Electrochemical Impedance Measurements Research Articles

Nitrogen-Doped Carbon Nanothin Film as a Buffer Layer between Anodic Graphite and Solid Electrolyte Interphase for Lithium-Ion Batteries.

Lithium-ion batteries are essential batteries for electric vehicle drive systems. Such batteries must provide stable performance over a long period of time. Therefore, the degradation or aging of the battery capacity must be improved. In the case of the current graphite anodes, graphite coated with an amorphous layer is used. It is known that the amorphous layer can reduce the irreversible capacity loss caused by the solid electrolyte interphase (SEI) layer. The amorphous carbon layers reduce the initial capacity due to higher electrical resistance. In this study, we aim to develop a buffer layer using nitrogen-containing graphene that would prevent the increase in electrical resistance while maintaining the amorphous structure. Coatings with different film thicknesses were prepared by using the solution plasma method. The thinnest sample was oven sintered to optimize the structure, especially the surface and interface of the layer. The battery capacity from charge-discharge experiments and the resistance change of each part from electrochemical impedance measurements were evaluated. The results showed that the coating layer increased the electrical resistance of the graphite anode. On the other hand, the resistance of the SEI layer was reduced by the coating layer. It can be predicted that the addition of the coating layer will increase the total charge transfer resistance (R ct) of the cell but will also improve the period average capacity in the long run. To be used as a practical material, the film thickness would need to be further reduced, and the balance between the loss of charge transfer resistance and the gain of SEI layer resistance would need to be further optimized.

Effect of normalizing treatments on microstructure and electrochemical corrosion properties of U75V-welded joints in an acidic environment

Corrosion poses a significant threat to the structural integrity of steel rails, especially in an acidic environment. In this study, we evaluate the corrosion properties of U75V-welded joints using potentiodynamic polarization curves, electrochemical impedance measurements, and corrosion morphology studies under simulated acidic conditions. Compared to non-normalized joints, the normalized joints exhibit a higher self-corrosion current (4.65 × 10−5 A/cm2) and a more negative self-corrosion potential (−0.56919 mV). The smaller and more uniform grain size obtained after normalizing provides multiple active sites on the surface for polarization reactions. Furthermore, owing to significant erosion caused on the rail surface by the acidic solutions, normalizing treatment enhances the passivation effects on the surface, resulting in increased corrosion resistance (221.96 Ω cm2). Our findings provide insights into the impact of normalizing treatments on the corrosion mechanism of U75V rail joints under acidic conditions.

Long-Term Performance of Ag/AgCl Reference Electrodes for Corrosion Potential Monitoring in Radioactive Tank Waste at the Hanford Site

This work studied the exposure effects of radioactive tank waste on the long-term performance of single junction Ag/AgCl reference electrodes for corrosion potential monitoring at the Hanford Site. Electrodes from three manufacturers with very different designs were studied using open-circuit potential and electrochemical impedance measurements in radioactive tank waste. Post-test analyses were conducted on some failed electrodes using destructive and nondestructive techniques. The intrusion of the aggressive and radioactive chemicals in tank waste through the porous frit materials was the primary mechanism that led to the clogging of frit, physical and chemical degradation of AgCl bonded to Ag wire, and alteration of the internal electrolyte. Radiolytic chemical species such as H2O2 and HNO3 may have also induced the degradation of the Ag wire. The extent of electrode degradation and failure probability highly depended on the electrode design and environmental conditions. Chemicals in tank waste had stronger effects than radiation on the long-term performance of the Ag/AgCl reference electrodes.

Nanoporous Au Behavior in Methyl Orange Solutions.

Nanoporous (NP) gold, the most extensively studied and efficient NP metal, possesses exceptional properties that make it highly attractive for advanced technological applications. Notably, its remarkable catalytic properties in various significant reactions hold enormous potential. However, the exploration of its catalytic activity in the degradation of water pollutants remains limited. Nevertheless, previous research has reported the catalytic activity of NP Au in the degradation of methyl orange (MO), a toxic azo dye commonly found in water. This study aims to investigate the behavior of nanoporous gold in MO solutions using UV-Vis absorption spectroscopy and high-performance liquid chromatography. The NP Au was prepared by chemical removal of silver atoms of an AuAg precursor alloy prepared by ball milling. Immersion tests were conducted on both pellets and powders of NP Au, followed by examination of the residual solutions. Additionally, X-ray photoelectron spectroscopy and electrochemical impedance measurements were employed to analyze NP Au after the tests. The findings reveal that the predominant and faster process involves the partially reversible adsorption of MO onto NP Au, while the catalytic degradation of the dye plays a secondary and slower role in this system.

