Diameter Of Semicircle Research Articles

Facile synthesis of spherical-shaped CeC2–TiO2 nanocomposite electrocatalyst with boosted alkaline OER

Developing noble metal-free multifunctional electrocatalysts to catalyze water oxidation is vital for future renewable energy systems. Herein, through several defect modifications, the CeC2–TiO2 nanocomposite on the strength of enriched oxygen vacancies was successfully fabricated by facile hydrothermal method on SS (stainless steel) substrate, attributed to the conductive ability for fast electron transportation. A well-defined phase growth, vibrational bonding of metal atoms, morphological determination, and elemental composition for synthesized heterostructured electrocatalysts were revealed by XRD, FTIR, TEM, and EDX, respectively. XPS has complied to understand the moderate binding energies of CeC2–TiO2 for OER intermediates, which signifies the strong interactions between electronic states of Ce, C, Ti, and O atoms. With the plentiful catalytic active sites, the resultant CeC2–TiO2 entails low overpotentials of only 169 mV and 108.8 mV/dec Tafel slope to afford 10 mA cm−2 for OER in 1.0 M KOH are tested through cyclic and linear sweep voltammogram measurements, thereby exhibit promising activity in alkaline water electrolysis. EIS measurements revealed a decreased polarization resistance for the composite dominated by the small semicircle diameter, corresponding to the adsorption of intermediates. Finally, observed results strongly recommended that the CeC2–TiO2 catalyst exhibited superior OER performance due to excellent electrical chemical coupling between CeC2 and TiO2.

Water Quality Monitoring: All-Solid-State 3D-Printed Sensors for Phosphate Detection in River Water

INTRODUCTION High phosphate ( PO4 3- or P) levels in surface water cause eutrophication, which negatively impacts aquatic life and causes an economic loss of ~$2.2 billion per year. Currently, no low-cost sensors exist for long-term continuous monitoring of phosphate in water. Existing meters (HANNA colorimeter, and HORIBA) can detect P-levels but can neither perform continuous monitoring nor detect low concentrations. A paper-based colorimeter sensor for phosphate detection was demonstrated [1], however, this sensor takes a longer time to test. A Fabry−Perot phosphate sensor was introduced [2], but it is not a field-deployable sensor. Although many sensors have been developed to detect P-level [3 - 5], these sensors cannot detect a low concentration of P-level. This is an important concern as river water has a P-level below 1 ppm. As such, the applicability of existing devices in practical scenarios is not suitable for reliable measurement.Thus, we are motivated to develop lithography-free, low-cost, and solid-state 3D-printed sensors for the ultra-sensitive detection of phosphate in river water. Our 3D-printed sensors are innovative compared to traditional fabrication techniques in the literature. We have characterized, calibrated, validated, and analyzed river samples and the results are superior to existing state-of-the-art P-sensors. Our 3D-printed P sensors showed an analytical sensitivity of 0.001 ppm of PO4 3- in river water within a detection range of 0 – 10 ppm and a detection time not exceeding 30 seconds. DEVICE FABRICATION First, we made a 3D design (CAD model) of the sensor (Fig. 1a). The sensor has one working electrode (WE) and a reference electrode (RE) having diameters of 8 and 3 mm, respectively. The CAD model was then exported to the 3D printer software, and the software was programmed based on the desired material and parameters. Fig.1b illustrates the 3D printing setup. The material used for the printing was high-temperature resin (an epoxy polymer). The resulting sensor structure was removed from the printing build platform, washed in an isopropyl alcohol bath, and dried. The sensor was then cured by treating it with UV light at 80 °C. A 100 nm-thick layer of gold (Au) was then coated on the sensor with a Kapton shadow mask and using an electron-beam evaporator. Then the RE was coated with an Ag/AgCl ink and dried at 80 °C for 2 hours. Fig.1d depicts the fabricated sensor with its Au electrode upon which poly(3-octylthiophene) (POT) and phosphate ion-selective membrane (p-ISM) were prepared and drop-coated on the WE in layers. Fig.1c summarizes the detection principle for phosphate ion exchange at different electrode layers. RESULTS AND DISCUSSION Fig.1e shows the sensor characterization based on electrochemical impedance spectroscopy (EIS). The charge transfer resistance (RCT) of the EIS curve was evaluated using its semicircle diameter. The RCT observed for the Au, POT/Au, and ISM/POT/Au electrodes were 263.67, 652.64, and 893.13 Ω, respectively. The p-ISM coating suppressed the electrochemical current in the ISM/POT/Au electrode due to the negatively charged buffer solution containing ferro/ferricyanide. Further, the 3D-printed sensor was calibrated using known standard solutions and the potential between the WE and RE decreased while we increased the phosphate concentration (Fig.1f – g). The sensor showed a slope of 37.4 mV/dec and an analytical sensitivity of 0.001 ppm. We believe that the high sensitivity of our sensor is due to the large surface area of our 3D-printed sensor structure which has wrinkled polymer surfaces that enhance more PO4 3- ion exchange. Our sensor also showed an excellent selectivity (Fig.1h) with various interfering ions.Real water samples were collected from five locations at the Rappahannock River in eastern Virginia, USA. Fig.1i shows the open circuit potentiometry (OCP) for all five river water samples. Fig.1j shows the comparison between our sensor readings and those of a commercial phosphate meter (purchased from Hanna Instruments Inc.). Here, we observed a close relation between the two readings while our sensor showed a higher sensitivity, suggesting the usefulness of our sensor in practical scenarios. Our sensor achieved excellent detection of low concentrations of P-levels in river water. In the future, our 3D-printed sensors will be deployed into river water for continuous monitoring of the P-levels in the Rappahannock River. REFERENCES [1] V. Choudhary and L. Philip, Microchemical Journal, 2021,171, p. 106809.[2] J. Zhu et al., ACS Sens, 2020, 5:5, pp. 1381–1388.[3] R. V Manurung, et al., IOP Conf Ser Mater Sci Eng, 2019, 620:1, p. 012093.[4] M. Sarwar, J. Leichner, G. M. Naja, and C.-Z. Li, Microsyst Nanoeng, 2019, 5:1, p. 56.[5] M. M. Grand et al., Front. Mar. Sci., 2017, 4:255, doi: 10.3389/fmars.2017.00255. Figure 1

