Showing papers on "Cyclic voltammetry published in 2017"

Ultrathin and Porous Ni3S2/CoNi2S4 3D-Network Structure for Superhigh Energy Density Asymmetric Supercapacitors

Abstract: 3D-networked, ultrathin, and porous Ni3S2/CoNi2S4 on Ni foam (NF) is successfully designed and synthesized by a simple sulfidation process from 3D Ni–Co precursors. Interestingly, the edge site-enriched Ni3S2/CoNi2S4/NF 3D-network is realized by the etching-like effect of S2− ions, which made the surfaces of Ni3S2/CoNi2S4/NF with a ridge-like feature. The intriguing structural/compositional/componental advantages endow 3D-networked-free-standing Ni3S2/CoNi2S4/NF electrodes better electrochemical performance with specific capacitance of 2435 F g−1 at a current density of 2 A g−1 and an excellent rate capability of 80% at 20 A g−1. The corresponding asymmetric supercapacitor achieves a high energy density of 40.0 W h kg−1 at an superhigh power density of 17.3 kW kg−1, excellent specific capacitance (175 F g−1 at 1A g−1), and electrochemical cycling stability (92.8% retention after 6000 cycles) with Ni3S2/CoNi2S4/NF as the positive electrode and activated carbon/NF as the negative electrode. Moreover, the temperature dependences of cyclic voltammetry curve polarization and specific capacitances are carefully investigated, and become more obvious and higher, respectively, with the increase of test temperature. These can be attributed to the components' synergetic effect assuring rich redox reactions, high conductivity as well as highly porous but robust architectures. This work provides a general, low-cost route to produce high performance electrode materials for portable supercapacitor applications on a large scale.

Earth-Abundant Iron Diboride (FeB2) Nanoparticles as Highly Active Bifunctional Electrocatalysts for Overall Water Splitting

Abstract: Developing efficient, durable, and earth-abundant electrocatalysts for both hydrogen and oxygen evolution reactions is important for realizing large-scale water splitting. The authors report that FeB2 nanoparticles, prepared by a facile chemical reduction of Fe2+ using LiBH4 in an organic solvent, are a superb bifunctional electrocatalyst for overall water splitting. The FeB2 electrode delivers a current density of 10 mA cm−2 at overpotentials of 61 mV for hydrogen evolution reaction (HER) and 296 mV for oxygen evolution reaction (OER) in alkaline electrolyte with Tafel slopes of 87.5 and 52.4 mV dec−1, respectively. The electrode can sustain the HER at an overpotential of 100 mV for 24 h and OER for 1000 cyclic voltammetry cycles with negligible degradation. Density function theory calculations demonstrate that the boron-rich surface possesses appropriate binding energy for chemisorption and desorption of hydrogen-containing intermediates, thus favoring the HER process. The excellent OER activity of FeB2 is ascribed to the formation of a FeOOH/FeB2 heterojunction during water oxidation. An alkaline electrolyzer is constructed using two identical FeB2-NF electrodes as both anode and cathode, which can achieve a current density of 10 mA cm−2 at 1.57 V for overall water splitting with a faradaic efficiency of nearly 100%, rivalling the integrated state-of-the-art Pt/C and RuO2/C.

Boron‐Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction

Abstract: Molybdenum-based materials have been considered as alternative catalysts to noble metals, such as platinum, for the hydrogen evolution reaction (HER). We have synthesized four binary bulk molybdenum borides Mo2 B, α-MoB, β-MoB, and MoB2 by arc-melting. All four phases were tested for their electrocatalytic activity (linear sweep voltammetry) and stability (cyclic voltammetry) with respect to the HER in acidic conditions. Three of these phases were studied for their HER activity and by X-ray photoelectron spectroscopy (XPS) for the first time; MoB2 and β-MoB show excellent activity in the same range as the recently reported α-MoB and β-Mo2 C phases, while the molybdenum richest phase Mo2 B show significantly lower HER activity, indicating a strong boron-dependency of these borides for the HER. In addition, MoB2 and β-MoB show long-term cycle stability in acidic solution.

Self-Assembled and One-Step Synthesis of Interconnected 3D Network of Fe3O4/Reduced Graphene Oxide Nanosheets Hybrid for High-Performance Supercapacitor Electrode.

