Facile and Eco-Friendly Synthesis of Finger-Like Co?O? Nanorods for Electrochemical Energy Storage.
ABSTRACT: Co?O? nanorods were prepared by a facile hydrothermal method. Eco-friendly deionized water rather than organic solvent was used as the hydrothermal media. The as-prepared Co?O? nanorods are composed of many nanoparticles of 30-50 nm in diameter, forming a finger-like morphology. The Co?O? electrode shows a specific capacitance of 265 F g-1 at 2 mV s-1 in a supercapacitor and delivers an initial specific discharge capacity as high as 1171 mAh g-1 at a current density of 50 mA g-1 in a lithium ion battery. Excellent cycling stability and electrochemical reversibility of the Co?O? electrode were also obtained.
Project description:The current paper describes enhanced electrochemical capacitive performance of chemically grown Cobalt hydroxide (Co(OH)2) nanorods (NRs) decorated porous three dimensional graphitic carbon foam (Co(OH)2/3D GCF) as a supercapacitor electrode. Freestanding 3D porous GCF is prepared by carbonizing, high internal phase emulsion (HIPE) polymerized styrene and divinylbenzene. The PolyHIPE was sulfonated and carbonized at temperature up to 850?°C to obtain graphitic 3D carbon foam with high surface area (389?m2 g-1) having open voids (14??m) interconnected by windows (4??m) in monolithic form. Moreover, entangled Co(OH)2 NRs are anchored on 3D GCF electrodes by using a facile chemical bath deposition (CBD) method. The wide porous structure with high specific surface area (520?m2 g-1) access offered by the interconnected 3D GCF along with Co(OH)2 NRs morphology, displays ultrahigh specific capacitance, specific energy and power. The Co(OH)2/3D GCF electrode exhibits maximum specific capacitance about ~1235?F g-1 at ~1?A g-1 charge-discharge current density, in 1?M aqueous KOH solution. These results endorse potential applicability of Co(OH)2/3D GCF electrode in supercapacitors and signifies that, the porous GCF is a proficient 3D freestanding framework for loading pseudocapacitive nanostructured materials.
Project description:In this study, a novel negative electrode material was prepared by aligning ?-Fe<sub>2</sub>O<sub>3</sub> nanorods on a hierarchical porous carbon (HPC) skeleton. The skeleton was derived from wheat flour by a facile hydrothermal route to enhance conductivity, improve surface properties, and achieve substantially good electrochemical performances. The ?-Fe<sub>2</sub>O<sub>3</sub>/HPC electrode exhibits enhanced specific capacitance of 706 F g<sup>-1</sup>, which is twice higher than that of ?-Fe<sub>2</sub>O<sub>3</sub>. The advanced ?-Fe<sub>2</sub>O<sub>3</sub>/HPC//PANI/HPC asymmetrical supercapacitor was built with an expanded voltage of 2.0 V in 1 M Li<sub>2</sub>SO<sub>4</sub>, possessing a specific capacitance of 212 F g<sup>-1</sup> at 1 A g<sup>-1</sup> and a maximum energy density of 117 Wh kg<sup>-1</sup> at 1.0 kW kg<sup>-1</sup>, along with an excellent stability of 5.8% decay in capacitance after 5,000 cycles. This study affords a simple process to develop asymmetric supercapacitors, which exhibit high electrochemical performances and are applicable in next-generation energy storage devices, based on ?-Fe<sub>2</sub>O<sub>3</sub> hybrid materials.
Project description:The practical implementation of supercapacitors is hindered by low utilization and poor structural stability of electrode materials. Herein, to surmount these critical challenges, a three-dimensional hierarchical α-Co(OH)2/α-Ni(OH)2 heterojunction nanorods are built in situ on Ni foam through a mild two-step growth reaction. The unique lamellar crystal structure and abundant intercalated anions of α-M(OH)2 (M = Co or Ni) and the ideal electronic conductivity of α-Co(OH)2 construct numerous cross-linked ion and electron transport paths in heterojunction nanorods. The deformation stresses exerted by α-Co(OH)2 and α-Ni(OH)2 on each other guarantee the excellent structural stability of this heterojunction nanorods. Using nickel foam with a three-dimensional network conductive framework as the template ensures the rapidly transfer of electrons between this heterojunction nanorods and current collector. Three-dimensional hierarchical structure of α-Co(OH)2/α-Ni(OH)2 heterojunction nanorods provides a large liquid interface area. These result together in the high utilization rate and excellent structure stability of the α-Co(OH)2/α-Ni(OH)2 heterojunction nanorods. And the capacitance retention rate is up to 93.4% at 1 A g-1 from three-electrode system to two-electrode system. The α-Co(OH)2/α-Ni(OH)2//AC device also present a long cycle life (the capacitance retention rate is 123.6% at 5 A g-1 for 10000 cycles), a high specific capacitance (207.2 F g-1 at 1 A g-1), and high energy density and power density (72.6 Wh kg-1 at 196.4 W kg-1 and 40.9 Wh kg-1 at 3491.8 W kg-1), exhibiting a fascinating potential for supercapacitor in large-scale applications.
