Cyclic Voltammograms Tests Research Articles

Few-layer MoS2 nanosheets coated onto multi-walled carbon nanotubes as a low-cost and highly electrocatalytic counter electrode for dye-sensitized solar cells

In the current study, the nanocomposite of molybdenum disulfide and multi-walled carbon nanotubes (MWCNT@MoS2) was proposed for the first time as a counter electrode (CE) catalyst in dye-sensitized solar cells (DSSCs) to speed up the reduction of triiodide (I3−) to iodide (I−). This novel catalyst was synthesized by simply mixing MWCNTs and MoS2 in an acidic solution and then converting the solid intermediate into the MWCNT@MoS2 nanocomposite in a H2 flow at 650 °C. X-ray powder diffraction, Raman and X-ray photoemission spectroscopy confirmed the composition and the structure of the MWCNT@MoS2 nanocomposite. The microstructure details of the nanocomposite were studied by transmission electron microscopy, showing that only a few-layers of the MoS2 nanosheets were formed on the MWCNT surface. This unique structure is beneficial to the improvement of the catalytic activity of MWCNT@MoS2 towards the reduction of I3−. The extensive cyclic voltammograms (CV) showed that the cathodic current density of the MWCNT@MoS2 CE was higher than those of MoS2, MWCNT and sputtered Pt CEs due to the increased active surface area of the former. Moreover, the peak current densities of the MWCNT@MoS2 CE showed no sign of degradation after consecutive 100 CV tests, suggesting the great electrochemical stability of the MWCNT@MoS2 CE. Furthermore, the MWCNT@MoS2 CE demonstrated an impressive low charge-transfer resistance (1.69 Ω cm2) for I3− reduction. Finally, the DSSC assembled with the MWCNT@MoS2 CE showed a high power conversion efficiency of 6.45%, which is comparable to the DSSC with Pt CE (6.41%).

Pulse electropolymerization of high performance PEDOT/MWCNT counter electrodes for Pt-free dye-sensitized solar cells

High performance poly(3,4-ethylenedioxythiophene) (PEDOT) nano-meadows were electropolymerized onto multi-wall carbon nanotube (MWCNT) as counter electrodes (CEs) for Pt-free dye-sensitized solar cells (DSCs) for the first time. This composite film was fabricated using an electrophoresis of MWCNTs onto a fluorinated tin oxide glass substrate and then subjected to PEDOT electropolymerization by using the pulse potentiostatic method. The surface of MWCNTs was wrapped with nano-meadows PEDOT thin film of ∼55 nm in thickness. The extensive cyclic voltammograms (CV) showed PEDOT/MWCNT CE with excellent electrocatalytic activity for I3− reduction. Moreover, the peak current densities of the PEDOT/MWCNT CE showed no sign of degradation after consecutive 200 CV tests, suggesting the great electrochemical stability of the PEDOT/MWCNT CE. The electrochemical impedance spectroscopy demonstrated that the PEDOT/MWCNT CE had the lowest charge-transfer resistance among all CEs tested in this study. The DSC assembled with the PEDOT/MWCNT composite CE demonstrated an enhanced photovoltaic conversion efficiency of 7.03% compared to that using conventional Pt CE (5.88%) under full sunlight illumination (100 mW cm−2, AM1.5 G) due to the intrinsic superior electrocatalytic activity of the nano-meadows PEDOT material, highly specific surface area and high electrical conductivity of the MWCNTs. Therefore, the PEDOT/MWCNT CE can be considered as a promising alternative CE for use in Pt-free DSCs.

EXCELLENT CYCLING PERFORMANCE OF THREE-DIMENSIONAL-ORDERED MACROPOROUS NiFe2O4 AS ANODE MATERIAL FOR LITHIUM ION BATTERIES

Three-dimensional ordered macroporous (3DOM) nickel ferrite ( NiFe2O4 ) anode material is synthesized via colloidal crystal template. A Close-packed poly(methyl methacrylate) (PMMA) spheres is used as template. Scanning electron microscopy observations reveal that the obtained 3DOM NiFe2O4 material has uniform spherical macropores with diameter about 140-nm and 20-nm size walls. The cyclic voltammogram and galvanostatic test are employed to evaluate the electrochemical characteristics of the as-prepared NiFe2O4 . It shows high initial discharge capacity (up to 1370 mAh g-1) and reversible capacity of 670 mAh g-1 at the current density of 0.2 mA cm-2. The results suggest that 3DOM nickel ferrite is a good candidate for anode material of lithium ion batteries.

