Anodic Peak Current Density Research Articles

Fabrication of fMW@TiO2@MoS2-Sm2S3/GCE electrochemical nanosensor for simultaneous measurement of sertraline and buspirone neuroleptic drugs

In this paper for the first time, due to the importance of simultaneous administration of sertraline (SRT) and buspirone (BPH), a sensitive electrochemical nanosensor was fabricated and used for simultaneous measurement of them. Firstly, fMW@TiO2@MoS2-Sm2S3 was synthesized and characterized by different techniques. The performance of fMW@TiO2@MoS2-Sm2S3/GCE nanocomposite was investigated for simultaneous quantifications of SRT and BPH using different electrochemical methods. Response surface methodology (RSM) indicated that pH 7.0 for phosphate buffer solutions (PBS), scan rate of 0.08 V s-1, accumulation potential of 0.4 V and accumulation time of 125 s in CHA get maximum anodic currents. The anodic peak current densities of SRT and BPH drugs were improved excellently on the surface of fMW@TiO2@MoS2-Sm2S3/GCE compared to bare GCE. With the DPV method, the linear response 1.53–38.46, 38.46–74.07 µM and 1.11–29.12, 29.12–90.90 µM were obtained for SRT and BPH, respectively. Also, the detection limit of 0.50 µM and 0.36 µM were acquired for SRT and BPH, respectively. The catalytic rate constants were calculated to be 3.63 × 107 and 2.80 × 107 cm3 mol-1 s-1 for SRT and BPH, respectively. The practical application of the fMW@TiO2@MoS2-Sm2S3 for measurements of the SRT and BPH in human plasma and tablets showed good recovery percentage.

New type nanocomposite based on metal-organic frameworks decorated with nickel nanoparticles as a potent electrocatalyst for methanol oxidation in alkaline media

Methanol oxidation reaction (MOR) is used to provide electrical energy via direct methanol fuel cell (DMFC), which requires a practical design of electrocatalysts to accelerate the sluggish MOR. In this study, we successfully fabricated the carbon black nanoparticles/graphite ceramic electrode (CBNPs/GCE) supported metal-organic frameworks (MOFs) and decorated with nickel nanoparticles (NiNPs) as a new type nanocomposite modified electrode (NiNPs/MOFs/CBNPs/GCE) via a chemical and an electrochemical process, respectively. The surface morphology and structure of the synthesized nanocomposite materials and modified electrodes were characterized using field emission scanning electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, X-ray diffraction and thermogravimetric analysis. Then, the NiNPs/MOFs/CBNPs/GCE was used as a non-platinum electrocatalyst for electrocatalytic oxidation of methanol in alkaline media. The obtained results show the efficient electrocatalytic activity of the NiNPs/MOFs/CBNPs/GCE toward the MOR with high anodic peak current density (Jpa = 34.8 mA cm−2) compared with the other prepared electrocatalysts; MOFs/CCE, NiNPs/CCE, MOFs/CBNPs/GCE, NiNPs/CBNPs/GCE, and NiNPs/MOFs/CCE, due to the synergistic effect of nanocomposite components; NiNPs, MOFs and CBNPs. The prepared electrocatalyst; NiNPs/MOFs/CBNPs/GCE, not only shows a high electrochemically active surface area (ECSA = 2.15 cm2) but also has long-term durability in MOR. In general, it can be said the NiNPs/MOFs/CBNPs/GCE is a promising candidate for application in DMFC.

Electrocatalytic performance of Shape-Controlled synthesized PdNi-rGO nano Cube on sodium borohydride and methanol electrooxidation

In recent years, increasing climate change, environmental pollution and water problems have increased the need for sustainable and environmentally friendly solutions in energy production. In this context, renewable energy sources, especially fuel cells, have become an important focus. In this study, the synthesis and characterization of the shape-controlled synthesized PdNi-rGO Cube electrocatalyst was carried out. X-ray diffraction (XRD), scanning electron microscopy with energy dispersive x-ray (SEM-EDX), and transmission electron microscope (TEM) characterization experiments were performed to examine the shape of the particles. TEM analysis revealed the formation of nanostructures with a size of 19.18 nm in the cubic structure of the PdNi-rGO. Furthermore, cyclic voltammetry (CV) measurements evaluated the usability of this electrocatalyst in the electrooxidation of sodium borohydride (NaBH4), and methanol (CH3OH). In this context, the anodic peak current density values were 77.34 mA/cm2 and 13.47 mA/cm2, for electrooxidation of sodium borohydride (NaBH4), and methanol (CH3OH), respectively. This study demonstrates that PdNi-rGO cube contains shape-controlled nanostructure, and these structures can play an important role in future renewable energy sources. It can also be considered an important step forward in the development of nanomaterial-based electrocatalysts capable of efficient energy conversion.

