Tailoring a facile electronic and ionic pathway to boost the storage performance of Fe3O4 nanowires as negative electrode for supercapacitor application.

Today, high-energy applications are devoted to boosting the storage performance of asymmetric supercapacitors. Importantly, boosting the storage performance of the negative electrodes is a crucial topic. Fe3O4-based active materials display a promising theoretical storage performance as a negative electrode. Thus, to get a high storage performance of Fe3O4, it must be tailored to have a higher ionic and electronic conductivity and outstanding stability. Functionalized graphite felt (GF) is an excellent candidate for tailoring Fe3O4 with a facile ionic and electronic pathway. However, the steps of the functionalization of GF are complex and time-consuming as well as the energy loss during this step. Thus, the in-situ functionalization of the GF surface throughout the synthesis of Fe3O4 active materials is proposed herein. Fe3O4 is electrodeposited at the in-situ functionalized GF surface with the crystalline nanowires-like structure as revealed from the various analyses; SEM, TEM, Mapping EDX, XPS, XRD, wettability test, and Raman analysis. Advantageously, the synthetic approach introduces full homogeneous and uniform coverage of the large surface area of the GF. Thus, Fe3O4 nanowires with high ionic and electronic conductivity are characterized by a higher storage performance. Interestingly, Fe3O4/GF possesses a high specific capacity of 1418 mC cm-2 at a potential scan rate of 10 mV s-1 and this value retained to 54% at a potential scan rate of 50 mV s-1 at an extended potential window of 1.45 V. Remarkably, the diffusion-controlled reaction is the main contributor of the storage of Fe3O4/GF electrode as revealed by the mechanistic studies.

Enhancing the performance of Ni nanoparticle modified carbon felt towards glycerol electrooxidation: impact of organic additive.

Organic additives are widely used in the deposition baths of metals and alloys thanks to their special function which affects the growth and the building of the crystal. This study investigates the effect of glycerol on Ni deposition onto carbon felt (CF) and its effect on the catalytic activity towards glycerol electrooxidation. The impact of glycerol on the morphology, distribution, and particle size of the electrodeposited Ni is disclosed using a scanning electron microscope (SEM). X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV) techniques were used to probe the possible changes of the electrodeposited Ni oxide phases. Electrochemical measurements show that the as-synthesized Ni0.05@CF electrocatalyst prepared in the presence of 50 mM glycerol has a marked activity towards glycerol electrooxidation, as confirmed by the impressive increase of the oxidation current by about 1.6 times concurrently with a favorable negative shift of its onset potential. Moreover, the charge transfer resistance (R ct) is much reduced from 140 to 87 ohm. The addition of glycerol to the deposition bath is believed to retard the growth of the formed Ni deposits while enhancing the nucleation rate and thus increases the particle density and, consequently, the distribution of deposited Ni over the entire CF is improved along with increasing the surface concentration and surface-active sites. This assumption is supported by density functional theory (DFT) calculations.

Tailor-designed binary Ni-Cu nano dendrites decorated 3D-carbon felts for efficient glycerol electrooxidation.

Herein, 3D-Carbon Felt (CF) are decorated with nickel-copper (Ni-Cu@CF) bimetallic nanostructures through either sequential or co-electrodeposition tactics. Their catalytic activity towards glycerol electrooxidation is investigated by employing cyclic voltammetry (CV) and linear sweep voltammetry LSV. The morphology and composition of the various Ni-Cu@CF are investigated using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) together with various electrochemical measurements (e.g., CV, chronoamperometry, LSV). The co-deposition of Ni-Cu shows a dendritic-like structure with higher electrocatalytic activity towards glycerol electrooxidation compared to the monometallic counterparts. Interestingly, the best electrode (NiCu@CF Ni particles as the top layer) prepared by sequential electrodeposition shows 1.6-fold higher glycerol oxidation activity, manifested in oxidation current, compared to Ni-coated CF due to Ni particles covering the surface of dendritic copper uniformly. Thus, the surface concentration of Ni is increased and at the same time a synergistic effect occurs between Ni and Cu by the simple addition of Cu which reinforces the surface concentration of Ni from 3.4 × 10-8 to 1.1 × 10-7 mol cm-2.

Promoted glucose electrooxidation at Ni(OH)2/graphene layers exfoliated facilely from carbon waste material.

Nowadays, the glucose electro-oxidation reaction (GOR) is considered one of the most important solutions for environmental pollution. The GOR is the anodic reaction in direct glucose fuel cells and hybrid water electrolysis. In this study, the GOR is boosted using a carbon support modified with Ni(OH)2 as a non-precious catalyst. The carbon support, with in situ generated graphene nanosheets having a large surface area, grooves, and surface functional groups, is prepared via a simple electrochemical treatment of the carbon rods of an exhausted zinc-carbon battery. Ni(OH)2 is electrodeposited on the surface of the functionalized exfoliated graphite rod (FEGR) via the dynamic hydrogen bubbling technique (DHBT) and tested for GOR. The thus-prepared Ni(OH)2/FEGR electrode is characterized by SEM, mapping EDX, HR-TEM, XRD, and XPS characterization tools. Ni(OH)2/FEGR displays an onset potential of 1.23 V vs. the reversible hydrogen electrode (RHE) and attains high current densities at lower potentials. Additionally, Ni(OH)2/FEGR showed prolonged stability toward GOR by supporting a constant current over a long electrolysis time. The enhanced catalytic performance is attributed to the superb ionic and electronic conductivity of the catalyst. Importantly, ionic conductivity increased, due to (i) a large surface area of in situ generated graphene layers, (ii) enhanced distribution of active material during deposition using DHBT, and (iii) increased hydrophilicity of the underlying substrate. Therefore, the Ni(OH)2/FEGR electrode can be used efficiently for GOR as a low-cost catalyst, achieving low onset potential and high current densities at low potentials.