Exploration of rice husk ash as a green corrosion inhibitor immersed in NH4Cl 7.5 % solution

The study reports the development of a liquid smoke solution of rice husk ash (RHA) as a green corrosion inhibitor in NH4Cl solution in approaching corrosion protection for refinery facilities. The recent utilization of RHA has a partial solution to address the possible chemical to form a filming layer to disconnect bare metal and their environment. This work prepared the RHA solution by condensing the RHA vapor before adding it to various concentrations. The corrosion test of potentiodynamic and electrochemicals intends to discover the inhibitor's corrosion resistance before examining the electronic transition corresponding to the contribution of several functional groups using Ultraviolet Visible (UV–Vis) and Fourier-Transform Infrared Spectroscopy (FTIR). Surface evaluation intends to unveil the nature of the corrosion by utilizing the Scanning Electronic and Atomic Force Microscope. The corrosion test result shows the depression of corrosion rate to 0.120 mmpy with high efficiency beyond 96 % in the addition of 7.5 ppm RHA inhibitor. The greater Nyquist semicircle diameter at high concentrations increases the adsorption of the RHA on the surface of C1018. The electronic transition of n–π* and π –π* shows an extensive contribution of CC, CO, and –OH based on the UV–Vis and FTIR test. The formation of a complex compound of Fe-(NH4Cl-RHA)n blocks the corrosion active sites to reduce the corrosion. This study paves the way for using RHA as an organic compound under NH4Cl conditions, such as in a refinery process facility.

Tailoring magnetic properties of SrFe12O19 ferrites through Dy–Ni Co-substitution: A comprehensive study

A solid-phase synthesis method was utilized to create a range of ferrite samples, specifically Sr1-xDyxFe12-xNixO19, where x values varied (0, 0.01, 0.02, 0.03, and 0.05). Through X-ray diffraction (XRD) analysis, it was found that up to x ≤ 0.03, the XRD pattern showed no discernible impurity phases. However, at x = 0.05, an observable impurity peak attributed to α-Fe2O3 emerged. Room temperature hysteresis loop measurements revealed consistent hard magnetic behavior across all samples. Notably, changes in coercive force directly correlated with magnetocrystalline anisotropy. As substitution increased, the initial saturation magnetization (MS) of 59.68 emu/g (at x = 0.00) moderately reduced to 57.79 emu/g (at x = 0.05), representing a modest decline of 3.17 %. A clear trend was observed: decreasing grain size led to diminishing dielectric constants. Moreover, a strong link between the Nyquist diagram's semicircle diameter and sample resistivity was evident, showing distinctive metal-semiconductor behavior. These findings shed light on the structural and magnetic characteristics of Dy and Ni co-substituted SrFe12O19 ferrites, suggesting potential for enhanced performance in advanced magnetic and electronic devices. This study significantly contributes to the field of ferrite materials, deepening our insights and paving the way for innovative applications in diverse technological domains.

Hydrogen and oxygen production on Ag2O/NiO hybrid nanostructures via electrochemical water splitting

Among the different available methods, hydrogen production by electrocatalytic water splitting is the most attractive method. Here, Ag2O/NiO hybrid nanostructures with different molar ratios of silver and nickel ions were synthesized by co-precipitation method. Nickel oxide and silver oxide nanostructures was also prepared to compare with Ag2O/NiO nanocomposites. Investigations indicated that the as-prepared Ag2O/NiO nanocomposite with an equal molar ratio of metal ions shows high water splitting activity in 1 M KOH solution and only 430 and 140 mV are needed as overpotentials under a current density of 10 mA cm−2 for oxygen and hydrogen evolution reactions (OER and HER), respectively. Ag2O/NiO has the largest electrochemically active surface area, the lowest Tafel slope, the smallest semicircle diameter in the Nyquist plots, and the lowest charge transfer resistance for both OER and HER among all tested nanomaterials. Furthermore, Ag2O/NiO showed excellent stability for OER and HER for at least 30 h.

