Mahmoud A. Hefnawy

The construction of highly efficient electrode material is of considerable interest, particularly for high capacitance and water-splitting applications. Herein, we present the preparation of a NiCo2O4-Chitosan (NC@Chit) nanocomposite using a simple hydrothermal technique designed for applications in high capacitance and water-splitting. The structure/composition of the NC@Chit composite was characterized using different analytical methods, containing electron microscope (SEM and TEM), and powder X-ray diffraction (XRD). When configured as an anode material, the NC@Chit displayed a high capacitance of 234 and 345 F g−1 (@1Ag−1 for GC/NC and NC@Chit, respectively) in an alkaline electrolyte. The direct use of the catalyst in electrocatalytic water-splitting i.e., HER and OER achieved an overpotential of 240 mV and 310 mV at a current density of 10 mA cm−2, respectively. The obtained Tafel slopes for OER and HER were 62 and 71 mV dec−1, respectively whereas the stability and durability of the fabricated electrodes were assessed through prolonged chronoamperometry measurement at constant for 10 h. The electrochemical water splitting was studied for modified nickel cobaltite surface using an impedance tool, and the charge transfer resistances were utilized to estimate the electrode activity.

One of the most effective electrocatalysts for electrochemical oxidation reactions is NiMn2O4 spinel oxide. Here, a 3-D porous substrate with good conductivity called carbon felt (CF) is utilized. The composite of NiMn2O4-supported carbon felt was prepared using the facile hydrothermal method. The prepared electrode was characterized by various surface and bulk analyses like powder X-ray diffraction, X-ray photon spectroscopy (XPS), Scanning and transmitted electron microscopy, thermal analysis (DTA), energy dispersive X-ray (EDX), and Brunauer–Emmett–Teller (BET). The activity of NiMn2O4 toward the electrochemical conversion of ethylene glycol at a wide range of concentrations was investigated. The electrode showed a current density of 24 mA cm−2 at a potential of 0.5 V (vs. Ag/AgCl). Furthermore, the ability of the electrode toward hydrogen evaluation in an alkaline medium was performed. Thus, the electrode achieved a current density equal 10 mA cm−2 at an overpotential of 210 mV (vs. RHE), and the provided Tafel slope was 98 mV dec−1.

The production of green hydrogen using water electrolysis is widely regarded as one of the most promising technologies. On the other hand, the oxygen evolution reaction (OER) is thermodynamically unfavorable and needs significant overpotential to proceed at a sufficient rate. Here, we outline important structural and chemical factors that affect how well a representative nickel ferrite-modified graphene oxide electrocatalyst performs in efficient water splitting applications. The activities of the modified pristine and graphene oxide-supported nickel ferrite were thoroughly characterized in terms of their structural, morphological, and electrochemical properties. This research shows that the NiFe2O4@GO electrode has an impact on both the urea oxidation reaction (UOR) and water splitting applications. NiFe2O4@GO was observed to have a current density of 26.6 mA cm−2 in 1.0 M urea and 1.0 M KOH at a scan rate of 20 mV s−1. The Tafel slope provided for UOR was 39 mV dec−1, whereas the GC/NiFe2O4@GO electrode reached a current of 10 mA cm−2 at potentials of +1.5 and −0.21 V (vs. RHE) for the OER and hydrogen evolution reaction (HER), respectively. Furthermore, charge transfer resistances were estimated for OER and HER as 133 and 347 Ω cm2, respectively.

The growing interest in energy demand became an important issue for several sectors like industry and transportation. Recently, fuel cells generated a new solution for global energy deficiency. Therefore, we developed a new catalyst for fuel cell applications that included nickel oxide nanoflower with polyaniline to enhance the electrooxidation of ethanol. The structure of the modified electrode was characterized by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). At the same time, surface morphology and structural thermal stability were utilized by Scanning electron spectroscopy (SEM) and Thermal gravimetric analysis (TGA), respectively. Otherwise, ethanol electrooxidation was studied by several electrochemistry techniques like cyclic voltammetry (CVs) and chronoamperometry (CA). The activity of the electrocatalyst toward ethanol conversion reached 32 mA cm−2 at a potential of 0.46 V (vs. Ag/AgCl). The effect of changing the thickness of the conducting polymer was studied to find out the optimum catalysis condition. Several chemical kinetics were calculated, like diffusion coefficient (D), Tafel slope, and transfer coefficient. The long-term stability of the modified electrode for 240 min. Whereas the anodic current decreased by 15% after continuous oxidation of ethanol in an alkaline medium.

