AC Impedance Spectra Research Articles

A simple and efficient electrochemical sensor for folic acid determination on Ti(OH)4 modified carbon paste electrode

Folic acid (FA) has a crucial function in pregnant women and anemic patients. Having adequate FA prior to and during the gestation period can protect the brain of the child and spine from significant birth abnormalities. It reduces the risk of stroke, heart disease and some types of cancers, etc. Thus, FA is employed as a reliable biomarker in the early identification of various disorders. In the present study, we synthesized titanium tetra hydroxide [Ti(OH)4] nanoparticles (NPs) by precipitation method with annealing at 100 °C, which is used to modify carbon paste electrode (Ti(OH)4 /MCPE). FA is detected here by voltammetry method using Ti(OH)4/MCPE in the phosphate buffer of pH 6 and compared with bare and TiO2-400, TiO2-600 and TiO2-800 °C NPs MCPE. Based on ac-impedance spectra, the conductivity of Ti(OH)4/MCPE was found to be higher, and consequently this electrode showed excellent sensitivity of 5.5 µA µM−1 cm−2. Lower detection limit (1.3 nM) was observed in the concentration range of 0.4–30 μM by differential pulse voltammetry. The Ti(OH)4/MCPE was also effective for the determination of FA in real samples such as orange, banana, spinach and tablet. The electrochemical sensor investigated here showed excellent stability (92 %) up to 30 days.

Co3+ Doped CdFe2O4 Nanoparticles: Structural, Optical, Magnetic, and Electrical Properties

Through the citrate-gel auto-combustion technique, we synthesized Co-doped cadmium nano ferrites (NFs) with the formula CoxCd1−xFe2O4 (where 0 ≤ x ≤ 1.0 with increments of 0.2). The synthesized materials underwent comprehensive analysis utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy. Magnetic and electrical properties were evaluated using a vibrating sample magnetometer and LCR meter, respectively. XRD analysis confirmed the spinel phase structure and FD3M space group. SEM analysis revealed agglomerations of nanoparticles and grain boundaries. Elemental analysis of the synthesized nanomaterials was provided by energy dispersive spectroscopy. FTIR spectroscopy identified two main broad bands corresponding to the tetrahedral (A) and octahedral (B) sites, confirming the spinel structure. Magnetic properties such as magnetic saturation, coercivity, and remanent magnetization were characterized using VSM. Additionally, the LCR meter assessed frequency and temperature-dependent dielectric parameters, including AC conductivity (σAC), dielectric permittivity, dielectric loss (tan δ), and impedance spectra. An increase in AC conductivity (σAC) was observed with increasing temperature and frequency.

Understanding how junction resistances impact the conduction mechanism in nano-networks

Networks of nanowires, nanotubes, and nanosheets are important for many applications in printed electronics. However, the network conductivity and mobility are usually limited by the resistance between the particles, often referred to as the junction resistance. Minimising the junction resistance has proven to be challenging, partly because it is difficult to measure. Here, we develop a simple model for electrical conduction in networks of 1D or 2D nanomaterials that allows us to extract junction and nanoparticle resistances from particle-size-dependent DC network resistivity data. We find junction resistances in porous networks to scale with nanoparticle resistivity and vary from 5 Ω for silver nanosheets to 24 GΩ for WS2 nanosheets. Moreover, our model allows junction and nanoparticle resistances to be obtained simultaneously from AC impedance spectra of semiconducting nanosheet networks. Through our model, we use the impedance data to directly link the high mobility of aligned networks of electrochemically exfoliated MoS2 nanosheets (≈ 7 cm2 V−1 s−1) to low junction resistances of ∼2.3 MΩ. Temperature-dependent impedance measurements also allow us to comprehensively investigate transport mechanisms within the network and quantitatively differentiate intra-nanosheet phonon-limited bandlike transport from inter-nanosheet hopping.

Effects of Fe2+ on dielectric and magnetic properties in rare earth garnet type high entropy oxides

Given the important role played by the valence state of the transition metal in determining material this paper investigates the effect of Fe2+ content on the structure and dielectric properties of garnet-structured high entropy oxides (Y0.2Eu0.2Er0.2Dy0.2Lu0.2)3(Al0·5Fe0.5)5O12 through Fe2+ doping. The results of XPS and Mӧssbauer spectra showed that the Fe2+ content in the tetrahedron increased with Fe2+ doping. With increasing Fe2+ content, the dielectric constants gradually increased, and the maximum dielectric constant reached 2.78 × 104 at 100 Hz under 30 °C. The analysis of the AC impedance spectrum and electrical conductivity revealed that the difference between the activation energy of grain boundary and grain conductivity resulted in increased dielectric constants of the samples. In addition, the doping of Fe2+ increased the maximum magnetization of the samples. This work provides a new idea for designing giant dielectric materials and magnetic materials with a high entropy strategy.