Evolution of Electrochemical Impedance Spectra Characteristics of Cementitious Materials after Capturing Carbon Dioxide

The electrochemical parameters of cement-based materials with different water–cement ratios in carbon curing and water curing were measured with electrochemical impedance spectroscopy (EIS). The optimized circuit model and corresponding electrical parameters were obtained to illustrate the variation of the microstructure of cementitious materials after carbon capturing. The results show that, to a large extent, the semicircle diameter in the high frequency area gradually increased along with carbon curing and water curing. However, carbon curing showed a difference that the semicircle diameter in the high frequency appeared at the minimal value at 3 days, which was higher than that at 1 day and 7 days. This should be the result of the joint influence of water content and porosity in the cement matrix. It was also found that the mass increase rates of carbonation with water–cement ratios of 0.4, 0.5, and 0.6 were basically stable at 3.4%, 5.0%, and 5.5%, respectively. The electrochemical parameters ρct2 of cement mortar corresponding to carbon curing were around three times that of water curing specimens, mainly due to the reduction of soluble materials and refinement of connecting pores in the microstructure of cementitious materials. A quadratic function correlation between the mass increase rate and ρct2 in the carbonation process of cement mortar was built, which proved that EIS analysis could be applied to monitor the carbon capturing of cement-based materials, either for newly mixed concrete or for recycled concrete aggregates.

Enhanced Performance of LiFePO4 Cathodes Protected By Atomic Layer Deposited Ultrathin Alumina Films

The LiFePO4 (LFP) cathode has a theoretical specific capacity of 170 mAh/g. This material is stable, safe, and environmentally benign. Li-ion batteries with LFP cathodes have a long cycle life with excellent charging/discharging performance. In our contribution, we show that the surface modification of the LFP cathode using ultrathin alumina films grown by atomic layer deposition (ALD) can improve Li-ions charge transfer and rate performance of the Li-ion in half-cell configuration with the LFP cathode.We used two types of LFP cathodes in our study with Li-metal as an anode in a half cell configuration. The first LFP electrode had a thickness of 25 μm and consisted of particles of 0.5 - 1 μm in size [1], while the second one (commercial NANOMYTE BE-60E (NEI Corp.)) had a thickness of 70 μm and the average LFP particle size was 2 μm.Ultrathin Al2O3 films were grown on LFP cathodes by ALD at 100 °C using trimethylaluminum (TMA) and water vapors. Due to the self-saturation surface-limited nature of the ALD reaction, even substrates of highly complex morphology can be uniformly coated, where the limitation is the reach of the precursor vapor molecules. The thickness of the ALD layers depends linearly on the number of ALD cycles and ranges from 0.5 to 2 nm for 5 to 20 cycles.Galvanostatic charging/discharging experiments were performed to evaluate the rate capability of the electrodes. Pristine and Al2O3 coated LFP electrodes were laser cut to 18 mm diameter circular electrodes, inserted in the electrochemical test cells PAT-Cell (EL-CELL), and tested using PAT-Tester-x-8 analyzer. LFP with Al2O3 protecting layers was compared to the pristine LFP electrode.For the LFP cathode with the thickness of 25 μm the pristine sample saturates at the specific capacity of 32 mAh/g at 1.8 c-rate, while for the electrode treated with 5 and 20 cycles of Al2O3 the specific capacity dropped to 80 and 60 mAh/g, respectively. The electrodes protected by Al2O3 film always exhibited better rate capability than the pristine sample.A more detailed analysis of the performance was accomplished for the NANOMYTE electrodes. A specific discharge capacity of 160 mAh/g at a c-rate of 0.2 was achieved for both pristine and Al2O3-protected electrodes. Two supercycles with the c-rate 0.2, 0.5, and 1 were applied to the samples. The specific capacity of the pristine LFP electrode dropped from 160 mAh/g for the c-rate 0.2 to about 90 mAh/g at the c-rate 1, while the electrode which was protected by 5 cycles of Al2O3 exhibited a capacity of 120 mAh/g.Investigation of the rate capability fading using electrochemical impedance spectroscopy revealed a gradual increase of the Nyquist plot semicircle diameter as a function of cycles. According to the equivalent circuit model, the semicircle diameter corresponds to the charge transfer at the solid/electrolyte interface. The charge transfer resistance at the solid/electrolyte interface increases with charge/discharge cycling. The charge transfer resistance of the pristine electrode increased more steeply than that of the electrode with 5 cycles of Al2O3. Improvement of the charge transfer resistance of the LFP electrode covered by thin Al2O3 film can be explained by the formation of the Li3.4Al2O3 phase upon lithiation. The diffusivity of the Li ions in the Li3.4Al2O3 phase is several orders of magnitude higher than that of in the Al2O3 film [2]. The results obtained by electrochemical characterization are compared to the X-ray photoelectron spectroscopy performed on samples before and after galvanostatic charging/discharging measurements.[1] A. Fedorkova et al., J. Power Sources 195 (2010) 3907.[2] S. C. Jung et al., J. Phys. Chem. Lett. 4 (2013) 2681.

