Fourier Transformed Alternating Current Voltammetry Research Articles

Combustion Growth of NiFe Layered Double Hydroxide for Efficient and Durable Oxygen Evolution Reaction.

NiFe layered double hydroxide (LDH) with abundant heterostructures represents a state-of-the-art electrocatalyst for the alkaline oxygen evolution reaction (OER). Herein, NiFe LDH/Fe2O3 nanosheet arrays have been fabricated by facile combustion of corrosion-engineered NiFe foam (NFF). The in situ grown, self-supported electrocatalyst exhibited a low overpotential of 248 mV for the OER at 50 mA cm-2, a small Tafel slope of 31 mV dec-1, and excellent durability over 100 h under the industrial benchmarking 500 mA cm-2 current density. A balanced Ni and Fe composition under optimal corrosion and combustion contributed to the desirable electrochemical properties. Comprehensive ex-situ analyses and operando characterizations including Fourier-transformed alternating current voltammetry (FTACV) and in situ Raman demonstrate the beneficial role of modulated interfacial electron transfer, dynamic atomic structural transformation to NiOOH, and the high-valence active metal sites. This study provides a low-cost and easy-to-expand way to synthesize efficient and durable electrocatalysts.

Practical Guide to Large Amplitude Fourier-Transformed Alternating Current Voltammetry-What, How, and Why.

Fourier-transformed alternating current voltammetry (FTacV) is a technique utilizing a combination of a periodic (frequently sinusoidal) oscillation superimposed onto a staircase or linear potential ramp. The advanced utilization of a large amplitude sine wave induces substantial nonlinear current responses. Subsequent filter processing (via Fourier-transformation, band selection, followed by inverse Fourier-transformation) generates a series of harmonics in which rapid electron transfer processes may be separated from non-Faradaic and competing electron transfer processes with slower kinetics. Thus, FTacV enables the isolation of current associated with redox processes under experimental conditions that would not generate meaningful data using direct current voltammetry (dcV). In this study, the enhanced experimental sensitivity and selectivity of FTacV versus dcV are illustrated in measurements that (i) separate the Faradaic current from background current contributions, (ii) use a low (5 μM) concentration of analyte (exemplified with ferrocene), and (iii) enable discrimination of the reversible [Ru(NH3)6]3+/2+ electron-transfer process from the irreversible reduction of oxygen under a standard atmosphere, negating the requirement for inert gas conditions. The simple, homebuilt check-cell described ensures that modern instruments can be checked for their ability to perform valid FTacV experiments. Detailed analysis methods and open-source data sets that accompany this work are intended to facilitate other researchers in the integration of FTacV into their everyday electrochemical methodological toolkit.

High entropy alloy/C nanoparticles derived from polymetallic MOF as promising electrocatalysts for alkaline oxygen evolution reaction

Recently, high entropy alloy (HEA) based materials have been vigorously explored as viable catalysts in water electrolysis for their unique properties. However, the synthesis of efficient and robust high entropy catalysts remains a challenge. Here a facile and scalable approach is reported to synthesize advanced HEA (CoNiCuMnAl)/C nanoparticles from the polymetallic Metal–organic framework (MOF). The novel core-shell nanoarchitectures feature face-centered cubic HEA wrapped in ultra-thin carbon shell. The optimized catalyst (deposited upon Ni foam) boosted alkaline Oxygen evolution reaction (OER) (in 1.0 M KOH) with an ultralow overpotential of 215 mV at 10 mA/cm2 (also by a low Tafel slope of 35.6 mV dec−1). The enhanced performance is closely tied to surface reconstruction (i.e., formation of oxyhydroxide catalytic active species) and the high entropy effect, revealed by Fourier-transformed alternating current voltammetry (FTACV) and in-situ Raman spectrum analysis, in conjunction with Density Functional Theory (DFT) computations. Furthermore, the new design showed excellent long-term OER stability with negligible decay through 30 h testing (under 200 mA cm−2). The present work demonstrates the feasibility and advantage of utilizing highly efficient and durable high entropy alloys for catalyzing electrochemical water splitting process.