Influence of Solid Fraction on Particle Size during Wet-Chemical Synthesis of β-Li3PS4 in Tetrahydrofuran

For all-solid-state batteries, the particle size distribution of the solid electrolyte is a critical factor. Small particles are preferred to obtain a high active mass loading of cathode active material and a small porosity in composite cathodes. In this work, the influence of the solid fraction in the wet-chemical synthesis of β-Li3PS4 in tetrahydrofuran (THF) is investigated. The solid fraction is varied between 50 and 200 mg/mL, and the obtained samples are evaluated using X-ray diffraction, SEM and electrochemical impedance measurements. The sizes of the resulting particles show a significant dependency on the solid fraction, while a good ionic conductivity is maintained. For the highest concentration, the particle sizes do not exceed 10 µm, but for the lowest concentration, particles up to ~73 µm can be found. The ionic conductivities at room temperature are determined to be 0.63 ± 0.01 × 10−4 S/cm and 0.78 ± 0.01 × 10−4 S/cm for the highest and lowest concentrations, respectively. These findings lead to an improvement towards the production of tailored sulfide solid electrolytes.

Accurate ion type and concentration detection using two bare electrodes by machine learning of non-faradaic electrochemical impedance measurements of an automated fluidic system

Detecting ion types and their concentrations in multi-ion aqueous solutions poses a complex challenge with significant implications for sensing applications. This paper introduces an automated fluidic system using two bare electrodes to measure electrochemical impedance spectroscopy (EIS) data and evaluates deep neural network (DNN) for ion type and concentration detection. Additionally, a data-augmentation model is proposed for non-faradaic voltage sweep EIS data, intended for neural network training. To validate the effectiveness of our approach, prepared solutions featuring varying concentrations of LiCl, NaCl, and KCl are experimented. Impedance (Z) vs DC bias voltage (V) data, i.e., ZV-EIS are measured from −400 mV to + 400 mV at 9 different frequencies up to ∼ 200 kHz, for 148 automatically prepared solutions, having total salt concentrations up to 200 mM. DNN models are trained with augmented samples and successfully identified individual ions in test set solutions and their concentrations with 4.51 mM average deviation. The study delves into the nuanced impacts of factors such as sampling voltage window, and measurement frequency on the performance of the machine learning models, 8 mV and 20 Hz giving the most significant results.

Comparison of Approaches for Assessing Linearity of Impedance Measurements

Electrochemical impedance spectroscopy experiments are inherently nonlinear for systems affected by faradaic reactions. The methods used to determine whether an experiment is sufficiently linear include observation of current as a function of potential, known as Lissajous plots, measurement of total harmonic distortion, and post-experiment assessment of consistency with the Kramers–Kronig relations. An experimental approach is employed to compare sensitivity of these methods to determination of nonlinear response in electrochemical impedance measurements. The Lissajous figures showed linear behavior for a total harmonic distortion equivalent to 1 percent of the fundamental; whereas, the measurement model analysis revealed nonlinear behavior only for larger perturbation amplitudes.

Transfer of Sodium Ion across Interface between Na+-Selective Electrode Membrane and Aqueous Electrolyte Solution: Can We Use Nernst Equation If Current Flows through Electrode?

Electrochemical impedance and chronopotentiometric measurements with Na+-selective solvent polymeric (PVC) membranes containing a neutral ionophore and a cation exchanger revealed low-frequency resistance, which is ascribed to Na+ ion transfer across the interface between the membrane and aqueous solution. The attribution is based on the observed regular dependence of this resistance on the concentration of Na+ in solutions. The respective values of the exchange current densities were found to be significantly larger than the currents flowing through ion-selective electrodes (ISEs) during an analysis in non-zero-current mode. This fact suggests that the interfacial electrochemical equilibrium is not violated by the current flow and implies that the Nernst equation can be applied to interpret the data obtained in non-zero-current mode, e.g., constant potential coulometry.

Electrochemical Doping Effect on the Conductivity of Melanin-Inspired Materials.

