Constant Phase Element Research Articles

Double percolation approach for hybrid graphene Nanoplatelet-Carbon black nanocomposites based on electrical impedance Spectroscopy

A double-percolation model for predicting electrical properties in hybrid carbon black (CB)-graphene nanoplatelet (GNP) nanocomposites is proposed. This model is based on DC and EIS measurements. From DC measurements, a non-ohmic behavior is observed for low-filled nanocomposites whereas at high-filled ones, an ohmic behavior is noticed. From EIS analysis, the behavior of the system can be modeled by an equivalent circuit formed by a series of inductance-resistance capacitance (LRC), for contact and intrinsic electrical mechanisms, and resistance–capacitance (RC) elements, for tunneling transport, where the capacitances are substituted by Constant Phase Elements (CPEs) due to the presence of scattering effects. The complex impedance analysis shows a GNP-dominated electrical behavior at a high CB/GNP ratio. At a medium CB/GNP ratio a double percolating network is formed. At a low CB/GNP ratio, the electrical transport is CB-dominated. The proposed model based on the classical percolation theory with a double threshold properly fits the electrical measurements.

Experimental and theoretical insights into Artemisia Stems aqueous extract as a sustainable and eco-friendly corrosion inhibitor for mild steel in 1M HCl environment.

The present research demonstrates an innovative investigation of environmentally friendly mild steel (M-steel) corrosion inhibition using the artemisia stems aqueous extract (ASAEx) as an inhibitor in hydrochloric acid 1M. The standard extraction technique of hydrodistillation was used for producing the aqueous solutions of ASAEx. To assess the ratios of the chemical components, phytochemical screening was used to identify the stems of this plant. We used a variety of methods and techniques in our research on corrosion inhibition, including weight loss measures, surface analysis methods like XPS and SEM/EDS, electrochemical testing like PDP and EIS, as well as computational lead compound evaluation. Maximum inhibitory efficacy was achieved with 400mg/L ASAEx in 1M HCl at 303K, i.e. 90%. The PDP investigation verified the mixed-kind inhibitor status of the ASAEx extract. To describe the surface of M-steel, fitting and synthetic data were used to identify a constant phase element (CPE). SEM surface analysis was also used to detect the ASAEx effect on the surface of M-steel. X-ray photoelectron spectroscopy (XPS) analysis shows the presence of trace molecules of ASAEx on M-steel surface characterizing the bands in Maj-ASAEx (major compound of ASAEx). Density functional theory (DFT) and molecular dynamics simulations (MDs) were used in computational chemistry to clarify the adsorption mechanism and inhibitory impact.

Temperature dependency of impedance, dielectric, and conductivity properties for Si-p/beta-FeSi2-n heterostructures created through facing target sputtering

To connect thermal dependency with Si-p/beta-FeSi2-n heterostructure efficiency, this work explored the impedance characteristics accompanied by dielectric and conductivity properties under different temperatures of 160–400 K. The Nyquist impedance plots for the heterostructures showed a semicircular arc that shrank as the temperature increased. These can be equivalently interpreted as a loop of single resistance paralleled to single constant phase element representing the heterostucture which also paralleled to inductive elements representing the inductive effect, serially connected to electrode resistance. The dielectric properties implied a shift in behavior for the relaxation process since donor-acceptor deionization occurred when the temperatures reached 320 K or higher due to shorter relaxation time and higher thermal dissipation. The conductivity properties indicate that the transport mechanism at 180 K or lower involves a prolonged transitional movement before transitioning into localized hopping at higher temperatures, corresponding to faster carrier movement. The relaxation and activation energy of the heterostructure reveal drastic transition of the energy from a low temperature of 160–240 K to a higher temperature of 320–400 K, where the electrical mechanism of the heterostructures become highly dependent on the temperature likely due to the high carrier density based on unevenly high activation energy.