Facile In-Situ Electrosynthesis of MnO2/RGO Nanocomposite for Enhancing the Electrochemical Performance of Symmetric Supercapacitors

One-pot galvanostatic reverse pulse electrochemical deposition (RPED) was used to create a supercapacitive electrode made of manganese dioxide/reduced graphene oxide (MnO2/RGO) nanocomposite. Systematic changes of two independent parameters of the reverse pulse current, including times of the anodic and cathodic pulses (ta and tc), were investigated to achieve the desired physicochemical and electrochemical properties. Galvanostatic charge–discharge, cyclic voltammetry, and electrochemical impedance spectroscopy tests were employed to perform electrochemical evaluations. According to the results, the MG50-5 nanocomposite, synthesized at ta = 50 ms, tc = 5 ms, and anodic peak current density of 2 mA cm−2, was selected as the optimal sample. This sample showed the highest specific surface area of 284.6 m2 g−1 and the specific capacitance of 789.0 F g−1 at a current density of 0.5 A g−1. The specific capacitances of the MG50-5 symmetric supercapacitor at current densities of 0.5 and 10 A g−1 were 660.14 and 402.50 F g−1, respectively. Maintaining 84.8 % of the specific capacitance after 5000 consecutive cycles at 4 A g−1 indicated stable cycle performance of the MG50-5 symmetric cell. The MG50-5 symmetric supercapacitor presented the maximum energy density of 22.92 Wh kg−1 at a power density of 156.3 W kg−1 and the maximum power density of 3.125 kW kg−1 at an energy density of 13.97 Wh kg−1. Therefore, optimizing reverse pulse current parameters in the galvanostatic RPED of MnO2/RGO nanocomposite leads to an outstanding electrochemical performance of the fabricated supercapacitors.

Impact of some inorganic anions on the corrosion of nickel in a solution containing Na2SO4 and NaClO4

Potentiodynamic study was carried out on nickel in Na2SO4 solution in the presence of ClO4–, WO42–, MoO42–, NO2– and NO3– ions. The anodic excursion spans of the metal nickel in a solution of Na2SO4 are marked by the appearance of clearly defined anodic peak, passive region, and transpassive shoulder. According to the data, the anodic peak current density (IPAI) rise from 1.82 to 8.12 mA cm–2 as the concentration of the Na2SO4 solution rises from 0.2 to 1.0 M. It is clear that as scan rate increases, the IPAI rises reaching to 11.8 mA cm–2. The apparent activation energy of nickel corrosion in Na2SO4 is 33.25 kJ mol–1. ClO4– anion addition speeds up nickel’s active dissolution, as well tends to break down the passive layer, and causes pitting penetration. It was found that, the pitting potential (Epit) of nickel in solutions containing the two anions ClO4– and SO42– shifts to the positive direction by addition of WO42–, MoO42–, NO2– anions and shifts to the negative direction by addition NO3- anion. Epit increased by 0.67, 0.37 and 0.15 V in the presence of WO42–, MoO42– and NO2–, respectively. WO42– > MoO42– > NO2– was the order in which the inhibitors were most effective.

Enhanced electrocatalytic activity of palladium electrocatalysts supported on corncob biochar for ethanol oxidation reaction in alkaline medium

AbstractIn this study, palladium particles supported on carbon black (Vulcan XC‐72) (Pd/C) and corncob biochar (Pd/CB800, Pd/CB900, and Pd/CB1000) were successfully synthesized using borohydride reduction. The biochar support was obtained from corncob waste via pyrolysis from 800 to 1000°C. Scanning electron microscopy with energy dispersive x‐ray (SEM–EDX) revealed successful deposition of Pd metal particles on the carbon support materials. X‐ray diffraction (XRD) analysis confirmed the crystalline structures of Pd, and the crystallite size was found to be smallest in Pd/CB900. The electrocatalytic activity of the Pd electrocatalyst composites towards ethanol oxidation reaction (EOR) in an alkaline medium was investigated using cyclic voltammetry (CV). CV analysis has shown that Pd/CB900 gave the least positive onset potential (Eonset = −0.587 ± 0.0065 V), highest electrochemically active surface area (EASA = 31.51 ± 2.24 m2·g−1), and highest anodic peak current density (If = 20.77 mA·cm−2) compared with Pd/CB800, Pd/CB1000, and Pd/C. Furthermore, the Tafel plot and chronoamperometry have shown that Pd/CB900 exhibited faster kinetics (Tafel slope = 297.6 ± 4.62 mV·dec−1) and durability (% current retention = 50.64 ± 2.99%) than Pd/C towards EOR in an alkaline medium. This study highlights the simple and straightforward synthesis of the anode electrocatalyst material for direct ethanol fuel cell application.

