Electron Impedance Spectroscopy Research Articles

Polymer blending and nanophotocatalyst loading synergy in visible light‐driven photocatalytic PES/SPSf mixed matrix membranes

AbstractThe synergy of polymer blending and loading photocatalytic titania–amorphous carbon nanotubes (TiO2–aCNT) in tailoring the morphological, surface, and optoelectrical properties of membranes is investigated. High energy band gap (Eg) polyethersulfone (PES), and low Eg sulfonated polyethersulfone (SPSf) polymer blends were loaded with TiO2–aCNT nanocomposite fillers. SEM reveals membranes consisting of a selective layer, a dense sublayer and a spongy layer with the latter two consisting of a network of nanofibers whose diameters decrease with increasing TiO2–aCNT loading. The downshifting in the wavenumbers of sulfonyl and sulfone peaks in Fourier transform infrared and Raman spectra confirms bonding of TiO2–aCNT with PES/SPSf via these groups. Blending PES with SPSf decreases the Eg of the membranes while loading TiO2–aCNT produces a second band edge corresponding to = 2.8 eV. Suppression of charge recombination in membranes is realized at 1.2 filler wt.%. Charge separation occurrs via shuttling of the positive holes to the aCNTs and valence band of TiO2 while electrons are shuttled to the conduction bands of PES and SPSf. Electron impedance spectroscopy shows TiO2–aCNT loading reduces polymer membrane resistance to charge transport. Dye degradation up to 85% is realized under direct sunlight irradiation accompanied by mineralization.

Structural and dielectric properties of CaSnO3-doped Sr2.1Na0.8Nb5O15 ceramics

The crystallographic, microstructural, and dielectric properties of Sr2.1Na0.8-xCaxNb5-xSnxO15 (x = 0.00, 0.01, 0.05, 0.10) polycrystalline ceramics have been studied by X-ray diffraction, scanning electron microscopy, dielectric spectroscopy (DS) and impedance spectroscopy (IS). For x = 0.00, 0.05, and 0.10, samples are single phase with P4bm symmetry at room temperature with x = 0.01 showing a small quantity of secondary phase(s). All compositions show typical ceramic microstructures and d50 grain sizes ranging from 5.1 to 26.6 μm. DS shows a clear trend in the high temperature ferroelectric-paraelectric transition with the Curie temperature, T0, decreasing from ∼ 160 to ∼ 110 °C, and an additional relaxation at approximately 120 °C with increasing CaSnO3. IS reveals all samples have a homogeneous electrical microstructure with predominantly electronic conduction. The activation energy of conduction calculated from Arrhenius plots of the conductivity increases with CaSnO3 content from 1.27 to 1.38 eV likely due to the expansion of the band gap.

Silver Nanoparticles Decorated in In Situ Reduced Graphene Oxide Nanohybrids Improved Properties in Poly(vinylidene fluoride)/Poly(methyl methacrylate) Blends

In this paper, reduced graphene oxide decorated with silver nanoparticle (rGO-Ag) nanohybrids were prepared using an environmentally friendly approach and incorporated as reinforcement in poly(vinylidene fluoride)-poly(methyl methacrylate) blends via a melt mixing process. The microstructure of rGO-Ag nanohybrids and its effect on the microstructure, mechanical, thermal, and electrical properties of the PVDF/PMM/rGO-Ag was studied using Fourier transform infrared (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), tensile, thermogravimetric analysis (TGA), and impedance spectroscopy methods. FTIR and TEM analysis confirmed that rGO-Ag successfully synthesized and Ag nanoparticles are located on the rGO surface. The tensile analysis demonstrated that incorporating 1 wt.% of rGO-Ag in PVDF/PMMA blend increases Young’s modulus and strength of nanocomposite up to 31% and 35%, respectively. The Halpin-Tsai model was also used for PVDF/PMMA/rGO-Ag nanocomposites, and the results confirmed that this model works well to predict the tensile modulus. Impedance spectroscopy analysis showed that the presence of rGO-Ag nanohybrids in PVDF/PMMA blend effectively enhanced the conductivity of PVDF/PMMA blend. TGA results demonstrated that the presence of rGO-Ag nanohybrids enhanced the thermal stability of nanocomposites and increased the degradation temperature of PVDF/PMMA/rGO-Ag nanocomposites in the range of 20°C compared to PVDF/PMMA blend.