Disk flower-like structure of PANI Modulated electronic transport dynamics of Sr[formula omitted] ferrite

This study conducted a comprehensive analysis of the low frequency-based electrical characteristics of ferrite composites, exploring the influence of morphology on tunning and optimizing dielectric and conductivity relaxation. Specifically, composites of PANI: Sr CoxZnxFe12−2xO19 in 1:4 ratio by weight, with varying levels of substitution x = 0.0, 0.4, 0.8, 1.2, 1.6, and 2.0 were synthesized using the physical blending method. X-ray diffraction analysis of composites shows the existence of M-type hexagonal and PANI particles, along with some secondary phases in all synthesized samples. The morphology of composites revealed disk flower-like and hexagonal platelet-type structures of PANI and hexagonal ferrite, respectively. Substituting Co–Zn ions induced a non-linear increase in grain size from 0.781 to 1.566 μm, calculated using ImageJ software. The dielectric and electrical properties of composites were examined over the frequency range of 20 Hz to 2 MHz. The replacement of Fe ions with Co–Zn ions resulted in a non-linear variation in conductivity and is maximum for FP3 (1.33 × 10−2 Ω−1m−1) at 2 MHz. The complex impedance spectra deviated from an ideal Debye type and were modeled using an equivalent circuit encompassing resistances of grain boundaries and grains, grain capacitance, and a constant phase element. Modulus and impedance spectra analysis illustrated the contribution of both grain and grain boundaries in their respective relaxations. The simulation of impedance parameters in EIS software elucidated a substantial value of Cg = 290 μF for FP1, which aligned with the large-sized grain observed in FESEM micrographs.

Voltammetry of Constant Phase Elements: Analyzing Scan Rate Effects

Here we introduce a new method for characterizing the constant phase element (CPE) in electrochemical systems using cyclic voltammetry (CV), presenting an alternative to the conventional electrochemical impedance spectroscopy (EIS) approach. While CV is recognized for its diagnostic capabilities in electrochemical analysis, it traditionally encounters difficulties in accurately measuring CPE systems due to a lack of clear linearity with scan rates, unlike capacitors. Our research demonstrates a linear relationship between current and scan rate on a log–log plot, enabling the calculation of <italic>n</italic> and <italic>Y</italic>0 values for CPE from the slopes of these linear relationships. For validation of our method, it is applied to two kinds of capacitors and the results agree with those measured by EIS. Although EIS is known to be accurate in measuring CPE systems, our alternative approach offers a timely and reasonably precise diagnostic tool, balancing between ease of use and accuracy, especially beneficial for preliminary assessments before conducting further in-depth analysis.

Impedance and Dielectric Analysis of Nickel Ferrites: Revealing the Role of the Constant Phase Element and Yttrium Doping

This paper presents the analysis of electrical and dielectric properties of the yttrium-doped nickel ferrite nano-powders synthesized using the co-precipitation method. Impedance and dielectric measurements have been carried out as a function of frequency at different temperatures from 200 to 25 °C in the range of 0.1 kHz–1 MHz. In order to investigate the conduction mechanism and highlight the role of yttrium doping in different concentrations, impedance spectroscopy was employed. The obtained data were analyzed in terms of equivalent circuits made of resistor and capacitor components describing the contributions from different electrical active regions in a material. Further, this study highlights the importance of a single constant phase element (CPE) in the description of dispersion behavior of the impedance response of the investigated samples in the given frequency range. The use of this technique enabled the characterization of grain and grain boundaries contribution in overall conductivity mechanism. The dielectric dispersion nature of all investigated materials is reflected in this study. Very high values of the real part of permittivity at low frequencies are assigned to space-charge polarization. The dependence of the real part of dielectric permittivity values of the yttrium content was also discussed. Doping with yttrium in different concentrations that reflects in different electric and dielectric responses is concluded in this study. The greatest change is noticed for the sample with the minimum dopant content for a x = 0.05 atomic percent share of yttrium. To reveal the potential role of more than one ion contribution to the overall relaxation process in investigated compounds, a modified Debye’s equation was utilized.