High Performance Metal Oxide–Reduced Graphene Oxide Electrocatalyst for All Vanadium Redox Flow Batteries

Vanadium redox flow battery (VRFB) is one of the most favorable technologies for large-scale energy storage applications owing to its numerous gorgeous features, such as flexible design, high safety, and long cycle life. In this study, metal oxide (MOx)–reduced graphene oxide (rGO) nanohybrid was successfully synthesized via a facile hydrothermal route followed by annealing and employed as an electrocatalyst to modify the graphite felt (GF) electrode material for all-vanadium redox flow batteries (VRFBs) application. The as-synthesized MOx–rGO nanohybrid reveals good electrocatalytic reversibility and higher anodic and cathodic peak current density for V3+/V2+ and VO2 +/VO2+ redox couples compared with those of rGO and MOx samples. The voltage efficiency of the VRFB using MOx–rGO nanohybrid reaches 84% at 80 mA cm−2, which is 4% and 13% higher than the VRFBs using the rGO-loaded GF electrode and the pristine GF electrode, respectively. It still shows the voltage efficiencies of 76% and 70% at relatively high current densities of 120 mA cm−2 and 140 mA cm−2, respectively, but other samples have no effective discharge. This improvement is accredited to the uniform distribution of MOx nanoparticles on the rGO surfaces, avoiding the restacking of the rGO sheets and conquering nanoparticles aggregation, which might boost the effective active surface area and improve mass transport at the electrode-electrolyte interfaces. Besides, the existence of oxygen vacancies on MOx, the high electrical conductivity of rGO, and the high content of oxygen functional groups play the prodigious roles to facilitate the reversibility of vanadium ions redox reactions.

Assessment of antioxidant and DPPH free radical scavenging activity of 1,2-dithiole-3-thione derivatives by using cyclic voltammetry, spectroscopic, and molecular docking studies

The antioxidant and the DPPH free radical scavenging activity of 4-phenyl-3H-1,2-dithiole-3-thione (DT1), 5-(4-fluorophenyl)−3H-1,2-dithiole-3-thione (DT2), 5-(4-phenyl-3-thioxo-3H-1,2dithiol-5-yl)-benzo[d]oxazole-2(3H)thione (DT3) and 4-methyl-5-((phenylamino)methyl)−3H-1,2-dithiole-3-thione (DT4) was investigated using cyclic voltammetry (CV) and electronic spectroscopy (ES) assays. The diminution in anodic peak current density of an acetonitrile solution of DPPH in the absence and presence of gradually increasing amounts of 1,2-dithiole-3-thione derivatives (DT) was successfully exploited for measuring the antioxidant activity and the DPPH free radical scavenging activity. The EC50 values obtained from the CV and ES experiments suggested that all compounds had potential DPPH radical scavenging ability with the derivative DT3 possessing the highest potency of 21.5 ± 1.30 from CV and 20.6 ± 1.05 from ES. A molecular docking simulation indicated that all DT derivatives interacted with amino acid residues of glutathione reductase via hydrogen bonding and hydrophobic interactions. Based on the inhibitory concentration and docking score values, compound DT4 was the second inactive compound against the glutathione reductase enzyme having values equal to 41.4 µM and a docking score of −25.6 kJ/mol respectively. Toxicity perdition studies revealed that compounds DT1 and DT2 were non-toxic.

