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1.
Small Methods ; 5(10): e2100700, 2021 Oct.
Article in English | MEDLINE | ID: mdl-34927933

ABSTRACT

The electrocatalytic reduction of carbon dioxide into organic fuels and feedstocks is a fascinating method to implement the sustainable carbon cycle. Thus, a rational design of advanced electrocatalysts and a deep understanding of reaction mechanisms are crucial for the complex reactions of carbon dioxide reduction with multiple electron transfer. In situ and operando techniques with real-time monitoring are important to obtain deep insight into the electrocatalytic reaction to reveal the dynamic evolution of electrocatalysts' structure and composition under experimental conditions. In this paper, the reaction pathways for the CO2 reduction reaction (CO2 RR) in the generation of various products (e.g., C1 and C2 ) via the proposed mechanisms are introduced. Moreover, recent advances in the development and applications of in situ and operando characterization techniques, from the basic working principles and in situ cell structure to detailed applications are discussed. Suggestions and future directions of in situ/operando analysis are also addressed.

2.
Sci Rep ; 10(1): 18956, 2020 Nov 03.
Article in English | MEDLINE | ID: mdl-33144659

ABSTRACT

In this work, nickel cobaltite (NiCo2O4) nanosheets with a porous structure were fabricated on nickel foam as a working electrode for supercapacitor applications. The nanosheets were fabricated by electrochemical deposition of nickel-cobalt hydroxide on the nickel foam substrate at ambient temperature in a three-electrode cell followed by annealing at 300 °C to transform the coating into a porous NiCo2O4 nanosheet. Field emission scanning electron microscopy and transmission electron microscopy revealed a three-dimensional mesoporous structure, which facilitates ion transport and electronic conduction for fast redox reactions. For one cycle, the NiCo2O4 electrodeposited nickel foam has a high specific capacitance (1734.9 F g-1) at a current density (CD) of 2 A g-1. The electrode capacitance decreased by only approximately 12.7% after 3500 cycles at a CD of 30 A g-1. Moreover, a solid-state asymmetric supercapacitor (ASC) was built utilising the NiCo2O4 nanosheets, carbon nanotubes, and a polyvinyl alcohol-potassium hydroxide gel as the anode, cathode, and solid-state electrolyte, respectively. The ASC displayed great electrochemical properties with a 42.25 W h kg-1 energy density at a power density of 298.79 W kg-1.

3.
Nanomaterials (Basel) ; 10(7)2020 Jun 30.
Article in English | MEDLINE | ID: mdl-32630131

ABSTRACT

In this study, we synthesized binder-free NiCo2O4@NiCo2O4 nanostructured materials on nickel foam (NF) by combined hydrothermal and cyclic voltammetry deposition techniques followed by calcination at 350 °C to attain high-performance supercapacitors. The hierarchical porous NiCo2O4@NiCo2O4 structure, facilitating faster mass transport, exhibited good cycling stability of 83.6% after 5000 cycles and outstanding specific capacitance of 1398.73 F g-1 at the current density of 2 A·g-1, signifying its potential for energy storage applications. A solid-state supercapacitor was fabricated with the NiCo2O4@NiCo2O4 on NF as the positive electrode and the active carbon (AC) was deposited on NF as the negative electrode, delivering a high energy density of 46.46 Wh kg-1 at the power density of 269.77 W kg-1. This outstanding performance was attributed to its layered morphological characteristics. This study explored the potential application of cyclic voltammetry depositions in preparing binder-free NiCo2O4@NiCo2O4 materials with more uniform architecture for energy storage, in contrast to the traditional galvanostatic deposition methods.