Effect of Recombinant Antibodies and MIP Nanoparticles on the Electrical Behavior of Impedimetric Biorecognition Surfaces for SARS-CoV-2 Spike Glycoprotein: A Short Report

Electrochemical immunosensors are often described as innovative strategies to tackle urgent epidemiological needs, such as the detection of SARS-CoV-2 main biomarker, the spike glycoprotein. Nevertheless, there is a great variety of receptors, especially recombinant antibodies, that can be used to develop these biosensing platforms, and very few reports compare their suitability in analytical device design and their sensing performances. Therefore, this short report targeted a brief and straightforward investigation of the performance of different impedimetric biorecognition surfaces (BioS) for SARS-CoV-2, which were crafted from three commonly reported recombinant antibodies and molecularly-imprinted polymer (MIP) nanoparticles (nanoMIP). The selected NanoMIP were chosen due to their reported selectivity to the receptor binding domain (RBD) of SARS-CoV-2 spike glycoprotein. Results showed that the surface modification protocol based on MUDA and crosslinking with EDC/NHS was successful for the anchoring of each tested receptor, as the semicircle diameter of the Nyquist plots of EIS increased upon each modification, which suggests the increase of Rct due to the binding of dielectric materials on the conductive surface. Furthermore, the type of monoclonal antibody used to craft the BioS and the artificial receptors led to very distinct responses, being the RBD5305 and the NanoMIP-based BioS the ones that showcased the highest increment of signal in the conditions herein reported, which suggests their adequacy in the development of impedimetric immunosensors for SARS-CoV-2 spike glycoprotein.

Functionalized graphene oxide dispersed polyvinyl alcohol-epoxidized linseed oil composite: An eco-friendly and promising anticorrosion coating material

Polyvinyl alcohol (PVA) is an extensively used biodegradable polymer including corrosion inhibition, but it fails to withstand long time protection due to water solubility. The present work emphasized an efficient way to transform PVA to hydrophobic nature and further modification for corrosion protection of mild steel (MS). In this backdrop, PVA was blended with varying amounts of the synthesized amine-functionalized graphene oxide (AGO) and then assimilated with the epoxidized linseed oil (ELO). The fabricated composite material was coated on MS surface by the doctor's blade technique, and their adhesion character, roughness, wettability, and sustainability in saline media were confirmed by atomic force microscopy (AFM), contact angle, and electrochemical techniques. The chemical bonding as well as structural interactions of the prepared AGO were ascertained by Fourier-transform infrared (FT-IR), X-ray powder diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) methods. Electrochemical impedance spectroscopy (EIS) measurements of the PVA coatings showed improved Nyquist semicircle diameter by increasing the AGO content, and the potentiometric polarization (PP) data supports the EIS results. The different weight percentages of AGO dispersed PVA/ELO composite coatings revealed enormous changes in their Nyquist, Bode, and phase angle plots. The highest impedance and charge transfer resistance of PVA/ELO-AGO (0.25 wt%) coating are found to be 108.6 Ω cm2 and 4.541 × 108 Ω cm2, respectively. Further, the composite coating was sustained for 20 days in 3.5 wt% NaCl solution showing its enhanced barrier property. This can be ascribed due to the strong cross-linkages in PVA/ELO-AGO that makes it a durable and promising anti-corrosion coating material.

On the impedance spectroscopy of field‐effect biosensors

AbstractImpedance spectroscopy is an electrochemical technique widely used for the electrical characterization of the behavior of biomaterials in all kinds of biosensors. Field‐effect devices, and in particular ion‐sensitive field‐effect transistors (ISFETs), have been extensively studied as transducers for biosensing. They however have not been much analyzed with impedance spectroscopy, because they typically generate non‐Faradaic capacitance measurements, since there is no charge transfer through the insulating gate in contact with the liquid solution. We have recently experimentally shown that Faradaic‐like impedance spectroscopy spectra can be obtained with ISFET devices, allowing high‐sensitivity measurements for different pH and biomarker concentrations. In this paper, we report that both Faradaic‐like and non‐Faradaic impedance behavior can be well understood by a DC and small‐signal AC model of the ISFET working in different conditions. Faradaic‐like impedance measurements are described by the operation of the ISFET in subthreshold conditions. A Nyquist plot semicircle is obtained, corresponding to the transimpedance 1/gmof the ISFET in parallel to the gate capacitances. We show that this behavior is independent of the presence of membrane material on the gate surface. In these conditions, the change in the semicircle diameter for different pH or biomarker concentrations can be understood by the change of 1/gmcorresponding to a threshold voltage shift of the transistor. This description is illustrated with our recent results for pH measurements and the detection of tumor necrosis factor‐α with functionalized devices in standard solutions in the concentration range of 1–20 pg/ml. The use of the impedance spectroscopy technique takes advantage of the exponential behavior of thegm(VGS) curves in the subthreshold (weak inversion) operation of the ISFET. This results in a large signal amplification, where a small change in the threshold voltage results in a large change in the impedance spectrum, thus achieving an increased precision in the measurement of the device response to changes in the analyte concentration.