Microstructures and Dielectric Permittivity Properties of Fe3O4/Cdots Nanocomposites Synthesized by Green Route Utilizing Moringa Oleifera Extract and Watermelon Peel

Dielectric materials are beneficial for storing electrical energy due to their insulating and polarization properties in response to external electric fields. Magnetite has shown promise as a dielectric material among other materials due to its good magnetic properties, low toxicity, and biocompatibility. However, the weakness of Fe3O4, which has low stability and easy agglomeration, requires a modification on its surface by using Carbon dots (Cdots). This research investigates the dielectric properties of Fe3O4/Cdots obtained through the green synthesis method. Fe3O4 nanoparticles were synthesized using the co-precipitation method with Moringa oleifera leaf extract as a reducing and stabilizing agent. In contrast, Cdots were synthesized using the hydrothermal method with watermelon peel waste as a carbon source. The Fe3O4 composite nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), ultraviolet-visible spectroscopy (UV-Vis), and impedance spectroscopy. The XRD spectra revealed the existence of cubic inverse spinel and a reduction in crystal size as the concentration of Cdots increased, measuring 7.8 and 7.1 nm, respectively. SEM-EDX revealed that the sample is composed of Fe, O, and C elements and has a spherical shape with Cdots distributed on the surface of Fe3O4. The UV-Vis spectrum showed the absorption peak of Cdots at 282 nm. The Fe3O4 absorption peak is identical to the Fe3O4/Cdots absorption peak at 193 nm. The increase in band gap energy from 2.96 to 3.33 eV is related to the increase in Cdots concentration. In the 10-900 kHz frequency range, dielectric property tests demonstrated peak dielectric permittivity values (real and imaginary). A substantial decrease was observed between 10 kHz and 200 kHz, followed by a relatively stable pattern up to 900 kHz. The loss tangent value obtained has a tanδ value <0.5, which means that the addition of Cdots affects reducing the energy loss stored in Fe3O4.

Defect-induced improved structural and electrical properties of Gd-Sr co-doped ceria for solid oxide fuel cell applications

Compositions of Ce1-x-yGdxSryO2-δ (x = 0.1, 0.2, and y = 0.025, 0.05, 0.075) are prepared using the sol-gel auto combustion method. The as-prepared powders are calcined at 500 °C for 2 h, followed by pelletization and sintering at 1450 °C for 4 h. Phase identification, defect distribution, microstructural analysis, and conductivity are examined using X-ray diffraction, Raman spectroscopy, scanning electron microscopy and impedance spectroscopy, respectively. A single crystalline phase is formed, and the lattice parameter variation with dopant concentration exhibits anomalous behavior. All the samples show relative densities higher than 92 %. The partial liquid phase sintering is also observed. In co-doped samples, the doping of 10 % Gd with 2.5 % Sr exhibits the highest conductivity, i.e., 1.20 × 10−2 S cm−1 at 600 °C. The developed materials are used in anode-supported cell testing. It shows a maximum power density of 112.7 mW cm−2 and a current density of 288.7 mA cm−2 at 600 °C with wet hydrogen and air on the anode and cathode side, respectively.

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers.

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

Synthesis of Pure and Bi‐Doped Lead Oxides via Microwave‐Assisted Solvothermal Methodology and their Electrochemical Characterization

AbstractIn this study, we have reported the synthesis of both pure and bismuth‐doped lead oxide nanoparticles using solvothermal method. The synthesized nanomaterials were analyzed to assess their structure, crystallinity, phase, maximum absorption and band gap. The electrical characteristics of the fabricated nanostructures were evaluated using cyclic voltammetry (CV) and electron impedance spectroscopy (EIS). The maximum specific capacitance and energy density, 349.96 F/g and 95.27 Wh/g respectively, were attained at a scan rate of 200 mV/s in pure lead oxide. The synthesized pure lead oxide has displayed remarkable cyclic stability, retaining approximately 83 % of its performance even after undergoing 2000 cycles. The addition of bismuth to the lead oxide appeared to inhibit the electrochemical properties of lead oxide due to bismuth ion adsorption. This effect is directly concerned with the amount of dopant which predicted the increase in bismuth contents potentially suppressed the performance of the lead oxide. Our study provides insights into the possible uses of lead oxides in energy storage and conversion devices by revealing a previously unexplored method for optimizing their electrochemical characteristics. The understanding of oxide‐based materials in materials science and electrochemistry is expected to advance with the use of this novel technology.