Eumelanin is a natural pigment that can be particularly valuable for sustainable bioelectronic devices due to its inherent biocompatibility and hydration-dependent conductivity. However, the low conductivity of eumelanin limits its technological development. In this research, electrochemical doping was proposed as an alternative route to increase the electronic conductivity of synthetic eumelanin derivatives. Thin films of sulfonated eumelanin were deposited on platinum interdigitated electrodes and electrochemically treated by using cyclic voltammetry and chronoamperometry treatments. X-ray photoelectron spectroscopy analysis confirmed ion doping in sulfonated melanin. Current-voltage, current-time, and electrochemical impedance measurements were used to investigate the effect of different aqueous electrolytes (including KCl and LiClO4) treatments on the charge transport of sulfonated eumelanin. We show that the conductivity depends on the type and size of the anion used and can reach 10-3 S·cm-1. Additionally, depending on the electrolyte, there is a change in charge transport from mixed ionic/electronic to a predominantly electronic-only conduction. Our results show that the chemical nature of the ion plays an important role in the electrochemical doping and, consequently, in the charge transport of eumelanin. These insights serve as inspiration to explore the use of alternative electrolytes with different compositions further and develop eumelanin-based devices with tunable conductivities.

Corrosion of 316L stainless steel produced by laser powder bed fusion and powder metallurgy in pressurized water reactor primary coolant

Corrosion mechanism of 316 L stainless steel produced by laser powder bed fusion-hot isostatic pressing (LPBF-HIP) and powder metallurgy-hot isostatic pressing (PM-HIP) is studied with in-situ electrochemical impedance measurements coupled to detailed oxide film characterization. Quantitative analysis of impedance spectra using the Mixed-Conduction Model and estimation of local kinetic and transport parameters by interpretation of in-depth elemental composition profiles indicated lower corrosion and oxidation rates of LPBF-HIP and PM-HIP materials in comparison to conventional wrought 316 L. This owes to a higher fraction of low-angle grain boundaries, smaller grain size, the presence of nano-sized oxide particles and elevated Cr and Ni contents.

Unraveling the structure-property relationship of pyrimidine-derivatives as CO2 corrosion inhibitors: Experimental and periodic DFT investigations

CO2-containing environments commonly cause corrosion of carbon steel (CS) pipelines used in the oil and gas industry. In this work, the inhibition of corrosion by three derivatives of pyrimidine, namely 2-mercaptopyrimidine (MPY), 4-hydroxy-2-mercapto-6-methylpyrimidine (HMMP), and 4,5-Diamino-2,6-dimercaptopyrimidine (DDMP) for C1018 CS in CO2 saturated 3.5% NaCl brine was investigated. The corrosion rates and inhibition efficiency were investigated at 25 and 70 °C using open circuit potential, linear polarization resistance, potentiodynamic polarization and electrochemical impedance measurements. The post-immersion surface characterization of the exposed C1018 CS with and without the three molecules was carried out using SEM and 3D surface optical profilometer. Theoretical computation using DFT was further utilized to examine the role of the molecular structures and the mechanism of inhibition of the three molecules on steel surface at the atomic level. The experimental results indicate the following order of inhibition efficiency: MPY > DDMP > HMMP. Our experimental work proved that MPY molecule (the smaller one with the least number of heteroatoms) as the most efficient corrosion inhibitor. Surface characterization analysis confirmed the order of inhibition efficiency. The theoretical results revealed that the stability of molecules adsorbed on Fe (110) surface in the parallel orientation and on FeCO3 (104) is identical on both surfaces, which is completely consistent with the experiment. Our study provides a feasible strategy for developing new corrosion inhibitors by understanding how similar organic inhibitors work.

Enhanced organic pollutant and AOX degradation of lignin-biochar/ZnAl2O4/BiPO4 with adsorption-photocatalysis synergy: Roles of lignin-biochar

In this work, lignin-biochar (LC)/ZnAl2O4/BiPO4 with adsorption and photocatalysis synergy were fabricated through hydrothermal process. The roles of lignin-biochar on the crystalline structure, shape and photoelectrochemical capacities of LC/ZnAl2O4/BiPO4 were carried out by X-ray power diffractometer pattern (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet-visible diffusion reflectance spectra (UV–Vis DRS), photoluminescence spectra (PL), transmission electron microscope (TEM), scanning electron microscope (SEM), electrochemical impedance and transient photocurrent measurements. Photocatalytic experiment showed that the adsorption and photocatalytic efficiencies of ZnAl2O4/BiPO4 were greatly boosted with the introduced lignin-biochar, which is owing to its higher surface specific area, larger aromatic ring structure and superior electron transmission capacity. The highest kinetic constant of LC/ZnAl2O4/BiPO4 on the MB degradation is 2.1342 h−1 under UV illumination, increased by 5.52-fold for BiPO4 and 2.23-fold for ZnAl2O4/BiPO4, respectively. Meanwhile, the LC/ZnAl2O4/BiPO4 composites display excellent performance in the bamboo pulp bleaching wastewater treatment, and the CODCr and AOX removals of the wastewater are 65.2 % and 69.2 %, respectively. The lignin-biochar in the composites can not only enhance the adsorption of pollutant in the wastewater, but accept the photo-generated electrons from the semiconductor, leading to an enrichment of the pollutant and accelerated separation of electrons-holes pairs, ultimately enhancing the photocatalytic activities. The superior adsorption and photocatalytic efficiency of lignin-biochar-based composite makes it a promising candidate for the elimination of refractory pollutant in the industrial wastewater.