Understanding of nitrogen fixation electro catalyzed by molybdenum–iron carbide through the experiment and theory

The electrochemical method is considered being a sustainable alternative to the industrial Haber-Bosch process (150–350 atm, 350–550 °C) because it can produce ammonia (NH3) from nitrogen (N2) and water (H2O) at room temperature and pressure. However, since the N≡N triple bond in N2 is one of the strongest bonds in nature, it requires a more negative potential for N2 reduction, which often leads to violent hydrogen evolution reaction (HER) in aqueous electrolysis systems. Therefore, it is a great challenge for the electrocatalytic N2 reduction reaction (ENRR) to find catalysts that can reduce the energy barrier of N2 fixation and inhibit the HER. Herein, inspired by the Mo–Fe site in the biological nitrogenase, we found that the catalyst containing Mo3Fe3C active material has excellent N2-fixing catalytic performance and can effectively inhibit the HER. At −0.05 V vs RHE, the Faraday efficiency (FE) of ENRR was as high as 27.0%. In addition, we innovatively used the Fourier-transformed alternating current voltammetry (FTACV) to explore the electron transfer process in ENRR, indicating that Mo3Fe3C is more conducive to reducing N2 at low potential. According to density functional theory (DFT) calculations, compared with Mo2C and Fe3C, Mo3Fe3C is more helpful in promoting N2 activation and hydrogenation. Due to the synergistic effect of the Mo–Fe site, N2 hydrogenation needs to overcome a lower energy barrier in potential-determining step (PDS). Our research extends the knowledge into bimetallic active sites in ENRR and provides a new insight for the subsequent synthesis of high selectivity catalysts.

Application of Bayesian Inference in Fourier-Transformed Alternating Current Voltammetry for Electrode Kinetic Mechanism Distinction.

Estimation of parameters of interest in dynamic electrochemical (voltammetric) studies is usually undertaken via heuristic or data optimization comparison of the experimental results with theory based on a model chosen to mimic the experiment. Typically, only single point parameter values are obtained via either of these strategies without error estimates. In this article, Bayesian inference is introduced to Fourier-transformed alternating current voltammetry (FTACV) data analysis to distinguish electrode kinetic mechanisms (reversible or quasi-reversible, Butler-Volmer or Marcus-Hush models) and quantify the errors. Comparisons between experimental and simulated data were conducted across all harmonics using public domain freeware (MECSim).

Fabrication of a novel DNA affinity biosensor based on hybridisation induced current by electrostatic repulsion of silicotungstic acid as a redox indicator

We report on a novel DNA affinity biosensor which utilises the capture of a neutral charged single stranded (ss) morpholino DNA on a gold electrode to trigger an electrostatic repulsion of negatively charged silicotungstate anions and, in turn, enabled detection of the hybridisation of complementary base pairs. The repulsion of the anions, as a redox indicator, is reflected by a decrease in its electrochemical response with increasing target ss-DNA concentration. A theoretical framework for DNA detection by the affinity biosensor is proposed and verified by electrochemical measurements in the presence of the target ss-DNA by either dc cyclic voltammetry or Fourier transformed alternating current voltammetry (FTACV). The optimised conditions for the capture of the target ss-DNA and the electrochemical detection include 1 μM thiolated neutral morpholino oligo-nucleotide probe, hybridisation time of 10 min, 0.25 mM [α-SiW12O40]4-, and 25 mM phosphate buffer. In addition, the use of the 5th harmonic component of the FTACV gave the most sensitive response for the detection of the target ss-DNA. Under these conditions, the DNA affinity biosensor, based on FTACV detection, achieved a minimum detectable concentration of 0.1 pM ss-DNA and a linear concentration range of 0.1–1000 pM. The biosensor also successfully distinguished between some matched and mismatched base pairs.

Controllable Synthesis of Few-Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance.

Two-dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few-layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO2 reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co-existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier-transformed alternating current voltammetry (FTacV) are attributed to CO2 reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO2.- is the rate determining step for bismuth catalysed CO2 reduction.