Abstract: In the present work, we have synthesized three-dimensional (3D) reduced graphene oxide nanosheets (rGO NSs) containing iron oxide nanoparticles (Fe3O4 NPs) hybrids (3D Fe3O4/rGO) by one-pot microwave approach. Structural and morphological studies reveal that the as-synthesized Fe3O4/rGO hybrids were composed of faceted Fe3O4 NPs induced into the interconnected network of rGO NSs. The morphologies and structures of the 3D hybrids have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectrometer (XPS). The electrochemical studies were analyzed by cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy, which demonstrate superior electrochemical performance as supercapacitors electrode application. The specific capacitances of 3D hybrid materials was 455 F g–1 at the scan rate of 8 mV s–1, which is superior to that of bare Fe3O4 NPs. Addi...

Fe-g-C3N4/graphitized mesoporous carbon composite as an effective Fenton-like catalyst in a wide pH range

Abstract: Heterogeneous Fe-N complexes are a kind of promising catalysts for the Fenton-like reaction. The present study selected a stable and inexpensive g-C 3 N 4 as the chelating agent and combined with the graphitized mesoporous carbon (GMC). The fabricated Fe-g-C 3 N 4 /GMC composite was characterized by several techniques including FTIR, XRD, XPS, TEM and STXM. Results showed clear sheets of g-C 3 N 4 and graphite with Fe evenly distributed mostly in the Fe-N coordination form. The catalyst expressed high activity in the Fenton-like reaction in a wide pH range of 4–10. 99.2% removal of Acid Red 73 was obtained in 40 min, and the degradation data well fitted with the pseudo-first-order kinetics model. By correlating the constant of reaction rates calculated from the model and the Fe speciation contents of the samples prepared at different conditions, we deduced that Fe-N species are the most important active sites for the Fenton-like reaction. More importantly, hydroxyl radicals played a great role in the whole reaction yet their generation was independent of visible light. Cyclic voltammetry results confirmed that the GMC can accelerate the Fe(III)/Fe(II) redox cycle by enhancing electron transfer, and thus enable this Fenton-like catalyst to perform well in a wide pH range.

Preparation of NiCoP Hollow Quasi-Polyhedra and Their Electrocatalytic Properties for Hydrogen Evolution in Alkaline Solution

Abstract: Double metal phosphide (NiCoP) with hollow quasi-polyhedron structure was prepared by acidic etching and precipitation of ZIF-67 polyhedra and further phosphorization treatment with NaH2PO2. The morphology and microstructure of NiCoP quasi-polyhedron and its precursors were investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and a micropore and chemisorption analyzer. Electrocatalytic properties were examined by typical electrochemical methods, such as linear sweep voltammetry, cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy in 1.0 M KOH aqueous solution. Results reveal that, compared with CoP hollow polyhedra, NiCoP hollow quasi-polyhedra exhibit better electrochemical properties for hydrogen evolution with a low onset overpotential of 74 mV and a small Tafel slope of 42 mV dec–1. When the current density is 10 mA cm–2, the corresponding overpotential is merely 124 mV, and 93% of its electrocatalytic activity can be maintain...

Molybdenum Disulfide–Black Phosphorus Hybrid Nanosheets as a Superior Catalyst for Electrochemical Hydrogen Evolution

Abstract: Engineering electronic properties is a promising way to design nonprecious-metal or earth-abundant catalysts toward hydrogen evolution reaction (HER). Herein, we deposited catalytically active MoS2 flakes onto black phosphorus (BP) nanosheets to construct the MoS2–BP interfaces. In this case, electrons flew from BP to MoS2 in MoS2–BP nanosheets because of the higher Fermi level of BP than that of MoS2. MoS2–BP nanosheets exhibited remarkable HER performance with an overpotential of 85 mV at 10 mA cm–2. Due to the electron donation from BP to MoS2, the exchange current density of MoS2–BP reached 0.66 mA cm–2, which was 22 times higher than that of MoS2. In addition, both the consecutive cyclic voltammetry and potentiostatic tests revealed the outstanding electrocatalytic stability of MoS2–BP nanosheets. Our finding not only provides a superior HER catalyst, but also presents a straightforward strategy to design hybrid electrocatalysts.

Supercapacitor electrode materials with hierarchically structured pores from carbonization of MWCNTs and ZIF-8 composites

Abstract: Due to their high specific surface area and good electric conductivity, nitrogen-doped porous carbons (NPCs) and carbon nanotubes (CNTs) have attracted much attention for electrochemical energy storage applications. In the present work, we firstly prepared MWCNT/ZIF-8 composites by decoration of zeolitic imidazolate frameworks (ZIF-8) onto the surface of multi-walled CNTs (MWCNTs), then obtained MWCNT/NPCs by the direct carbonization of MWCNT/ZIF-8. By controlling the reaction conditions, MWCNT/ZIF-8 with three different particle sizes were synthesized. The effect of NPCs size on capacitance performance has been evaluated in detail. The MWCNT/NPC with large-sized NPC (MWCNT/NPC-L) displayed the highest specific capacitance of 293.4 F g−1 at the scan rate of 5 mV s−1 and only lost 4.2% of capacitance after 10 000 cyclic voltammetry cycles, which was attributed to the hierarchically structured pores, N-doping and high electrical conductivity. The studies of symmetric two-electrode supercapacitor cells also confirmed MWCNT/NPC-L as efficient electrode materials that have good electrochemical performance, especially for high-rate applications.