The Phosphidosilicates AE2 Li4 SiP4 (AE=Ca, Sr, Eu) Ba4 Li16 Si3 P12.

The quaternary phosphidosilicates AE2 Li4 SiP4 (AE=Ca, Sr, Eu) and Ba4 Li16 Si3 P12 were synthesized by heating the elements and Li3 P under argon atmosphere. Their crystal structures were determined by single crystal X-ray diffraction. AE2 Li4 SiP4 crystallize in a new layered structure type (P21 /m, Z=2) with CdI2 -analoguos layers. Edge sharing CaP6 octahedra are separated by layers of vertex-sharing SiP4 and LiP4 tetrahedra, which contain additional chains of LiP6 octahedra. Ba4 Li16 Si3 P12 forms likewise a new structure type (P21 /c, Z=16) with a three-dimensional network of SiP4 , Si2 P6 and LiP4 entities as well as one phosphorus site not bonded to silicon. Barium is located in capped trigonal prisms of phosphorus which form strongly corrugated layers. 31 P and 29 Si solid-state NMR spectra confirm the crystal structures of the compounds AE2 Li4 SiP4 . 7 Li spectra show only one signal in spite of quite different crystallographic positions, which indicate possible Li+ mobility. However, this signal is much broader compared to the known Li+ conducting phosphidosilicates. Accordingly, electrochemical impedance measurements show low Li+ conductivities.

Cost-effective lab-made graphite- and aluminum oxide-integrated polylactic acid composite electrodes for electrochemical sensing of minoxidil

The development of new sensors, which are low-cost, portable, and disposable, is currently highly required. In this sense, this work describes a simple way for lab-made fabrication of new composite electrodes exploiting an environmental friendly matrix based on thermoplastic polylactic acid (PLA). Great conductive features were achieved using graphite and aluminum oxide in PLA. The amount of aluminum oxide has been carefully optimized (0 to 12.25 % m/m). The manufacturing process presented reproducibility (between-device % relative standard deviation (RSD) < 7.3). Additionally, the electrode was characterized by electrochemical, spectroscopy, and morphological techniques. Improved cyclic voltammetric responses regarding Ipa, Ipc, and ΔEp were obtained towards the detection of the redox probes [Fe(CN)6]3-/4- and dopamine using the electrode incorporated with aluminum oxide. Moreover, electrochemical impedance measurements revealed a more facilitated charge transfer process in the alumina-loaded electrode (Rct = 2070 Ω) than without alumina (Rct = 2810 Ω). The developed sensor was associated with batch injection analysis for the simple, fast, and sensitive amperometric monitoring of minoxidil (MXD) in pharmaceuticals, achieving a greater sensitivity with a detection limit of 2.9 µmol/L. A wide linear behavior from 10 to 1000 µmol/L and a between-measurement % RSD of less than 6 were acquired. Also, the method is free of interference from compounds commonly used as excipients in pharmaceutical products. When applied to the pharmaceutical sample, results statistically comparable to the reference method (UV–Vis spectrometry) were achieved, which confirmed the method's accuracy. Thus, the proposed sensor proves to be a powerful alternative tool for MXD monitoring, providing comparable and even better results with other high-cost electrochemical sensors.

Enhanced solar-driven photoelectrochemical water splitting using nanoflower Au/CuO/GaN hybrid photoanodes.

