Cubic Spinel AB₂O₄ Type Porous ZnCo₂O₄ Microspheres: Facile Hydrothermal Synthesis and Their Electrochemical Performances in Pseudocapacitor

Rajesh, John Anthuvan,Min, Bong-Ki,Kim, Jae-Hong,Kim, Hyunsoo,Ahn, Kwang-Soon The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.10

<P>Microspheres of cubic spinel ZnCo2O4 were synthesized using a facile ethylene glycol-mediated hydrothermal method. The size and crystallinity of the ZnCo2O4 microspheres were tuned by simply varying the reaction times. The as-synthesized ZnCo2O4 microspheres had porous structures that were constructed by numerous small building blocks of primary nanoparticles, leading to the formation of sphere-like morphology. The ZnCo2O4 microspheres exhibited a large surface area of 37.27 m(2) g(-1) with mesopores, 24.66 nm in size, resulting in significantly enhanced electrochemical activity toward pseudocapacitors. Remarkably, the as-made ZnCo2O4 microspheres electrode delivered a high specific capacitance (853.6 F g(-1) at a current density of 2 A g(-1)), good rate performance (417.1 F g(-1) at 10 A g(-1)) and excellent cyclic stability (92.7% capacitance retention after 3000 cycles at a current density of 10 A g(-1)). Moreover, a symmetric supercapacitor based on ZnCo2O4 microsphere electrodes achieved an energy density of 11.8 Wh kg(-1) and a maximum power density of 2.5 kW kg(-1). The good electrochemical performances can be attributed to the unique porous microsphere texture, high surface area and good electrical conductivity due to the synergistic effect between the two metal elements. (C) 2016 The Electrochemical Society. All rights reserved.</P>

Rambutan-like cobalt nickel sulfide (CoNi₂S₄) hierarchitecture for high-performance symmetric aqueous supercapacitors

Rajesh, John Anthuvan,Park, Jeong-Hyun,Vinh Quy, Vu Hong,Kwon, Jong Myeong,Chae, Jiyoung,Kang, Soon-Hyung,Kim, Hyunsoo,Ahn, Kwang-Soon THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.63 No.-

<P><B>Abstract</B></P> <P>A novel hierarchical cobalt nickel sulfide (CoNi<SUB>2</SUB>S<SUB>4</SUB>) nanostructure resembling the rambutan fruit was obtained by a simple one-step hydrothermal method using ethylene glycol as the solvent. Scanning and transmission electron microscopic analyses revealed that the as-synthesized CoNi<SUB>2</SUB>S<SUB>4</SUB> consists of numerous hairy nanorods grown radially on top of individual sphere-like core structures. The CoNi<SUB>2</SUB>S<SUB>4</SUB> hierarchical material was applied as a potential electrode for supercapacitors in both three- and two-electrode systems. The hairy nanorods and spheres were highly interconnected to form hierarchical rambutan-like CoNi<SUB>2</SUB>S<SUB>4</SUB> structure with increased active areas of the electrode, and this facilitate effective charge transport from the nanorods to the spherical core structure. When evaluated as an electrode material in a three-electrode system, CoNi<SUB>2</SUB>S<SUB>4</SUB> with the hierarchical structure delivered a high specific capacitance of 1102.22Fg<SUP>−1</SUP> at a current density of 1Ag<SUP>−1</SUP> with excellent rate capability (68.55% capacitance retention as the current increases from 1 to 10Ag<SUP>−1</SUP>) and significant cycling stability (75% retention after 3000 cycles). The electrochemical properties of the hierarchical CoNi<SUB>2</SUB>S<SUB>4</SUB> were also investigated in a symmetrical cell arrangement using 2M aqueous KOH as the electrolyte. The symmetric aqueous supercapacitor exhibited a specific capacitance of 482Fg<SUP>−1</SUP> at 1Ag<SUP>−1</SUP> with maximum energy density of 16.74Whkg<SUP>−1</SUP> and maximum power density of 10.2kWkg<SUP>−1</SUP>. Furthermore, the symmetric supercapacitor exhibited excellent cycling stability, showing 92.85% capacitance retention even after 5000 cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel hierarchical CoNi<SUB>2</SUB>S<SUB>4</SUB> nanostructure resembling the rambutan fruit is synthesized by hydrothermal method. </LI> <LI> The hierarchical rambutan structure delivers excellent electrochemical properties in both three and two electrode systems. </LI> <LI> A high specific capacitance of 1102.22Fg<SUP>−1</SUP> is obtained at a current density of 1Ag<SUP>−1</SUP>. </LI> <LI> The symmetric supercapacitor exhibits high power and energy density, and long-term cycling stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile hydrothermal synthesis and electrochemical supercapacitor performance of hierarchical coral-like ZnCo₂O₄ nanowires