The pivot to achieve high current density for biomass electrooxidation: Accelerating the reduction of Ni3+ to Ni2+

Electrochemical oxidation is a promising method to convert 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA) with high selectivity at room temperature. Developing catalysts with high current densities is crucial for the industrial application of HMF electrooxidation reaction (HMFOR). Herein, we demonstrate that the current densities exhibited by the LSV curves are falsely high and propose to evaluate catalyst activity using anodic peak current density rather than overpotential for the comparison of actual efficiency. Besides, the reduction of Ni3+ to Ni2+ accompanied by proton coupled electron transfer (PCET) process of HMF dehydrogenation is confirmed as the rate-determining step affecting the conversion efficiency of HMF rather than Ni2+ electrooxidated to Ni3+. Theoretical calculations reveal differences in the hydrogen transfer energy barriers of PCET process. Furthermore, Ni(OH)2/NF with appropriate Cr doping shows superb activity with actual current densities of over 230 mA cm−2 at HMF concentrations of 10 mM and over 360 mA cm−2 at 20 mM (the ever highest current densities for HMFOR), and obtain a yield of more than 98% of FDCA.

Porous Nickel Electrode for Highly Sensitive Non-Enzyme Electrochemical Glucose Detection

Porous metals have great potential for applications in non-enzyme glucose detection because they have a high surface area and therefore improved the sensitivity of detection and the accuracy of measurement. An LCS/DHBT porous nickel with both macropores (710–1000 μm) and microscale pores (1–25 μm) has been produced by combining the Lost Carbonate Sintering (LCS) and Dynamic Hydrogen Bubble Template (DHBT) processes. Its behavior for glucose measurement has been studied by cyclic voltammetry and compared with a nickel plate and the LCS porous nickel substrate. The as-fabricated porous nickel has an electroactive surface area 18% higher than the LCS porous nickel. The anodic peak current density of the LCS/DHBT electrode in an electrolyte of 0.1 M KOH containing 0.5 mM glucose at scan rates in the range of 25–300 mV/s are in the range of 3.43–13.94 mA/cm2, which is approximately 2 and 10 times those of the plate and LCS electrodes. Increasing the scan rate results in a higher current density and a larger anodic peak potential shift. Current density increases with glucose concentration in several linear segments. The sensitivity and limit of detection of LCS/DHBT nickel electrode in the glucose measurement are 5775 μA/cm2mM and 0.66–2.91 μΜ, respectively. It shows excellent performance for glucose measurement due to its porous nanostructure and its highly effective surface area.

Porous structure Ni/CuCo2O4 core–shell as a novel type of three-dimensional electrode with facile fabrication and binder-free toward enhanced methanol oxidation and supercapacitor performances

In this present research, three dimensional nickel/copper cobaltite (3D-Ni/ CuCo2O4) core–shell nanocomposites have been successfully synthesized on 304 stainless steel as a substrate through the combination of electrodeposition and sol–gel methods followed by annealing treatment. The crystallographic configuration, chemical structure and surface morphology as-prepared materials are characterized systematically by different spectroscopy and microscopy techniques such as X-ray diffraction (XRD), fourier transformation spectroscopy (FT-IR), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and field emission scanning electron microscope (FE-SEM). Bi-functional performance of samples are studied for supercapacitor and methanol fuel cell. According to achieved galvanostatic charge–discharge (GCD) results, 3D-Ni/ CuCo2O4 and CuCo2O4 electrodes maintains nearly 89.97 % and 56.55 % of the preliminary areal capacitance in high current density of 1.27 mA cm−2, indicating high rate capability of 3D-Ni/ CuCo2O4 nanocomposite. Furthermore, it illustrates remarkable cycling stability in 1 M KOH solution during charge/discharge cycles in judgment with individual CuCo2O4. Enhanced electrochemical performances of nanocomposite are mainly due to the unique porous structure of 3D-Ni core and high electronic conductivity of CuCo2O4 as shell that synergistic effects of two component can eventually decrease the charge transfer resistance to improve the ion–electron transportations ability. More importantly, 3D-Ni/ CuCo2O4 exhibits the anodic peak current density of 18.67 mA cm−2 for methanol oxidation reaction at 0.55 V potential in 1 M KOH mixed with methanol which is greater than of 7.45 mA cm−2 CuCo2O4 when applied as catalyst of fuel cell. Unlike commonly accepted techniques, we reported a spin coater route for tight and stable deposition CuCo2O4 onto 3D-Ni surface without any adhesive.