Controllable Synthesis of Few‐Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance

AbstractTwo‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO2 reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO2 reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO2.− is the rate determining step for bismuth catalysed CO2 reduction.

Fourier transformed alternating current voltammetry in electromaterials research: Direct visualisation of important underlying electron transfer processes

Recent advances in materials science have significantly broadened the range of electrodes available for use in dynamic forms of electrochemistry. In the modern era of dc voltammetry when the kinetic model of electron transfer with coupled chemical reactions was introduced, initial emphasis in theory-experiment comparison was placed on use of the ideal homogenous liquid mercury electrode with significant attention also given to polycrystalline and faceted metal electrodes. Nowadays, there are a plethora of carbon-based electrodes such as glassy carbon, edge and basal plane graphite, boron doped diamond, graphene and carbon nanotubes that may be extremely heterogeneous. These are supplemented by chemical modifications designed for example to improve the efficiency of electrocatalysis. In this review, it is shown that analysis of the higher harmonics available in large amplitude Fourier transformed alternating current voltammetry (FTacV) allows key processes to be detected, that are masked under commonly used dc voltammetric conditions. In particular it is shown how underlying fast electron processes that facilitate carbon dioxide reduction at tin electrodes and oxygen evolution at cobalt based electrodes can be directly detected and analysed for the first time. FTacV also experimentally reveals that structural defects or adatoms can give rise to well-defined higher order ac harmonics suggesting that a fast electron transfer process is associated with the active sites during electrocatalytic oxidation or reduction. Importantly, electron transfer processes often can be evaluated by FTacV in the presence and absence of the electrocatalysis, unlike dc voltammetric methods. The ability to analyse third and higher order ac harmonics that are essentially devoid of background charging current and which allow the electron transfer and catalytic steps to be resolved, presents new opportunities for fundamental advances in understanding complex electrochemical reaction mechanisms taking place at heterogeneous electrodes. Related advantages in studying electron transfer of surface confined metallo-enzymes or proteins in the presence and absence of their catalytically oxidised or reduced biologically relevant substrate partners are also surveyed. Finally, prospects for providing quantitative accounts of complex reactions at highly heterogeneous electrodes by FTacV are considered.

A Tribute to Alan Bond on his 70th Birthday: 50 Years of Electrochemistry

This issue of ChemElectroChem highlights contributions from the friends, colleagues and students of Professor Alan Bond on the occasion of his 70th birthday. As is well illustrated in this special issue, Alan Bond has advanced the theories, experiments and discoveries of electrochemical science for more than half a century. He has contributed almost one thousand research publications, books, book chapters, reports and patents. In this special issue of ChemElectroChem we acknowledge Alan's inspiration, support, guidance, enthusiasm and training that he has provided and continues to provide in the pursuit of electrochemistry.

Experimental Studies of the Capacitive-Potential Relationship for Ionic Liquid – Electrode Interfaces