Rapid time-domain simulation of fractional capacitors with SPICE

Fractional capacitors, commonly called constant-phase elements or CPEs, are used in modeling and control applications, for example, for rechargeable batteries. Unfortunately, they are not natively supported in the well-used circuit simulator SPICE. This manuscript presents and demonstrates a modeling approach that allows users to incorporate these elements in circuits and model the response in the time domain. The novelty is that we implement for the first time a particular configuration of RC elements in parallel in a Foster-type network with SPICE in order to simulate a constant-phase element across a defined frequency range. We demonstrate that the circuit produces the required impedance spectrum in the frequency domain, and shows a power-law voltage response to a step change in current in the time domain, consistent with theory, and is able to reproduce the experimental voltage response to a complicated current profile in the time domain. The error depends on the chosen frequency limits and the number of RC branches, in addition to very small SPICE numerical errors. We are able to define an optimum circuit description that minimizes error while maintaining a short computation time. The scientific value is that the work permits rapid and accurate evaluation of the response of CPEs in the time domain, faster than other methods, using open source tools.

Electrical characterization of interfacial transition zone in concrete during freeze-thaw process

The interfacial transition zones (ITZs) between aggregates and mortar are weak regions of concrete, which are more critical to the frost resistance of concrete due to a larger localized water-to-cement ratio. The effective conductivity of the ITZ was determined by separating electrical parameters in the AC impedance spectrum (ACIS), and the changes in microstructure within ITZ during the freeze-thaw (F-T) process were studied. First, based on the microstructure characteristics of Cement-Based Materials (CBMs), a circuit model of conduction path of conductive unit was established. The microstructure changes of CBMs during the F-T process (−50 °C to 10 °C) were characterized using ion conduction activation energy and the impedance of the constant phase element (CPE), which were classified into different regions in the F-T process. Circuit simplification and impedance parameters of CPE in different regions were analyzed. Subsequently, the composite effective conductivity formula (CECF) was proposed to separate the ITZ conductivity from the mortar or concrete conductivity. The relative change rate of conductivity during F-T process was used to define the freezing degree of CBMs, and the freezing degree of ITZ was calculated by CECF. The results indicated that in the F-T process of mortar and concrete, despite the volume fractions of ITZ being only 15.8% and 10.6%, its contribution to the freezing degree of the overall sample was 66%−70% and 57%−60%, respectively. This method can quantitatively characterize the effect of ITZ during F-T process and help understand the damage mechanism of F-T process.

Nature inspired algorithm based design of near ideal fractional order low pass Chebyshev filters and their realization using OTAs and CCII

Fractional order filters offer greater freedom of design and a precise control over stopband attenuation in electronic circuits and systems. This paper presents the design of a fractional order low pass Chebyshev filter (FOLCF) that achieves near-ideal response characteristics. The methodology introduced utilizes metaheuristic optimization methods, including particle swarm optimization, firefly algorithm, and grey wolf optimization. These techniques are employed to precisely adjust the filter coefficients for the orders (1+α), (2+α), and (3+α). The adjustment is carried out by comparing the desired behaviour of the FOLCF with generalized fractional order low pass transfer functions. Throughout these instances, the parameter α is varied within the range of (0, 1). The designed filters are then tested and compared on the basis of various factors. Simulation results demonstrate that the designed filters closely follow the behaviour of an ideal Chebyshev filter with maximum passband and stopband magnitude errors being −31.93 dB and −52.74 dB respectively for (1+α) order filters. These values for (2+α) and (3+α) order FOLCF have been observed to be −30.04 dB and −55.91 dB; −17.72 dB and −49.52 dB respectively. Furthermore, it has been observed that the proposed work outperforms existing state-of-the-art approaches in various aspects, including magnitude error, stopband attenuation, and cut-off frequency. The stability of the designed filters has been verified through stability analysis. Additionally, practical feasibility of the proposed FOLCF is demonstrated through SPICE simulations for α = [0.2,0.5,0.8] using second generation current conveyor (CCII) and operational transconductance amplifier (OTA) based topologies while approximating the constant phase element using fifth order continued fraction expansion. The SPICE implementations closely follow the behaviour of ideal filter with −48.67 dB and −62.8 dB as mean square errors for CCII and OTA circuits respectively, showcasing the proposed filters' superiority and practical applicability in advanced electronic design.

