Electrochemical Impedance Data Research Articles

Durability analysis of polymer electrolyte membrane fuel Cell's gas diffusion layer based on distribution relaxation time analysis: Influence of the presence or absence of a micro-porous layer

The U.S. Department of Energy accelerated stress test carbon protocol emphasizes improving the durability of both the catalyst layer and the micro-porous layer (MPL) carbon support. This underscores the need for research focused solely on the degradation of the Gas Diffusion Layer (GDL). Traditionally, electrochemical impedance spectroscopy impedance data used to analyze resistance due to GDL durability has been interpreted through equivalent circuit models. However, this method simplifies simultaneous response and multiple models for the same data, which reduces the objectivity of the analysis. Therefore, this study analyzed the durability characteristics of GDLs with and without MPLs using distribution of relaxation times, a method less prone to subjectivity. In short, the results showed that substrates without MPL are more susceptible to performance degradation and loss, and highlighted the emergence of Warburg resistance due to limited diffusion under harsh environmental conditions.

Isothermal Microcalorimetry Analysis of Li/β-MnO2 Discharge

Despite widespread use over several decades, the lithium/manganese dioxide (Li/MnO2) discharge mechanism is not completely understood owing to the structural complexity of the material. However, an improved understanding could lead to broader adoption as a primary and even secondary cathode material. Here, we examine the discharge of single-phase β-MnO2 using isothermal microcalorimetry for the first time. Equilibrium voltage and entropy changes are characterized over the entire discharge range and used to rationalize the results. These measurements are supplemented by electrochemical impedance and X-ray diffraction data that give the clearest picture of the β-MnO2 lithiation process to date. We find that the first half of discharge is dominated by a two-phase reaction to form Li0.5MnO2 followed by single-phase insertion to a composition of Li1.0MnO2, which confirms prior first-principles calculations. The tetragonal β-MnO2 lattice undergoes asymmetric expansion from Jahn-Teller distorted Mn3+ to form an orthorhombic LiMnO2 phase which retains the 1 × 1 tunnel structure. Microcalorimetry results suggest the presence of parasitic reactions occurring during the second half of discharge, which could arise from decomposition of electrolyte or release and reaction of residual water retained in the structure.

Investigating the Influence of PbS Quantum Dot-Decorated TiO2 Photoanode Thickness on Photoelectrochemical Hydrogen Production Performance.

To maximize the photoelectrochemical (PEC) hydrogen production performance of quantum dot (QD)-decorated photoelectrodes, it is crucial to prioritize the optimization of electrode's structure, including thickness and porosity. In this study, we prepare PbS QD-decorated mesoporous TiO2 photoanodes for PEC hydrogen production, and systematically investigate the influence of the photoanode thickness on optical properties and PEC performances. As the thickness of photoanodes increases from 6.4 µm to 16.3 µm, the light absorption capability is enhanced across the entire visible and near-infrared (IR) spectrum due to the improved loading of PbS QDs. However, the photocurrent density is optimized for the 11.9 µm thick photoanode (15.19 mA/cm2), compared to the 6.4 µm thick (10.80 mA/cm2) and 16.3 µm thick photoanodes (11.93 mA/cm2). This optimization is attributed to the trade-off between the light absorption capability and the efficient mass transfer of the electrolyte as the photoanode thickness increases, which is confirmed by the lowest charge transfer resistance (Rct) evaluated from the electrochemical impedance data.

Enhancing solar energy conversion with nickel/iron oxyhydroxide-modified hematite photoanodes: The role of Fe species in alkaline electrolyte

Hematite photoanodes have shown potential for use in practical applications of photoelectrochemical (PEC) water splitting cells due to their abundance and stability, yet their efficiency needs to be improved. To optimize photoanode performance, co-catalysts such as amorphous nickel/iron oxyhydroxide layers are often deposited on the surface of hematite to enhance activity by catalyzing oxygen evolution. Recent studies have shown that the role of oxyhydroxide layers in changing PEC activity can vary depending on factors such as film morphology, co-catalyst layer thickness, and electrolyte composition. In this study, we investigate the effect of NiOOH and (Ni,Fe)OOH layers on the PEC activity of electrodeposited nanostructured hematite films. Our analysis of charge transfer and recombination rate constants determined from chronoamperometry and electrochemical impedance data suggests that the coatings' role is purely passivating, which is crucial for discontinuous electrodeposited films. Importantly, we show that the passivating properties of these coatings are enhanced by the presence of ppm concentrations of Fe in the electrolyte. We believe that our findings will be useful for further development of hematite photoanodes.