Application of molecularly imprinted electrochemical sensor for trace analysis of Metribuzin herbicide in food samples.

Metribuzin (MTZ) is an important herbicide widely used in fields and represents a big threat to the environment and health. Herein, an electrochemical sensor was designed for its detection in commercial product (Egyscor® 70%), spiked tomatoes and potatoes samples with recovery values ranging from 97.12 to 103.41%. Bulk-polymerized MTZ molecularly imprinted polymer (MIP) was developed, using itaconic acid (functional monomer), ethylene glycol dimethacrylate (cross-linker) at an optimum molar ratio 1:5:30, respectively. Differential pulse voltammetry was used to examine the optimization variables of the MIP based sensor such as the variation of (template: monomer: cross-linker) ratio, accumulation time, multi walled carbon nanotubes amount, pH and scan rate, while cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the sensor. The sensor showed selective adsorption ability and a good linearity over the concentration range of 0.2 ng/mL to 21.429 µg/mL, with LOD and LOQ of 0.1 pg/mL and 0.3 pg/mL, respectively.

Adsorption of the Xanthan Gum Polymer and Sodium Dodecylbenzenesulfonate Surfactant in Sandstone Reservoirs: Experimental and Density Function Theory Studies.

Chemical flooding using a polymer and/or surfactant has been widely applied in oilfields worldwide for enhanced oil recovery. Chemical adsorption in reservoirs has a significant effect on the rock permeability and wettability and hence can affect the overall oil production. In this work, two chemicals, namely, the xanthan gum (XG) biopolymer and sodium dodecylbenzenesulfonate (SDBS) anionic surfactant, were used individually as displacement fluids. The amount of chemical adsorption on the rock surface and the residual resistance factor (permeability reduction) were calculated throughout the flooding experiments using an unconsolidated sandstone (SS) pack model. The effects of the injected chemicals' concentration and reservoir salinity on adsorption capacity have been examined. Additionally, the effect of the addition of nanosilica particles (NSPs) to the injected fluid on the rock adsorption was also investigated. The results showed that the amount of XG and SDBS adsorption on the rock surface increased, albeit to a different extent, by increasing the chemical concentration at the applied salinities (0, 3.5, 5, and 10%) of the displacement fluids. Also, the permeability reduction increased with the increase in XG and SDBS concentrations; however, permeability reduction due to SDBS flooding was lower than that of XG in SS. The use of NSPs as a coinjectant to the XG and SDBS displacement fluids increased the adsorption on the SS rock. A plausible mechanism for the adsorption of the XG/NSP and SDBS/NSP blends on the SS surface was proposed. A density function theory calculation was employed to establish a relation between the adsorptivity of NSPs on SDBS and XG and the total energy and dipole moment of the molecules.

In situ generation of exfoliated graphene layers on recycled graphite rods for enhanced capacitive performance of Ni-Co binary hydroxide.

A functionalized exfoliated graphite rod (FEGR), with a high surface area, is produced for use as a promising substrate for supercapacitors, via controlled oxidative treatment of a recycled graphite rod of exhausted zinc-carbon batteries. SEM, EDX, XPS, FT-IR, Raman, and contact angle measurements are carried out to disclose the surface characteristics of the FEGR. The surface of the FEGR is characterized by in situ generated grooves, together with graphene layers which are directly attached to the underlying graphite base. The FEGR electrodes enhance the capacitive performance of Ni(OH)2 and binary Ni-Co(OH)2. The Ni-Co(OH)2/FEGR electrode displays a superb specific capacity value (2552.6 C g-1) at a current density of 5 A g-1 and this value is retained to 70.8% at a high current density of 50 A g-1 indicating the outstanding rate performance of this electrode material. This enhanced behavior is attributed to the facile interaction of electrolyte species, even at high current density, with the active sites of the redox catalyst layer (distributed over a larger fraction of the underlying substrate with enhanced hydrophilicity). Moreover, the excellent electrical conductivity of the in situ surface generated graphene layers is another promoting factor.

Propitious Dendritic Cu2O-Pt Nanostructured Anodes for Direct Formic Acid Fuel Cells.

This study introduces a novel competent dendritic copper oxide-platinum nanocatalyst (nano-Cu2O-Pt) immobilized onto a glassy carbon (GC) substrate for formic acid (FA) electro-oxidation (FAO); the prime reaction in the anodic compartment of direct formic acid fuel cells (DFAFCs). Interestingly, the proposed catalyst exhibited an outstanding improvement for FAO compared to the traditional platinum nanoparticles (nano-Pt) modified GC (nano-Pt/GC) catalyst. This was evaluated from steering the reaction mechanism toward the desired direct route producing carbon dioxide (CO2); consistently with mitigating the other undesired indirect pathway producing carbon monoxide (CO); the potential poison deteriorating the catalytic activity of typical Pt-based catalysts. Moreover, the developed catalyst showed a reasonable long-term catalytic stability along with a significant lowering in onset potential of direct FAO that ultimately reduces the polarization and amplifies the fuel cell's voltage. The observed catalytic enhancement was believed to originate bifunctionally; while nano-Pt represented the base for the FA adsorption, nanostructured copper oxide (nano-Cu2O) behaved as a catalytic mediator facilitating the charge transfer during FAO and providing the oxygen atmosphere inspiring the poison's (CO) oxidation at relatively lower potential. Surprisingly, moreover, nano-Cu2O induced a surface retrieval of nano-Pt active sites by capturing the poisoning CO via "a spillover mechanism" to renovate the Pt surface for the direct FAO. Finally, the catalytic tolerance of the developed catalyst toward halides' poisoning was discussed.