Project description:In this study, a new nanoporous material comprising NiMoO4 nanorods and Co3O4 nanoparticles derived from ZIF-67 supported by a cellulose-based carbon aerogel (CA) has been successfully synthesized using a two-step hydrothermal method. Due to its chemical composition, the large specific surface and the hierarchical porous structure, the NiMoO4@Co3O4/CA ternary composite yields electrodes with an enhanced specific capacitance of 436.9 C/g at a current density of 0.5 A/g and an excellent rate capability of 70.7% capacitance retention at 5.0 A/g. Moreover, an advanced asymmetric supercapacitor (ASC) is assembled using the NiMoO4@Co3O4/CA ternary composite as the positive electrode and activated carbon as the negative electrode. The ASC device exhibits a large capacitance of 125.4 F/g at 0.5 A/g, a maximum energy density of 34.1 Wh/kg at a power density of 208.8 W/kg as well as a good cyclic stability (84% after 2000 cycles), indicating its wide applicability in energy storage. Finally, our results provide a general approach to the construction of CA and MOF-based composite materials with hierarchical porous structure for potential applications in supercapacitors.
Project description:ZnO-nanorods/graphene heterostructure was synthesized by hydrothermal growth of ZnO nanorods on chemically reduced graphene (CRG) film. The hybrid structure was demonstrated as a biosensor, where direct electron transfer between glucose oxidase (GOD) and electrode was observed. The charge transfer was attributed to the ZnO nanorod wiring between the redox center of GOD and electrode, and the ZnO/graphene heterostructure facilitated the transport of electrons on the hybride electrode. The glucose sensor based on the GOD-ZnO/CRG/Pt electrode had a high sensitivity of 17.64??A?mM(-1), which is higher than most of the previously reported values for direct electron transfer based glucose biosensors. Moreover, this biosensor is linearly proportional to the concentration of glucose in the range of 0.2-1.6?mM. The study revealed that the band structure of electrode could affect the detection of direct electron transfer of GOD, which would be helpful for the design of the biosensor electrodes in the future.
Project description:In this work, CoMoO<sub>4</sub>@NiMoO<sub>4</sub>·xH<sub>2</sub>O core-shell heterostructure electrode is directly grown on carbon fabric (CF) via a feasible hydrothermal procedure with CoMoO<sub>4</sub> nanowires (NWs) as the core and NiMoO<sub>4</sub> nanosheets (NSs) as the shell. This core-shell heterostructure could provide fast ion and electron transfer, a large number of active sites, and good strain accommodation. As a result, the CoMoO<sub>4</sub>@NiMoO<sub>4</sub>·xH<sub>2</sub>O electrode yields high-capacitance performance with a high specific capacitance of 1582?F?g<sup>-1</sup>, good cycling stability with the capacitance retention of 97.1% after 3000 cycles and good rate capability. The electrode also shows excellent mechanical flexibility. Also, a flexible Fe<sub>2</sub>O<sub>3</sub> nanorods/CF electrode with enhanced electrochemical performance was prepared. A solid-state asymmetric supercapacitor device is successfully fabricated by using flexible CoMoO<sub>4</sub>@NiMoO<sub>4</sub>·xH<sub>2</sub>O as the positive electrode and Fe<sub>2</sub>O<sub>3</sub> as the negative electrode. The asymmetric supercapacitor with a maximum voltage of 1.6?V demonstrates high specific energy (41.8?Wh?kg<sup>-1</sup> at 700?W?kg<sup>-1</sup>), high power density (12000?W?kg<sup>-1</sup> at 26.7?Wh?kg<sup>-1</sup>), and excellent cycle ability with the capacitance retention of 89.3% after 5000 cycles (at the current density of 3A?g<sup>-1</sup>).