Molten-salt decomposition synthesis of SnO 2 nanoparticles as anode materials for lithium ion batteries

SnO 2 nanoparticles were synthesized by a simple, easily scaled-up molten-salt decomposition method with SnSO 4 as the molten salt and the reactive phase. During the synthesis process, the undecomposed molten SnSO 4 makes it possible to obtain SnO 2 nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. The as-prepared SnO 2 had a tetragonal rutile structure with an average particle size of 50 nm. When used as anode materials for lithium ion battery, SnO 2 nanoparticles retained the charge capacity still as high as 402 mAh g − 1 at a current density of 156 mA g − 1 after 40 cycles. Moreover, cyclic voltammograms tests showed the formation/deformation of Li 2O was partially reversible.

Effects of complexants on [Ni1/3Co1/3Mn1/3]CO3 morphology and electrochemical performance of LiNi1/3Co1/3Mn1/3O2

LiNi1/3Co1/3Mn1/3O2 cathode materials for the application of lithium ion batteries were synthesized by carbonate co-precipitation routine using different ammonium salt as a complexant. The structures and morphologies of the precursor [Ni1/3Co1/3Mn1/3]CO3 and LiNi1/3Co1/3Mn1/3O2 were investigated through X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The electrochemical properties of LiNi1/3Co1/3Mn1/3O2 were examined using charge/discharge cycling and cyclic voltammogram tests. The results revealed that the microscopic structures, particle size distribution, and the morphology properties of the precursor and electrochemical performance of LiNi1/3Co1/3Mn1/3O2 were primarily dependent on the complexant. Among all as-prepared LiNi1/3Co1/3Mn1/3O2 cathode materials, the sample prepared from Na2CO3–NH4HCO3 routine using NH4HCO3 as the complexant showed the smallest irreversible capacity of 19.5 mAh g−1 and highest discharge capacity of 178.4 mAh g−1 at the first cycle as well as stable cycling performance (98.7% of the initial capacity was retained after 50 cycles) at 0.1 C (20 mA g−1) in the voltage range of 2.5–4.4 V vs. Li+/Li. Moreover, it delivered high discharge capacity of over 135 mAh g−1 at 5 C (1,000 mA g−1).

Efficient electrocatalysis of cathodic oxygen reduction with Pt–Fe alloy catalyst in microbial fuel cell

To develop efficient and cost-effective cathodic electrocatalyst for microbial fuel cell (MFC), this study investigates the feasibility of Pt–Fe alloy immobilized on carbon material for electrochemical oxygen reduction reaction (ORR). By performing cyclic voltammogram tests, the carbon supported Pt–Fe alloy (C/Pt–Fe) exhibited an improved catalytic activity toward ORR compared to both C/Fe and C/Pt catalyst. Based on 0.5 mg/cm 2 Pt utilization, the maximum power density of 1097.6 ± 51.2 mW/m 2 produced from the MFC with C/Pt–Fe catalyst was 6.5% higher than that of 1030.4 ± 47.8 mW/m 2 obtained from the MFC using C/Pt catalyst. The Pt-based alloy proposed herein suggests a promising approach to efficient ORR of MFC, which makes it more technically and economically viable to recover electrical energy from biomass materials.

Study of synthesis and electrochemical properties of spinel LiNi0.5Mn1.2Ti0.3O4 by different methods

Two spinel LiNi0.5Mn1.2Ti0.3O4 samples were successfully synthesized by the sol-gel method using chemicals LiAc·2H2O, Mn(Ac)2·2H2O, Ni(Ac)2·4H2O and Ti(OCH3)4 as reactants. When reactants are calcined in air, a sample of LiNi0.5Mn1.2Ti0.3O4 (1), which contains Mn3+ and Mn4+ ions, is obtained. The sample of LiNi0.5 Mn1.2Ti0.3O4 (2), which contains only Mn4+ ions, is obtained when reactants are calcined in an oxygen atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge test and cyclic voltammogram test were employed to investigate the two samples. XRD results show that there is a small shift towards a larger diffraction angle for peaks of the LiNi0.5Mn1.2Ti0.3O4 (2) sample. SEM indicates that the two samples exhibit polyhedral shapes. The cyclic voltammogram test demonstrates that reduction-oxidation reactions take place at different voltages for the two samples. The prepared sample of LiNi0.5Mn1.2Ti0.3O4 with Mn3+ ions exhibits excellent cycle performance at different current rates. Its discharge capacity is 133.9 mAh/g at 0.1C.