Highly Efficient and Stable Water‐Oxidation Electrocatalysis with a Very Low Overpotential using FeNiP Substitutional‐Solid‐Solution Nanoplate Arrays

Abstract: The development of efficient water-oxidation electrocatalysts based on inexpensive and earth-abundant materials is significant to enable water splitting as a future renewable energy source. Herein, the synthesis of novel FeNiP solid-solution nanoplate (FeNiP-NP) arrays and their use as an active catalyst for high-performance water-oxidation catalysis are reported. The as-prepared FeNiP-NP catalyst on a 3D nickel foam substrate exhibits excellent electrochemical performance with a very low overpotential of only 180 mV to reach a current density of 10 mA cm-2 and an onset overpotential of 120 mV in 1.0 m KOH for the oxygen evolution reaction (OER). The slope of the Tafel plot is as low as 76.0 mV dec-1 . Furthermore, the long-term electrochemical stability of the FeNiP-NP electrode is investigated by cyclic voltammetry (CV) at 1.10-1.55 V versus reversible hydrogen electrode (RHE), demonstrating very stable performance with negligible loss in activity after 1000 CV cycles. This present FeNiP-NP solid solution is thought to represent the best OER catalytic activity among the non-noble metal catalysts reported so far.

Investigation on electrochemical behaviors of NiCo2O4 battery-type supercapacitor electrodes: the role of an aqueous electrolyte

Abstract: Mesoporous NiCo2O4 flower-like structures are prepared successfully by a facile solvothermal route. The electrochemical performance of the as-synthesized products as electrode materials for battery-type supercapacitors is systematically investigated at various concentrations of potassium hydroxide (KOH) aqueous solution by cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy. NiCo2O4 supercapacitor electrode in the 6 M KOH electrolyte delivers high specific capacity (122.5 C g−1 at 1 A g−1), excellent rate performance (82.5 C g−1 at 10 A g−1) and cycling stability (21.7% capacity loss after 6000 cycles at 2 A g−1). The results show that KOH electrolyte at high concentrations plays an important role in improving electrochemical performance of NiCo2O4 battery-type supercapacitor electrodes.

3D NiO hollow sphere/reduced graphene oxide composite for high-performance glucose biosensor

Abstract: The 3D NiO hollow sphere/reduced graphene oxide (rGO) composite was synthesized according to the coordinating etching and precipitating process by using Cu2O nanosphere/graphene oxide (GO) composite as template. The morphology, structure, and composition of the materials were characterized by SEM, TEM, HRTEM, XPS, and Raman spectra, and the electrochemical properties were studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry. Moreover, the electrochemical activity of the composite materials with different morphologies were also investigated, which indicating a better combination of the NiO hollow sphere and the rGO. Used as glucose sensing material, the 3D NiO hollow sphere/rGO composite modified electrode exhibits high sensitivity of ~2.04 mA mM−1 cm−2, quick response time of less than 5 s, good stability, selectivity, and reproducibility. Its application for the detection of glucose in human blood serum sample shows acceptable recovery and R.S.D. values. The outstanding glucose sensing performance should be attributed to the unique 3D hierarchical porous superstructure of the composite, especially for its enhanced electron-transfer kinetic properties.

Simultaneous determination of trace Cd(II), Pb(II) and Cu(II) by differential pulse anodic stripping voltammetry using a reduced graphene oxide-chitosan/poly-l-lysine nanocomposite modified glassy carbon electrode