Thermogravimetric and temperature-dependent electrical investigations of Pr3+ doped multi-component silicate glasses for microelectronic technology

Multi-component silicate glasses doped with 0, 0.5, 1, and 1.5 mol% of praseodymium (Pr3+) were synthesized by the sol–gel method. Thermal analysis of the glasses, evinced a high working temperature of 351 °C and Hruby coefficient, K H = 1.415 in the highly doped system, corroborating the effective role of Pr3+ ions in endowing superior thermal stability to the glass. Broadband dielectric spectroscopy was applied to study the temperature-dependent electrical behavior of the glasses for their suitability as electrodes and solid electrolyte materials in batteries. A high dielectric constant of 4797 was evidenced at 1 kHz when recorded at 473 K. The AC conductivity of the glass doped with 1 mol% was observed to be the highest with 94.8 × 10−5 S cm−1 at 10 MHz and 473 K. Jonscher’s power law exponent decreased with temperature, attributing the conducting mechanism to the Correlated Barrier Hopping (CBH) model. The Nyquist impedance spectra demonstrated a depressed semicircle with a spur at the low-frequency end, validating the non-Debye relaxation in the glasses. The equivalent circuitry of the plot predicted parallel combinations of resistor and constant phase elements which reflects a Warburg diffusion and capacitive approach. Bode’s phasor diagram confirmed the capacitive nature by a phase angle of −90° in all the glasses. While a uniform increase in dielectric constant and conductivity was observed up to 1 mol% of Pr3+, a sharp decline in the electrical phenomenon was observed with 1.5 mol% of Pr3+, due to the possible blockade of the hopping of charge carriers by the largely quantified dopant ions. Extracting a high dielectric constant, and ionic conductivity at high frequencies, with an optimal dopant concentration of 1 mol% Pr3+, the composite glasses could be considered for their potential use in integrated microcomponent storage devices as cathode and solid electrolyte materials.

Electrochromic nickel-oxide-based thin films in KOH electrolyte: Ionic and electronic effects elucidated by impedance spectroscopy

Ni-oxide-based thin films, prepared by sputtering, are investigated by electrochemical impedance spectroscopy in a KOH electrolyte. The films are electrochromic, and an increase of the applied potential leads to a variation from a bleached to a colored state as a result of proton (H+) extraction together with extraction of electrons from the valence band. The complex frequency-dependent impedance displays different features in different potential ranges. At low potentials, where coloration is weak, the spectra give evidence for a constant-phase element in parallel with a leak resistance. At intermediate and high potentials, the impedance spectra indicate the presence of a diffusion process, and a model for anomalous diffusion gives excellent fits to the spectra except in a crossover region. The applicability of this model in a significant part of the studied potential range suggests the presence of a multiple-trapping process for the ions. The potential dependence of the chemical capacitance, as well as the diffusion coefficient of un-trapped ions, are analyzed. The electrochemical density-of-states of the charge-compensating electrons gives indications of the top of the valence band and of a band tail extending into the band gap. Diffusion coefficients are found to increase steeply in the crossover potential region to very high values at high potentials. These features are discussed and related to the electrochromic behavior of Ni-oxide-based thin films.