Harnessing solar energy for large-scale hydrogen fuel (H2) production shows promise in addressing the energy crisis and ecological degradation. This study focuses on the development of GaN-based photoelectrodes for efficient photoelectrochemical (PEC) water splitting, enabling environmentally friendly H2 production. Herein, a novel nanoflower Au/CuO/GaN hybrid structure was successfully synthesized using a combination of methods including successive ionic layer adsorption and reaction (SILAR), RF/DC sputtering, and metal-organic chemical vapour deposition (MOCVD) techniques. Structural, morphological, and optical characteristics and elemental composition of the prepared samples were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-Vis spectroscopy, and energy-dispersive X-ray (EDX) spectroscopy, respectively. PEC and electrochemical impedance measurements were performed for all samples. The nanoflower Au/CuO/GaN hybrid structure exhibited the highest photocurrent density of ∼4 mA cm-2 at 1.5 V vs. RHE in a Na2SO4 electrolyte with recorded moles of H2 of about 3246 μmol h-1 cm-2. By combining these three materials in a unique structure, we achieved improved performance in the conversion of solar energy into chemical energy. The nanoflower structure provides a large surface area and promotes light absorption while the Au, CuO, and GaN components contribute to efficient charge separation and transfer. This study presents a promising strategy for advancing sustainable H2 production via efficient solar-driven water splitting.

Development of an Al-Zn-Bi alloy sacrificial anode for the protection of steel in artificial seawater: an electrochemical analysis

The Al-Zn sacrificial anodes are widely used for cathodic protection in marine steel structures. This study evaluates the impact of bismuth addition on the electrochemical properties of the Al-Zn sacrificial anode in artificial seawater. The microstructure analysis confirms the presence of uniformly distributed intermetallic β-AlFeSi and spherical Bi within the α-Al matrix. The open circuit potential (OCP) comparison between Al-Zn-Bi and carbon steel reveals a potential difference of approximately 400 mV, indicating sufficient cathodic protection for the steel. Electrochemical impedance measurements indicate the initial hindered dissolution of the anode due to surface film formation, which later dissociates due to the aggressive attack of Cl− species in the electrolyte. The sufficiently negative surface potential (−0.875 Vvs. Ag/AgCl) observed at 10 mA cm−2 demonstrates the suitability of anode for fulfilling the cathodic protection criteria of steel structures.

Fabrication of polycrystalline phosphorus-doped diamond electrodes from red phosphorus.

Polycrystalline phosphorus-doped diamond was fabricated by the quartz-tube-type microwave plasma-assisted chemical vapor deposition method. Significantly, red phosphorus was used as a source of phosphorous, instead of PH3. Phosphorus-doped diamond electrodes with hydrogen-terminated and oxygen-terminated surfaces were investigated for the redox reactions of K3[Fe(CN)6] and [Ru(NH3)6]Cl3. The carrier concentration was estimated as 2.1-5.3 × 1018 cm-3 from electrochemical impedance measurements. Polycrystalline phosphorus-doped diamond shows great promise as chemical electrode materials.

Defect engineered N-doped black-V2O5 nanostructures for hydrogen production via solar-catalytic water splitting in the presence of different sacrificial agents

In this study, vanadium pentoxide (V2O5) is synthesized via hydrothermal method and annealed in a normal and NH3 gas ambience, which led to the formation of pristine and defective-V2O5 systems, respectively. This defective-V2O5 contained both doped-nitrogen and oxygen-vacancies defects, confirmed through XRD and XPS analysis. Interestingly, this process also led to the exfoliation of V2O5 into a 2D layered structure, confirmed by FESEM analysis. A band gap energy of ∼2.11 and 2.26 eV is estimated for the defective and pristine-V2O5, respectively from the Tauc's plots. The solar-catalytic green H2 production efficiency (in mmol g−1 h−1) of the pristine and defective-V2O5 in presence of different sacrificial is investigated and estimated, and it is found to the order of glycerol (2.369) > methanol (1.969) > triethanolamine (1.441) > sodium sulphate/sodium sulfide mixture (1.210) > ethylene glycol (0.967). While accounting the inherent properties of the various sacrificial agents, the observed enhanced efficiency of defective-V2O5 is attributed to their surface-active sites, suitable band structure along with the modulations in the charge carrier separation and transfer characteristics of the system, confirmed through BET, PL, Mott–Schottky, electrochemical impedance, and photocurrent measurements. Further, the cyclic photocatalytic efficiency of defective-V2O5 is found to be consistent in all the 3 cycles in a total period of 9 h. The post-characterizations of the recycled defective-V2O5 system suggested that the developed photocatalyst is stable in terms of its photo-chemical and physical properties, suitable for scale up green H2 productions.

Nanostructure-Based Solution Sensor Fabricated with p-CuOx/n-TiO2 Nanojunctions To Identify Species and Concentrations of Alcohol Molecules.