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.

Inhibition of corrosion of mild steel in simulated oil well waterby aqueous extract of Hibiscus rosa-sinensis flower

controlling the corrosion of mild steel in simulated oil well water (SOWW). Weight loss method reveals that 10 % v/v of the extract offers 82 % inhibition efficiency (IE) to mild steel (MS) immersed SOWW. The mechanistic aspects of corrosion inhibitive effect have been investigated by polarization study and AC impedance spectra. Polarization study reveals that the mixed type of inhibitor in the presence of inhibitor system. The corrosion inhibition effect is confirmed by the increase in the linear polarization resistance value and decrease in the corrosion current value. The protective layer is formed on the metal surface is confirmed by the AC impedance spectra. This is confirmed by the fact that there is increase in charge transfer resistance value and decrease in the double layer capacitance value. The adsorption of inhibitor molecule obey Langmuir adsorption isotherm. The protective coating is characterized by FTIR spectroscopy. It confirms that the inhibitor has coordinated with ferrous ion the metal surface through the active principle component of β-sitosterol, quercetin and kaempferol-3-xylosylglucoside. The surface morphology has been investigated by scanning electron microscopy (SEM). Hence, aqueous extract of Hibiscus rosa-sinensis flower with simulated oil well water good corrosive inhibitive effect on pipeline made of mild steel.

Corrosion inhibition by fruit extracts -Inhibition of corrosion of mild steel in simulated concrete pore solution prepared in sea water by an aqueous extract of apple juice- A Case study

The inhibition efficiency of an aqueous extract of apple juice in controlling corrosion of mild steel immersed in simulated concrete pore solution (SCPS) prepared in sea water, has been evaluated by weight loss method. Langmuir adsorption isotherm has been investigated. The mechanistic aspect of corrosion inhibition has been investigated by Electrochemical impedance spectra (AC impedance spectra). The protective film has been analysed by Fluorescence spectroscopy, FTIR spectroscopy and AFM. The SCPS system offers 60% inhibition efficiency to mild steel immersed in sea water. In presence of apple juice extract the inhibition efficiency increases as the concentration of the extract increases. When 10 ml of extract is added, 85% inhibition efficiency is obtained. Electrochemical impedance spectra (AC impedance spectra) reveal that a protective film is formed on the metal surface. In the presence of inhibitor system, charge transfer resistance value increases, impedance value increases, phase angle value increases whereas double layer capacitance value decreases as expected. The FTIR spectral study reveals that the protective film consists of complexes consisting of iron-active principles of the apple juice extract. AFM study reveals that when the inhibition efficiency increases the roughness of the surface decreases or in other words the smoothness of the system increases.

The Corrosion Resistance of Concrete-Filled Steel Tubes with the Assembly Unit of Na2MoO4 and Benzotriazole

Steel pipes are commonly used to strengthen the concrete’s load-bearing capacity. However, they are prone to corrosion in salt erosion environments. In this study, the influence of Na2MoO4 and benzotriazole on concrete-filled steel tubes’ corrosion performance is investigated. The steel pipes’ mass loss rates (MRs), ultrasonic velocity, electrical resistance, and the AC impedance spectrum and Tafel curves of concrete-filled steel tubes were used to characterize the degree of corrosion in the steel pipes. Scanning electron microscopy–energy-dispersive spectrometry and X-ray diffraction were used for studying the composition of steel pipe rust. The research results revealed that the NaCl freeze–thaw cycles (F-C) and NaCl dry–wet alternation (D-A) actions had a reducing effect on the mass and ultrasonic velocity of the concrete-filled steel tubes. After 300 NaCl F-C and 30 NaCl D-A, the MRs were 0%~0.00470% and 0%~0.00666%. The corresponding ultrasonic velocities were 0%~21.1% and 0%~23.6%. When a rust inhibitor was added, the results were the opposite. The MRs decreased by 0%~80.3% and 0%~81.6% with the added Na2MoO4 and benzotriazole. Meanwhile, the corresponding ultrasonic velocities were 0%~8.1% and 0%~8.3%. The steel tubes were corroded after 300 NaCl F-C and 30 NaCl D-A. The addition of rust inhibitors improved the corrosion resistance of the concrete-filled steel tubes by increasing the electrical resistance before NaCl erosion. The corrosion area rate decreased by using the rust inhibitors. The corrosion resistance effect of benzotriazole was higher than that of Na2MoO4. The concrete-filled steel tube with an assembly unit comprising 5 kg/m3 of Na2MoO4 and 15 kg/m3 of benzotriazole had the best corrosion resistance under the erosion induced by NaCl F-C and D-A. Rust inhibitors reduced the content of iron-containing crystals and iron elements. The specimens with 5 kg/m3 Na2MoO4 and 15 kg/m3 benzotriazole had the lowest concentration of iron-containing crystals and iron elements.