4.
J Hazard Mater ; 388: 121768, 2020 Apr 15.
Article in English | MEDLINE | ID: mdl-31843409

ABSTRACT

This study combined electro-oxidation (EO) and electrocoagulation (EC) process (EO/EC) to treat landfill leachate by using RuO2-IrO2/Ti plate and microscale zero-valent iron powder composite anode. EO was achieved by direct oxidation and indirect oxidation on RuO2-IrO2/Ti plate, whereas EC was achieved using iron powder to lose electrons and produce coagulants in situ. The influences of variables including type of anode material, applied voltage, zero-valent iron dosage, interelectrode gap, and reaction temperature on EO/EC were evaluated. Results showed that at an applied voltage of 10 V, zero-valent iron dosage of 0.2 g, interelectrode gap of 1 cm, and non-temperature-controlled mode, the removal efficiencies were 72.5 % for total organic carbon (TOC), 98.5 % for ammonia, and 98.6 % for total phosphorus (TP). Some heavy metals and hardness were also removed. Further analysis indicated that the removal of TOC, ammonia, and TP followed pseudo-first order, pseudo-zero order, and pseudo-second order kinetic models, respectively. Other characteristics were examined by scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, and X-ray photoelectron spectroscopy. Overall, our results showed that EO/EC can be used to efficiently remove organic matter, ammonia, TP, and heavy metals from landfill leachate.

5.
Water Res ; 169: 115239, 2020 Feb 01.
Article in English | MEDLINE | ID: mdl-31706129

ABSTRACT

Electro-oxidation using RuO2-IrO2/Ti plate anode and electrocoagulation using iron plate anode were widely applied to remove ammonia and phosphate in an aquatic environment, respectively. In this work, we designed magnetically bound ZVI microparticles on RuO2-IrO2/Ti plate as a composite electrode for the simultaneous removal of ammonia and phosphate from aqueous solution via combined EO and EC (EO/EC) processes. We present a series of experiments to study such simultaneous removal under an electric field via the EO/EC process. In the electrochemical unit, mZVI-RuO2-IrO2/Ti, mZVI-graphite, and RuO2-IrO2/Ti electrodes were used as anodes. The influence of applied voltage, initial pH, zero-valent iron dosage, reaction temperature, and organic compounds on the EO/EC process was also examined. Ammonia and phosphate could be completely removed at an applied voltage of 10 V, pH of 7, zero-valent iron dosage of 0.1 g, and reaction temperature of 35 °C using mZVI-RuO2-IrO2/Ti anode when influent ammonia and phosphate concentrations is 200 and 100 mg L-1. Ammonia degradation was consistent with pseudo-zero-order kinetic model. The characterization was analyzed by scanning electron microscope-energy dispersive spectrometer (SEM-EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Hence, the mZVI-RuO2-IrO2/Ti electrode can be used for efficient simultaneous removal of ammonia and phosphate.


Subject(s)
Ammonia , Water Pollutants, Chemical , Electrocoagulation , Electrodes , Iron , Oxidation-Reduction , Phosphates
6.
Dalton Trans ; 48(1): 150-157, 2018 Dec 18.
Article in English | MEDLINE | ID: mdl-30516189

ABSTRACT

High performance of an electrode relies largely on scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. Here, a 3D heterostructured core-shell architecture was fabricated as a supercapacitor electrode, in which Co3O4 nanowire cores were grown on nickel foam prior to the in situ deposition of layered double hydroxide (LDH) nanosheet shells. Owing to the unique configuration and hybridization, the as-fabricated Co3O4@LDH core-shell electrode exhibited high capacities of 818.6 C g-1 at 2 A g-1 and 479.3 C g-1 at 40 A g-1 (3.2 C cm-2 at 7.8 mA cm-2 and 1.87 C cm-2 at 156 mA cm-2), which were much higher than those of the individual components, namely, Co3O4 and LDH. A hybrid supercapacitor with Co3O4@LDH as the positive electrode and graphene nanosheets as the negative electrode yielded an energy density of 53.2 W h kg-1 and a power density of 16.4 kW kg-1, which outperformed devices reported in the literature; the device also exhibited long-term cycling stability and retained 71% of its initial capacity even after 10 000 cycles at 6 A g-1. The rational design of the core-shell architecture may lead to the development of new strategies for fabricating promising electrode materials for electrochemical energy storage.