Measurement model for analysis of electrochemical impedance data

Measurement model for analysis of electrochemical impedance data

Mechanism for corrosion inhibition of pure iron in 1 M HCl by Rauiella Fujisana: Experimental, GC[sbnd]MS, DFT, VASP and solid[sbnd]liquid modeling studies

Extracts of the green plant Rauiella Fujisana (Paris) Reimers (RFEs) exhibit excellent inhibition of pure iron corrosion in a 1 M HCl corrosive solution. The active ingredients 2-ethyl-3,5-dimethylpyrazine (EDMP) and 2,5-di-tert-butylphenol (DTBP) were monitored with FT-IR and GCMS, and the corrosion inhibition provided by the two components for pure iron was confirmed by quantum chemical and adsorption simulations. The experimental results showed that the efficiency for RFE inhibition of iron corrosion in 1 M HCl reached 96.19%, as determined with the weight loss method; SEM/EDS, 3D metal surface morphology, and XPS studies showed that the RFE produced a film layer that inhibited the corrosion of pure iron. Adsorption curve fitting, electrochemical impedance data, polarization curves, and the Bockris-Devanathan-Müller (BDM) solidliquid model indicated that the active ingredient in the RFE was physically adsorbed via van der Waals forces and quickly migrated to the adsorption site and replaced the water in the Helmholtz layer on the pure iron surface, which inhibited charge transfer and prevented corrosion.

Ni-YSZ Electrode Stability in Solid Oxide Electrolysis Cells Operated in 90-98% Steam

Ni-YSZ electrode-supported SOECs were tested at 750 and 800oC using extremely high steam concentrations, 90, 95, and 98%. The performance was compared to SOECs tested in 50% steam with 50% hydrogen. Multiple cells were tested simultaneously with several repeats, all cells configured into a single furnace for each test to ensure a reasonable side-by-side comparison and results reproducibility. The Ni/YSZ electrodes was reduced by hydrogen in situ at each operating temperature and then 50-98% steam was added. Cells were tested at a fixed current or voltage for 1000-3000 hours. The electrochemical impedance data was periodically collected followed by the DRT analyses to identify any changes in polarization losses in time. Minimal to no changes in cell performance in time was observed when compared cell operation in 90+% steam vs 50% steam. Slightly higher degradation was seen for cells tested at 800oC vs those tested at 750oC during the initial 500 hours. After the initial break-in period, the degradation rates for all cells in the following >1000 hours remained the same.A separate set of tests was performed to characterize break-in period and to understand how the initial Ni thermal aging at different temperatures affects the time to a pseudo steady-state, i.e., if the Ni aging/conditioning could be used to accelerate the initial degradation and shorten break-in. Symmetrical cells with two Ni-YSZ electrodes on each side of 10 micron YSZ electrolyte were also tested.The extensive SEM/EDS analyses were performed on all cells to quantify the Ni particle size and describe any microstructural changes. The 2-dimensional SEM images were reconstructed into the 3D microstructures to calculate the triple phase boundary density, species transport paths tortuosity, and particle/pore size distribution.

