Binary metal hydroxide nanorods and multi-walled carbon nanotube composites for electrochemical energy storage applications

Salunkhe, Rahul R.,Jang, Kihun,Lee, Sung-won,Yu, Seongil,Ahn, Heejoon The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.40

<P>Carbon nanotube and metal oxide/hydroxide hybrids have attracted much interest as electrode materials for electrochemical supercapacitors because of their dual storage mechanism. They can complement or replace batteries in electrical energy storage and harvesting applications, where high power delivery or uptake is needed. Multi-walled carbon nanotube (MWCNT) and nickel–cobalt binary metal hydroxide nanorod hybrids have been developed through the chemical synthesis of binary metal hydroxide on a MWCNT surface. These hybrids show enhanced supercapacitive performance and cycling ability. Growth of a thin film consisting of a coating of binary metal hydroxide, as well as further growth of nanorod structures, is demonstrated using FESEM and TEM, showing that this film is a promising structure for supercapacitor applications. These electrodes yield a significantly high capacitance of 502 F g<SUP>−1</SUP> with a high energy density of 69 W h kg<SUP>−1</SUP> at a scan rate of 5 mV s<SUP>−1</SUP>. The film is stable up to 5000 cycles with greater than 80% capacitance retention.</P> <P>Graphic Abstract</P><P>A novel composite material composed of cost effective pseudocapacitive nanostructures like Ni–Co hydroxide nanorods and CNT was fabricated on a stainless steel substrate and further utilized for supercapacitor applications. The electrodes yield a significantly high specific capacitance of ∼502 F g<SUP>−1</SUP> with an energy density of 69 W h kg<SUP>−1</SUP>. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm32638h'> </P>

General template-free strategy for fabricating mesoporous two-dimensional mixed oxide nanosheetsviaself-deconstruction/reconstruction of monodispersed metal glycerate nanospheres

Kaneti, Yusuf Valentino,Salunkhe, Rahul R.,Wulan Septiani, Ni Luh,Young, Christine,Jiang, Xuchuan,He, Yan-Bing,Kang, Yong-Mook,Sugahara, Yoshiyuki,Yamauchi, Yusuke The Royal Society of Chemistry 2018 Journal of materials chemistry. A, Materials for e Vol.6 No.14

<P>In this work, we propose a general template-free strategy for fabricating two-dimensional mesoporous mixed oxide nanosheets, such as metal cobaltites (MCo2O4, M = Ni, Zn) through the self-deconstruction/reconstruction of highly uniform Co-based metal glycerate nanospheres into 2D Co-based metal glycerate/hydroxide nanosheets, induced by the so-called “water treatment” process at room temperature followed by their calcination in air at 260 °C. The proposed ‘self-deconstruction/reconstruction’ strategy is highly advantageous as the resulting 2D metal cobaltite nanosheets possess very high surface areas (150-200 m<SUP>2</SUP>g<SUP>−1</SUP>) and mesoporous features with narrow pore size distribution. In addition, our proposed method also enables the crystallization temperature to achieve pure metal cobaltite phase from the precursor phase to be lowered by 50 °C. Using the 2D mesoporous NiCo2O4nanosheets as a representative sample, we found that they exhibit 6-20 times higher specific capacitance and greatly enhanced capacitance retention compared to the NiCo2O4nanospheres achieved through the direct calcination of the Ni-Co glycerate nanospheres. This highlights another advantage of the proposed strategy for enhancing the electrochemical performance of the mixed oxide products for supercapacitor applications. Furthermore, the asymmetric supercapacitor (ASC) assembled using the 2D NiCo2O4nanosheets//graphene oxide (GO) exhibits a maximum energy density of 38.53 W h kg<SUP>−1</SUP>, while also showing a high capacitance retention of 91% after 2000 cycles at 5 A g<SUP>−1</SUP>. It is expected that the proposed general method may be extended to other transition metal elements for creating 2D mixed oxide nanosheets with enhanced surface areas and improved electrochemical performance.</P>

Facile Low-temperature Chemical Synthesis and Characterization of a Manganese Oxide/multi-walled Carbon Nanotube Composite for Supercapacitor Applications

장기훈,이성원,유성일,Rahul R. Salunkhe,정일두,최성민,안희준 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.10

Mn3O4/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing Mn3O4 nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline Mn3O4 nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the Mn3O4 nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The Mn3O4/ MWCNT composite exhibits a specific capacitance of 257 Fg−1 at a scan rate of 5 mVs−1, which is about 3.5 times higher than that of the pure Mn3O4. Cycle-life tests show that the specific capacitance of the Mn3O4/ MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure Mn3O4 electrode. The improved supercapacitive performance of the Mn3O4/MWCNT composite electrode can be attributed to the synergistic effects of the Mn3O4 nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from Mn3O4 nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.