Rajesh, John Anthuvan,Min, Bong-Ki,Kim, Jae-Hong,Kang, Soon-Hyung,Kim, Hyunsoo,Ahn, Kwang-Soon Elsevier 2017 Journal of Electroanalytical Chemistry Vol.785 No.-

<P><B>Abstract</B></P> <P>This paper reports a facile hydrothermal synthesis of hierarchical coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanostructures comprised of necklace type nanowires without the use surfactants. The hierarchical coral structure is composed of an interconnected necklace-type nanowire arrangement on the nanoscale, facilitating charge transportation. In addition, the coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires were mesoporous (29.36m<SUP>2</SUP> g<SUP>−1</SUP> and 18.96nm), leading to large electrochemical active sites for the redox reaction and fast ion transport within the ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires. When used in electrochemical supercapacitors, the interconnected necklace type, coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires exhibited a significantly high specific capacity (694Fg<SUP>−1</SUP> at a current density of 2Ag<SUP>−1</SUP>), high rate capability (264Fg<SUP>−1</SUP> at 10Ag<SUP>−1</SUP>), and excellent cycling stability (capacitance retention of ∼85% even after 2000cycles at a charge-discharge current density of 10Ag<SUP>−1</SUP>). These results suggest that hierarchical coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires are a promising electrode material for energy storage applications in high-performance pseudocapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires were synthesized by facile hydrothermal method. </LI> <LI> The ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires exhibited a large electrochemically active surface area of 29.36m<SUP>2</SUP> g<SUP>−1</SUP>. </LI> <LI> Coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires delivered a specific capacitance of 694Fg<SUP>−1</SUP> at a current density of 2Ag<SUP>−1</SUP>. </LI> <LI> Coral-like ZnCo<SUB>2</SUB>O<SUB>4</SUB> nanowires showed ∼85% capacitance retention after 2000cycles at a current density of 10Ag<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Potentiostatic deposition of CoNi₂Se₄ nanostructures on nickel foam as efficient battery-type electrodes for supercapacitors

Rajesh, John Anthuvan,Lee, Young-Hoon,Yun, Yong-Han,Quy, Vu Hong Vinh,Kang, Soon-Hyung,Kim, Hyunsoo,Ahn, Kwang-Soon Elsevier 2019 Journal of Electroanalytical Chemistry Vol.850 No.-

<P><B>Abstract</B></P> <P>Bimetallic CoNi<SUB>2</SUB>Se<SUB>4</SUB> nanostructures on nickel-foam substrates were fabricated by a potentiostatic deposition method by adjusting the deposition solution p<SUP>H</SUP>, and used as electrode materials in battery-type supercapacitors. The electrodeposition solution p<SUP>H</SUP> had an important role in the fabrication of the desirable CoNi<SUB>2</SUB>Se<SUB>4</SUB> nanostructures. At a deposition solution p<SUP>H</SUP> of 2.0, the synthesized product contained CoNi<SUB>2</SUB>Se<SUB>4</SUB> nanoparticles. In contrast, a partially converted flake-like morphology was obtained at p<SUP>H</SUP> = 2.5. The appropriate flake-like morphology was formed by increasing the deposition solution p<SUP>H</SUP> to 3.0. The robust flake-like structure facilitated the electron transport during redox reactions, providing an excellent electrochemical behavior in terms of specific capacity, rate capability, and cyclic stability. A battery-type supercapacitor based on the flake-like CoNi<SUB>2</SUB>Se<SUB>4</SUB> structure exhibited a maximum specific capacity of 632.5 C g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP> and excellent rate performance (capacity retention of 91%) in the range of 1 to 40 A g<SUP>−1</SUP>. The material retained 83.31% of its initial capacity after 3000 cycles of charging/discharging at a current density of 40 A g<SUP>−1</SUP>, which suggests a high long-term cycling stability. The excellent electrochemical performance of the CoNi<SUB>2</SUB>Se<SUB>4</SUB> electrode material make it very promising for application in supercapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CoNi<SUB>2</SUB>Se<SUB>4</SUB> nanostructures were fabricated by a potentiostatic deposition method. </LI> <LI> The electrodeposition solution p<SUP>H</SUP> is a key role in the electrochemical performance. </LI> <LI> The flake-like CoNi<SUB>2</SUB>Se<SUB>4</SUB> structure exhibited a maximum specific capacity of 632.5 C g<SUP>−1</SUP>. </LI> <LI> The electrode exhibited the excellent rate performance (capacity retention of 91%). </LI> </UL> </P>