Influences of ZrO2 content on microstructural and ionic conductivity of Li1.4Al0.4Ti1.6(PO4)3 solid-state electrolytes

NASICON-type electrolyte Li1.4Al0.4Ti1.6(PO4)3 attracts great attention with its high grain conductivity and stable microstructure. In this work, the Li1.4Al0.4Ti(1.6-x)Zrx(PO4)3 solid-state electrolytes were synthetized. And the influences of ZrO2 addition on microstructural evaluation and ionic conductivity of Li1.4Al0.4Ti(1.6-x)Zrx(PO4)3 were studied using powder X-ray diffraction, scanning electron microscopy and impedance spectroscopy. All synthetic samples adopted single phase LiTi2(PO4)3 with NASICON type structure. The highest ionic conductivity of 0.54 mS/cm and the minimum activation energy of 0.232 eV were achieved for x = 0.04 sample sintered at 850 °C. These results indicate that ZrO2 added Li1.4Al0.4Ti1.6(PO4)3 ceramic has a potential application in solid electrolytes.

Impact of ZnMn2O4/CdS nanocomposite on the structural, optical and dielectric characteristics of PMMA/PEO blend

Herein, polymethyl methacrylate (PMMA)/ polyethylene oxide (PEO) blend doped with nanocomposite (1 − x) ZnMn2O4/xCdS samples were prepared through two steps, the first comprising nanocomposite (1 − x) ZnMn2O4/xCdS samples synthesizing, while the second was the incorporation of nanocomposites into the blend matrix, and finally the films were obtained through the casting solution method. Various techniques, such as X-ray diffraction, scanning electron microscopy, diffused reflection and impedance spectroscopy were used to determine the change in the PMMA/PEO structure after the inclusion of the nanocomposites. The direct and indirect optical bandgap values for the PMMA/PEO blend decreased from 5.04 and 4.8 eV to 4.99 and 4.7 eV, respectively, as the blend doped with (1 − x) ZnMn2O4/xCdS samples. At 600 nm, the refractive index of the blend was raised from 1.37 to 1.53 as it doped with 0.9 ZnMn2O4/0.1CdS sample. The linear and nonlinear optical parameters grow with the insertion of (1-x)ZnMn2O4/xCdS nanocomposites into the PMMA/PEO blend. Variation of CdS in the doped nanocomposites affects slightly the linear and nonlinear optical parameters of the host blend. Blend containing 10 % CdS has the highest linear and nonlinear optical parameters as compared with other doped blends. All of the blends exhibited different shades of blue color, except for the blend that contained 10 % CdS, which displayed a violet color. The effect of doping on the dielectric properties of different blends was also explored. Blend with 20 % CdS has the highest energy density. This improvement implies the use of prepared blends in different optoelectronic, photocatalytic and storage device applications.

Electrochemical investigation of an anticancer drug 5-Fluorouracil in the presence of Theophylline using low-cost and disposable poly(GLY) modified pencil graphite electrode

Herein this study, a facile, efficient and disposable electrochemical sensor has been prepared by electropolymerization of glycine (poly(GLY)) on the surface of pencil graphite electrode (PGE). The surface topology of the equipped poly(GLY) modified pencil graphite electrode (poly(GLY)/PGE) and bare pencil graphite electrode (BPGE) has been characterized by the scanning electron microscopy (SEM) combined with energy dispersive x-ray analysis (EDX) and charge transfer behaviour was measured by electron impedance spectroscopy (EIS) method. The voltammetric behaviour of anticancer, 5-fluorouracil (5-FU) in the presence of theophylline (THP) has been carried out in 0.1 M phosphate buffer solution (PBS) of physiological pH 7.0 using different techniques such as cyclic voltammetry (CV), linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV). The proposed poly(GLY)/PGE shows augmented peak current for 5-FU at lower potential side over the BPGE due to the electrocatalytic behaviour of modifier layers wrapped on the electrode surface. The kinetic behaviour of 5-FU at modified electrode surface was studied by varying different parameters such as pH, scan rate and concentration study in 0.1 M PBS used as a supporting electrolyte. The limit of detection (LOD) for 5-FU was attained using DPV method with different concentrations (1.0–13.0 μM) and it was found to be 0.012 μM. The possible electrochemical reaction of 5-FU was proposed and it was incorporated by two electrons and two protons mechanism at modified electrode surface. The voltammetric response of poly(GLY)/PGE towards the determination of 5-FU was unaffected in the presence of some excipients in addition to the remarkable stability and reproducibility. The applicability of the proposed sensor has been performed by real sample investigation of 5-FU with a substantial percentage of recovery results in all optimized conditions.