The electrochemical double layer (EDL) in ionic liquid (IL) solvents plays an important role in myriad energy storage and conversion applications. A clear description of molecular organization within this interfacial region requires a multipronged approach. This presentation will discuss studies of the IL – electrode interface using AC voltammetry, electrochemical impedance spectroscopy (EIS), and vibrational spectroscopy covering slow (re)orientation / movement of ILs within the EDL as it relates to capacitive hysteresis, and make critical comparisons of capacitance vs. potential relationships to theoretical predictions. ILs at an electrified interface have been shown to exhibit capacitive hysteresis depending on the applied potential scan direction (e.g. cathodic or anodic), the extent of which depends on electrode surface material and the measurement technique employed.1-3 Recent work in our group examined several aprotic and protic ILs on metallic, carbon, and semiconducting electrodes demonstrating that capacitive hysteresis is not necessarily a uniform feature of the IL electrified interface. Our studies use large amplitude Fourier transformed alternating current (FT-AC) voltammetry, which demonstrates little (<10 %) hysteresis in the resulting capacitance vs. potential curve respective to the electrochemical potential scan direction. This highlights the benefits of utilizing large amplitude FT-AC voltammetry to probe capacitive currents in ILs. Additional work employs vibrational spectroscopy to study the evolution of the IL EDL under an applied potential. This data provides a vantage point to discuss capacitive hysteresis and how it could relate to molecular (re)orientation in ILs. Our preliminary data show that the IL vibrational profile shows small changes when responding to a potential step of 2 V within the EDL potential window. However, the vibrational profile exhibits noticeable hysteresis in IR peak intensities when undergoing positive- and negative-going applied potential scan directions further demonstrating the slow response times in ILs. It has been suggested that slow (re)orientation of ILs within the EDL could be the mechanism behind the observed hysteresis and that these processes are likely a common feature of the IL – electrode interface.4-5 Depending on the electrochemical technique employed the effective ‘scan rate’ can vary from less than one minute (e.g. FT-AC voltammetry) to several hours (e.g. EIS) when acquiring capacitance data over a range of potentials. Our work using broadband EIS to study the 1-ethyl-3-methylimidazolium tris(pentafluoroethyl)-trifluorophosphate – polycrystalline gold interface demonstrates over a 2 V window that capacitive hysteresis is absent based on several potential scan directions employed compared to Au(111) which exhibits this phenomenon.1 Further this work spanning from 1 MHz to 0.01 Hz suggests the slow process (visible in the complex capacitance plane plot as an arc in the low frequency region) is also absent on the polycrystalline gold electrode compared to the Au(111) single-crystal surface.1 Our work with large amplitude FT-AC voltammetry suggests three possible scenarios to explain contradictions with previous reports: (1) large amplitude FT-AC voltammetry scans the potential window cycle fast enough (~100 mV s-1) relative to slow movement of IL EDL ions to not capture any hysteresis processes, (2) the large perturbation amplitude employed overcomes the energetic barrier for interfacial IL ion movement to exhibit hysteresis processes or (3) capacitive hysteresis and slow (re)orientation are not necessarily common features of the IL – electrode interface. Capacitance curvature in published scientific literature show a wide range of results, even for similar electrochemical systems. Additionally, it has proved challenging to unite theoretical predictions with experimental observations for IL capacitance responses. ILs are concentrated in the sense that they contain no molecular solvent and one viewpoint is they are composed entirely of dissociated ions. However, recent reports challenge this view to suggest they are not well dissociated and behave as dilute electrolytes. Our work examining the 1-butyl-3-methylimidazolum tetrafluoroborate – polycrystalline gold interface corroborates the latter viewpoint. Furthermore, our studies of the IL – semiconductor electrode interface demonstrate a capacitance response analogous to dilute aqueous electrolytes at a semiconductor electrode. Specifically, we report relatively featureless, ‘rising’ capacitance curvature that shows minimal dependence on the nature of the IL (i.e. protic vs. aprotic). Capacitance-potential curvature suggests at the ensemble behavior of the EDL but coupling potential control with spectroscopy can provide a powerful method of probing interfacial chemistry. It is anticipated that this presentation will bring to light some basic questions of IL behavior at an electrified interface.

Large-Amplitude Fourier-Transformed AC Voltammetric Study of the Capacitive Electrochemical Behavior of the 1-Butyl-3-methylimidazolium Tetrafluoroborate–Polycrystalline Gold Electrode Interface

In this paper, the capacitive electrochemical behavior of the 1-butyl-3-methylimidazolium tetrafluoroborate (Bmim BF4)–polycrystalline gold electrode interface is reported over the potential range from −0.37 to 0.53 V vs Fc/Fc+ (Fc = ferrocene). Experimental results are generated by analysis of data (RC model) obtained from large-amplitude Fourier-transformed alternating current voltammetry (FT-ACV) over the frequency range of 10 Hz to 1 kHz. Results suggest a parabolic, U-shaped capacitance versus potential relationship, in stark contrast to present ionic liquid (IL) electrochemical double-layer (EDL) theory. The potential range analyzed was carefully selected to be free of Faradaic current and displays minimal hysteresis with respect to the potential scan direction. Over the selected potential window spanning 0.9 V, the capacitance versus potential curve at 9 Hz exhibits a U-shape, with a capacitance minimum of 19.9 ± 1.3 μF cm–2 at 0.13 ± 0.04 V, flanked by maximum values of 21.2 ± 1.3 and 20.8 ± 1.4 μ...