Rambutan-like cobalt nickel sulfide (CoNi2S4) hierarchitecture for high-performance symmetric aqueous supercapacitors

John Anthuvan Rajesh,박정현,Vu Hong Vinh Quy,권종명,최지영,강순형,김현수,안광순 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.63 No.-

A novel hierarchical cobalt nickel sulfide (CoNi2S4) nanostructure resembling the rambutan fruit was obtained by a simple one-step hydrothermal method using ethylene glycol as the solvent. Scanning and transmission electron microscopic analyses revealed that the as-synthesized CoNi2S4 consists of numerous hairy nanorods grown radially on top of individual sphere-like core structures. The CoNi2S4 hierarchical material was applied as a potential electrode for supercapacitors in both three- and two-electrode systems. The hairy nanorods and spheres were highly interconnected to form hierarchical rambutan-like CoNi2S4 structure with increased active areas of the electrode, and this facilitate effective charge transport from the nanorods to the spherical core structure. When evaluated as an electrode material in a three-electrode system, CoNi2S4 with the hierarchical structure delivered a high specific capacitance of 1102.22 F g−1 at a current density of 1 A g−1 with excellent rate capability (68.55% capacitance retention as the current increases from 1 to 10 A g−1) and significant cycling stability (75% retention after 3000 cycles). The electrochemical properties of the hierarchical CoNi2S4 were also investigated in a symmetrical cell arrangement using 2 M aqueous KOH as the electrolyte. The symmetric aqueous supercapacitor exhibited a specific capacitance of 482 F g−1 at 1 A g−1 with maximum energy density of 16.74 Wh kg−1 and maximum power density of 10.2 kW kg−1. Furthermore, the symmetric supercapacitor exhibited excellent cycling stability, showing 92.85% capacitance retention even after 5000 cycles.

Preparation of copper sulfide electrocatalyst using electrodeposited Cu-Zn alloy for quantum dot-sensitized solar cells

채지영,( Vu Hong Vinh Quy ),( Elayappan Vijayakumar ),( Anthuvan Rajesh ),안광순 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0

Quantum dot-sensitized solar cells (QDSSCs) are a reliable renewable energy source. A QDSSC is assembled with the components in the following order: FTO/TiO2/QD/polysulfide electrolyte/CE/FTO. Recently, multiple efforts have been made to increase the power conversion efficiency of by modifying the materials by optimize chemical and physical properties. In QDSSCs, the counter electrodes (CEs) plays a key role in completing the electrical circuit and in the regeneration of sulfur redox couple through a reduction process. Among the CE materials, copper(I) sulfide (Cu2S) is a promising alternative to Pt CE, primarily due to its favorable electrochemical properties in the S2-/Sn2- redox couple, low cost, and high stability compared to other. In this study, we have reported Cu2S CE deposited Cu-Zn alloy on FTO and removed Zn using HCl after sulfurization. We simply increased surface area of CEs by removing Zn. These samples exhibited better electrocatalytic activity than FTO/Cu2S CEs.

One-Step Electrodeposited Nickel Cobalt Sulfide Electrocatalyst for Quantum Dot-Sensitized Solar Cells

Quy, Vu Hong Vinh,Min, Bong-Ki,Kim, Jae-Hong,Kim, Hyunsoo,Rajesh, John Anthuvan,Ahn, Kwang-Soon The Electrochemical Society 2016 Journal of the Electrochemical Society Vol.163 No.5

<P>This paper reports a new facile one-step cyclic voltammetry electrochemical co-depositing method to prepare a novel nickel cobalt sulfide (NiCo2S4) counter electrode (CE) on a FTO glass substrate as well as its promising application as an efficient CE in CdSe quantum dot-sensitized solar cells (QD-SSCs). The QD-SSCs fabricated using NiCo2S4 as a CE exhibited a significantly enhanced short circuit current and fill factor, resulting in a significantly improved overall energy conversion efficiency (3.67%) compared to those with the Pt (2.26%), CoS (2.70%) and NiS (2.56%) CEs under 1 sun illumination. This can be attributed to the significantly enhanced electrocatalytic activity and superior electrical conductivity of the NiCo2S4 and the excellent electrical contact at the electrodeposited NiCo2S4/FTO interface. (C) 2016 The Electrochemical Society. All rights reserved.</P>

Electrodeposited MoS₂ as electrocatalytic counter electrode for quantum dot- and dye-sensitized solar cells

