Showing papers on "Cyclic voltammetry published in 2018"

Nickel telluride as a bifunctional electrocatalyst for efficient water splitting in alkaline medium

Abstract: Designing efficient electrocatalysts has been one of the primary goals for water electrolysis, which is one of the most promising routes towards sustainable energy generation from renewable sources. In this article, we have tried to expand the family of transition metal chalcogenide based highly efficient OER electrocatalysts by investigating nickel telluride, Ni3Te2 as a catalyst for the first time. Interestingly Ni3Te2 electrodeposited on a GC electrode showed very low onset potential and overpotential at 10 mA cm−2 (180 mV), which is the lowest in the series of chalcogenides with similar stoichiometry, Ni3E2 (E = S, Se, Te) as well as Ni-oxides. This observation falls in line with the hypothesis that increasing the covalency around the transition metal center enhances catalytic activity. Such a hypothesis has been previously validated in oxide-based electrocatalysts by creating anion vacancies. However, this is the first instance where this hypothesis has been convincingly validated in the chalcogenide series. The operational stability of the Ni3Te2 electrocatalyst surface during the OER for an extended period of time in alkaline medium was confirmed through surface-sensitive analytical techniques such as XPS, as well as electrochemical methods which showed that the telluride surface did not undergo any corrosion, degradation, or compositional change. More importantly we have compared the catalyst activation step (Ni2+ → Ni3+ oxidation) in the chalcogenide series, through electrochemical cyclic voltammetry studies, and have shown that catalyst activation occurs at lower applied potential as the electronegativity of the anion decreases. From DFT calculations we have also shown that the hydroxyl attachment energy is more favorable on the Ni3Te2 surface compared to the Ni-oxide, confirming the enhanced catalytic activity of the telluride. Ni3Te2 also exhibited efficient HER catalytic activity in alkaline medium making it a very effective bifunctional catalyst for full water splitting with a cell voltage of 1.66 V at 10 mA cm−2. It should be noted here that this is the first report of OER and HER activity in the family of Ni-tellurides.

3D-Printed Graphene/Polylactic Acid Electrodes Promise High Sensitivity in Electroanalysis.

Abstract: Additive manufacturing provides a unique tool for prototyping structures toward electrochemical sensing, due to its ability to produce highly versatile, tailored-shaped devices in a low-cost and fast way with minimized waste. Here we present 3D-printed graphene electrodes for electrochemical sensing. Ring- and disc-shaped electrodes were 3D-printed with a Fused Deposition Modeling printer and characterized using cyclic voltammetry and scanning electron microscopy. Different redox probes K3Fe(CN)6:K4Fe(CN)6, FeCl3, ascorbic acid, Ru(NH3)6Cl3, and ferrocene monocarboxylic acid) were used to assess the electrochemical performance of these devices. Finally, the electrochemical detection of picric acid and ascorbic acid was carried out as proof-of-concept analytes for sensing applications. Such customizable platforms represent promising alternatives to conventional electrodes for a wide range of sensing applications.

Enhanced Catalysis of the Electrochemical Oxygen Evolution Reaction by Iron(III) Ions Adsorbed on Amorphous Cobalt Oxide

Abstract: The oxygen evolution reaction (OER) is the bottleneck in the efficient production of hydrogen gas fuel via the electrochemical splitting of water. In this work, we present and elucidate the workings of an OER catalytic system which consists of cobalt oxide (CoOx) with adsorbed Fe3+ ions. The CoOx was electrodeposited onto glassy-carbon-disk electrodes, while Fe3+ was added to the 1 M KOH electrolyte. Linear sweep voltammetry and chronopotentiometry were used to assess the system’s OER activity. The addition of Fe3+ significantly lowered the average overpotential (η) required by the cobalt oxide catalyst to produce 10 mA/cm2 O2 current from 378 to 309 mV. The Tafel slope of the CoOx + Fe3+ catalyst also decreased from 59.5 (pure CoOx) to 27.6 mV/dec, and its stability lasted ∼20 h for 10 mA/cm2 O2 evolution. Cyclic voltammetry showed that oxidation of the deposited CoOx, from Co2+ to Co3+ occurred at a more positive potential when Fe3+ was added to the electrolyte. This could be attributed to interactions ...