Flexible-wire shaped all-solid-state supercapacitors based on facile electropolymerization of polythiophene with ultra-high energy density

Ambade, Rohan B.,Ambade, Swapnil B.,Salunkhe, Rahul R.,Malgras, Victor,Jin, Sung-Ho,Yamauchi, Yusuke,Lee, Soo-Hyoung The Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.19

<P>The new generation of miniaturized energy storage devices offers high energy and power densities and is compatible with flexible, portable, or wearable textile electronics which are currently in great demand. Here, we demonstrate the successful development of flexible, wire shaped (f-WS) all-solid-state symmetric supercapacitors (SCs) based on a facile electropolymerization of polythiophene (e-PTh) on titania (Ti) wire. The f-WS all-solid-state symmetric SCs, exhibiting high electrochemical performance, are fabricated by slightly intertwining two similar e-PTh electrodes to form both the cathode and anode which are then individually coated with a thin layer of H2SO4-PVA gel, acting both as electrolyte and as separator. The optimized devices (∼1.5 cm long), based on e-PTh/Ti wire show a high capacitive performance (1357.31 mF g<SUP>−1</SUP>or 71.84 mF cm<SUP>−2</SUP>) and an extremely high energy density (23.11 μW h cm<SUP>−2</SUP>) at a power density of 90.44 μW cm<SUP>−2</SUP>using an operational potential window of 1.8 V, which is beneficial for applications requiring high energy and power. The robust f-WS all-solid-state symmetric SCs also exhibit excellent mechanical flexibility with minimal change in capacitance upon bending at 360°. Furthermore, the SCs were implemented in the textile of a wearable/portable electronic device using a conventional weaving method, thus demonstrating a high potential for next-generation wearable textile electronic applications.</P>

Facile Low-temperature Chemical Synthesis and Characterization of a Manganese Oxide/multi-walled Carbon Nanotube Composite for Supercapacitor Applications

Jang, Kihun,Lee, Sung-Won,Yu, Seongil,Salunkhe, Rahul R.,Chung, Ildoo,Choi, Sungmin,Ahn, Heejoon Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.10

$Mn_3O_4$/multi-walled carbon nanotube (MWCNT) composites are prepared by chemically synthesizing $Mn_3O_4$ nanoparticles on a MWCNT film at room temperature. Structural and morphological characterization has been carried out using X-ray diffraction (XRD) and scanning and transmission electron microscopies (SEM and TEM). These reveal that polycrystalline $Mn_3O_4$ nanoparticles, with sizes of about 10-20 nm, aggregate to form larger nanoparticles (50-200 nm), and the $Mn_3O_4$ nanoparticles are attached inhomogeneously on MWCNTs. The electrochemical behavior of the composites is analyzed by cyclic voltammetry experiment. The $Mn_3O_4$/MWCNT composite exhibits a specific capacitance of $257Fg^{-1}$ at a scan rate of $5mVs^{-1}$, which is about 3.5 times higher than that of the pure $Mn_3O_4$. Cycle-life tests show that the specific capacitance of the $Mn_3O_4$/MWCNT composite is stable up to 1000 cycles with about 85% capacitance retention, which is better than the pure $Mn_3O_4$ electrode. The improved supercapacitive performance of the $Mn_3O_4$/MWCNT composite electrode can be attributed to the synergistic effects of the $Mn_3O_4$ nanoparticles and the MWCNTs, which arises not only from the combination of pseudocapacitance from $Mn_3O_4$ nanoparticles and electric double layer capacitance from the MWCNTs but also from the increased surface area, pore volume and conducting property of the MWCNT network.