Electrical double-layer capacitor performance of nitrogen-doped ordered mesoporous carbon prepared by nanotemplating method

In this work, the electrical double-layer capacitive properties of nitrogen-doped ordered mesoporous carbons (N-OMCs) were investigated. Ordered mesoporous carbons (OMCs) with 3D body-centered Ia3d structure has been prepared by KIT-6 mesoporous silica as a hard template with aniline for N-OMC and sucrose for Su-OMC as a carbon precursor. Using the different carbon precursor, moderate amounts of nitrogen atoms could be doped to the OMC structures. The obtained materials were characterized by powder X-ray diffraction (XRD), nitrogen adsorption isotherms at 77 K, elemental analysis, and X-ray photoelectron spectroscopy (XPS). Prepared OMCs had mesopore properties such as a high surface area with narrow pore-size distribution. From cyclic voltammograms (CVs) test, N-OMC compared to Su-OMC exhibit higher capacitance and fast charge/discharge characteristics, which results from their pseudo-capacitive effect of incorporated nitrogen atoms. It was thought that N-OMC prepared by the nanotemplating method with KIT-6 and aniline were suitable electrode materials for electrical double-layer capacitors.

Cathode electrodeposition and characterization of Ru nanoparticles doped a-CN x:H composite films

Well-dispersed and stable Ru nanocrystalline particles with diameter in the range of 2–4 nm embedded in the amorphous carbon nitride matrix were synthesized on single crystal silicon (100) substrate by cathode electrochemical deposition using acetonitrile and Ru 3(CO) 12 as carbon source and dopant, respectively. The results obtained from high-resolution transmission electron microscopy showed that the Ru nanoparticles were presented in the form of hexagonal Ru crystal structure with preferred orientation of (101). X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy confirmed that the as-obtained films are composed of C, N, Ru and H. Raman spectroscopy indicated that the films contained tetrahedral (sp3) and trigonal (sp2) bonding structures. After doping Ru into the amorphous carbon nitride matrix, the conductivity of the composite films is commendably enhanced and the cyclic voltammograms tests show evident oxidation and visible reduction peaks of Ru, also indicating the presence of Ru immobile phase in the amorphous carbon matrix.

Preparation and characterization of a new carbonaceous material for electrochemical systems

A new carbonaceous material was successfully prepared by the pyrolysis of scrap tire rubber at 600?C under a nitrogen atmosphere. The physical characteristics of the prepared carbonaceous material were studied by scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was proved that the carbonaceous material had a disordered structure and spherical morphology with an average particle size about 100 nm. The prepared carbonaceous material was also used as electrodes in electrochemical systems to examine its electrochemical performances. It was demonstrated that it delivered a lithium insertion capacity of 658 mA h g-1 during the first cycle with a coulombic efficiency of 68 %. Cyclic voltammograms test results showed that a redox reaction occurred during the cycles. The chemical diffusion coefficient based on the impedance diagram was about 10-10 cm2 s-1. The pyrolytic carbonaceous material derived from scrap tire rubber is therefore considered to be a potential anode material in lithium secondary batteries or capacitors. Furthermore, it is advantageous for environmental protection.

Synthesis and electrochemical properties of multi-doped LiFePO 4/C prepared from the steel slag

The paper presents and discusses a novel route to synthesize a multi-doped LiFePO 4/C composite by using steel slag as a raw material. A ferroalloy with suitable molar ratio of Fe, Mn, V, and Cr is recovered from the slag by a selective carbothermic method, and successfully used as source materials of Fe and multiple dopants for preparing the multi-doped LiFePO 4/C. XRD and Rietveld-refined results show that the multi-doped LiFePO 4/C is single olivine-type phase and well crystallized, Mn, V, and Cr atoms occupy Fe site. Elemental mapping image confirms that the elements (Fe, P, Mn, V, and Cr) distribute homogeneously in particles of the multi-doped LiFePO 4/C. The electrochemical performance of prepared cathode was evaluated by galvanostatic charge/discharge and cyclic voltammogram tests. Compared to the undoped LiFePO 4/C prepared only by chemical reagents, the multi-doped LiFePO 4/C exhibits lesser capacity drops with increasing of charge/discharge current density due to the improvement of the electrode reactivity by multi-doping. The results suggest that steel slag is an abundant and inexpensive source materials of iron and dopants for preparing multi-doped LiFePO 4/C.

