantage of this relationship to predict the effect of changing a system property (e.g., concentration, scan rate, or rate constant) with high accuracy. This insight enhances understanding of the link between experimental settings and their resulting effects and further allows optimal values to be determined before the experiment begins. This work introduces the electrochemical theory and process of building one of these models for an example system of ferricyanide undergoing reduction during a linear sweep voltammogram, a common experiment in undergraduate laboratories. A MATLAB code for finite difference implementation of this model is provided, as well as a list of suggested exercises for modifying or extending this code, which could be used a problem set in undergraduate or graduate course work.