Ni2+-doped Na2Ti6O13 nanotubes to enhance the electrochemical performance of sodium ion batteries

Here, Ni2+-doped Na2Ti6O13 nanotubes (NNTONT) were successfully synthesized by a simple hydrothermal ultrasound method. It could be found that Na2Ti6O13 partly transformed to TiO2 with the addition of Ni2+, and affected the electrochemical properties of sodium ion batteries (SIBs). When the added Ni source got to 40 wt% (NNTONT-40), the capacity of charge–discharge approached the best value: 130.4 mAh/g after 100 cycles at 1C (1C = 177 mA g−1 in this paper), and increased by 41 % compared with undoped NTONT (92.2 mAh/g), and increased by 76 % even at a high rate (10C) after 1000 cycles. Subsequently, the analyses of CV (cyclic voltammetry), EIS (AC impedance spectrum) and GITT (galvanostatic intermittent titration technique) confirmed that Ni2+-doping resulted in lower Na+ insertion-extraction voltage, smaller charge transfer resistance and higher ion diffusion rate and lager BET specific surfaces. Therefore, Ni2+-doping is an effective strategy to improve the capacity, rate performance and energy density, which is a promising SIBs’ anode material.

Phase Transition Behavior of Biphasic Systems Affected By the Charge-Transfer Process

Lithium-ion batteries have attracted attention with the development of electric vehicles and the introduction of renewable energy. For use in these applications, lithium-ion batteries with fast charge and discharge acceptability are particularly important. The charge and discharge reactions of lithium-ion batteries are limited by several factors such as ion and electron transfer in the electrode and electrolyte, charge transfer at the electrode-electrolyte interface, and reaction rates during phase transitions. It has been reported that the rate limiting factor of the biphasic materials is the phase boundary rearrangement, and the activation energy of such phase transition has been investigated in previous studies. However, there are variations in the reported activation energy values even for the same electrode material. Since there are many unexplored factors that affect the phase transition rate, we have examined the effect of these factors on the phase transition rate using LiFePO4as model electrodes. In our previous presentation, we showed that the phase transition behavior of LiFePO4 electrode changes depending on the electrolyte, suggesting the influence of the electrode/electrolyte interface. (1) In this presentation, we report the relationship between the activation energy of the biphasic reaction and that of the solvation/desolvation of the electrolyte measured using a four-probe cell (2), and the effect on the phase transition behavior when the transferred ion species is changed from Li+ to Na+. A non-aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, lithium foils as a counter and reference electrodes, and a 1 mol dm–3 solution of LiPF6 in ethylene carbonate and diethyl carbonate (1:1 v/v) as an electrolyte solution and was constructed in an Ar-filled glove box. An aqueous-type three-electrode cell was composed of the LiFePO4 as a working electrode, a Ni wire as a counter electrode, Ag/AgCl/sat’d KCl aq as a reference electrode, and a 0.5 mol dm–3 Li2SO4 aqueous solution as an electrolyte solution. The charging–discharging behavior was firstly measured to confirm the cell characteristics and then the potential step measurement was employed. The Avrami plots based on the potential step results (3) were used to obtain the reaction rate constant k. Further experiments at different temperatures were performed and the Arrhenius plots were drawn to calculate the activation energy of the phase transition. (3) The activation energy for solvation/desolvation of the electrolyte was calculated by making a four-probe cell with the counter electrode and reference electrode symmetrically arranged across the solid electrolyte Li2OAl2O3SiO2P2O5TiO2 (OHARA) and measuring AC impedance spectra at different temperatures. For the Na+ system, the LiFePO4 electrode was electrochemically delithiated to produce FePO4, and then Na+ was inserted into FePO4 to obtain NaFePO4 in the aqueous electrolyte. Electrochemical measurements were performed with the obtained electrode. The potential step measurements were performed with the aqueous and non-aqueous electrolyte cells. Their activation energies were obtained from the Arrhenius plots with the k values and compared. The activation energy measured in the aqueous electrolytes was smaller than that measured in the nonaqueous electrolyte. The activation energy for the solvation/desolvation processes was also smaller for the aqueous electrolytes system, suggesting that the charge transfer process between electrode and electrolyte is involved in the rate-determining process of the phase transition. Next, we performed the same experiment by changing the mobile ion species from Li+ to Na+. The activation energy for Na+extraction was nearly zero, suggesting very fast phase transition. If the volume change corresponding to the phase transition limits the rate, large Na+ extraction would lead to high activation energy than Li+ extraction. The tendency was the opposite, suggesting that the weak interaction of Na+ and water affects the whole phase transition.References(1) C. Yamamoto, A. Ikezawa and H. Arai, The 242nd Electrochemical Society Meeting, A02-0130 (2022).(2) Z. Ogumi., Electrochemistry, 78, 319 (2010).(3) J. Allen, T.R. Jow, and J. Wolfenstine, Chem. Mater., 19, 2108-2011 (2007).(4) Y. Orikasa, T. Maeda, Y. Koyama, T. Minato, H. Murayama, K. Fukuda, H. Tanida, H. Arai, E. Matsubara, Y. Uchimoto, and Z. Ogumi, J. Electrochem. Soc. 160, A3061-A3065 (2013). Figure 1