A study on lithium/air secondary batteries—Stability of NASICON-type glass ceramics in acid solutions

The stability of a NASICON-type lithium ion conducting solid electrolyte, Li 1+ x+ y Ti 2− x Al x P 3− y Si y O 12 (LTAP), in acetic acid and formic acid solutions was examined. XRD patterns of the LTAP powders immersed in 100% acetic acid and formic acid at 50 °C for 4 months showed no change as compared to the pristine LTAP. However, the electrical conductivity of LTAP drastically decreased. On the other hand, no significant electrical conductivity change of LTAP immersed in lithium formate saturated formic acid–water solution was observed, and the electrical conductivity of LTAP immersed in lithium acetate saturated acetic acid–water increased. Cyclic voltammogram tests suggested that acetic acid was stable up to a high potential, but formic acid decomposed under the decomposition potential of water. The acetic acid solution was considered to be a candidate for the active material in the air electrode of lithium–air rechargeable batteries. The cell reaction was considered as 2Li + 2 CH 3COOH + 1/2O 2 = 2CH 3COOLi + H 2O. The energy density of this lithium–air system is calculated to be 1477 Wh kg −1 from the weights of Li and CH 3COOH, and an observed open-circuit voltage of 3.69 V.

Electrochemical performance of sulfur composite cathode materials for rechargeable lithium batteries

The structure and characteristic of carbon materials have a direct influence on the electrochemical performance of sulfur–carbon composite electrode materials for lithium–sulfur battery. In this paper, sulfur composite has been synthesized by heating a mixture of elemental sulfur and activated carbon, which is characterized as high specific surface area and microporous structure. The composite, contained 70% sulfur, as cathode in a lithium cell based on organic liquid electrolyte was tested at room temperature. It showed two reduction peaks at 2.05 V and 2.35 V, one oxidation peak at 2.4 V during cyclic voltammogram test. The initial discharge specific capacity was 1180.8 mAh g −1 and the utilization of electrochemically active sulfur was about 70.6% assuming a complete reaction to the product of Li 2S. The specific capacity still kept as high as 720.4 mAh g −1 after 60 cycles retaining 61% of the initial discharge capacity.

Facile synthesis of hierarchically porous carbons and their application as a catalyst support for methanol oxidation

We report the facile synthesis of hierarchically porous carbons and their application as a catalyst support for methanol oxidation. The honeycomb-like hierarchically porous carbons were synthesized by a facile self-assembly strategy, in which the template/carbon-precursor composite could be prepared in a one-pot approach by directly evaporating the reactant mixture solution of tetraethyl orthosilicate (TEOS) and phenolic resin. This synthesis process is simple and time-saving in comparison with the conventional casting methods. The as-prepared porous texture combines micropores, mesopores and macropores, mainly originating from the carbonized phenolic resin as well as the silica template formed with different sizes. The porous carbons have a large BET surface area of 664.75 m2 g−1 and partially graphitized structures. The morphology and porosity of the carbon product can be obviously affected by the corresponding experimental parameters. A preliminary study of the application of the as-prepared hierarchically porous carbons as the support for a Pt catalyst for methanol oxidation is performed. The porous carbon-supported Pt catalyst exhibits higher current density (120.6 mA mg−1) and stability in comparison with the carbon black-supported Pt catalyst. The as-prepared carbons with a hierarchically porous structure can effectively stabilize the Pt particles and alleviate the agglomeration of the particles during the cyclic voltammogram tests, suggesting potential application in the catalysts of direct methanol fuel cells.

Syntheses and Substituent Effects on the Properties of Unsymmetrical Photochromic Diarylethenes Bearing a Benzothiophene Unit

Photochromic unsymmetrical diarylethenes 1a–5a that bear different electron-donating or electron-withdrawing substitutes have been synthesized, and the structures of 2a–5a determined by single-crystal X-ray diffraction analysis. Substituent effects on their optoelectronic properties, including photochromism, fluorescence, and electrochemical properties are investigated in detail. The strong electron-donating substituents have effective contributions to the absorption maxima of the closed-ring isomers and the molar coefficients, whereas the electron-withdrawing substituents can shift significantly the absorption maxima of the diarylethenes to a longer wavelength and increase their cyclization quantum yield. Diarylethenes 2, 3, and 4 show good photochromism both in solution and in the single crystalline phase. However, diarylethenes 5 shows no photochromism in the crystalline phase. Diarylethenes 1, 2, and 3 exhibit good fluorescent switching upon alternating irradiation with UV and visible light, and their fluorescent conversions in the photostationary state are all larger than 80% in hexane. In addition, cyclic voltammogram tests show that different electron-donating and electron-withdrawing substituents have a remarkable effect on the electrochemical behaviours of these diarylethenes.