Mechanical behavior and corrosion properties of Ti-7Mo-8Nb alloy for biomedical applications

The present study investigates the microstructural, mechanical and corrosion properties of Ti-7Mo-8Nb alloy manufactured through powder metallurgy. The performance of the developed alloy is benchmarked against cast Ti-6Al-4V. Microstructure examination of Ti-7Mo-8Nb revealed a Widmanstätten structure containing equiaxed β grains along with acicular α phase. In regards to the mechanical properties, Ti-7Mo-8Nb possessed higher compressive yield strength, higher hardness but lower elastic modulus than Ti-6Al-4V. The elastic modulus of Ti-7Mo-8Nb was almost 44.9 GPa, approaching the usually desired value of 30 GPa for cortical bone. Wear test revealed also a lower wear rate for Ti-7Mo-8Nb. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments were carried out for both Ti-7Mo-8Nb and Ti-6Al-4V immersed in Hank’s solution as a simulated body fluid at a temperature of 37 °C. Both experiments revealed higher corrosion resistance for Ti-7Mo-8Nb manifested by lower corrosion and passivation current densities, higher negative phase angle, higher impedance modulus and larger Nyquist semicircle diameter as compared to Ti-6Al-4V alloy. The superior corrosion properties of Ti-7Mo-8Nb are indicative of the development of a more stable passive layer on the surface. The fitting of EIS data into an equivalent circuit suggested the formation of a double oxide layer consisting of an inner compact base passive film along with an external porous layer. The presented combination of high strength, high corrosion resistance along with low elastic modulus puts forward the Ti-7Mo-8Nb alloy as a good candidate for orthopedic biomedical applications.

Effects of Bi and S co-doping on the enhanced photoelectric performance of ZnO: Theoretical and experimental investigations

The enhanced photoelectric performance of (Bi, S) co-doping ZnO is explored by combining the density functional theory (DFT) calculations with experimental measurements. The crystal structures, formation energies, electronic properties and relative effective mass of photogenerated electrons and holes of pure and (Bi, S) co-doped ZnO are investigated by DFT calculations. Results indicate that Bi/S co-doping can generate impurity states and shift the conduction band into the lower energy region, causing the decrease in band gap. Relative effective mass show that the separation rates of photogenerated carriers are enhanced after modification. Moreover, experimental measurements are carried out on the basis of the above theoretical analysis. Pure and Bi/S co-doped ZnO samples with different doping ratios are synthesized and characterized. The results confirm that the presence of (Bi, S) has major effects on oxygen defects in crystal structure. XPS, UV–vis and PL studies evidence the roles of these oxygen defects on band gap narrowing for 2% ZnO samples. As expected, 2% doping sample has the highest photocurrent value (23.58 μA cm−2, nearly 4.7 times higher than pure ZnO) and the smallest Nyquist semicircle diameter. This work will provide some new insights into the design of high performance photoelectrocatalysis materials.

Dependence of Impedance Response of Li-S Battery on Polysulfide Solubility of Electrolyte I - Initial Stage of Discharge

Lithium-sulfur (Li-S) battery has higher theoretical specific capacity than commercial lithium-ion batteries. However, one of serious problems in sulfur cathode to be solved to realize a commercial Li-S battery is polysulfide dissolution, causing lowering charge-discharge capacity and round-trip efficiency. In previous studies, glyme-Li+ solvent ionic liquid (SIL)1) and polypyrrole film containing ionic liquid2) were proposed to mitigate dissolution of polysulfide. Meanwhile, dependence of sulfur cathode’s reaction mechanism on polysulfide solubility of electrolyte is still unclear. In this study, electrochemical impedance spectroscopy (EIS) at various depth of discharge was performed in two types of lithium-sulfur batteries using electrolytes with different polysulfide solubility. This paper describes that polysulfide solubility in electrolyte largely influences the impedance response at initial stage of discharge in Li-S batteries. For cathode and electrolyte, X-ray absorption near edge structure (XANES) was also performed in order to analyze the valence of sulfur species at various depth of discharge.Figure 1 shows discharge curves of Li-S cells with polysulfide soluble electrolyte (1M LiTFSI in 1,3-dioxolane (DOL)/1,2-dimethoxyethane (DME) 1:1 (v/v)) and with polysulfide insoluble SIL electrolyte (Li(G3)TFSI/hydrofluoroether (HFE) 1:4 (v/v)). Figure 2 (a) and (b) show Nyquist plots obtained by the cells using DOL/DME and SIL, respectively. A remarkable difference was observed in the diameter of semicircles in a frequency range of 1 kHz – 10 Hz; in both cases, semicircle decrease as discharge progression in the same manner, while decrease of the semicircles with DOL/DME was more notable. In addition, another semicircle in a frequency range of 10 Hz - 1 Hz was observed only in the Nyquist plots with SIL electrolyte. These results indicate that the semicircles in higher frequency region (1 kHz – 10 Hz) are attributed to dissolved polysulfide and the semicircle in lower frequency region (10 Hz – 1 Hz) is attributed to undissolved polysulfide. XANES measurement confirms that signal by sulfur (2472 eV) decreased until potential reached 2.1 V with DOL/DME and until 1.5 V with SIL. These results indicate that reduction of sulfur proceeds until 2.1 V with DOL/DME and until 1.5 V with SIL which is in good agreement with the result from impedance response by EIS. Acknowledgement This work was partly supported by Advanced Low Carbon Technology Research, Development Program Special Priority Research Area “Next-Generation Rechargeable Battery” (ALCA-Spring) from the Japan Science and Technology Agency (JST) (Grant Number JPMJAL1301). Reference (1) Kaoru Dokko et al., Journal of the Electrochemical Society, Volume 160, Issue 8, A1304-A1310 (2013).(2) Natsuki Nakamura et al., J Power Sources, 274, 1263-1266 (2015). Figure 1