Effects of varied building solid wastes, particle sizes and substitution ratios on the performance and impedance spectrum of recycled fine aggregate mortar and the feasibility of developing a prediction method

In this study, three solid waste materials (sintered bricks (SB), aerated blocks (AB) and cementitious mortar (CM)) were studied to analysis the influence on the impedance characteristics and mechanical properties of recycled sand mortar. Mortar containing recycled sand obtained similar or even higher compressive strengths as to the control group at 15% substitution rate. The density of the mortar decreased with the substitution rate of recycled sand. The porosity increased by 18% compared to the control group with an inclusion of 45% of SB. The bulk density of recycled mortar was found to be related to the particle size of the recycled sand, for instance, the bulk density of ABCS45 was 6% less than ABFS45. The AC impedance spectrum results showed that the high-frequency arc was the smallest for AB and the largest for CM. The R1 values of AB were 0.27 and 0.14 times that of SB and CM, respectively. The high-frequency arc of the mortar increased with hydration, consuming OH− ions and raising R0 values, while the compacting matrix led to a rise in R1 values. After 28 days curing, mortars containing SB and CM sands displayed higher R1 values, with CMCS45 being approximately 50% higher than the control group. Through analyzing the physical, mechanical, and impedance properties, it revealed a correlation coefficient −0.88 between porosity and R0 values, with bulk density and compressive strength demonstrating stronger correlation with R1 values. These findings offer valuable guidance for utilizing and nondestructively testing recycled materials.

Structure refinement, Raman vibration, impedance spectra and microwave dielectric properties of MgZrNb2-x(Ge1/2W1/2)xO8 (0.02≤x≤0.08) ceramics with the high quality factor

The prosperous development of 5G technology requires the development of new high-performance microwave dielectric ceramics. MgZrNb2-x(Ge1/2W1/2)xO8 (MZNGW) (0.02≤ x ≤ 0.08) ceramics were synthesized by the solid-state reaction with the high quality factor. The connection between the microstructure and microwave dielectric properties of MZNGW ceramics was systematically analyzed. Crystal structure refinement showed that MZNGW ceramics with monoclinic wolframite structure were synthesized in all samples. The sintering behavior and surface morphology indicate that doping of (Ge1/2W1/2)5+ can improve the densification and promote the grain growth. The effect of (Ge1/2W1/2)5+ doping on the phonon vibration can be obtained from Raman spectra, and the shift of Raman vibrational mode at 840 cm−1 and the change of half-height width have a great influence on the dielectric constant and quality factor. XPS spectra and AC impedance spectra are analyzed to show the influence of the crystalline defects on the macroscopic properties of the interlayer. The MgZrNb1-x(Ge1/2W1/2)xO8 (x = 0.04) ceramic exhibits excellent microwave dielectric performance sintered at 1420 °C for 4 h: εr = 27.1, Qf = 94,450 GHz, τf = −41.65 ppm/°C, with great potential for applications in modern communications.