(Keynote) On Interpretation of Impedance Spectroscopy Data

Impedance spectroscopy represents a rich area of science that has been applied to many research disciplines, including those associated with corrosion and corrosion control, energy systems, and biological systems. In laboratory settings, impedance has been used to study the kinetics and mechanisms of electrochemical reactions. Impedance spectroscopy has also been applied in industrial applications to quality control and corrosion monitoring and constitutes the basis of a class of sensors [1].Impedance spectra are easily measured by used of modern instrumentation. The difficulty lies in interpretation of impedance spectra in terms of physically meaningful information. While graphical methods [2], distribution of relaxation times analyses [3], and measurement model analyses [4] can guide model development, interpretation is generally based on use of a deterministic model that describes the physics of the system under study [5]. Such models may be coupled with electrical circuits that account for the double layer formed at the electrified interface and for the electrolyte resistance. The deterministic model approach is often perceived as being much more complicated than use of electrical circuits alone because it requires mathematical expertise.In general, interpretation of the impedance response requires both a quantitative evaluation of the error structure of the impedance measurement and insight into the physics and chemistry of the system under study. Analysis of the error structure yields a standard deviation for the stochastic errors, which can be used to weight subsequent regressions. The error analysis also identifies the range of frequencies that are consistent with the Kramers–Kronig relations and are, therefore, suitable for regression analysis. The physical insight is used to guide the interpretation model development. It should be noted that interpretation models are not unique. The models may suggest other experiments which can be used to reject the proposed model. Greater confidence may be assigned to a model that explains a variety of experimental observations.The objective of this paper is to review our work on interpretation of impedance data, including the identification and quantification of the error structure associated with impedance spectroscopy measurements. The presentation makes use of a program that allows users to access the power of the measurement model concept and to fit custom process models [6].References S. Wang, J. Zhang, O. Gharbi, V. Vivier, M. Gao, and M. E. Orazem, “Electrochemical Impedance Spectroscopy,” Nat. Rev. Methods Primers, 1, 41 (2021), 1-21.M. E. Orazem, and N. Pébère, and B. Tribollet, “Enhanced Graphical Representation of Electrochemical Impedance Data,” J. Electrochem.Soc., 153 (2006), B129-B136.B. A. Boukamp, “Distribution (Function) of Relaxation Times, Successor to Complex Nonlinear Least Squares Analysis of Electrochemical Impedance Spectroscopy?” J. Phys. Energy, 4 (2020), 042001.H. Liao, W. Watson, A. Dizon, B. Tribollet, V. Vivier, and M. E. Orazem, “Physical Properties Obtained from Measurement Model Analysis of Impedance Measurements,” Electrochim. Acta, 354 (2020), 136747.V. Vivier and M. E. Orazem, “Impedance Analysis of Electrochemical Systems,” Chem. Rev., 122 (2022), 11131-11168.W. Watson and M. E. Orazem, EIS: Measurement Model Program, ECSArXiv, 2020, https://ecsarxiv.org/kze9x/.

Generalized Inversion of Electrochemical Impedance Data for Battery Systems

Electrochemical Impedance Spectroscopy (EIS) is a key technique for taking a snapshot of an electrochemical system near equilibrium conditions. Due to the richness of the complex-valued dataset and its simple experimental operation, it is currently being investigated as a test to diagnosis battery health and degradation details. Nevertheless, challenges with use of EIS is in interpreting the measured impedance. Current methods for analysis involving either fitting simplified equivalent circuit models or inverting distribution of relaxation times with a singular basis function. Because of these methods' simplifications, their results sometime fail to capture both the complex and heterogeneous underlying physics.Here, we present a novel algorithm for the inversion of EIS data for battery systems, which generalizes the inversion problem to any given linear equivalent circuit model, allowing for the analysis of complicated electrochemical systems. Importantly, this algorithm provides two clear benefits. First, it allows for the analysis of both bounded and unbounded processes, something quite common to battery systems and is vital in understanding non-obvious relationships in degraded batteries. Second, the distribution of independent processes, which can correspond to different physical phenomena, are also inverted by this algorithm. These distributions contain vital features in the identification and prediction of battery state-of-health. Overall, this tool will be indispensable in the analysis of degradation extent over battery aging, and provide an algorithmic framework for interpreting EIS measurements of complicated electrochemical systems.