KINETICS OF CATHODIC HYDROGEN EVOLUTION ON MOLYBDENUM DISILICIDE IN ACID SULPHATE MEDIA

The kinetics and mechanism of hydrogen evolution on the MoSi2 electrode in x M H2SO4 + (0.5 - x) M Na2SO4 (x = 0.50; 0.35; 0.20) solutions have been studied. The cathodic polarization curves of MoSi2 in the studied solutions are characterized by Tafel region with a slope of (-0.070)±0.002 V. The reaction order of the cathodic process with respect to hydrogen ions at the potentials of Tafel region is ~1.0; the derivative of the electrode potential with a change in electrolyte acidity is ~0.072 V. The impedance spectra of the MoSi2 electrode in the studied potential range have the shape of a semicircle located in the capacitive half-plane, with the centre in the region of positive values of the imaginary impedance component; in the region of the highest frequencies, a short straight section is recorded on the impedance plots, indicating the presence of pores in the surface layer of the electrode. To describe the hydrogen evolution reaction on MoSi2, we used an equivalent electrical circuit, the Faraday impedance of which consists of series-connected charge transfer resistance (R1) and a parallel R2C2Zd-chain responsible for the adsorption of atomic hydrogen on the surface and its diffusion into the depth of the electrode material. The equivalent circuit also includes the solution resistance (Rs) and the double layer capacitance impedance, which is modeled by the constant phase element CPE1. It is shown that the hydrogen evolution reaction on molybdenum disilicide in a sulphuric acid electrolyte proceeds along the discharge - recombination route with a quasi-equilibrium discharge stage when the Temkin logarithmic isotherm for adsorbed atomic hydrogen is fulfilled. The hydrogen evolution reaction is complicated by hydrogen absorption proceeding in the mode of solid-phase diffusion kinetics.

FT-Raman spectroscopic and electrical investigations of RE3+ doped multi-functional silicate glasses for cathode plating and integrated microelectronic technology

Lanthanide-doped silicate glasses were subjected to structural and temperature-dependent electrical investigations to validate their multi-functionality in the integrated microelectronic industries. Raman-active vibrations around 920 cm−1 and 1330 cm−1 confirmed the silicate and phosphate tetrahedra respectively. The Er3+ doped glass demonstrated the highest dielectric constant of 9.21 × 105, while Sm3+ infused glass exhibited the lowest dielectric constant of 4.37 × 104 at 0.1 Hz and 473 K. The Sm3+ doped glasses are prospective for plating on copper chips in printed circuit boards that necessitate low dielectric constants to minimize propagation delay. The equivalent circuitry fitted for the Nyquist impedance plot of Er3+ doped glass constituted parallel combinations of a resistor and Constant Phase Element (CPE), in series with Warburg diffusion impedance. The CPE approaching a capacitive nature in the Er3+ doped glass could be suggested for cathode plating in batteries, and fabrication of multi-layer dielectric substrates in radio frequency condensers.

Novel mixed heterovalent (Mo/Co)Ox-zerovalent Cu system as bi-functional electrocatalyst for overall water splitting

A novel hybrid ternary metallic electrocatalyst of amorphous Mo/Co oxides and crystallized Cu metal was deposited over Ni foam using a one-pot, simple, and scalable solvothermal technique. The chemical structure of the prepared ternary electrocatalyst was systematically characterized and confirmed via XRD, FTIR, EDS, and XPS analysis techniques. FESEM images of (Mo/Co)Ox–Cu@NF display the formation of 3D hierarchical structure with a particle size range of 3–5 µm. The developed (Mo/Co)Ox–Cu@NF ternary electrocatalyst exhibits the maximum activity with 188 mV and 410 mV overpotentials at 50 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Electrochemical impedance spectroscopy (EIS) results for the (Mo/Co)Ox–Cu@NF sample demonstrate the minimum charge transfer resistance (Rct) and maximum constant phase element (CPE) values. A two-electrode cell based on the ternary electrocatalyst just needs a voltage of about 1.86 V at 50 mA cm−2 for overall water splitting (OWS). The electrocatalyst shows satisfactory durability during the OWS for 24 h at 10 mA cm−2 with an increase of only 33 mV in the cell potential.