Lu2O3–Y2O3–ZrO2: A Lu3+ co-doped YSZ system—Oxygen-ion conductor with high electrical conductivity and improved mechanical properties

This study investigates the electrical and mechanical properties of a Lu2O3–Y2O3–ZrO2 system (ZrO2 co-doped with Lu2O3 and Y2O3) and evaluates its possibility for use as a high-performance oxygen-ion conducting ceramic suitable for intermediate/high-temperature solid electrolytes. The use of electrochemical impedance spectroscopy (EIS) in the analysis and fitting of AC impedance spectra arcs on 8 mol% (Lu2O3–Y2O3)– ZrO2 has allowed to compare with the Y2O3-doped ZrO2 (YSZ) and Sc2O3-doped ZrO2 (ScSZ). (ZrO2)0.92(Y2O3)0.07(Lu2O3)0.01, with 1 mol% Lu2O3 co-doped with Y2O3, shows a bulk conductivity of 9.60 × 10−1 S/cm at 1000 °C and 3.47 × 10−2 S/cm at 800 °C, which are least several times higher than the corresponding values of any other sample in the experimental group, including Sc2O3-doped ZrO2, over the entire measured temperature range. (ZrO2)0.92(Y2O3)0.075(Lu2O3)0.005 also shows an outstanding conductivity; over two times higher than that of ScSZ. Thus, Lu2O3 co-doping can enhance mechanical properties such as flexural strength (19.5 % (1 mol% Lu2O3) and 21.5 % (2 mol% Lu2O3) higher than that of YSZ), as confirmed by the flexural strength and Vickers hardness tests. After 8 mol% sesquioxide doping of YSZ, the maximum improvement in the electrical and mechanical properties occurs at approximately 1 mol% (for electrical properties) and 2 mol% (for mechanical properties) Lu2O3 co-doping, respectively. The results of this work suggest that a small amount of Lu doping, performed during the development of materials for use in electrochemical devices (including high-efficiency energy conversion apparatus), could be a considerable approach to overcome the limitations of conventional solid oxide electrolytes.

Effect of Sr doping on electronic transport properties of SnS2 hexagonal nanoplates

In this work, the electronic transport properties of SrxSn1-xS2 (x = 0, 0.02, 0.04, 0.06 and 0.08) nanoplates synthesized by hydrothermal method have been reported. AC conductivity, electric modulus and impedance spectra nanoplates have been studied in frequency and temperature ranging from 1Hz to 1 MHz and 313K–453K, respectively. AC conductivity data of the SrxSn1-xS2 nanoplates obeys the Almond-West relationship. In SrxSn1-xS2 nanoplates conduction governs by overlapping large-polaron tunnelling (OLPT), quantum mechanical tunnelling (QMT) and small polaron quantum mechanical tunnelling (SPQMT) mechanisms for x = 0, x = 0.02 and x = 0.04, 0.06 and 0.08, respectively. A modified KWW model has been used to understand the electric modulus behaviour of SrxSn1-xS2 nanoplates. The observed scaling behaviour of the imaginary component of the electric modulus supports the assertion of frequency exponent (s) with temperature about the conduction mechanism. The Nyquist plots are well-fitted with a double R-CPE model. The activation energy values estimated from conductivity (0.68–0.73 eV) and electric modulus (0.69–0.72 eV) analysis are in coherence.