Quy, Vu Hong Vinh,Vijayakumar, Elayappan,Ho, Phuong,Park, Jeong-Hyun,Rajesh, John Anthuvan,Kwon, JongMyeong,Chae, Jiyoung,Kim, Jae-Hong,Kang, Soon-Hyung,Ahn, Kwang-Soon Elsevier 2018 ELECTROCHIMICA ACTA Vol.260 No.-

<P><B>Abstract</B></P> <P>Molybdenum disulfide (MoS<SUB>2</SUB>) films are electrochemically synthesized on F-doped SnO<SUB>2</SUB> (FTO) substrates using potentiostatic electrodeposition (ED) at a constant −1 V for 20–60 min. The MoS<SUB>2</SUB> is deposited according to island growth mode. As the ED time increases to 40 min, the clusters of MoS<SUB>2</SUB> nano particles enlarge and thicken, but maintain nanopores between the clusters. Additional increase in ED time (to 60 min) causes clusters to merge and make the film denser. Furthermore, this MoS<SUB>2</SUB> film exhibits cracks due to stress accumulated in the film. The film FTO/MoS<SUB>2</SUB> (40 min) shows significantly enhanced electrocatalytic activity compared to other films. This is because the FTO/MoS<SUB>2</SUB> (40 min) not only has more electrochemically active sites but also significantly facilitates charge transfer and mass transport. When it is employed as the counter electrode (CE) for quantum-dot and dye-sensitized solar cells (QD-SSC, D-SSC), the QD-SSC with FTO/MoS<SUB>2</SUB> (40 min) CE exhibits even higher overall energy conversion cell efficiency (3.69%) than that with Pt CE (2.16%). Moreover, the D-SSC with FTO/MoS<SUB>2</SUB> (40 min) CE exhibits cell efficiency (7.16%) similar to that with FTO/Pt CE (7.48%). This indicates that MoS<SUB>2</SUB> is a promising CE for all QD-SSCs and D-SSCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> MoS<SUB>2</SUB> films were electrochemically synthesized on F-doped SnO<SUB>2</SUB> substrates. </LI> <LI> Change in electrodeposition time affected particle size and pore condition. </LI> <LI> FTO/MoS<SUB>2</SUB> -ED 40 min had better electrocatalytic activity and more active sites. </LI> <LI> FTO/MoS<SUB>2</SUB> -40 also showed much improved charge transfer and mass transport. </LI> <LI> FTO/MoS<SUB>2</SUB>-40 CEs in QD-SSC and D-SSC showed better efficiency than Pt CE. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile hydrothermal synthesis of cubic spinel AB₂O₄ type MnFe₂O₄ nanocrystallites and their electrochemical performance

Kwon, JongMyeong,Kim, Jae-Hong,Kang, Soon-Hyung,Choi, Cheol-Jong,Rajesh, John Anthuvan,Ahn, Kwang-Soon Elsevier BV * North-Holland 2017 Applied Surface Science Vol. No.

<P><B>Abstract</B></P> <P>Cubic spinel MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles were synthesized using a simple hydrothermal method followed by post-annealing. The effects of the reaction temperature on the crystallinity, morphology, and electrochemical performance were studied. The reaction temperature played an important role in the synthesis of highly crystalline MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles. At low reaction temperatures (<160°C), the synthesized product contained a secondary inactive Fe<SUB>2</SUB>O<SUB>3</SUB> phase as well as MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles. In contrast, pure MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles were obtained at temperatures above 180°C. Furthermore, the crystallinity of the MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles was enhanced significantly by increasing the reaction temperature to 200°C. The cubic spinel MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles synthesized at 200°C delivered a maximum specific capacitance of 282.4Fg<SUP>−1</SUP> at a current density of 0.5Ag<SUP>−1</SUP> in a 2M aqueous KOH solution, and exhibited long-term cyclic stability of 85.8% capacitance retention after 2000 cycles. This was attributed to the cubic spinel ferrite nanocrystallite particles not only providing the more active sites for OH<SUP>−</SUP> ion diffusion but also reducing the path lengths for OH<SUP>−</SUP> ion diffusion. These results show that the synthesized MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles are promising candidates for pseudocapacitors and other electrochemical applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Cubic spinel MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles were synthesized using a simple hydrothermal method. </LI> <LI> The effects of the reaction temperature on the crystallinity, morphology, and electrochemical performance were studied. </LI> <LI> MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles delivered a specific capacitance of 282.4Fg<SUP>−1</SUP> at a current density of 0.5Ag<SUP>−1</SUP>. </LI> <LI> MnFe<SUB>2</SUB>O<SUB>4</SUB> nanoparticles showed ∼85.8% capacitance retention after 2000 cycles at a current density of 3Ag<SUP>−1</SUP>. </LI> </UL> </P>