Functionalized Graphene-MoO2 frameworks: An efficient electrocatalyst for iron-based redox flow battery and supercapacitor application with enhanced electrochemical performances

Grid level energy storage systems have gravitated towards redox flow batteries due to their great performance, economic factors and supercapacitors have gained prime importance as they bridge the void between batteries and capacitors. The electrochemical behavior of the Iron redox flow battery is directly co-related to the positive electrode. Herein the positive electrode is modified with able metal oxide and graphene-based composite to increase the electrochemical activity of the system. MoO2-GP was synthesized using one-step hydrothermal process and characterized by XRD, SEM, EDAX, TEM, XPS, and Elemental mapping. Different Electrochemical techniques are evidenced for significant anodic and cathodic peak current densities, least charge transfer resistance, least solution resistance, reversibility, and reduced polarization resistance. A 132 cm2 IRFB with composite modified positive electrode showcased improved CE, VE, and EE. Wherein the MoO2-GP composite was also incorporated as an active material for supercapacitors, focusing to increase the stability and the Cs of the system. The combined effect of electrical double layer capacitance (EDLC) and pseudocapacitive or faradaic nature of composite material, contributed to the increased electrochemical activity of supercapacitors. The results demonstrate that the MoO2-GP composite material leaps providing better active sites, improving the reactions thus acting as an excellent electrochemically active material for energy storage devices.

Enhanced methanol electrooxidation by electroactivated Pd/Ni(OH)2/N-rGO catalyst

Direct methanol fuel cells, in which electrocatalytic oxidation of methanol takes place, are one of the most promising technologies for facilitating the shift to renewable energy sources. However, they still suffer from high-catalyst-prices, as well as sluggish kinetics of methanol oxidation reaction (MOR). Therefore, herein, palladium/Nickel(II) hydroxide/nitrogen doped reduced graphene oxide (Pd/Ni(OH)2/N-rGO) hybrid was fabricated via facile two-step solution method and utilized as electrocatalyst for MOR. The in-situ electrochemical activation pre-treatment was proposed to engineer a highly active electrocatalyst. The Pd/Ni(OH)2/N-rGO, which had distinctive structural features along with robust synergistic effects, outperformed the commercial Pd electrocatalyst in terms of catalytic activity towards MOR, with elevated anodic peak current density values. The in-situ electrochemical activation pre-treatment lead to 3.3, 3.0, and 2.0-fold increase in activity of Pd/Ni(OH)2/N-rGO, Pd/N-rGO, and Pd/C, respectively. This research lays the door for a unique technique to manufacture high-performance, low-cost electrocatalysts that might be used in fuel cell technology instead of existing Pd electrocatalysts.

Electrooxidation of Iohexol in Its Commercial Formulation Omnipaque on Boron Doped Diamond Electrode

This study investigated the electrochemical behavior of iohexol in its commercial formulation omnipaque on a boron-doped diamond electrode using cyclic voltammetry and chronoamperometry. The dependence of the anodic peak current density vs. iohexol concentration is linear and can be applied to the determination of the substrate concentration in environmental samples and pharmaceuticals. The iohexol electrooxidation on boron-doped diamond electrode is diffusion-controlled process and proceed via two ways: a direct electron transfers at the surface of boron-doped diamond electrode and an indirect oxidation mediated by in situ oxidative species. The iohexol electrooxidation in pH range from 2 to 6 includes exchange of 4 electrons and 1 proton, at pH superior to 6 it includes an exchanged of 2 electrons and 1 proton. The values of activation energy, anodic transfer coefficient, heterogenous rate constant, diffusion coefficient and the catalytic rate constant were 14.164 kJ mol-1, 0.428, 1.06 s-1, 4.47 cm2 s-1 and 3.61 M-1 s-1 respectively. It appears from those results that, on our electrode, for the high potential scan rates, few actives sites mainly those located at the electrode surface are involved in the iohexol oxidation process. As the potential scan rate decreases, more actives sites are involved in the process.

