A facile one-step approach to hierarchically assembled core–shell-like MnO2@MnO2 nanoarchitectures on carbon fibers: An efficient and flexible electrode material to enhance energy storage

Nagaraju, G.,Ko, Y. H.,Cha, S. M.,Im, S. H.,Yu, J. S. Springer Science + Business Media 2016 NANO RESEARCH Vol.9 No.5

<P>Hierarchical core-shell-like MnO2 nanostructures (NSs) were used to anchor MnO2 hexagonal nanoplate arrays (HNPAs) on carbon cloth (CC) fibers. The NSs were prepared by a novel one-step electrochemical deposition method. Under an external cathodic voltage of -2.0 V for 30 min, hierarchical core-shell-like MnO2-NS-decorated MnO2 HNPAs (MnO2 NSs@MnO2 HNPAs) were uniformly grown on CC with reliable adhesion. The phase purity and morphological properties of the samples were characterized by various physicochemical techniques. At a constant external cathodic voltage, growth of MnO2 NSs@MnO2 HNPAs on CC was carried for different time periods. When utilized as a flexible, robust, and binder-free electrode for pseudocapacitors, the hierarchical core-shell-like MnO2 NSs@MnO2 HNPAs on CC showed clearly enhanced electrochemical properties in 1 M Na2SO4 electrolyte solution. The results indicate that the MnO2 NSs@MnO2 HNPAs on CC have a maximum specific capacitance of 244.54 F/g at a current density of 0.5 A/g with excellent cycling stability compared to that of bare MnO2 HNPAs on CC (112.1 F/g at 0.5 A/g current density). We believe that the superior charge storage performance of the pseudocapacitive electrode can be mainly attributed to the hierarchical MnO2 NSs@MnO2 HNPAs building blocks that have a large specific surface area, offering additional electroactive sites for efficient electrochemical reactions. The facile and single-step approach to growth of hierarchical pseudocapacitive materials on textile based electrodes opens up the possibility for the fabrication of high-performance flexible energy storage devices.</P>

Tricobalt tetroxide nanoplate arrays on flexible conductive fabric substrate: Facile synthesis and application for electrochemical supercapacitors

Nagaraju, Goli,Ko, Yeong Hwan,Yu, Jae Su Elsevier 2015 Journal of Power Sources Vol.283 No.-

<P><B>Abstract</B></P> <P>Tricobalt tetroxide (Co<SUB>3</SUB>O<SUB>4</SUB>) nanoplate arrays (NPAs) were synthesized on flexible conductive fabric substrate (FCFs) by a facile two-electrode system based electrochemical deposition method, followed by a simple heat treatment process. Initially, cobalt hydroxide (Co(OH)<SUB>2</SUB>) NPAs were electrochemically deposited on FCFs by applying an external voltage of −1.5 V for 30 min. Then, the Co<SUB>3</SUB>O<SUB>4</SUB> NPAs on FCFs was obtained by thermal treatment of as-deposited Co(OH)<SUB>2</SUB> NPAs on FCFs at 200 °C for 2 h. From the analysis of morphological and crystal properties, the Co<SUB>3</SUB>O<SUB>4</SUB> NPAs were well integrated and uniformly covered over the entire surface of substrate with good crystallinity in the cubic phase. Additionally, the fabricated sample was directly used as a binder-free electrode to examine the feasibility for electrochemical supercapacitors using cyclic voltammetry and galvanic charge–discharge measurements in 1 M KOH electrolyte solution. The Co<SUB>3</SUB>O<SUB>4</SUB> NPAs coated FCFs electrode exhibited a maximum specific capacitance of 145.6 F/g at a current density of 1 A/g and an excellent rate capability after 1000 cycles at a current density of 3 A/g. This facile fabrication method for integrating the Co<SUB>3</SUB>O<SUB>4</SUB> nanostructures on FCFs could be a promising approach for advanced flexible electronic and energy-storage device applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Co<SUB>3</SUB>O<SUB>4</SUB> nanoplate arrays (NPAs) were fabricated on flexible conductive fabric substrate (FCFs). </LI> <LI> The Co<SUB>3</SUB>O<SUB>4</SUB> NPAs were uniformly entrapped on FCFs with good adhesion. </LI> <LI> Optimized growth of Co<SUB>3</SUB>O<SUB>4</SUB> NPAs on FCFs leads to a superior electrochemical performance in supercacpitors. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile synthesis of ZnO/CuO nanostructures on cellulose paper and their p-n junction properties

Nagaraju, G.,Hwan Ko, Y.,Su Yu, J. North-Holland 2014 Materials letters Vol.116 No.-

A cellulose paper based p-n junction device was fabricated by synthesizing the ZnO/CuO nanostructures via a hydrothermal process. The CuO nanospindles (NSs) were decorated on the surface of cellulose paper substrate by a simple soaking process. Subsequently, ZnO nanorod arrays were grown on the surface of the CuO NSs decorated cellulose paper (i.e., CuO NSs/paper) by the hydrothermal process. The synthesized ZnO/CuO nanostructures on cellulose paper exhibited good crystal and optical properties and favorably formed the p-n heterojunction with a rectifying behavior.