Supercapacitive behavior and energy storage properties of molybdenum carbide ceramics synthesized via ball milling technique

Energy production and energy storage materials are highly in demand due to their versatility, stability, sustainability, and better conductivity. Low-cost and highly efficient electrode materials (cathode/anode) for electrochemical supercapacitors (SCs) have been highly explored in the last two decades. Herein, we have synthesized Mo2C via a facile, cost-efficient, and green approach (ball milling). This work provides a new route to synthesize Mo2C, as compared with traditional techniques, to reduce the emission of poisonous gases at high temperatures. Furthermore, a comparison of the electrochemical performance of the bulk and nanostructured Mo2C was also investigated. The obtained results proved that smaller particle sizes and higher surface area are the efficient edges for the competitive performance of nanostructured Mo2C. Electron impedance spectroscopy (EIS), galvanostatic charge/discharge (GCD), and cyclic voltammetry (CV) were used to assess the electrochemical performance of bulk and nanostructured Mo2C. Nanostructured Mo2C has delivered 206 F/g at a current density of 0.1 A/g in 3M-KOH electrolyte. Nanostructured Mo2C has shown ultra-long cyclic stability after 20000th GCD cycles with 92 % retention with 100 % Coulombic efficiency. These results predicted that nanostructured Mo2C is a good electrode material for supercapacitors.

Electrochemical Reduction of Ytterbium in Non-Aqueous Solvents - Towards Production of Pure Medical Lutetium-177

In recent years targeted radionuclide therapy has become a topic of great interest as a growing number of cancers can potentially be treated with radionuclides like lutetium-177 and samarium-153. To facilitate this growth and meet the demand, preparation and purification of lutetium-177 is increasing in importance. In the most common production route, enriched ytterbium-176 targets are irradiated and the produced lutetium-177 is separated from the ytterbium target material. This challenging separation is commonly performed using ion exchange resins, a method limited in scalability as the chemical similarity between ytterbium and lutetium results in poor separation at higher concentrations.An alternative method to aid the separation of lutetium from ytterbium is the electrochemical reduction of ytterbium as a change in oxidation states changes chemical properties significantly. Ytterbium has an accessible divalent state, whereas lutetium has not. However, the very negative value of the Yb(III)/Yb(II) standard reduction potential (E0= -1.04 V vs. SHE) does pose some challenges as it becomes a necessity to work in non-aqueous solvents with a very low water content. Similar research has already been performed in our group, looking into the separation of samarium-153 from europium-154, reducing europium in nitrate media, followed by a separation over TEVA resin. In this study, we investigated the reduction of ytterbium in ethylene glycol, dimethyl sulfoxide, tetrahydrofuran and N,N-dimethyl formamide by cyclic voltammetry, linear sweep voltammetry and electronic impedance spectroscopy. The influence of multiple variables such as moisture content on the reduction kinetics and stability of Yb(II) was determined and a Koutecky-Levich analysis was performed. Our results demonstrate that the reduction of ytterbium in non-aqueous solvents is feasible but attempts to perform bulk electrolysis were not successful yet. Ethylene glycol, dimethyl sulfoxide and N,N-dimethyl formamide demonstrate favorable conditions and in each solvents clear reduction and oxidation peaks were observed. It was found that the solvents do affect the peak separation, reduction potential and sensitivity to passivation. Figure 1

Biogas Reforming Combined with Co-Electrolysis inside AC:DC Operated Solid Oxide Electrolyser Cells