Hot hole direct photoelectrochemistry of Au NPs: Interband versus Intraband hot carriers

Optically-excited gold nanoparticles (Au NPs) generate plasmon oscillations that induce hot charge carriers by non-radiative decay. These hot charge carriers are to improve the energy conversion efficiency of photochemical and photoelectrochemical reactions. Depending on the mode of excitation (i.e., interband or intraband), the energy of the hot electrons and hot holes vary significantly. Although, both interband and intraband hot carriers were used separately for driving photoelectrochemical reactions, a comparison between these two types of hot carriers in directly driving electrochemical reactions, without the use of semiconductive layers, is still lacking. Herein, we compare the hot hole mediated photocurrent generation efficiencies of Au NPs deposited on screen printed carbon electrodes when excited at 405 nm and 532 nm wavelengths that correspond to interband and intraband excitation, respectively. Oxidation of ascorbic acid was used as a model reaction system due to its strong hole scavenging properties. Interband excitations showed higher anodic photocurrents than the photocurrent achieved from intraband excitation. The efficiency of photocurrent generation was found to be strongly dependent on the surface distribution of Au NPs. The optimized electrodes, obtained by varying the size and density of Au NPs on the electrode surface, were further used to evaluate methanol electro-oxidation with both interband and intraband excitations. An anodic peak current density of 56 µA/µg was achieved when interband carriers were excited, which is ∼30% higher than the current achieved with intraband excitation (43 µA/µg).

“Painted CNT”@Au nanoparticles: a nanohybrid electrocatalyst of direct methanol oxidation

In an era of global new energy rush, hybrid nanomaterials have raised huge interest as their components can synergistically improve the expected performances in terms of power. In this regard, direct methanol oxidation (DMO) is among the most investigated reactions for implementation in portable and other devices. Herein, we report on the design of gold-decorated multiwalled carbon nanotube-aryl nanohybrids as electrocatalyst of DMO. In a first step, Azure A (AA), Neutral Red (NR), and Congo Red (CR) dye diazonium salts were reacted with multiwalled carbon nanotubes (hereafter CNTs) to provide CNT-Dye nanoscale platforms for the immobilization of gold NPs. This step was conducted with CNT-Dye platforms evenly spread over glassy carbon (GC) electrodes. The CNT-Dye@Au nanohybrid electrode materials served for DMO electrocatalysis. Cyclic voltammograms show that bare CNT-Dye nanohybrids exhibit high electrocatalytic activity, particularly for the CNT-CR nanohybrid which returned a threefold improvement. With anchored Au NPs, a further 4 time remarkable increase in the oxidation peak intensity was achieved (i.e., about 12-fold the peak intensity recorded in the absence of any nanocatalyst). The forward to the backward anodic peak current density ratio Jf/Jb was found to be as high as is 1.68. This work provides an efficient approach for designing robust, nanohybrid electrocatalyst for DMO, based on the smart combination of CNTs, diazotized dyes, and gold NPs.Graphical abstract EMMA-D-20-00232R1

Generation of a Highly Efficient Electrode for Ethanol Oxidation by Simply Electrodepositing Palladium on the Oxygen Plasma-Treated Carbon Fiber Paper

In this study, a highly efficient carbon-supported Pd catalyst for the direct ethanol fuel cell was developed by electrodepositing nanostructured Pd on oxygen plasma-treated carbon fiber paper (Pd/pCFP). The oxygen plasma treatment has been shown to effectively remove the surface organic contaminants and add oxygen species onto the CFP to facilitate the deposition of nano-structured Pd on the surface of carbon fibers. Under the optimized and controllable electrodeposition method, nanostructured Pd of ~10 nm can be easily and evenly deposited onto the CFP. The prepared Pd/pCFP electrode exhibited an extraordinarily high electrocatalytic activity towards ethanol oxidation, with a current density of 222.8 mA mg−1 Pd. Interestingly, the electrode also exhibited a high tolerance to poisoning species and long-term stability, with a high ratio of the forward anodic peak current density to the backward anodic peak current density. These results suggest that the Pd/pCFP catalyst may be a promising anodic material for the development of highly efficient direct alcohol fuel cells.

Synthesis, Antioxidant Activity, and Determination of Binding Parameters of Meso-Tetra-4-Actophenyl-Porphyrin and its Palladium (II) Complex with Superoxide Anion Radicals