Electrochemical behavior of additively manufactured patterned titanium alloys under simulated normal, inflammatory, and severe inflammatory conditions

The electrochemical behavior of a biomaterial surface in local conditions is a significant factor affecting the success of the implant placement. This is of a particular importance of metallic biomaterials which can undergo oxidation, corrosion and subsequent degradation. This study reports new data on the electrochemical behavior of additively manufactured (AM) patterned titanium alloys, analyzed after 1 and 12 h immersion in three different media mimicking normal, inflammatory and severe inflammatory conditions. Polarization study showed that corrosion resistance increases with increasing immersion time in all cases. It was found that in inflammatory condition a destructive effect on the passive layer's resistance was triggered by H2O2 whereas in severe inflammatory condition, albumin, lactate, and H2O2 all have a synergistic effect towards decreasing the corrosion resistance of patterned titanium layers. Electrochemical impedance data suggests that in the severe inflammatory condition the charged albumins are attracting to the localized pitting areas, changing diffusion transport of corrosive species at the interface of the metal/passive layer. The electrochemical tests also proven that laser-assisted patterned titanium alloys surfaces have an improved corrosion resistance in simulated solutions compared to untreated titanium of the same composition. It is suggested that new surface topography and wettability are also positive factors contributing to this improved corrosion performance in patterned specimens.

Electrochemical performances investigation of bismuth selenide Bi2Se3 layer for capacitors application

Bismuth selenide (Bi2Se3) layers have proved useful as electrode materials for capacitors. This material was prepared via electrodeposition method with the different deposition time and characterized by X-ray diffraction, Scanning electron microscopy, and Energy dispersive X-ray spectroscopy techniques. It is found that the films of Bi2Se3 provoke the formation of a biphasic, orthorhombic and rhombohedral crystal structure, with uniform spherical particles. Furthermore, the electrochemical properties of Bi2Se3 were investigated using cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy in 1 M HNO3 aqueous electrolyte. Galvanostatic charge-discharge measurements deliver a specific capacitance of 49.7 mF g−1 which leads to a specific energy density of 0.0034 Wh kg−1 and specific power of up to 5 kW kg−1 at a current of 0.01 A g−1. The electrochemical impedance data were fitted with an equivalent circuit containing a constant phase element and fitted parameters were calculated.

One-Step High-Temperature Electrodeposition of Fe-Based Films as Efficient Water Oxidation Catalysts

Electrolysis of water to produce hydrogen requires an efficient catalyst preferably made of cheap and abundant metal ions for the improved water oxidation reaction. An Fe-based film has been deposited in a single step by electrochemical deposition at temperatures higher than the room temperature. Until now, the electrodeposition of iron oxide has been carried out at 298 K or at lower temperatures under a controlled atmosphere to prohibit atmospheric oxidation of Fe2+ of the iron precursor. A metal inorganic complex, ferrocene, and non-aqueous electrolyte medium propylene carbonate have been used to achieve electrodeposition of iron oxide without the need of any inert or controlled atmosphere. At 298 K, the amorphous film was formed, whereas at 313 K and at higher temperatures, the hematite film was grown, as confirmed by X-ray diffraction. The transformation of iron of the ferrocene into a higher oxidation state under the experimental conditions used was further confirmed by X-ray photoelectron spectroscopy, ultraviolet-visible, and electron paramagnetic resonance spectroscopic methods. The films deposited at 313 K showed the best performance for water oxidation with remarkable long-term electrocatalytic stability and an impressive turnover frequency of 0.028 s-1 which was 4.5 times higher than that of films deposited at 298 K (0.006 s-1). The observed overpotential to achieve a current density of 10 mA cm-2 was found to be 100 mV less for the film deposited at 313 K compared to room-temperature-derived films under similar experimental conditions. Furthermore, electrochemical impedance data revealed that films obtained at 313 K have the least charge transfer resistance (114 Ω) among all, supporting the most efficient electron transport in the film. To the best of our knowledge, this is the first-ever report where the crystalline iron-based film has been shown to be electrodeposited without any post-deposition additional treatment for alkaline oxygen evolution reaction application.