Project description:Uniform rectangular ?-Fe2O3 nanorods (R-Fe2O3) and irregular ?-Fe2O3 nanorods (D-Fe2O3) with a random size vertically aligned on fluorine-doped tin oxide were prepared with a facile one-step hydrothermal procedure. X-ray diffraction (XRD) measurements and Raman spectra confirm that the obtained samples are ?-Fe2O3, and XRD patterns show that D-Fe2O3 has two extra (012) and (104) planes of hematite in addition to the identical peaks to R-Fe2O3. The carrier density of the D-Fe2O3 sample is four times larger than that of R-Fe2O3. Finally, the D-Fe2O3 photoelectrode exhibited a better photoelectrochemical (PEC) performance under visible illumination than that of R-Fe2O3, achieving the photocurrent density of 0.15 mA cm-2 at 1.23 V versus reversible hydrogen electrode. In addition, incident photo-to-current conversion efficiency of D-Fe2O3 is nearly three times larger than that of R-Fe2O3. Hence, the improved PEC performance of D-Fe2O3 can be ascribed to higher carrier density resulting from the amount of oxygen vacancies and more activated exposed surface facets.
Project description:A facile and phase-controlled synthesis of ?-NiS nanoparticles (NPs) embedded in carbon nanorods (CRs) is reported by in-situ sulfurating the preformed Ni/CRs. The nanopore confinement by the carbon matrix is essential for the formation of ?-NiS and preventing its transition to ?-phase, which is in strong contrast to large aggregated ?-NiS particles grown freely without the confinement of CRs. When used as electrochemical electrode, the hybrid electrochemical charge storage of the ultrasmall ?-NiS nanoparticels dispersed in CRs is benefit for the high capacitor (1092, 946, 835, 740?F g(-1) at current densities of 1, 2, 5, 10?A g(-1), respectively.). While the high electrochemical stability (approximately 100% retention of specific capacitance after 2000 charge/discharge cycles) is attributed to the supercapacitor-battery electrode, which makes synergistic effect of capacitor (CRs) and battery (NiS NPs) components rather than a merely additive composite. This work not only suggests a general approach for phase-controlled synthesis of nickel sulfide but also opens the door to the rational design and fabrication of novel nickel-based/carbon hybrid supercapacitor-battery electrode materials.
Project description:Porous carbon materials produced by biomass have been widely studied for high performance supercapacitor due to their abundance, low price, and renewable. In this paper, the series of nitrogen-doped hierarchical porous carbon nanospheres (HPCN)/polyaniline (HPCN/PANI) nanocomposites is reported, which is prepared via in-situ polymerization. A novel approach with one-step pyrolysis of wheat flour mixed with urea and ZnCl2 is proposed to prepare the HPCN with surface area of 930 m2/g. Ultrathin HPCN pyrolysised at 900°C (~3 nm in thickness) electrode displays a gravimetric capacitance of 168 F/g and remarkable cyclability with losing 5% of the maximum capacitance after 5,000 cycles. The interconnected porous texture permits depositing of well-ordered polyaniline nanorods and allows a fast absorption/desorption of electrolyte. HPCN/PANI with short diffusion pathway possesses high gravimetric capacitance of 783 F/g. It can qualify HPCN/PANI to be used as cathode in assembling asymmetric supercapacitor with HPCN as anode, and which displays an exceptional specific capacitance of 81.2 F/g. Moreover, HPCN/PANI//HPCN device presents excellent cyclability with 88.4% retention of initial capacity over 10,000 cycles. This work will provide a simple and economical protocol to prepare the sustainable biomass materials based electrodes for energy storage applications.
Project description:Spinel zinc manganese oxide (ZnMn2O4) nanorods were successfully prepared using the previously synthesized ?-MnO2 nanorods by a hydrothermal method as template. The nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV-Vis absorption, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and Fourier transform infrared spectroscopy. The ZnMn2O4 nanorods in well-formed crystallinity and phase purity appeared with the width in 50-100 nm and the length in 1.5-2 ?m. They exhibited strong absorption below 500 nm with the threshold edges around 700 nm. A significant photovoltage response in the region below 400 nm could be observed for the nanorods calcined at 650 and 800°C.