An adaptive fractional-order extended Kalman filtering approach for estimating state of charge of lithium-ion batteries

This paper proposes an adaptive fractional-order extended Kalman filter (AFEKF) approach for estimating state of charge (SOC) of a lithium-ion battery. Firstly, the fractional-order model (FOM) with a constant phase element module is established to describe the fractional-order characteristics inside a lithium-ion battery. Then, the augmented state equation including SOC is built by using the augmented vector approach. To avoid the calculation of the coefficients of the measurement equation, a linear adaptive integer-order Kalman filter is adopted. The AFEKF approach with the Sage-Husa filter is proposed to update the unknown parameters and unknown noises on the basis of augmented state equations. Finally, the comparison experiment between AFEKF approach and adaptive integer-order extended Kalman filter (AIEKF) approach is designed. Besides, the applicability of the AFEKF approach under different working conditions is also tested. The experimental tests indicate that the SOC estimation accuracy of the AFEKF approach is higher than that of the AIEKF approach, and the AFEKF approach can also be applicable in complex environments.

Mechanistic insights into the corrosion inhibition of mild steel by eco-benign Asphodelus Tenuifolius aerial extract in acidic environment: Electrochemical and computational analysis

This study explores the novel application of Asphodelus Tenuifolius aerial extract (ATAE) as a corrosion inhibitor for mild steel in a 0.5 M HCl acidic environment. By utilizing techniques such as electrochemical measurements, gravimetric analysis, SEM, and CA assessments, the inhibitory potential of ATAE has been comprehensively evaluated. The results revealed a concentration-dependent enhancement in corrosion resistance, classifying ATAE as a mixed-type inhibitor by measuring the anodic (βa) and cathodic (βc) polarization slope values of 108.89 and −129.33 mV/dec. The peak inhibition efficiency was observed at 250 ppm, reaching an impressive IE% of 94.40 % at 298 K (Kelvin). The electrochemical analysis demonstrated a significant increase in charge transfer resistance (Rct) and polarization resistance (Rp) values, coupled with a decrease in Constant Phase Element (CPE.Yo) value to 162.94 μF, indicating heightened corrosion inhibition potential. Additionally, Theoretical calculations emphasized a strong interaction between ATAE and mild steel surface, characterized by a low energy gap (ΔE), indicating excellent anti-corrosion abilities at the micro-level. This study positions ATAE as a promising corrosion inhibitor, offering insights for further research in corrosion prevention strategies using a sustainable corrosion inhibitor.

Detection of water content in tomato stems by electrical impedance spectroscopy: Preliminary study

Tomatoes lack drought-resistant genes, rendering seedlings susceptible to slow growth and death during drought stress. To gauge the water deficit in tomato plants, the electrical impedance spectra of tomato seedlings were measured at distinct water content levels (pristine, 92%, 91%, 90%, and 89%). These measurements tracked changes in water state, microstructure, and shear stress during water loss. The results revealed that impedance values and the real and imaginary parts decreased with increasing frequency, displaying a negative correlation with water content. Notably, the absolute mid-frequency slope (F2) exhibited an R2 of 0.9996, serving as an effective variable to characterize water content changes in tomato seedlings. Drought-induced alterations in stem cells shifted the seedling's equivalent circuit from the improved Hayden model to two parallel constant phase element (CPE) models. Concurrently, as water was lost, the proportion of free water diminished while water-binding capacity increased. This shift was accompanied by the wilting of cells, which reduced tissue rigidity, weakened ion conductivity, and altered the ratio of free water to bound water from 36.22 to 5.43. The pot experiment revealed that the F2 could be utilized to monitor the situation of short and sharp water shortages; however, additional research is required to explore its potential for long-term water monitoring. These findings establish a solid theoretical basis for monitoring water content in tomato plants in field settings.