Dependence of Impedance Response of Li-S Battery on Polysulfide Solubility of Electrolyte II - Mid - End Stage of Discharge

Sulfur is a promising cathode material for the lithium based battery because of its advantages such as eco-friendness, abundance in nature, and high theoretical capacity of 1675 mAh g-1. However, sulfur cathodes are not without their own intrinsic problems such as low ionic and electronic conductivity, large volumetric expansion upon lithiation from S8 to Li2S, and the dissolution of so-called polysulfide intermediates (Li2Sx where x represents a value between 4 and 8). In previous studies, glyme-Li+ solvent ionic liquid (SIL)1) and polypyrrole film containing ionic liquid2) were proposed to mitigate dissolution of polysulfide. Meanwhile, dependence of sulfur cathode’s reaction mechanism on polysulfide solubility of electrolyte is still unclear. In this study, electrochemical impedance spectroscopy (EIS) at various depth of discharge was performed in two types of lithium-sulfur batteries using electrolytes with different polysulfide solubility. This paper describes that polysulfide solubility in electrolyte largely influences the impedance response at mid - end stage of discharge in Li-S batteries. Figure 1 shows discharge curves of Li-S cells with polysulfide soluble electrolyte (1M LiTFSI in 1,3-dioxolane (DOL)/1,2-dimethoxyethane (DME) 1:1 (v/v)) and with polysulfide insoluble SIL electrolyte (Li(G3)TFSI/hydrofluoroether (HFE) 1:4 (v/v)). Figure 2 (a) and (b) show Nyquist plots obtained by the cells using DOL/DME and SIL, respectively. A remarkable difference was observed in the diameter of semicircles in lower frequency range of 10Hz – 0.1 Hz at potential of 2.1 - 1.5 V. The semicircle was observed with SIL at 2.1 V, and the diameter of the semicircle increased with discharge progression. No semicircle was observed at 1.9-1.5V. On the other hand, no semicircle with DOL/DME was observed at 2.1 - 1.5 V. However, impedance response at 2.1 V changed to that at 1.9 - 1.5V. The difference at 2.1V was attributed to DOD and/or state of polysulfide in electrolyte. There was no large difference of impedance response with these electrolytes at 1.9 V -1.5 V. It is thought that similar (semi-) solid-state reactions without electrolyte was occurred, because of no effect of solving polysulfide of Li2S2 and Li2S in both electrolytes.AcknowledgementThis work was partly supported by Advanced Low Carbon Technology Research, Development Program Special Priority Research Area “Next-Generation Rechargeable Battery” (ALCA-Spring) from the Japan Science and Technology Agency (JST) (Grant Number JPMJAL1301).Reference(1) K. Dokko et al., J. Electrochem. Soc., 160, A1304-A1310 (2013).(2) N. Nakamura et al., J Power Sources, 274, 1263-1266 (2015). Figure 1

Fabrication of MSM-Based Biosensing Device for Assessing Dynamic Behavior of Adherent Mammalian Cells

Adherent mammalian cells are susceptible to the physiological conditions, i.e., physicochemical and topological properties of the extracellular microenvironment surrounding them. In this paper, cell-substrate interaction is taken as the primary step for exhibiting their optimal functions, including cell adhesion, proliferation, migration, and differentiation. Herein, the change in characteristic properties of transparent semiconducting metal oxide, ZnO thin film as a function of the progression of cellular processes and functions resulting from cell-substrate and cell-cell interactions is reported. We have monitored the change in characteristic electrical properties of ZnO thin film by a fabricated metal-semiconductor-metal (MSM) structure based biosensing platform. Further, we have demonstrated the improvement in cell adhesion on ZnO thin films through the gelatin functionalization process. Furthermore, the Nyquist plot characteristics are used to investigate the electrical properties of the fabricated MSM biosensor, which gets altered with the progression of cellular functions over time. Correspondingly, it is also observed that the true impedance of the fabricated device gets increased with a noticeable shift towards the higher resistance region with a significant increase in the semi-circle diameter. Hence, we anticipate that the fabricated MSM based biosensing platform can be used as a promising device for monitoring the functional behavior of adherent cells.