7.
ACS Appl Mater Interfaces ; 8(5): 3258-67, 2016 Feb 10.
Article in English | MEDLINE | ID: mdl-26757795

ABSTRACT

Flower-like copper cobaltite (CuCo2O4) nanosheets anchored on graphite paper have been synthesized using a facile hydrothermal method followed by a postannealing treatment. Supercapacitor electrodes employing CuCo2O4 nanosheets exhibit an enhanced capacitance of 1131 F g(-1) at a current density of 1 A g(-1) compared with previously reported supercapacitor electrodes. The CuCo2O4 electrode delivers a specific capacitance of up to 409 F g(-1) at a current density of as high as 50 A g(-1), and a good long-term cycling stability, with 79.7% of its specific capacitance retained after 5000 cycles at 10 A g(-1). Furthermore, the as-prepared CuCo2O4 nanosheets on graphite paper can be fabricated as electrodes and used as enzymeless glucose sensors, which exhibit good sensitivity (3.625 µA µM(-1) cm(-2)) and an extraordinary linear response ranging up to 320 µM with a low detection limit (5 µM).


Subject(s)
Biosensing Techniques , Copper/chemistry , Glucose/isolation & purification , Nanostructures/chemistry , Graphite/chemistry , Humans , Limit of Detection , Minerals/chemistry
9.
Sci Rep ; 5: 14229, 2015 Sep 18.
Article in English | MEDLINE | ID: mdl-26382852

ABSTRACT

New and novel 3D hierarchical porous graphene aerogels (HPGA) with uniform and tunable meso-pores (e.g., 21 and 53 nm) on graphene nanosheets (GNS) were prepared by a hydrothermal self-assembly process and an in-situ carbothermal reaction. The size and distribution of the meso-pores on the individual GNS were uniform and could be tuned by controlling the sizes of the Co3O4 NPs used in the hydrothermal reaction. This unique architecture of HPGA prevents the stacking of GNS and promises more electrochemically active sites that enhance the electrochemical storage level significantly. HPGA, as a lithium-ion battery anode, exhibited superior electrochemical performance, including a high reversible specific capacity of 1100 mAh/g at a current density of 0.1 A/g, outstanding cycling stability and excellent rate performance. Even at a large current density of 20 A/g, the reversible capacity was retained at 300 mAh/g, which is larger than that of most porous carbon-based anodes reported, suggesting it to be a promising candidate for energy storage. The proposed 3D HPGA is expected to provide an important platform that can promote the development of 3D topological porous systems in a range of energy storage and generation fields.

10.
Dalton Trans ; 43(29): 11305-8, 2014 Aug 07.
Article in English | MEDLINE | ID: mdl-24946839

ABSTRACT

Employing newly synthesized di-substituted tri-phenyl amine (HMP-9) and carbazole (HMP-11) dyes (with limited acidic carboxyl anchor groups), a power conversion efficiency as high as 7.03% in ZnO nanocrystallite (NC)-based dye-sensitized solar cells (DSSCs) is achieved. The specific molecular designs of HMP-09 and HMP-11 consisting of with and without hexyloxy spacer groups, and added tri-phenyl amine or 9-phenyl-9H-carbazole donor groups, respectively, attached on the ancillary ligands are advantageous, evidenced from electrochemical impedance spectroscopy measurements, for ZnO NC-based DSSCs.

11.
J Nanosci Nanotechnol ; 12(4): 3563-6, 2012 Apr.
Article in English | MEDLINE | ID: mdl-22849169

ABSTRACT

Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.