Large electrostrain at high temperature in bismuth sodium titanate-based piezoelectric ceramics

(1-x)[0.82Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3]-xAgNbO3 ceramics (abbreviated as BNKT-100xAN, x = 0–0.06) are fabricated by the solid state reaction method. It is discovered that silver niobate is completely dissolved into the lattice of 0.82Bi0.5Na0.5TiO3-0.18Bi0.5K0.5TiO3 ceramics based on characterization. The relaxation mechanism and characteristics of BNKT-100xAN ceramics are analyzed by dielectric temperature spectra and AC impedance spectra. The content of ordered domains and PNRs of BNKT-4AN ceramics is optimum, which enables it possess excellent electrostrain of 0.51%. The electrostrain almost remain constant after the 104 cycles test, suggesting that it also has great fatigue resistance. After polarization at high temperature, large electrostrain of 1.4% and inverse piezoelectric constants of 2004 pm/V are obtained at 150 °C in BNKT-4AN ceramics. The ultrahigh electrostrain is mainly promoted by the larger polarizability of the <111>-oriented and <001>-oriented defect dipoles, the same direction of defect dipoles and the spontaneous polarization direction of phase, the pinning effects of the defect dipoles on the PNRs and the collinear arrangement of the PNRs. This work indicates that lead-free piezoelectric ceramics is hopeful to be applied in piezoelectrics working at high temperature. Simultaneously, a new design paradigm also is provided for the preparation of piezoelectric ceramics with excellent performance.

Effects of plasma on electrochemical performance of carbon cloth-based supercapacitor

In this work, the surface of carbon cloth is treated by plasma jet to improve its hydrophilicity. The symmetrical carbon cloth-based supercapacitor is assembled with the carbon cloth treated by plasma as the active electrodes and sodium chloride solution as the electrolyte. With the discharge time (1 min, 2 min, 3 min) and working gas types (argon, air, helium) of plasma as variables, the effects of different plasma on the hydrophilicity of carbon cloth are observed, and the changes of the electrochemical properties of the supercapacitors with single or double carbon cloth electrodes treated by different plasma are studied. The contact angle test results show that the plasma of different working gases can weaken the hydrophobicity of carbon cloth, and the helium plasma can make the carbon cloth change from hydrophobicity to hydrophilicity. The electric capacity calculated by cyclic voltammetry shows that plasma can increase the electric capacity of carbon cloth-based supercapacitors. The electric capacity of carbon cloth-based supercapacitors with two carbon cloth electrodes treated by plasma is larger than that of single carbon cloth electrode treated by plasma. The argon and helium plasma with longer discharge time can significantly improve the electric capacity of carbon cloth-based supercapacitors. The galvanostatic charge-discharge curve shows that different working gases of plasma can make carbon cloth-based supercapacitors obtain pseudocapacitance, increase the charge-discharge time and electric capacity. From the AC impedance spectrum, it can be concluded that the plasma of any kind of working gas can reduce the impedance and charge transfer resistance of the carbon cloth-based supercapacitor. The longer plasma discharge time lead to the smaller impedance, and the impedance of the supercapacitor with both carbon cloth electrodes treated by plasma is smaller.

Corrosion Behavior of Reinforcing Steel in the Immersed Tube Tunnel (ITT) under Submarine Environment.

The corrosion behavior of reinforcing steel in the ITT under a submarine environment was investigated. Electrochemical tests were carried out to separately determine the linear polarization curves and the AC impedance spectra of rebars in the ITT scaled-down models subjected to pressurized seawater erosion, from which key parameters were obtained, including the self-corrosion potential (Ecorr), corrosion current density (icorr), polarization resistance (Rp), concrete resistance (Rc), and charge migration resistance (Rct). The results show that in the process of pressurized seawater erosion, the rebars on the seawater side of the ITT models corroded earlier than the rebars on the cavity side, and it is recommended that anti-chloride ion penetration measures be taken on the surface of the seawater side as a priority in the project. The corrosion rate of rebars on the seawater side was significantly higher than that on the cavity side, and the corrosion rate of rebars on the cavity side increased as the erosion time increased. The corrosion rate of rebars in the ITT models was affected by chloride ions to a greater extent than by oxygen. Furthermore, by regression equation, a linear function between Rp obtained from the polarization curves and Rct obtained from the AC impedance spectra was established.

Doping strategy on improving the overall cathodic performance of double perovskite LnBaCo2O5+δ (Ln=Pr, Gd) as potential SOFC cathode materials