Enhanced electrochemical properties of Co3O4 with morphological hierarchy for energy storage application: A comparative study with different electrolytes

A facile hydrothermal route synthesizes Co3O4 nanocrystals with urchin spine-like morphology. Structure and microstructural characterizations of the sample are carried out. Electrochemical properties have been explored in the presence of different electrolytes. In order to find out the best electrolyte, three electrolytes (Na2SO4, NaOH and Na2SO4 with Hq) of fixed concentration (1 M) are used to record the cyclic voltammetry data. In the presence of Na2SO4 as an electrolyte, specific capacitance becomes 218 F g−1, possibly because of low ionic conductivity of SO42−, higher charge transfer resistance. When NaOH and Na2SO4 (with Hq) are used as electrolytes, high specific capacitances of 1720 F g−1 and 2433 F g−1 respectively are obtained due to extra pseudocapacitive effect of redox reaction. It is worth noting that the semicircle diameter in the EIS plot is highest for Na2SO4 and lowest for Na2SO4 (with Hq) electrolyte. The Rct value depends on the type of electrode and the interaction between electrolyte ions with the electrode.

Polymer Ionic Liquids As Perspective Materials for Chemiresistors and QCM Sensors

Introduction Polymerized ionic liquids (PILs) have been reported for the first time in 1998, and a brief overview of their properties can be found e.g. in [1]. Their electrotransport properties are unique (when compared with other organic substances), as they are purely ionic conductors. Moreover, majority of them can be considered as single-ion conductors. PILs are characterized by large capacity to absorb analytes with small molecules – especially CO2 and water. When such absorption, the internal volume of polymer is modified, hence the mobility of ions changes [2]. Such a phenomenon could work as a prospective transducer mechanism in chemiresistors. This property of PILs is very valuable, because namely CO2 and numerous other analytes (whose molecule has neither redox properties, nor dipole moments) cannot be detected on chemiresistors by any other mechanism.In the field of chemical sensing, PILs are often employed in electrochemical sensors, but much rarely for sorbents in QCM sensors [3]. Surprising still, their applications in chemiresistors are at a pioneering stage [4]. This contribution presents the research of chemiresistors and QCM sensors with sensitive layers based on poly(tetrabutylphosphonium 3-sulfopropylacrylate) marked as poly(P4,4,4,4SPA) and poly(tributyl-octylphosphonium 3-sulfopropylacrylate) marked as poly(P4,4,4,8SPA). The response of prepared sensors to noble gases, hydrogen, carbon dioxide, alkanes and methanol vapours was evaluated by impedance spectroscopy. The purpose was to study the consequences between the molecular weight and/or chemical reactivity of the analyte on one side and the sensing mechanism (modulation of electrotransport parameters of PIL in chemiresistor; modulation of the amount of analyte absorbed in PIL in QCM) on the other side. Experimental Both the monomers P4,4,4,4SPA and P4,4,4,8SPA were synthesized as follows: the respective chlorides P4,4,4,4Cl and P4,4,4,8Cl were dissolved in distilled water and subsequently the 1.5 molar equivalent of potassium 3- sulfopropylacrylate was added dropwise; this solution was continuously stirred at 30°C for 18 h. Hence the ion exchange proceeded. Subsequently the water was evaporated in a high vacuum and the crystallic phase was dissolved in ethylacetate and filtered. The monomers were obtained after evaporation of ethylacetate. Subsequently 2% molar equivalent of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (initiator of polymerization) and 1% of thimethylolpropane ethoxylate triacrylate (cross-linking agent) in distilled water were added, the resulting mixture was dropped to sensor substrates. For chemiresistors we used glass sensor platforms with gold electrodes and in case of QCM sensors directly quartz crystal with gold electrode was applied. The photopolymerization was carried out by exposition to a source of "white" light Leica LMI-6000 Fiber-Lite for 45 min, thus obtaining final sensors – chemiresistors or QCM with sensitive layers based on two PILs - poly(P4,4,4,4SPA) and poly(P4,4,4,8SPA).The responses of both chemiresistors and QCM sensors to 10 000 ppm of noble gases (He, Ne, Ar, Kr), carbon dioxide, hydrogen, alkanes (n- penthane, n- hexane, n-heptane) and methanol vapours were tested. As a reference gas we used synthetic air. The impedance measurements of chemiresistors were carried out with GAMRY Reference 600 apparatus in the range of frequencies from 10 mHz to 1 MHz and their results evaluated as Nyquist plots. For QCM sensors the Agilent 4294 impedance analyzer operating in frequency range 1 – 100 MHz was used and the shift of the resonance frequency observed. Results and discussion An example of Nyquist plot of the chemiresistor with poly(P4,4,4,8SPA) is presented in Fig.1. The upper part corresponds to sensor exposed to synthetic air and the downer part to sensor in 10 000 ppm of CO2 in synthetic air. The experimental data (blue line) were fitted by Randles circuit (red line). In both plots two characteristic regions can be recognized – low frequency "tail", which can be described as the Warburg impedance and, further, high frequency semicircle attributed to charge transfer phenomena between PIL and the gold electrode of chemiresistor. On exposure to CO2 the value of Warburg impedance (Zw) decreased from (2.43 x 1011 Ω.s1/2) to (2.16 x 1011 Ω.s1/2). Also, on exposure to CO2 the resistance between PIL and gold electrode (corresponding to semicircle diameter) was lowered from 10.1 to 5.9 MΩ. Amongst the noble gases it was revealed that when detected on poly(P4,4,4,8SPA) the Warburg impedance increases monotonously with increasing molecular (in fact atomic) weight. When expressed relatively and taking the Warburg impedance in krypton Zw (Kr) as 100%, then Zw (He) ≈ 50%, then Zw (He) ≈ 50%, Zw (Ne) ≈ 60%, and Zw (Ar) ≈ 85%. The possibility to detect noble gases by chemiresitors is rather unique. The exposure of QCM sensors with poly(P4,4,4,4SPA) and poly(P4,4,4,8SPA) to the above mentioned analytes lead to change in resonance frequency by 101 – 102 Hz.