Application of self-adapting regularization, machine learning tools and limits in Levenberg–Marquardt algorithm to solve CNLS problem

The Electrochemical Spectroscopy Impedance (EIS) data are usually analyzed by solving different Complex Nonlinear Least Squares (CNLS) problems. These problems are generally solved by using the Levenberg–Marquardt algorithm (LMA), which is a self-adaptive regularization technique that applies the first derivatives values stored in the Jacobian matrix. The LMA convergence can be amplified by the application of both the limit tactics and the exact first derivative values. These exact values can be obtained by using the automatic differentiation (AD) algorithm embedded in PyTorch, which is an open-source machine learning framework. However, the joint application of AD, self-adapting regularization, and the limits has not been reported as a part of CNLS strategy yet.Herein, we have designed and developed a new CNLS strategy that applies the limits tactics, AD, and self-adapting regularization. Also, we claim that the new strategy can be straightforwardly employed as the exact first derivative values can be obtained by EEC and AD, which simplifies developing tasks. The results in this work clearly reveal that the LMA convergence is boosted when using the exact Jacobian matrix constructed by both the limits and AD. In addition to that, the new strategy decreases the impact of the poor starting parameters. The tests in this work, conducted by analyzing ZARCs and FRACs synthetic data, show a superior performance of the newly developed CNLS strategy.

Investigation of the Characteristics of MAO Coatings Formed on Ti6Al4V Titanium Alloy in Electrolytes with Graphene Oxide Additives

Coatings with a thickness from ~40 to ~50 µm on Ti6Al4V titanium alloy were formed by micro-arc oxidation in a silicate-hypophosphite electrolyte with additions of graphene oxide. Micro-arc oxidation treatment was carried out in the anode–cathode mode (50 Hz) with a ratio of anode to cathode currents of 1:1, a total density of 20 A/dm2, and a treatment duration of 30 min. The effect of the graphene oxide concentration in electrolytes on the thickness, roughness, hardness, surface morphology, structure, composition of micro-arc oxidation coatings, and its electrochemical corrosion behavior in 3.5% NaCl solution was studied. The input of graphene oxide additives into the base silicate hypophosphite electrolyte led to an increase in the hardness of micro-arc oxidation coatings. Electrochemical polarization studies and impedance data showed that the best characteristics in terms of corrosion-protective ability among coatings formed in electrolytes with graphene oxide additives were those formed in the electrolyte with a graphene oxide concentration of 0.1 g·L−l. A further increase in the graphene oxide concentration in the electrolyte did not improve the protective properties of micro-arc oxidation coatings.

Corrosion of alloy 690 in simulated steam generator chemistry with boiling-effect of chloride and sulfate impurities

Enrichment of impurities occurs in steam generators of nuclear plants due to intense boiling conditions prevailing within them. In this work, deposition and release of chloride and sulfate impurities were studied using a dedicated water circulation loop with Alloy 690 as steam generator tubing. Electrochemical impedance spectroscopy was employed to follow in-situ the corrosion behavior in non-boiling, boiling and after-boiling conditions. Deposition/release of impurities is quasi-first-order vs. concentration. Interpretation of electrochemical impedance data using an updated version of the Mixed-Conduction Model allows to obtain reaction orders of oxide growth and corrosion release with respect to chloride and sulfate additives.

Biopolymer sodium alginate based titania and magnetite nanocomposites as natural corrosion inhibitors for mild steel in acidic medium

Green biopolymeric materials and its hybrid nanocomposites, i.e. sodium alginate grafted polymethylmethacrylate based titanium dioxide and iron oxide (SA-g-PMMA/TiO2 and SA-g-PMMA/Fe3O4) have been explored for the prevention of mild steel's corrosion in 15% HCl. It is reflected from the electrochemical impedance data that SA-g-PMMA/TiO2 exhibits maximum inhibition efficiency of 97.28% followed by SA-g-PMMA/Fe3O4 that gives 96.82% efficiency while the unmodified sodium alginate possess merely 84.74% efficiency. The declining trend of inhibition efficiency with rising temperature has been explained through gravimetric studies conducted at 303 K- 333 K. The thermodynamic activation and adsorption parameters revealed the mixed mode of adsorption of inhibitors over mild steel surface which follow Langmuir adsorption isotherm. It has been observed from tafel polarization studies that all studied inhibitors are mixed type in nature. The surface morphological inspection of the mild steel samples was done through FE-SEM and AFM, which revealed the formation of better protective adsorption layer over the exposed metallic surface by the nanocomposites in comparison to sodium alginate alone. In addition to this, the elemental composition of adsorbed film on inhibited mild steel specimens was obtained by XPS technique. Quantum parameters obtained through Density Functional Theory (DFT) further corroborate the experimental outcomes.