A series of single-phase double perovskite Pr1-xGdxBaCo2-yFeyO5+δ (x = 0, 0.5 and 1, 0 ≤ y ≤ 1) materials were engineered through A/B site co-doping strategy to improve the mechanical, electrical and electrochemical properties as potential cathode materials for the application of intermediate solid oxide fuel cells (IT-SOFCs). The corresponding thermochemical stability, thermal expansion behavior, electrical conductivity and cathodic polarization resistance of the materials were systematically investigated. It was found that the A-site dual lanthanide doped Pr0.5Gd0.5BaCo2O5+δ (PGBCO) exhibits improved electrical conductivity, reduced thermal expansion, and comparatively low electrochemical polarization resistance versus single lanthanide double perovskite, PrBaCo2O5+δ (PBCO) and GdBaCo2O5+δ (GBCO) materials. Further investigation on the effect of B-site Fe-doping on Pr0.5Gd0.5BaCo2-yFeyO5+δ (PGBCF-y, 0 ≤ y ≤ 1) reveals that all the PGBCF-y compositions exhibit excellent chemical stability with Gd-doped ceria (GDC) at operating temperatures not higher than 1 100 °C. Besides, doping of Fe in B-site can effectively reduce the thermal expansion coefficients (TECs) of the Pr0.5Gd0.5BaCo2O5+δ ceramics at 30–1 000 °C. And the electrochemical impedance spectra (EIS) results show that the PGBCF-y|GDC| PGBCF-y symmetric cells have acceptable low area specific polarization resistances. Further examination of the cathodic polarization and characteristic capacitance from the AC impedance spectra by employing the relaxation time distribution (DRT) method demonstrated that charge transfer is the dominating sub-process for the oxygen transport through the materials.

Effect of CrYN/TiBN coating on friction performance and corrosion resistance of 316 stainless steel in artificial seawater

CrYN, TiBN, and CrYN/TiBN coatings were successfully deposited on 316 stainless steel substrates via multi-arc ion plating techniques to improve their wear and corrosion resistance properties in marine environments. The morphology, microstructure, friction performance, and corrosion resistance of the three coatings in artificial seawater were systematically studied. X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy investigations confirmed a dominant face-centered cubic CrN structure, accompanied by hexagonal TiB2 and amorphous BN in CrYN/TiBN coatings. The SEM cross-section shows that the TiBN and CrYN/TiBN coatings have a more compact cross-sectional structure than the CrYN monolayer coating. The CrYN/TiBN coatings exhibited the lowest smooth friction coefficient in artificial seawater, and the wear rate was ranked as TiBN < CrYN/TiBN < CrYN. Surface morphological studies performed after tribocorrosion revealed that the protection ability of all three coatings remained acceptable. The electrochemical test showed that the corrosion tendency was CrYN/TiBN < TiBN < CrYN, and the CrYN/TiBN coating had the best performance in the AC impedance spectrum and polarization curve.

The Influence of Aspect Ratio of Steel Fibers on the Conductive and Mechanical Properties of Compound Cement Reactive Powder Concrete

The performance of steel fibers reinforced RPC has a great relationship with the aspect ratio of the fibers. It is necessary to systematically study the relationship between the aspect ratio and the mechanical properties of RPC and the force-electricity response. In this paper, the flexural strength, the compressive strength and the flexural toughness and AC electrical resistance and AC impedance spectroscopy of reactive powder concrete are investigated. The flexural strength, compressive strength, and flexural toughness with the curing age of 1 day and 28 days are tested. The cement is the compound cement in this study, and the mass ratio of ordinary portland cement and sulphoaluminate cement is 1:1, and two kinds of steel fibers with aspect ratios of 30(AR-30) and 75(AR-75) are used. The fiber content is 2% of the concrete volume. Scanning electron microscope (SEM) and scanning electron microscope energy spectrum analysis (EDS) are investigated to analyze the composition of the hydration products. It can be obtained from the research results that the flexural strength and the compressive strength of reactive powder concrete decrease with the increase of steel fibers content with an aspect ratio of 30. The decreasing rates of the flexural strength and the compressive strength with the curing age of 1 d and 28 d are 14.93%~83.26% and 0.40%~46.36% with the incorporation of steel fibers with an aspect ratio of 30. The flexural toughness decreases in the form of a quadratic function with the mass ratio of steel fibers with an aspect ratio of 30. The electrical resistance of reactive powder concrete increases with the increase of steel fibers with an aspect ratio of 30. The maximum decreasing rate of electrical conductivity is 91.16%. The AC impedance spectrum is obtained, and the electric circuit of reactive powder concrete accords with the series conduction model, which parallel electrical resistance and capacitance of pore solution, rapid strength RPC and steel fibers respectively connect with a contact resistance of the electrode and specimens. It is found that the steel fibers network with an aspect ratio of 75 is closer by studying the equivalent circuit diagram.