Nanoparticles of Nd(OH)3-NiTe2 for electrocatalytic oxidation of glucose

Herein, the Nd(OH)3-NiTe2 nanoparticles were synthesized by hydrothermal synthesis. The crystal structure, morphology and surface element composition were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy. At the same time, the electrocatalytic performance of Nd(OH)3-NiTe2 for glucose oxidation in alkaline electrolyte was determined by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). It exhibits a high peak current density of about 21.09 mA/cm2 for glucose oxidation. The low semicircle diameter of 8000 Ω means fast electron transfer of Nd(OH)3-NiTe2. The oxidation signal of glucose at 0.5 V tends to be constant within 36000 s. Electrochemical experiments show that Nd(OH)3-NiTe2 nanoparticles exhibit good electrocatalytic activity and stability for the oxidation of glucose, which proves their potential application in the field of fuel cells.

Design of ultrafine nickel oxide nanostructured material for enhanced electrocatalytic oxidation of urea: Physicochemical and electrochemical analyses

Ultrafine nanostructured-NiO is designed via a simple electrodeposition process on a glassy carbon surface. The morphological and structural characteristics of the nickel oxide/glassy-carbon (NiO/GC) are investigated through field-emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX), transmission electron microscopy (TEM), and X-ray diffraction (XRD) techniques. The electrocatalytic performance of the designed material towards urea oxidation in 1.0 M KOH is studied under different conditions of deposition time, scan rate and urea concentration. Electrochemical characterizations of urea oxidation are accomplished using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronoamperometry (CA). The electrodeposited ultrafine NiO displays a distinctive electrocatalytic urea oxidation performance. Numerically, the produced anodic current reached up to 1.089 mA for 0.25 M urea, with clear peaks for electrooxidation of urea in the forward and reverse sweep. EIS measurements showed that the diameter of semicircles is dependent on the experimental conditions, and the resistances of charge transfer values are found to be lower in the solutions containing urea, which is related to the excellent urea electrooxidation performance. Here, ultrafine nanostructured NiO is introduced to serve a critical function as a catalytic moderator to accelerate the charge transfer in the anodic part of the urea fuel-cell (UFC), which can affect both the efficiency and cost of UFCs.

Structural, Impedance, and EDLC Characteristics of Proton Conducting Chitosan-Based Polymer Blend Electrolytes with High Electrochemical Stability.

In this report, a facile solution casting technique was used to fabricate polymer blend electrolytes of chitosan (CS):poly (ethylene oxide) (PEO):NH4SCN with high electrochemical stability (2.43V). Fourier transform infrared (FTIR) spectroscopy was used to investigate the polymer electrolyte formation. For the electrochemical property analysis, cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) techniques were carried out. Referring to the FTIR spectra, a complex formation between the added salt and CS:PEO was deduced by considering the decreasing and shifting of FTIR bands intensity in terms of functional groups. The CS:PEO:NH4SCN electrolyte was found to be electrochemically stable as the applied voltage linearly swept up to 2.43V. The cyclic voltammogram has presented a wide potential window without showing any sign of redox peaks on the electrode surface. The proved mechanisms of charge storage in these fabricated systems were found to be double layer charging. The EIS analysis showed the existence of bulk resistance, wherein the semicircle diameter decreased with increasing salt concentration. The calculated maximum DC conductivity value was observed to be 2.11 × 10−4 S/cm for CS:PEO incorporated with 40 wt% of NH4SCN salt. The charged species in CS:PEO:NH4SCN electrolytes were considered to be predominantly ionic in nature. This was verified from transference number analysis (TNM), in which ion and electron transference numbers were found to be tion = 0.954 and tel = 0.045, respectively. The results obtained for both ion transference number and DC conductivity implied the possibility of fabricating electrolytes for electrochemical double layer capacitor (EDLC) device application. The specific capacitance of the fabricated EDLC was obtained from the area under the curve of the CV plot.