Upgrading biogas into added-value fuels and chemicals is seen as one of the main pathways to reduce carbon dioxide emissions from the energy sector. In particular, green methanol represents a strategical product due to its high versatility in the transportation and chemical industry. Biogas reforming is a key step in the upgrading process and it can be integrated with Power-to-X technology. The reforming can be conducted using Solid Oxide Electrolysers (SOEs). Furthermore, the outlet syngas composition can be adjusted and optimized for methanol production, via the additional production of hydrogen provided by the simultaneous steam electrolysis.This research focuses on analysing the effects of Dynelectro’s patented AC:DC operation [EP3719171A1, WO2020/201485A1, EP3947779A1] applied to biogas-fed SOE cells. The principle of this novel operating condition is to impose an alternating current over a direct current, which for SOE translates into reversing the polarization of the cell and having a regular switch between fuel cell mode and electrolysis mode. When performing steam electrolysis, the benefits of AC:DC operation are already proven to consist in reduced degradation, due to impurities removal, and enhanced temperature control during dynamic operations [Skafte, 2022]. When the SOE cell is fed with a composition of methane, carbon dioxide and steam, the main issue to solve is the high energy requirement from the steam reforming process and the steam electrolysis performed simultaneously. In fact, both reactions are endothermic at SOE operating conditions (750°C and ambient pressure), with an enthalpy difference of respectively 225 kJ/mol and 248 kJ/mol. In this regard, the AC:DC operation can provide additional heat, because of the polarization switch to fuel cell mode, and avoid the temperature drop within the SOE. Moreover, it is possible to tune the rate of co-electrolysis and biogas reforming.A mathematical model is developed to simulate biogas reforming in an AC:DC operated SOE cell. The model includes mass transport, electrochemistry, catalytic reactions and energy balance. The composition of biogas is assumed to be mainly methane and carbon dioxide. By operating both in DC and AC:DC, this gives a first indication of the extent of the expected benefits. To validate the model, laboratory experiments are performed, where single SOE cells are operated in an imitated biogas compositions and the outlet gas is analysed using gas chromatography. These experiments include current-voltage (i-V) curves and electronic impedance spectroscopy (EIS) analysis, which can be used to measure the performances of such operations by observing the cell voltage and the degradation rate.The results from ordinary direct current operation and Dynelectro’s AC:DC operation are compared in terms of syngas composition and operating voltage. The optimal composition of syngas for methanol synthesis, consisting of a ratio of hydrogen to carbon monoxide of approximately 2 and low traces of methane, is achieved. Reduced methane content in the outlet gas is shown when operating the SOE cells with AC:DC current, compared to DC operations. The latter shows a CH4 molar fraction of approximately 1%, while the former allows the CH4 concentration to go below this level, depending on the AC:DC parameters. It is found that the rate of methane and carbon dioxide conversion is dependent on the frequency and duty cycle of the AC:DC operation. The achievement of stable conditions during these operations leads to an optimized biogas to syngas conversion, and a simplified overall biogas to methanol process.

The Influence of Silica Dioxide in the Electrocatalytic Performances of rGO/Fe&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;4&lt;/sub&gt; as Oxygen Reduction Electrocatalyst

In this study, synthesis of reduced graphene oxide-iron oxide-silica dioxide (rGO/Fe3O4/SiO2) was done through a facile chemical process. Physical characterization was carried out as such Fourier transform infrared spectroscopy (FTIR) which confirmed the presence of silica peak in the spectrum of rGO/Fe3O4/SiO2, while RAMAN displayed the vibrational bands of carbon materials studied. Results of SEM-EDX and TEM confirmed the unification of SiO2 on rGO/Fe3O4 nanocomposite with difference in morphologic structure. X-ray diffraction (XRD) analysis exhibited that addition of SiO2 increased the crystalline size of the nanocomposite. Nitrogen adsorption isotherm analysis describes the nanocomposites fall in the mesopore region. The nanocomposite was then drop-casted on the surface of glassy carbon electrode (GCE) for fabrication of the electrode which denoted as rGO/Fe3O4/SiO2/GCE. Electrochemical characterization of modified electrode was studied using electron impedance spectroscopy (EIS), which showed the minimal resistance charge transfer. Oxygen reduction reaction analysis shows that electrocatalytic reduction of oxygen was excellent with four-electron transfer when calculated using Randles-Sevcik equation. All the analysis was compared to the nanocomposites without the addition of silica oxide (rGO/Fe3O4). This work proves that addition of nanoparticle in a compound as a matrix improves the oxygen reduction potential of rGO/Fe3O4/SiO2/GCE composite.