A Dendritic Nickel Cobalt Sulfide Nanostructure for Alkaline Battery Electrodes

Abstract: A uniform dendritic NiCo 2 S 4 at NiCo 2 S 4 hierarchical nanostructure of width ≈100 nm is successfully designed and synthesized. From kinetic analysis of the electrochemical reactions, those electrodes function in rechargeable alkaline batteries (RABs). The dendritic structure exhibited by the electrodes has a high discharge-specific capacity of 4.43 mAh cm -2 at a high current density of 240 mA cm -2 with a good rate capability of 70.1% after increasing the current densities from 40 to 240 mA cm -2 . At low scan rate of 0.5 mV s -1 in cyclic voltammetry test, the semidiffusion controlled electrochemical reaction contributes ≈92% of the total capacity, this value decreases to ≈43% at a high scan rate of 20 mV s -1 . These results enable a detailed analysis of the reaction mechanism for RABs and suggest design concepts for new electrode materials.

Hierarchical CuO nanorod arrays in situ generated on three-dimensional copper foam via cyclic voltammetry oxidation for high-performance supercapacitors

Abstract: Unique hierarchical cyclic voltammetry oxidation (CVO) Cu@CuO nanorod arrays were obtained by an in situ oxidation reaction with the combination of calcination and cyclic voltammetry oxidation strategies. The areal capacitance of this CVO Cu@CuO electrode reaches 1.674 F cm−2 (594.27 F g−1) at a current density of 2 mA cm−2, which is significantly higher than those of Cu@Cu(OH)2 (0.207 F cm−2) and Cu@CuO (1.307 F cm−2) electrodes. In addition, an excellent rate capacity (1.085 F cm−2 at a current density of 30 mA cm−2) and remarkable cycling stability (96.45% after 4000 cycles) were observed. Additionally, the CVO Cu@CuO nanorod arrays can also be utilized as the positive electrode to manufacture asymmetric supercapacitor (ASC) devices, realizing a high cell voltage of 1.5 V and an outstanding energy density of up to 35.43 W h kg−1 at a power density of 520.99 W kg−1. The excellent electrochemical properties can be credited to the unique hierarchical structures. This work makes it attractive in that the CVO Cu@CuO can be utilized as a potential electrode material for supercapacitors.

Expanded biomass-derived hard carbon with ultra-stable performance in sodium-ion batteries

Abstract: A hard carbon sheet-like structure has been successfully prepared with a short flow process by simply using cherry petals (CPs) as the raw materials. The sodium storage mechanism in CPs was detected with cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). Encouragingly, when being assessed as an anode electrode for sodium-ion batteries (SIBs), the CP electrode can provide a high initial reversible capacity of 310.2 mA h g−1 with a favorable initial Coulomb efficiency of 67.3%, delivering a high retention rate of 99.3% at 20 mA g−1 after 100 cycles. Even at a high current density of 500 mA g−1, the reversible capacity can reach 146.5 mA h g−1, indicating that the high rate performance is excellent as well. Such a preferable performance may be derived from the prepared structures with sufficient mesopores, the presence of nitrogen/oxygen functional groups on the surface and the expanded interlayer distances (∼0.44 nm), which enable reversible sodium-ion storage through surface adsorption and sodium intercalation.

Highly Durable Platinum Single‐Atom Alloy Catalyst for Electrochemical Reactions

Abstract: Single atomic Pt catalyst can offer efficient utilization of the expensive platinum and provide unique selectivity because it lacks ensemble sites. However, designing such a catalyst with high Pt loading and good durability is very challenging. Here, single atomic Pt catalyst supported on antimony-doped tin oxide (Pt1/ATO) is synthesized by conventional incipient wetness impregnation, with up to 8 wt% Pt. The single atomic Pt structure is confirmed by high-angle annular dark field scanning tunneling electron microscopy images and extended X-ray absorption fine structure analysis results. Density functional theory calculations show that replacing Sb sites with Pt atoms in the bulk phase or at the surface of SbSn or ATO is energetically favorable. The Pt1/ATO shows superior activity and durability for formic acid oxidation reaction, compared to a commercial Pt/C catalyst. The single atomic Pt structure is retained even after a harsh durability test, which is performed by repeating cyclic voltammetry in the range of 0.05–1.4 V for 1800 cycles. A full cell is fabricated for direct formic acid fuel cell using the Pt1/ATO as an anode catalyst, and an order of magnitude higher cell power is obtained compared to the Pt/C.