12.
J Nanosci Nanotechnol ; 12(4): 3615-9, 2012 Apr.
Article in English | MEDLINE | ID: mdl-22849180

ABSTRACT

Nanowires (Co3O4 and NiCo2O4) and nanoplates (beta-Ni(OH)2) grown on Ni foam are successfully prepared by a template-free method and used as cathode electrodes for the electroreduction of H2O2, in an alkaline medium. Catalytic performance is investigated via cyclic voltammetry and chronoamperometry. The Co3O4 and NiCo2O4 nanowire electrodes exhibit much better catalytic activity, stability, and mass transfer properties for H2O2 electroreduction than pressed Co3O4 and NiCo2O4 nanoparticle/carbon/PTFE electrodes. A current density of 101.8 mA cm(-2) and 122.7 mA cm(-2) are respectively achieved on Co3O4 and NiCo2O4 nanowire electrodes at -0.4 V in 0.4 mol/L H2O2, and 3.0 mol/L NaOH solution at room temperature.

13.
Opt Express ; 17(12): 9873-8, 2009 Jun 08.
Article in English | MEDLINE | ID: mdl-19506637

ABSTRACT

A new design for a polychromatic light-emitting diode (LED) is proposed and demonstrated. LED chips of the primary colors are physically stacked on top of each other. Light emitted from each layer of the stack passes through each other, and thus is mixed naturally without additional optics. As a color-tunable device, a wide range of colors can be generated, making it suitable for display purposes. As a phosphor-free white light LED, luminous efficacy of 30 lm/watt was achieved.


Subject(s)
Color , Lighting/instrumentation , Optical Devices , Semiconductors , Computer-Aided Design , Equipment Design , Equipment Failure Analysis , Reproducibility of Results , Sensitivity and Specificity
14.
Opt Express ; 16(1): 13-8, 2008 Jan 07.
Article in English | MEDLINE | ID: mdl-18521128

ABSTRACT

An innovative spectral conversion scheme for light emitting diodes using fluorescent microspheres has been demonstrated. An optimally mixed proportion of green and red fluorescent microspheres were coated onto a high-extraction-efficiency GaN micro-LED with emission centred at 470 nm. The microspheres self-assemble into ordered hexagonally arrays, forming regular and uniform coating layers. Devices with cool and warm white emission were achieved. The bluish-white LED has a luminous efficacy of 27.3 lm/W (at 20 mA) with CIE coordinates of (0.26, 0.28) and 8500K CCT, while the yellowish-white LED has a luminous efficacy of 26.67 lm/W (at 20 mA) with CIE coordinates of (0.36, 0.43) and 13000K CCT.


Subject(s)
Color , Lighting/instrumentation , Semiconductors , Spectrometry, Fluorescence/instrumentation , Equipment Design , Equipment Failure Analysis , Lighting/methods , Microspheres , Spectrometry, Fluorescence/methods
15.
Nanotechnology ; 19(35): 355203, 2008 Sep 03.
Article in English | MEDLINE | ID: mdl-21828836

ABSTRACT

A hexagonally close-packed array consisting of fluorescent nanospheres was coated onto short-wavelength GaN light-emitting diodes to demonstrate polychromatic white light emission. The spherical particles self-assemble into ordered three-dimensional opal structures, performing the role of color conversion to generate a polychromatic spectrum with smooth and uniform emission patterns. Different ratios of green and orange-red fluorescent nanospheres were mixed and coated onto high-extraction-efficiency micro-LEDs. Four devices with different shades of white emission were demonstrated. Device A, with a high content of orange-red nanospheres, offers the highest CRI value of 80, whereas device C with a well-balanced ratio of green and orange-red nanospheres exhibits color characteristics closest to ideal white with CIE coordinate at (0.34, 0.34). At 20 mA driving current, the luminous efficacy of the devices A, B, C, and D are 40.5 lm W(-1), 57.7 lm W(-1), 63.1 lm W(-1), and 67.2 lm W(-1) respectively, while the correlated color temperatures (CCTs) of the corresponding devices are 3587, 4778, 5271, and 13 000 K.

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