Defect chemistry to trigger zirconia densification at low temperatures by Spark Plasma Sintering

In-depth control of reactivity and defects chemistry is shown to be mandatory to reach high density YSZ ceramics at sintering temperatures lower than 900°C. The combination of Cold Sintering Process (CSP) and Spark Plasma Sintering (SPS) has highlighted the role of transient chemistry on the densification of this material. More, optimised conditions were found for achieving densification of YSZ at 850°C in a one-step SPS process. In particular, the vacuum level in the SPS chamber is clearly shown to be a decisive parameter to obtain dense nanostructured YSZ tetragonal ceramics up to 95% below 900°C. The occurrence of oxygen vacancies has thus been addressed associating thermal analyses, X-ray photoelectron spectroscopy, Electron Paramagnetic Resonance, photoluminescence spectroscopy and impedance spectroscopy. Understanding defect chemistry mechanisms and their dependence on the process or combination of processes, is a lever towards high-quality YSZ nanostructured ceramics below 900°C.

Anode and cathode overpotentials under accelerated stress testing of a PEM electrolysis cell

An in-situ reference electrode was used under accelerated stress testing of a proton exchange membrane electrolysis cell. The reference electrode enabled the measurement of anodic and cathodic overpotentials. The accelerated stress test (dynamic load degradation) was conducted for over 1000 h, and it included half-cell measurements of the known anode and cathode potentials, repeated polarization curves, electron impedance spectroscopy and nano-scale imaging.The experiment had an average full-cell degradation rate of 77 μV/h. The anodic overpotential appears to be the main driver of the full-cell efficiency loss. The cathode EIS measurements indicate catalyst layer degradation despite minimal effect on the full-cell performance. The anodic EIS measurements yielded a resistance double that observed at the cathode. By simultaneously analyzing high frequency resistance, corrected half-cell polarization curves and half-cell EIS measurements, half-cell overpotentials can be attributed with greater confidence.

3D-graphene hydrogel and tungsten trioxide-MnO2 composite for ultra-high-capacity asymmetric supercapacitors: A comparative study

Researchers worldwide use graphene extensively in its powder form for various applications such as supercapacitors, solar cells, drug delivery, and polymer composites, owing to its considerably valuable properties. However, relatively few studies have been made on the 3D-hydrogel form of graphene for these applications. Here we report a simple and fresh method to prepare 3D graphene hydrogel (3DGH) and its bimetal composite with tungsten trioxide (WO3) and manganese dioxide (MnO2). The structure of 3DGH and its composite is confirmed by advanced characterization techniques viz. Raman Spectroscopy, X-Ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and tunneling electron microscope (TEM). Further, two symmetric devices using 3DGH, 3DGH-metal composite (3DGHMC), and one asymmetric 3DGHMC-3DGH device are comparatively studied using two electrode systems. The effects of scan rates, current densities, voltage window, and frequency were examined for each device by cyclic voltammetry (CV), galvanic charge-discharge (GCD), and Electron impedance spectroscopy (EIS). The asymmetric device showed a high specific capacitance of 657 F g−1 with an excellent energy density of 48.25 W h kg−1 and a high-power density of 596.06 W kg−1 at the current density of 1 A g−1. Also, the asymmetric device retains 100 % of its initial capacitance after 1000 charging-discharging cycles, also extends its stability after 1000 cycling test. Moreover, the quantitative analysis of the device is also made by Dunn's method to evaluate the percentage contribution from surface and diffusion capacitance.

Design and usage of NiO/g-C3N4/CNTs/TiO2 based nanocomposites as improved supercapacitor for energy storage devices

Scientists have been concentrating on storing and converting energy resources in significant scenarios as the entire globe is currently experiencing an extreme energy shortage issue owing to a variety of factors. Supercapacitors and other energy storage technologies based on transition metals are currently in high demand. In this study, multi-component NiO/g-C3N4/CNTs and NiO/g-C3N4/CNTs/TiO2 nanocomposites were effectively constructed, characterised, and the performance of the synthesized materials was reported as super capacitance. The synthesis of NiO/g-C3N4/CNTs and NiO/g-C3N4/CNTs/TiO2 using thermal, heat-treatment, hydrothermal and ultrasonic exfoliation techniques. With impressive findings, the characterisation of X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) was conducted. Cyclic Voltammetry (CV), Galvanic Charge Discharge (GCD), and scan rate influence on specific capacitance were used in the electrochemical experiments. Results of Electron Impedance Spectroscopy (EIS) experiments revealed that the NiO/g-C3N4/CNTs/TiO2 electrode had a higher specific capacitance (388.76 Fg−1) than the NiO/g-C3N4/CNTs electrode (362.12 Fg−1). In comparison to NiO/g-C3N4/CNTs (360 Fg−1), the NiO/g-C3N4/CNTs/TiO2 electrode had a gravimetric capacitance of 541 Fg−1. The GCD curve and EIS results also support the conclusion that the NiO/g-C3N4/CNTs/TiO2 electrode material is an excellent candidate with impressive capacitive performance to be used as an energy storing source or supercapacitor because TiO2 contents are available, improving the charge transfer capability linked with CNTs bridged in g-C3N4 interlayered stacked and porous structure, ensuring ion diffusion pathways for better and improved conductivity.