Background: Meso-tetra-4-actophenyl-porphyrin (TAcPPH2) was synthesized by reacting 4- acetyl-benzaldehyde with pyrrole in propionic acid, and used as a ligand for the synthesis of palladium (II) complex (PdTAcPP). The structure of the ligand and the complex were characterized by NMR and electronic spectroscopy. Methods: he antioxidant activity and the binding parameters of both the ligand and its complex with superoxide anion radical . (O2 -) were measured using cyclic voltammetry based assay. The assays were based on the measurement of the anodic peak current density of . O2− electrochemically generated by reduction of molecular oxygen in DMF. Results: The complex PdTAcPP showed the highest antioxidant activity (0.73 ± 0.01 mg/mL) which is four times higher than that of the standard antioxidant α-tocopherol (3.04 ± 0.03 mg/mL). Discussion: Binding parameters like binding constants, the ratio of binding constants and binding free energies were also measured. Conclusion: The value of the binding free energy ranging from -7.89 kJmol-1 for TAcPPH2 to -17.59 kJ.mol-1for PdTAcPP suggests an electrostatic interaction of . O2− with TAcPPH2 and PdTAcPP which has been found to be the dominant interaction mode. The kinetics of the interaction reaction of the ligand and complex was quantified having second-order rate constant values equal to 0.2 and 1.3 M-1 s-1, respectively.

MxOy/M/graphene coated multi-shelled nano-sphere as Bi-functional electrocatalysts for hydrogen and oxygen evolution

Multi-shelled NiO/Ni/Graphene and Co3O4/Co/Graphene nano-spheres for high performance electrocatalytic activity in water electrolysis have been synthesized using multi-step solvothermal process. The synthesis process was derived by Metal-Organic-Framework (MOF) with the successive carbonization and oxidation treatments, which results into the formation of NiO/Ni and Co3O4/Co nano-crystalline particles with a coverage of graphene shell. In the present work, the effect of variation in concentration of polyvinyl pyrrole (PVP) during synthesis has also been executed. XRD studies were confirmed the formation of Co0 and Co3O4 in Co3O4/Co/Graphene sample and Ni0 and NiO in NiO/Ni/Graphene. In both cases, the surface area values showed inclining nature with increase in the amount of PVP, till 1.21 g and 1.31 g during their synthesis for nickel and cobalt, respectively. Moreover, the nano-materials could not sustain their spherical shape above the optimal concentration of PVP during synthesis. The optimal concentration of PVP has been determined as 1.21 and 1.31 g in the nickel and cobalt nano-sphere formation, respectively. The SEM and TEM images have affirmed the morphological transformations from the MOFs to MxOy/M/graphene structures. The average diameter of MOFs got shrank down from 60 – 70 nm to 20–30 nm in MxOy/M/graphene nanospheres. It get decreased above the optimum concentration of PVP. The highest surface area value reached to 151.3 m2/g in the Co3O4/Co/graphene prepared with 1.31 g of PVP, whereas same with nickel it touched to maximum value of 146.5 m2/g with PVP concentration of 1.21 g. Both the materials were exhibited excellent electrocatalytic activity in HER and OER during water electrolysis in acidic media, however, Cobalt catalysts performed better in hydrogen production. The anodic and cathodic peak current density has reached maximum value of 50 and 30 A cm−2 in presence of cobalt catalysts (with 1.31 g of PVP). The performance of Co3O4/Co/graphene nano-sphere (1.31 g PVP) is evaluated up to 10 A cm−2, whereas this value is only analyzed as 3 A cm−2 in the case of cobalt non-sphere electrocatalysts during anodic polarization. All the hollow spherical nano-electrocatalysts have shown the electrocatalytic stability during 84 h long potentiometric study.

Studying the preparation, electrochemical performance testing, comparison and application of a cost-effective flexible graphene working electrode

−A cost-effective flexible graphene working electrode (FGWE) was fabricated using overhead projector transparent film (OPTF) and a screen-printing technique. The surface morphology and electrochemical behavior of the electrode were characterized by scanning electron microscopy and cyclic voltammetry. The electrode presented a very thin layer of conductive ink (16.0 ± 0.7 µm) on a large effective surface area (0.301 ± 0.001 cm−2). The anodic peak current density (jpa) of acetaminophen (ACT) in FGWE was 5.2, 3.7, 3.5 and 6.0 times greater than the jpa of glassy carbon electrode (GCE), flexible carbon working electrode (FCWE), SPE1, and SPE2, respectively. The electrochemical performance of FGWE toward ACT was evaluated by differential pulse voltammetry. Under optimized condition, ACT was quantified in a range of 4-100 µM, with good sensitivity, good accuracy (recovery = 82.3 ± 0.4 to 106 ± 3%), and excellent precision. FGWE was applied to determine ACT in commercial pharmaceutical formulations. The results of the study are in good agreement with those obtained by the standard spectrophotometric method. These results indicate that disposable FGWE is particularly useful for the detection of ACT, and its performance may serve as a platform for cost-effective flexible electrochemical sensors.