Probing Electrode Heterogeneity Using Fourier-Transformed Alternating Current Voltammetry: Application to a Dual-Electrode Configuration.

Quantitative studies of electron transfer processes at electrode/electrolyte interfaces, originally developed for homogeneous liquid mercury or metallic electrodes, are difficult to adapt to the spatially heterogeneous nanostructured electrode materials that are now commonly used in modern electrochemistry. In this study, the impact of surface heterogeneity on Fourier-transformed alternating current voltammetry (FTACV) has been investigated theoretically under the simplest possible conditions where no overlap of diffusion layers occurs and where numerical simulations based on a 1D diffusion model are sufficient to describe the mass transport problem. Experimental data that meet these requirements can be obtained with the aqueous [Ru(NH3)6]3+/2+ redox process at a dual-electrode system comprised of electrically coupled but well-separated glassy carbon (GC) and boron-doped diamond (BDD) electrodes. Simulated and experimental FTACV data obtained with this electrode configuration, and where distinctly different heterogeneous charge transfer rate constants (k0 values) apply at the individual GC and BDD electrode surfaces, are in excellent agreement. Principally, because of the far greater dependence of the AC current magnitude on k0, it is straightforward with the FTACV method to resolve electrochemical heterogeneities that are ∼1-2 orders of magnitude apart, as applies in the [Ru(NH3)6]3+/2+ dual-electrode configuration experiments, without prior knowledge of the individual kinetic parameters (k01 and k02) or the electrode size ratio (θ1:θ2). In direct current voltammetry, a difference in k0 of >3 orders of magnitude is required to make this distinction.

Analysis of HypD Disulfide Redox Chemistry via Optimization of Fourier Transformed ac Voltammetric Data.

Rapid disulfide bond formation and cleavage is an essential mechanism of life. Using large amplitude Fourier transformed alternating current voltammetry (FTacV) we have measured previously uncharacterized disulfide bond redox chemistry in Escherichia coli HypD. This protein is representative of a class of assembly proteins that play an essential role in the biosynthesis of the active site of [NiFe]-hydrogenases, a family of H2-activating enzymes. Compared to conventional electrochemical methods, the advantages of the FTacV technique are the high resolution of the faradaic signal in the higher order harmonics and the fact that a single electrochemical experiment contains all the data needed to estimate the (very fast) electron transfer rates (both rate constants ≥ 4000 s-1) and quantify the energetics of the cysteine disulfide redox-reaction (reversible potentials for both processes approximately -0.21 ± 0.01 V vs SHE at pH 6). Previously, deriving such data depended on an inefficient manual trial-and-error approach to simulation. As a highly advantageous alternative, we describe herein an automated multiparameter data optimization analysis strategy where the simulated and experimental faradaic current data are compared for both the real and imaginary components in each of the 4th to 12th harmonics after quantifying the charging current data using the time-domain response.

Electrode Material Dependence of the Electron Transfer Kinetics Associated with the [SVW11O40]3−/4− (VV/IV) and [SVW11O40]4−/5− (WVI/V) Processes in Dimethylformamide

In this study, large amplitude Fourier transformed alternating current (FTAC) voltammetry has been used to determine the heterogeneous electron-transfer kinetics (k° and α values) associated with the vanadium [SVW11O40]3−/4− (VV/IV, E°=0.050V vs. Fc/Fc+, where Fc=ferrocene) and tungsten [SVW11O40]4−/5− (WVI/V, E°=−1.530V vs. Fc/Fc+) processes in dimethylformamide containing tetrabutylammonium hexafluorophosphate as the supporting electrolyte. At glassy carbon (GC), platinum (Pt), gold (Au) and boron-doped diamond (BDD), the VV/IV process is kinetically more facile than the WVI/V one. Excellent simulation-experiment fits were achieved for the VV/IV process at all electrode materials, and at a supporting electrolyte concentration of 0.1M, the k° value associated with this process increases in the order BDD<Pt≈Au<GC. By contrast, at all electrode materials except GC, generally poor simulation-experiment fits were achieved for the WVI/V process, preventing the data from being analysed quantitatively by FTAC voltammetry. Changing the concentration of supporting electrolyte from 0.1 to 0.5M has a significant influence on the kinetics, with the k° value increasing at GC and decreasing at Pt, Au and BDD. Overall, the findings indicate that differences in density of states do not fully explain the electrode material dependence of the k° values and that other factors such as surface functional groups (on GC) and the double layer effect need to be taken into consideration.