Because of the complexity of various oxidation states of vanadium, vanadium oxides show a large variety of stable and metastable structures, which pose an inevitable challenge to synthesize vanadium oxides with high purity, well-controlled stoichiometry, to their different morphologies and meticulously designed nanostructures, a must for high electrochemical performance devices for Supercapacitors. Vanadium oxide-based materials have been extensively studied for their metal-insulator transition behavior, and their unique characteristics that making them a promising candidate for electrochemical performance, supercapacitors and energy storage capabilities. This review article will discuss the synthesis methods, structural characterization techniques, and applications of vanadium oxide-based materials. We will also highlight the recent advances in vanadium oxide and provide insights into these materials' prospects in the Supercapacitors field.

Calcium phosphate (CaPO4) coating is one of various methods that is used to modify the topography and the chemistry of Ti dental implant surface to solve sever oral problems that result from diseases, accidents, or even caries due to its biocompatibility. In this work, anodized (Ti-bare) was coated by CaPO4 prepared from amorphous calcium phosphate nanoparticles (ACP-NPs) and confirmed the structure by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR) techniques. Ti-bare was coated by prepared CaPO4 through the casting process, and the morphology of Ti/CaPO4 was characterized by scanning electron microscope (SEM) where the nano-flakes shape of CaPO4 and measured to be 60 ~ 80 nm was confirmed. The stability of Ti-bare and coated Ti/CaPO4 was studied in a simulated saliva solution using electrochemical impedance spectroscopy (EIS) and linear polarization techniques to deduce their corrosion resistance. Furthermore, three essential oils (EO), Cumin, Thyme, and Coriander, were used to stimulate their synergistic effect with the CaPO4 coat to enhance the corrosion resistance of Ti implant in an oral environment. The fitting EIS parameters based on Rs [RctC]W circuit proved that the charge transfer resistance (Rct) of Ti/CaPO4 increased by 264.4, 88.2, and 437.5% for Cumin, Thyme, and Coriander, respectively, at 2% concentration.

The acetaminophen is an antipyretic and nonopioid analgesic that is prescribed for the management of fever and mild to moderate pain. The detection of acetaminophen by ZnO and ZnO@Chitosan-modified electrodes made of glassy carbon was compared. Acetaminophen was detected using surfaces of ZnO and ZnO@Chitosan over a 10–50 µM concentration range. The detection limits for ZnO and ZnO@Chitosan were anticipated to be 0.94 and 0.71 μmol L−1, respectively. In a wide range of acidic, neutral, and basic mediums with varying pH values, the impact of a change in solution pH on acetaminophen sensitivity was investigated. Electrokinetic studies were used to evaluate the acetaminophen detection efficiency. The charge transfer resistance (Rc) for various surfaces was measured using electrochemical impedance spectroscopy (EIS). Using DFT studies, the synergistic effect of chitosan on zinc oxide was also shown. The Forcite model was used to calculate the surface interactions between chitosan and zinc oxide. Acetaminophen adsorption on the chitosan surface was also studied using the B3LYP density functional method.

Nickel-based catalysts have been widely recognized as highly promising electrocatalysts for oxidation. Herein, we designed a catalyst surface based on iron oxide electrodeposited on NiCo2O4 spinel oxide. Nickel foam was used as a support for the prepared catalysts. The modified surface was characterized by different techniques like electron microscopy and X-ray photon spectroscopy. The activity of the modified surface was investigated through the electrochemical oxidation of different organic molecules such as urea, ethanol, and ethylene glycol. Therefore, the modified Fe@ NiCo2O4/NF current in 1.0 M NaOH and 1.0 M fuel concentrations reached 31.4, 27.1, and 17.8 mA cm−2 for urea, ethanol, and ethylene glycol, respectively. Moreover, a range of kinetic characteristics parameters were computed, such as the diffusion coefficient, Tafel slope, and transfer coefficient. Chronoamperometry was employed to assess the electrode’s resistance to long-term oxidation. Consequently, the electrode’s activity exhibited a reduction ranging from 17% to 30% over a continuous oxidation period of 300 min.

Currently, wastewater containing high urea levels poses a significant risk to human health. Else, electrocatalytic methodologies have the potential to transform urea present in urea-rich wastewater into hydrogen, thereby contributing towards environmental conservation and facilitating the production of sustainable energy. The characterization of the NiCo2O4@chitosan catalyst was performed by various analytical techniques, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Furthermore, the activity of electrodes toward urea removal was investigated by several electrochemical techniques. As a function of current density, the performance of the modified NiCo2O4@chitosan surface was employed to remove urea using electrochemical oxidation. Consequently, the current density measurement was 43 mA cm−2 in a solution of 1.0 M urea and 1.0 M KOH. Different kinetic characteristics were investigated, including charge transfer coefficient (α), Tafel slope (29 mV dec−1), diffusion coefficient (1.87 × 10−5 cm2 s−1), and surface coverage 4.29 × 10−9 mol cm−2. The electrode showed high stability whereas it lost 10.4% of its initial current after 5 h of urea oxidation.