Abstract: The reduced graphene oxide (RGO) and Chitosan (CS) hybrid matrix RGO-CS were coated onto the glassy carbon electrode (GCE) surface, then, poly-l-lysine films (PLL) were prepared by electropolymerization with cyclic voltammetry (CV) method to prepare RGO-CS/PLL modified glassy carbon electrode (RGO-CS/PLL/GCE) for the simultaneous electrochemical determination of heavy metal ions Cd(II), Pb(II) and Cu(II). Combining the advantageous features of RGO and CS, RGO and CS are used together because the positively charged CS can interact with the negatively changed RGO to prevent their aggregation. Furthermore, CS has many amino groups along its macromolecular chains and possessed strongly reactive with metal ions. Moreover, PLL modified electrodes have good stability, excellent permselectivity, more active sites and strong adherence to electrode surface, which enhanced electrocatalytic activity. The RGO-CS/PLL/GCE was characterized voltammetrically using redox couples (Fe(CN)63-/4-), complemented with electrochemical impedance spectroscopy (EIS). Differential pulse anodic stripping voltammetry (DPASV) has been used for the detection of Cd(II), Pb(II) and Cu(II). The detection limit of RGO-CS/PLL/GCE toward Cd(II), Pb(II) and Cu(II) is 0.01μgL-1, 0.02μgL-1 and 0.02μgL-1, respectively. The electrochemical parameters that exert influence on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential, and deposition time, were carefully studied.

An aqueous electrolyte of the widest potential window and its superior capability for capacitors

Abstract: A saturated aqueous solution of sodium perchlorate (SSPAS) was found to be electrochemically superior, because the potential window is remarkably wide to be approximately 3.2 V in terms of a cyclic voltammetry. Such a wide potential window has never been reported in any aqueous solutions, and this finding would be of historical significance for aqueous electrolyte to overcome its weak point that the potential window is narrow. In proof of this fact, the capability of SSPAS was examined for the electrolyte of capacitors. Galvanostatic charge-discharge measurements showed that a graphite-based capacitor containing SSPAS as an electrolyte was stable within 5% deviation for the 10,000 times repetition at the operating voltage of 3.2 V without generating any gas. The SSPAS worked also as a functional electrolyte in the presence of an activated carbon and metal oxides in order to increase an energy density. Indeed, in an asymmetric capacitor containing MnO2 and Fe3O4 mixtures in the positive and negative electrodes, respectively, the energy density enlarged to be 36.3 Whkg-1, which belongs to the largest value in capacitors. Similar electrochemical behaviour was also confirmed in saturated aqueous solutions of other alkali and alkaline earth metal perchlorate salts.

Electroreduction of CO2 Catalyzed by a Heterogenized Zn-Porphyrin Complex with a Redox-Innocent Metal Center.

Abstract: Transition-metal-based molecular complexes are a class of catalyst materials for electrochemical CO2 reduction to CO that can be rationally designed to deliver high catalytic performance. One common mechanistic feature of these electrocatalysts developed thus far is an electrogenerated reduced metal center associated with catalytic CO2 reduction. Here we report a heterogenized zinc–porphyrin complex (zinc(II) 5,10,15,20-tetramesitylporphyrin) as an electrocatalyst that delivers a turnover frequency as high as 14.4 site–1 s–1 and a Faradaic efficiency as high as 95% for CO2 electroreduction to CO at −1.7 V vs the standard hydrogen electrode in an organic/water mixed electrolyte. While the Zn center is critical to the observed catalysis, in situ and operando X-ray absorption spectroscopic studies reveal that it is redox-innocent throughout the potential range. Cyclic voltammetry indicates that the porphyrin ligand may act as a redox mediator. Chemical reduction of the zinc–porphyrin complex further confirms...

A novel strategy for the synthesis of sulfur-doped carbon nanotubes as a highly efficient Pt catalyst support toward the methanol oxidation reaction

Abstract: Doped nanocarbon materials (e.g., carbon nanotubes, graphene) are considered as effective electrocatalyst supports for fuel cells, and their electrochemical properties are closely related to the synthetic methods and the types of doping elements. In the current paper, we report a novel approach to synthesize sulfur-doped multi-walled carbon nanotubes (S-MWCNTs) as a highly efficient support material for Pt nanoparticle catalysts. The S-MWCNTs are obtained by annealing poly(3,4-ethylenedioxythiophene) (PEDOT) functionalized multi-walled carbon nanotubes at 800 °C. The prepared nanohybrids were physically characterized by Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It has been found that the doping of sulfur into MWCNTs could significantly improve the dispersion of supported Pt nanoparticles of 2.37 nm in size and increase the electrochemically active surface area (ECSA, 161.4 m2 g−1). The doped sulfur atoms not only provide uniformly dispersed anchoring sites for the deposition of Pt nanoparticles on the surface of MWCNTs but also enhance the electron transfer interaction between Pt nanoparticles and the S-MWCNT support. The electrochemical properties of the catalysts were evaluated by using cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The results demonstrate that the as-prepared Pt/S-MWCNTs exhibit much higher electrocatalytic activity, long-term durability and CO-tolerance ability for the methanol oxidation reaction (MOR) compared to the undoped MWCNT supported Pt and commercial Pt/C catalysts.