Electrochemical evidence that pyranopterin redox chemistry controls the catalysis of YedY, a mononuclear Mo enzyme

A long-standing contradiction in the field of mononuclear Mo enzyme research is that small-molecule chemistry on active-site mimic compounds predicts ligand participation in the electron transfer reactions, but biochemical measurements only suggest metal-centered catalytic electron transfer. With the simultaneous measurement of substrate turnover and reversible electron transfer that is provided by Fourier-transformed alternating-current voltammetry, we show that Escherichia coli YedY is a mononuclear Mo enzyme that reconciles this conflict. In YedY, addition of three protons and three electrons to the well-characterized "as-isolated" Mo(V) oxidation state is needed to initiate the catalytic reduction of either dimethyl sulfoxide or trimethylamine N-oxide. Based on comparison with earlier studies and our UV-vis redox titration data, we assign the reversible one-proton and one-electron reduction process centered around +174 mV vs. standard hydrogen electrode at pH 7 to a Mo(V)-to-Mo(IV) conversion but ascribe the two-proton and two-electron transition occurring at negative potential to the organic pyranopterin ligand system. We predict that a dihydro-to-tetrahydro transition is needed to generate the catalytically active state of the enzyme. This is a previously unidentified mechanism, suggested by the structural simplicity of YedY, a protein in which Mo is the only metal site.

A Simultaneous Study of Kinetics and Thermodynamics of Anion Transfer across the Liquid/Liquid Interface by Means of Fourier Transformed Large-Amplitude Square-Wave Voltammetry at Three-Phase Electrode

This paper describes a novel application of Fourier transformed large-amplitude square-wave voltammetry (FT-SWV) in combination with three-phase edge plane pyrolytic graphite (EPPG) electrode to investigate both the kinetics and thermodynamics of anion transfer across the liquid/liquid interface using a conventional three-electrode arrangement. The transfer of anion from aqueous phase to organic phase was electrochemically driven by reversible redox transformation of confined redox probe in the organic phase. The kinetics and thermodynamics of anion transfer were inspected by a so-called "quasi-reversible maximum" (QRM) emerged in the profile of even harmonic components of power spectrum obtained by Fourier transformation (FT) of time-domain total current response and formal potential E(f) of first harmonic voltammogram obtained by application of inverse FT on the power spectrum. Besides, a systematic study of patterns of behavior of a variety of anions at the same concentration and a specific anion at different concentrations on kinetics and thermodynamics and the effect of amplitude ΔE on QRM were also conducted, aiming to optimize the measurement conditions. The investigation mentioned above testified that the ion transfer across the liquid/liquid interface controls the kinetics of overall electrochemical process, regardless of either FT-SWV or traditional SWV investigation. Moreover, either the kinetic probe f(max) or the thermodynamic probe E(f) can be served as a way for analytical applications. Interestingly, a linear relationship between peak currents of the first harmonic components and concentrations of perchlorate anion in the aqueous solutions can be observed, which is somewhat in accordance with a finding obtained by Fourier transformed alternating current voltammetry (FT-ACV) [Bond, A. M.; Duffy, N. W.; Elton, D. M.; Fleming, B. D. Anal. Chem. 2009, 81, 8801-8808]. This may open a new door for analytical detection of a wide spectrum of electrochemically inactive analytes of biological and environmental significance. Compared with traditional SWV, FT-SWV is much simpler and faster in ion transfer kinetics estimation and also provides a new access to thermodynamics evaluation.