Chemiresistive sensors fabricated based on metal-oxide-semiconductors, the most widely used high-sensitivity sensor materials, are required for detecting target solutions and gases and identifying them with a high degree of accuracy. In this study, we used p-n nanojunctions and nanowire shapes for identifying alcohol solutions. The solution sensors fabricated based on CuOx nanowires with p-CuOx/n-TiO2 nanojunctions detected ethanol, ethylene glycol, and diethylene glycol solutions via DC voltage and electrochemical impedance measurements. The p-n nanojunctions affected the sensors' sensitivity in the diethylene glycol solution, and the nanowire surface areas affected the relaxation time in ethanol and ethylene glycol solutions. To identify alcohol solutions, principal component analysis was performed based on the relationship between the sensor information, such as the presence of p-n nanojunctions and nanowire surface areas, and the sensing performance. This analysis identified alcohol molecular species and predicted alcohol-solution concentrations in the 0.1-20 vol % range with a high degree of accuracy. The concept of using sensors with different surface conditions with respect to p-n nanojunctions and nanowire surface areas offers designs for metal-oxide-semiconductor sensors to identify various molecules in solution.

Distribution of Relaxation Times of Fuel Electrodes for Reversible Solid Oxide Cells Fabricated Under Various Conditions

Introduction Reversible solid oxide cells (r-SOCs) are electrochemical energy devices that can switch reversibly between power generation as a solid oxide fuel cell (SOFC) and hydrogen production as a solid oxide electrolysis cell (SOEC). It is important to systematically understand the electrode reaction processes and degradation factors in these two modes to tailor high-performance and durable r-SOC electrodes. The dependence of polarization resistance on cell fabrication conditions and operating conditions has been individually investigated for SOFC and SOEC by impedance measurement and distribution of relaxation times (DRT) analysis [1-4], but it is necessary to evaluate r-SOC as a whole [5]. Here in this study, we aim to systematically clarify the similarities and differences in the electrode reaction processes at the fuel electrodes of both SOFC and SOEC modes of r-SOCs, with respect to fuel electrode fabrication conditions. Experimental Several types of cells were fabricated with different fuel electrode constituent materials, thicknesses, and sintering temperatures. Three types of fuel electrode materials were used: Ni-GDC cermet, a composite of Ni and mixed ionic-electronic conductor Gd0.9Ce0.1O3 (GDC); Ni-YSZ cermet, a composite of Ni and pure ionic conductor YSZ (8 mol% Y2O3 - stabilized ZrO2); and Ni-GDC co-impregnated electrode with LST-GDC as a backbone support (LST: La0.1Sr0.9TiO3). Scandia-stabilized zirconia (ScSZ) was used as the electrolyte plate, and (La0.6Sr0.4)(Co0.2Fe0.8)O3 (LSCF) was used as the air electrode. GDC buffer layer was prepared between the electrolyte and the air electrode to suppress the formation of interfacial insulting layers.Electrochemical impedance measurements were performed for the fuel electrode of the fabricated cell under SOFC and SOEC modes by supplying H2-H2O mixture and varying operating temperature, fuel humidification, and current density. The DRT analysis was conducted to separate various polarization resistance components of the fuel electrode with different relaxation times. The area of each DRT peak corresponds to the resistance of each electrode reaction process. In this study, activation energy was derived based on the assumption that the electrical conductance is of an Arrhenius-type thermally activated character. Its dependence on the fuel electrode fabrication conditions was investigated. Furthermore, electrode microstructure was observed by using focused-ion beam scanning electron microscopy (FIB-SEM). Results and Discussion Figure 1 shows typical DRT peaks of the Ni-GDC cermet fuel electrode in (a) SOFC and (b) SOEC modes, measured at different temperatures. In the range of 10-1 to 106 Hz where the frequency response was measured, three DRT peaks appeared, P1: 10-1 to 100 Hz, P2: 100 to 102 Hz, and P3: 102 to 103 Hz, all with a DRT peak area decreasing with increasing operating temperature. This indicates that there are at least three electrode reaction processes with different relaxation times, which are thermally active processes. Activation energies of 0.1-0.3 eV (SOFC mode) and 0.2-0.5 eV (SOEC mode) were obtained for P1, and 0.9-1.0 eV (SOFC mode) and 1.1-1.3 eV (SOEC mode) for P2. The activation energies in SOEC mode were higher than those in SOFC mode for both P1 and P2. In the presentation, the dependence of activation energies on the fuel electrode constituent materials and related electrode reaction processes will be discussed.