Water is essential for conserving biodiversity, ecology, and human health, but because of population growth and declining clean water supplies, wastewater must be treated to meet demand. Nitrite is one of the contaminants in wastewater that is well-known. It is crucial to identify nitrite since it can be fatal to humans in excessive doses. Utilizing a straightforward and effective electrochemical sensor, nitrite in actual water samples may be determined electrochemically. The sensor is created by coating the surface of a GC electrode with a thin layer of graphene oxide (GO), followed by a coating of silver nanoparticles. The modified electrode reached a linear detection range of 1–400 µM. thus, the activity of the electrode was investigated at different pH values ranging from 4 to 10 to cover acidic to highly basic environments. However, the electrode recorded limit of detection (LOD) is equal to 0.084, 0.090, and 0.055 µM for pH 4, 7, and 10, respectively. Additionally, the electrode activity was utilized in tap water and wastewater that the LOD reported as 0.16 and 0.157 µM for tape water and wastewater, respectively.

Energy storage applications received great attention due to environmental aspects. A green method was used to prepare a composite of nickel–iron-based spinel oxide nanoparticle@CNT. The prepared materials were characterized by different analytical methods like X-ray diffraction, X-ray photon spectroscopy (XPS), scanning electron microscopy (SEM), and transmitted electron microscopy (TEM). The synergistic effect between nickel–iron oxide and carbon nanotubes was characterized using different electrochemical methods like cyclic voltammetry (CV), galvanostatic charging/discharging (GCD), and electrochemical impedance spectroscopy (EIS). The capacitances of the pristine NiFe2O4 and NiFe2O4@CNT were studied in different electrolyte concentrations. The effect of OH− concentrations was studied for modified and non-modified surfaces. Furthermore, the specific capacitance was estimated for pristine and modified NiFe2O4 at a wide current range (5 to 17 A g−1). Thus, the durability of different surfaces after 2000 cycles was studied, and the capacitance retention was estimated as 78.8 and 90.1% for pristine and modified NiFe2O4. On the other hand, the capacitance rate capability was observed as 65.1% (5 to 17 A g−1) and 62.4% (5 to 17 A g−1) for NiFe2O4 and NiFe2O4@CNT electrodes.

A composite of NiCo2O4 modified electrocatalyst is prepared to enhance the ethylene glycol electrooxidation. Chitosan matrix is used to improve the activity and adsorption ability of the surface to enhance ethylene glycol conversion. A Comparative study is investigated between pristine NiCo2O4 and Chitosan-modified spinel oxide to evaluate the synergistic effect between spinel oxide and chitosan. The composite is studied in an alkaline solution using electrochemistry techniques. The electrochemical activity towards ethylene glycol electrooxidation is studied as a function of anodic oxidation current density. Thus, the oxidation current values for NiCo2O4 and NiCo2O4@Chitosan in 1.0 M EG and 1.0 M KOH are 36 and 42 mA cm−2, respectively. The long-term stability of the electrode is measured by constant potential chronoamperometry. Kinetic parameters like diffusion coefficient, Tafel slope, surface coverage, and transfer coefficient are calculated. The density-functional theory estimates the adsorption of small molecules like ethylene glycol, urea, and carbon monoxide. The adsorption energy is studied on the top site of Ni and Co atoms of NiCo2O4. Forcite model is used to study the interaction between spinel oxide and chitosan. The energy calculation assumes that chitosan is adsorbed on the spinel oxide surface and enhances chitosan's ability for the adsorption of small molecules.

Metal organic frameworks (MOFs) are a class of porous materials characterized by robust linkages between organic ligands and metal ions. Metal–organic frameworks (MOFs) exhibit significant characteristics such as high porosity, extensive surface area, and exceptional chemical stability, provided the constituent components are meticulously selected. A metal–organic framework (MOF) containing lead and ligands derived from 4-aminobenzoic acid and 2-carboxybenzaldehyde has been synthesized using the sonochemical methodology. The crystals produced were subjected to various analytical techniques such as Fourier-transform infrared spectroscopy (FT-IR), Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX), Brunauer–Emmett–Teller (BET), and thermal analysis. The BET analysis yielded results indicating a surface area was found to be 1304.27 m2 g−1. The total pore volume was estimated as 2.13 cm3 g−1 with an average pore size of 4.61 nm., rendering them highly advantageous for a diverse range of practical applications. The activity of the modified Pb-MOF electrode was employed toward water-splitting applications. The electrode reached the current density of 50 mA cm−2 at an overpotential of − 0.6 V (vs. RHE) for hydrogen evolution, and 50 mA cm−2 at an overpotential of 1.7 V (vs. RHE) for oxygen evolution.