Characterization of sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots

In this research we are reporting for the first time the elaboration y characterization of titanium dioxide sensitized solar cells based on nanocomposites of protoporphyrin IX and microwave reduced graphene oxide quantum dots. Reduced graphene oxide quantum dots were synthesized by microwave assisted cutting of reduced graphene oxide and mixed with protoporphyrin IX previous to be drop-casted on titanium dioxide. Characterization was done by dynamic light scattering, ultraviolet visible spectroscopy, Raman spectroscopy, atomic force microscopy, field electron scanning electron microscopy, impedance spectroscopy and current voltage measurements. There were blue and red shifts of Raman and absorption bands of protoporphyrin+reduced graphene oxide quantum dots nanocomposites, evidencing strong interactions because of π−π electrons stacking, this fact was confirmed by microscopy images showing full coverage of protoporphyrin surface by reduced graphene oxide quantum dots. Electrical characterization of titanium dioxide+protoporphyrin+reduced graphene oxide quantum dots showed one of the highest photo-responses and lowest resistivities, in line with impedance measurements in which these composites presented up to ∼200% increase in capacitance, versus TiO2 alone. Efficiency of the optimized cell was 6.13 %, this was a value 9.4 % higher versus titanium dioxide+protoporphyrin cell. The reasons for the behavior of optimized cells are discussed based on a bands diagram showing the possibility of a rectifier effect and because of the strong affinity between protoporphyrin and reduced graphene oxide quantum dots.

Graphene related materials as effective additives for electrical and electromagnetic performance of epoxy nanocomposites

The use of graphene as its ideal form remains an unsolved engineering and industrial challenge, which has led to the exploration of a range of materials called graphene related materials (GRM). Among GRM, graphene nanoplatelets (GNP) are highlighted to improve the general properties of polymers in nanocomposites. Other forms of GRM, such as nanographite and reduced graphene oxide (rGO), are also widely used. This work evaluated the effect caused by the addition of four types of GRM on the electrical, electromagnetic interference shielding efficiency (EMI SE), and Reflectivity (RL) behavior in the epoxy matrix. The nanocomposites with 5, 10, 15, 20, and 30 wt% of GRM were prepared by mechanical mixing of nanoparticles into the epoxy resin. The samples were characterized by Raman spectroscopy, scanning electron microscopy, X-ray diffraction, impedance spectroscopy, EMI SE, and reflectivity. A mathematical tool was also used to estimate the optimum thickness of samples to obtain the maximum reflection loss data. The performance evaluation at elevated GRM contents (20 and 30 wt%) had presented unique outcomes, not previously reported in the literature, which were observed aside from a deep study of the electrical and reflectivity behavior. According to the morphological analyses, each GRM studied presented different average thickness dispersion and lateral sizes. The functionalized graphene nanoplatelets with a higher aspect ratio (G4) achieved electrical percolation in the epoxy matrix for lower content (10 wt%), due to its better dispersibility into the matrix. The composition with 30 wt% of GNP (G2) also with small average thickness and lateral size, but without functionalization achieved the best electrical conductivity (10−4 S/cm) and EMI SE properties (∼20 dB), the G2 nanocomposites presented some GNP were stacked closely and aligned (as a cluster), which had activated an absorptive shielding component and increased the conductivity of the G2 pathways. The composition with 15 wt% of rGO(G3) presented promising reflection loss values RL < -12 dB and 1.3 GHZ wide for a thickness of 7.5 mm (simulated and validated), which was related to the best dissipation due to oxygen defects presence.