Highly Selective Molecular Catalysts for the CO2-to-CO Electrochemical Conversion at Very Low Overpotential. Contrasting Fe vs Co Quaterpyridine Complexes upon Mechanistic Studies

Abstract: [MII(qpy)(H2O)2]2+ (M = Fe, Co; qpy: 2,2′:6′,2″:6″,2‴-quaterpyridine) complexes efficiently catalyze the electrochemical CO2-to-CO conversion in acetonitrile solution in the presence of weak Bronsted acids. Upon performing cyclic voltammetry studies, controlled-potential electrolysis, and spectroelectrochemistry (UV–visible and infrared) experiments together with DFT calculations, catalytic mechanisms were deciphered. Catalysis is characterized by high selectivity for CO production (selectivity >95%) in the presence of phenol as proton source. Overpotentials as low as 240 and 140 mV for the Fe and Co complexes, respectively, led to large CO production for several hours. In the former case, the one-electron-reduced species binds to CO2, and CO evolution is observed after further reduction of the intermediate adduct. A deactivation pathway has been identified, which is due to the formation of a Fe0qpyCO species. With the Co catalyst, no such deactivation occurs, and the doubly reduced complex activates CO2....

Fine-tuned organic photoredox catalysts for fragmentation-alkynylation cascades of cyclic oxime ethers

Abstract: Fine-tuned organic photoredox catalysts are introduced for the metal-free alkynylation of alkylnitrile radicals generated via oxidative ring opening of cyclic alkylketone oxime ethers. The redox properties of the dyes were determined by both cyclic voltammetry and computation and covered an existing gap in the oxidation potential of photoredox organocatalysts.

Preparation of highly sensitive Pt nanoparticles-carbon quantum dots/ionic liquid functionalized graphene oxide nanocomposites and application for H2O2 detection

Abstract: There is current interest in developing carbon nanomaterials, which are a novel kind of nanomaterial, for uses in electrochemical sensing and biosensors. We constructed a novel sensor based on a Pt nanoparticles-carbon quantum dots/ionic liquid functionalized graphene oxide (PtNPs-CDs/IL-GO) nanocomposite for detecting H2O2. We characterized the morphology and electrochemical performance of the modified electrode using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and cyclic voltammetry, respectively. The unique chemical structure of PtNPs-CDs/IL-GO greatly accelerated the catalysis of H2O2 and provided plenty of active sites for electrochemical redox reactions. Electrochemical experiments demonstrated that the PtNPs-CDs/IL-GO sensor had high selectivity, a wide linear range from 1 to 900 μM, and a low detection limit of 0.1 μM with respect to the reduction of H2O2. These characteristics indicate good electrical conductivity and high electrocatalytic activity. This simple and effective method has potential applications in chemical sensors and electrochemical catalysis.

Mesoporous Silica Thin Films for Improved Electrochemical Detection of Paraquat.

Abstract: An electrochemical method was developed for rapid and sensitive detection of the herbicide paraquat in aqueous samples using mesoporous silica thin film modified glassy carbon electrodes (GCE). Vertically-aligned mesoporous silica thin films were deposited onto GCE by electrochemically assisted self-assembly (EASA). Cyclic voltammetry revealed effective response to the cationic analyte (while rejecting anions) thanks to the charge selectivity exhibited by the negatively-charged mesoporous channels. Square wave voltametry (SWV) was then used to detect paraquat via its one electron reduction process. Influence of various experimental parameters (i.e. pH, electrolyte concentration and nature of electrolyte anions) on sensitivity was investigated and discussed with respect to the mesopores characteristics and accumulation efficiency, pointing out the key role of charge distribution in such confined spaces on these processes. Calibration plots for paraquat concentration ranging from 10 nM - 10 µM were construc...