Platinum-macrocycle co-catalyst for electro-oxidation of formic acid

In this work, a new promoter, tetrasulfophthalocyanine (FeTSPc), one kind of environmental friendly material, was found to be very effective in both inhibiting self-poisoning and improving the intrinsic catalysis activity, consequently enhancing the electro-oxidation current during the electro-oxidation of formic acid. The cyclic voltammograms test showed that the formic acid oxidation peak current density has been increased about 10 times compared with that of the Pt electrode without FeTSPc. The electrochemical double potential step chronoamperometry measurements revealed that the apparent activity energy decreases from 20.64 kJ mol −1 to 17.38 kJ mol −1 after Pt electrode promoted by FeTSPc. The promoting effect of FeTSPc may be owed to the specific structure and abundant electrons of FeTSPc resulting in both the steric hindrance of the formation of poisoning species (CO) and intrinsic kinetic enhancement. In the single cell test, the performance of DFAFC increased from 80 mW cm −2 mg −1 (Pt) to 130 mW cm −2 mg −1 after the anode electrode adsorbed FeTSPc.

DC magnetron sputtering prepared Ag [sbnd]C thin film anode for thin film lithium ion microbatteries

An Ag C thin film was prepared by DC magnetron co-sputtering, using pure silver and graphite as the targets. The microstructure and morphology of the deposited thin film were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical performances of the Ag C thin film anode were investigated by means of discharge/charge and cyclic voltammogram (CV) tests in model cells. The electrochemical impedance spectrum (EIS) characteristics and the chemical diffusion coefficient, D Li of the Ag C thin film electrode at different discharging states were discussed. It was believed that the excellent cycling performance of the Ag C electrode was ascribed to the good conductivity of silver and the volume stability of the thin film.

마이크로 전극에 의한 2차 전지용 활물질 단일 입자의 전기화학적 평가

마이크로전극을 사용하여 니켈-수소 전지의 전극 활물질인 수소저장합금<TEX>$(MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3})$</TEX>과 수산화니켈의 단일입자에 대하여 전기화학적 특성을 평가하였다. 즉 마이크로 전극을 활물질 입자 한 개 위에 전기적인 접촉을 이루도록 조정하고 전위 주사(Cyclic Voltammograms) 및 포텐셜 스텝(Potential Step)으로 실험을 실시하였다. 그 결과 수소저장 합금 입자의 경우 -0.9, -0.75, -0.65V 부근에서 3개의 산화 피크 및 -0.98V에서 수소발생 전위, 그리고 수산화니켈 입자의 경우 프로톤 산화 환원 반응(0.45V, 0.32V)과 산소 발생 반응 전위를 보다 명확하게 확인 할 수 있었다. 그리고 수소흡장합금 입자 내에서의 수소 흡장 및 방출 전 과정에 대해 수소 확산계수 <TEX>$(D_{app})\;(10^{-9}\sim10^{-10}cm^2/s)$</TEX>가 얻어졌다. Electrochemical properties were studied for a single particle of active material of hydrogen storage alloy <TEX>$(MmNi_{3.55}Co_{0.75}Mn_{0.4}Al_{0.3})$</TEX> and nickel hydroxides <TEX>$(NiOH)_2$</TEX> for the secondary Nickel Metal Hydride (Ni-MH) batteries using the microelectrode, which was manipulated to make electrical contact with an active material particle for cyclic voltammograms (CV) and potential-step experiments. As a result of CV test, it was found that three kinds of hydrogen oxidation peaks at -0.9, -0.75 and -0.65 V and hydrogen evolution peak at -0.98 V for hydrogen storage alloy were separately observed and two kinds of peaks of proton oxidation/reduction at 0.45 and 0.32 V and oxygen evolution reaction (OER) at 0.6 V for nickel hydroxides were also more clearly observed. Furthermore hydrogen diffusion coefficient within a single particle was also found to vary the order between <TEX>$10^{-9}\;and\;10^{-10}cm^2/s$</TEX> over the course of hydrogenation and dehydrogenation process for potential-step experiments.

A 10 kW class PEM fuel cell stack based on the catalyst-coated membrane (CCM) method

A 60-cell 10 kW class PEM fuel cell stack has been developed and tested. By using the catalyst-coated membrane (CCM) method, a power density of 0.36 W / cm 2 was reached for a single cell with a 600 cm 2 active area. The total Pt loading was 0.6 mg / cm 2 for the anode and cathode catalyst layers. Cyclic voltammogram (CV) tests revealed that the CCM method had a higher Pt utilization when compared to the hydrophobic method. Furthermore, a maximum power of 10.9 kW was reached at an air utilization of 30%. A 400-h performance test showed a ± 2 V fluctuation of the stack voltages. Coupling the 10 kW class stack with an external humidifier gave a relatively poor result of 6 kW.