Vinylene carbonate, toluene and diethyl ether as electrolyte additives for a wide-temperature range operating of EDLCs

This work presents the development of an electrolyte solution based on 1.2 M TEMA BF4 AN:EA (3:1) electrolyte mixture modified with diethyl ether (5–20 vol%), or toluene (5–20 vol%), or vinylene carbonate (0.5–5 vol%) ensuring stable operation of the supercapacitors (SC) in a wide temperature range from −68 °C to +60 °C. Supercapacitor cells with electrolytes of various volume ratios of components were investigated using cyclic voltammetry, galvanostatic charge-discharge, and impedance spectroscopy (EIS) methods. Specific conductivity values have been measured and compared with electrochemical impedance data. It was shown that the additives to the base electrolyte blend expand the operating temperature range of the SC cells by at least 7–8°, enabling its exploitation at lower temperatures (−68 °C). It has been established that the addition of 10 vol% of diethyl ether or toluene stabilizes the operation of the SC at −65 °C, demonstrating stability during long-term exposure. Vinylene carbonate additive most effectively stabilizes the work of the SC at high temperatures (+60 °C). Diethyl ether as an additive effectively promotes the operation of SC only at low temperatures (−68 °C), while at high temperatures, it leads to the degradation of SC.

Impedance investigation of the surface film formed on aluminum alloy exposed to nuclear reactor emergency core coolant

A method was proposed for in-situ evaluating the thickness and resistivity of the oxide/hydroxide film formed on the surface of aluminum alloy exposed to sump water formed in the containment after a loss-of-coolant accident. The evaluation entailed fitting a model for the film impedance, which has film thickness and other variables describing the resistivity profile of the film along its thickness direction as fitting parameters, to the practically measured electrochemical impedance data. The obtained resistivity profiles implied that the films formed at pHs25°C 7, 8, 9, 10, and 11 all had a duplex structure; compared to the outer layer in contact with the solution, the inner layer of the film had a much higher resistivity and was inferred to be denser and provide most of the protectiveness of the film. Both the thickness and the total resistance of the film decreased with the increasing solution pH25°C, suggesting that the films formed in more alkaline solutions had less protectiveness against corrosion, consistent with the increasing aluminum alloy corrosion rates previously identified.

A single-phase gadolinium-doped ceria cathode for highly efficient CO2 electrolysis

We demonstrate high and stable performance of gadolinium-doped ceria as a cathode during CO2 electrolysis. Mechanistic insights are provided by transmission line modelling of electrochemical impedance data.

Role of scoria natural pozzolan in the passive film development for steel rebars in chloride-contaminated concrete environment

This communication reports the effect of scoria natural pozzolan (NP) on rebar corrosion in a simulated pore solution (SPSL) and in mortars. The mortar mixes consist of 100% Portland cement (control) and Portland cement with 25% scoria NP. A third mix utilizing 25% fly ash (FA) was also cast for benchmarking. Specimens from the three mortar mixes were subjected to aggressive wet/dry treatment for long durations. Electrochemical impedance data were extracted after different durations of exposure of the rebars in SPSL and mortars. The addition of NP and FA to SPSL increased the corrosion potential of the rebars immersed in these solutions with time, indicating the strengthening of the passive film formed on the surface of the rebars. However, the addition of chloride to the pore solution considerably reduced the open-circuit potential in the active direction and reduced the polarization resistance, indicating the deterioration of the passive film. NP and FA enhanced the protective properties of the passive film on the surface of rebars embedded in mortars compared with the control one. The initially observed beneficial effect of NP and FA for improving rebar corrosion protection was greater in mortar than in the pore solution, which was attributed to the dual effects of the improvement in the passive layer in addition to the reduction in porosity. Electrochemical impedance spectroscopy (EIS) was used to assess the effect of NP and FA on the properties of the passive film. Cations leached out in the pore solution were analyzed using inductively coupled plasma-optical emission spectrometry. Raman spectroscopy and X-ray diffraction techniques were used to characterize corrosion products on rebars. The data generated using the above-mentioned techniques also helped to understand the mechanism of action of NP and FA observed on the passive film.