Modeling cyclic voltammetry responses of porous electrodes: An approach incorporating faradaic and non-faradaic contributions through porous model and constant phase element

Porous electrodes, with their complex structure and finite diffusion domain, present a challenge in interpreting cyclic voltammetry (CV) responses using conventional methods. Previous efforts have aimed to mitigate the impact of electrode structure on CV responses, employing various experimental and numerical strategies. In this study, a versatile porous model using the Bruggeman correlation to account for porosity and tortuosity effects on CV responses that can accurately simulate CV responses in porous electrodes without relying on pore-scale information was proposed and validated. This model was further extended to incorporate the effects of non-Faradaic currents. A thorough investigation of various parameters, including electrode thickness, porosity, Bruggeman exponent, reaction rate constant, and electrochemically active surface area, was conducted. This approach simplifies the required geometrical parameters to surface-to-volume ratio, electrode thickness, porosity, and Bruggeman exponent, reducing the reliance on pore-specific characteristics. This study presents an alternative approach to simulate CV responses in porous electrodes without the need for pore-scale information to strike a balance between complexity and practicality. The insights gained not only facilitate simpler modeling of porous electrodes but also enhance our understanding and characterization of CV responses in these systems. This knowledge is crucial for advancing the performance of electrochemical energy devices and marks a significant step towards a cleaner energy society.

Is Unsupervised Dimensionality Reduction Sufficient to Decode the Complexities of Electrochemical Impedance Spectra?

AbstractAs electrochemical research undergoes rapid technological progression, the acquisition of substantial amounts of electrochemical impedance spectra (EIS) becomes increasingly feasible. Yet, this advancement introduces intricate challenges in data processing, automation, and interpretation. This paper delves into the sufficiency of unsupervised machine learning (ML) and in particular dimensionality reduction methods in decoding EIS complexities, examining its strengths, limitations, and potential pathways for optimization. As we navigated the intricacies of non‐linear dimensionality reduction, spotlighting t‐distributed stochastic neighbor embedding (t‐SNE) and uniform manifold approximation and projection (UMAP) algorithms, a pattern emerged: these techniques excel at categorizing divergent impedance spectra but show limitations when faced with analogous circuit configurations, especially those substituting a capacitor with a constant phase element. This observation not only underscores a limitation but also accentuates that unsupervised ML approaches, alone, may not fully unravel the nuances of EIS spectra. In the concluding section of our manuscript, we discuss the implications of this finding from a practical standpoint, particularly for electrochemists seeking to apply these methods in their work.

Electrocatalytic behavior of Ni–Mo alloy electrodeposited from deep eutectic solvents-assisted plating baths: electrochemical impedance spectroscopy study

The electrocatalytic behavior of electrodeposited Ni and Ni–Mo alloy coatings in the hydrogen evolution reaction in a 1 M NaOH aqueous solution was investigated by means of the electrochemical impedance spectroscopy method. The electrochemical deposition of electrocatalytic coatings was carried out using electrolytes based on deep eutectic solvents (eutectic mixtures of choline chloride with ethylene glycol or urea). To simulate the recorded Nyquist plots reflecting the electrocatalytic performance of deposited coatings, a modified Armstrong-Henderson equivalent circuit was employed, which accounts for the involvement of adsorbed intermediates in the reaction. The equivalent circuit included three polarization resistances and three constant phase elements, allowing for the consideration of the localization of the electrochemical process on different surface microdomains. It was found that the electrocatalytic activity of nickel coatings deposited from deep eutectic solvents exceeded the activity of nickel fabricated in an aqueous electrolyte. The increase in molybdenum content in the coating was shown to enhance electrocatalytic activity. It was established that the main reasons for improving the electrocatalytic properties of the Ni–Mo alloy coatings are structural-morphological factors (increase in the degree of microheterogeneity of the surface and the development of the surface area available for electrochemical reaction) and the formation of a favorable electronic structure of the metal, leading to the acceleration of the rate-determining Volmer step.