Fabrication of Amine-Modified Magnetite-Electrochemically Reduced Graphene Oxide Nanocomposite Modified Glassy Carbon Electrode for Sensitive Dopamine Determination

Abstract: Amine-modified magnetite (NH2–Fe3O4)/reduced graphene oxide nanocomposite modified glassy carbon electrodes (NH2–Fe3O4/RGO/GCEs) were developed for the sensitive detection of dopamine (DA). The NH2-Fe3O4/RGO/GCEs were fabricated using a drop-casting method followed by an electrochemical reduction process. The surface morphologies, microstructure and chemical compositions of the NH2–Fe3O4 nanoparticles (NPs), reduced graphene oxide (RGO) sheets and NH2–Fe3O4/RGO nanocomposites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray diffraction (XRD) and Fourier-transform infrared (FTIR) spectroscopy. The electrochemical behaviors of DA on the bare and modified GCEs were investigated in phosphate buffer solution (PBS) by cyclic voltammetry (CV). Compared with bare electrode and RGO/GCE, the oxidation peak current (ipa) on the NH2–Fe3O4/RGO/GCE increase significantly, owing to the synergistic effect between NH2–Fe3O4 NPs and RGO sheets. The oxidation peak currents (ipa) increase linearly with the concentrations of DA in the range of 1 × 10−8 mol/L – 1 × 10−7 mol/L, 1 × 10−7 mol/L – 1 × 10−6 mol/L and 1 × 10−6 mol/L – 1 × 10−5 mol/L. The detection limit is (4.0 ± 0.36) ×10−9 mol/L (S/N = 3). Moreover, the response peak currents of DA were hardly interfered with the coexistence of ascorbic acid (AA) and uric acid (UA). The proposed NH2–Fe3O4/RGO/GCE is successfully applied to the detection of dopamine hydrochloride injections with satisfactory results. Together with low cost, facile operation, good selectivity and high sensitivity, the NH2–Fe3O4/RGO/GCEs have tremendous prospects for the detection of DA in various real samples.

One-Dimensional BiFeO3 Nanowire-Reduced Graphene Oxide Nanocomposite as Excellent Supercapacitor Electrode Material

Abstract: In this work, we have reported a nanocomposite, composed of a BiFeO3 nanowire and reduced graphene oxide (BFO-RGO), as an electrode material for a high-performance supercapacitor A facile hydrothermal method was employed to prepare BFO-RGO nanocomposite The electrochemical measurements were performed by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy The specific capacitance of the BFO-RGO nanocomposite was 92843 F g–1 at current density 5 A g–1, which is superior to that of pure BiFeO3 Additionally, this nanocomposite shows good cyclic stability, and ∼8751% of specific capacitance is retained up to 1000 cycles It also exhibits a high charge density of 1862 W h kg–1 when the power density is 950 W kg–1 These attractive results suggest the potential of BiFeO3 nanowire-RGO nanocomposite as an active material for the construction of a high-performance supercapacitor electrode To the best of our knowledge, this is the first time the applica

Electrochemical Determination of Adrenaline Using MXene/Graphite Composite Paste Electrodes.

Abstract: MXene/graphite composite paste electrode (MXene/GCPE)-based electrochemical sensor has been fabricated for the detection of adrenaline. The electrode exhibits a sensitive response to adrenaline in phosphate buffer solution of pH 7.4, and its catalytic activity is much higher than that of the bare graphite paste electrode. The electron-transfer reaction of MXene/GCPE is a diffusion controlled process. The graph of concentration of adrenaline with the peak current exhibits two linearities, one in the lower and other in the higher concentration range with a detection limit of 9.5 nM. The simultaneous analyses of adrenaline, ascorbic acid, and serotonin reveal that the fabricated electrode could separate the overlapped cyclic voltammetric peaks of these ternary mixtures. This electrode has been further employed in the detection of adrenaline in pharmaceutical samples with 99.2-100.8% recoveries.