Facile Fabrication and Characterization of In₂O₃ Nanorods on Carbon Fibers

Nagaraju, Goli,Ko, Yeong Hwan,Yu, Jae Su The Korean Vacuum Society 2014 Applied Science and Convergence Technology Vol.23 No.4

Indium oxide ($In_2O_3$) nanorods (NRs) which can be expected to increase the device performance in various electronic and electrochemical applications were prepared on carbon fibers via an electrochemical deposition (ED) method. During the ED, the indium hydroxide ($In(OH)_3$) NRs were well grown and firmly attached onto the carbon fibers. After that, they were changed into $In_2O_3$ by dehydration through a thermal annealing. The morphological and structural properties were investigated using field-emission scanning electron microscope images. The crystallinity of as-prepared sample was evaluated by X-ray diffraction. The Fourier transform infrared results confirm that the functional groups are present in the $In_2O_3$ NRs. This facile process of metal oxide nanostructures on carbon fiber can be utilized for flexible electronic and energy related applications.

Highly flexible conductive fabrics with hierarchically nanostructured amorphous nickel tungsten tetraoxide for enhanced electrochemical energy storage

Nagaraju, G.,Kakarla, R.,Cha, S. M.,Yu, J. S. Springer Science + Business Media 2015 NANO RESEARCH Vol.8 No.12

Utilizing Waste Cable Wires for High-Performance Fiber-Based Hybrid Supercapacitors: An Effective Approach to Electronic-Waste Management

Nagaraju, Goli,Sekhar, S. Chandra,Yu, Jae Su Wiley (John WileySons) 2018 ADVANCED ENERGY MATERIALS Vol.8 No.7

Hierarchical Ni-Co layered double hydroxide nanosheets entrapped on conductive textile fibers: a cost-effective and flexible electrode for high-performance pseudocapacitors

Nagaraju, G.,Raju, G. S.,Ko, Y.,Yu, J. Royal Society of Chemistry 2016 Nanoscale Vol.8 No.2

<P>Hierarchical three-dimensional (3D) porous nanonetworks of nickel-cobalt layered double hydroxide (Ni-Co LDH) nanosheets (NSs) are grown and decorated on flexible conductive textile substrate (CTs) via a simple two-electrode system based electrochemical deposition (ED) method. By applying a proper external cathodic voltage of -1.2 V for 15 min, the Ni-Co LDH NSs are densely deposited over the entire surface of the CTs with good adhesion. The flexible Ni-Co LDH NSs on CTs (Ni-Co LDH NSs/CTs) architecture with high porosity facilitates enhanced electrochemical performance in 1 M KOH electrolyte solution. The effect of growth concentration and external cathodic voltage on the electrochemical properties of Ni-Co LDH NSs/CTs is also investigated. The Ni10Co5 LDH NSs/CTs electrode exhibits a high specific capacitance of 2105 F g(-1) at a current density of 2 A g(-1) as well as an excellent cyclic stability as a pseudocapacitive electrode due to the advantageous properties of 3D interconnected porous frameworks of Ni10Co5 LDH NSs/CTs. This facile fabrication of bimetallic hydroxide nanostructures on CTs can provide a promising electrode for low-cost energy storage device applications.</P>

Designed construction of yolk–shell structured trimanganese tetraoxide nanospheres via polar solvent-assisted etching and biomass-derived activated porous carbon materials for high-performance asymmetric supercapacitors

Nagaraju, Goli,Sekhar, S. Chandra,Rama Raju, G. Seeta,Bharat, L. Krishna,Yu, Jae Su The Royal Society of Chemistry 2017 Journal of Materials Chemistry A Vol.5 No.30

<▼1><P>Yolk–shell structured Mn3O4 nanospheres and biomass-derived activated carbon materials were prepared for use in high energy storage asymmetric supercapacitors.</P></▼1><▼2><P>Recently, yolk–shell structured electrode materials have attracted increasing interest in supercapacitors (SCs) due to their high surface area, good electrochemical activity and excellent mechanical stability towards superior energy storage performance. However, the synthesis strategies to prepare such yolk–shell structured materials without using chemical surfactants/solid templates are still inferior. Herein, a facile and cost-effective strategy to design yolk–shell structured trimanganese tetraoxide nanospheres (Mn3O4 NSs) with a distinctive core–void–shell configuration to use as an efficient positive electrode material in asymmetric SCs is demonstrated. Specifically, the yolk–shell structured Mn3O4 NSs were prepared by the inclusion of water droplets to the manganese precursor–isopropyl alcohol system, which facilitates the inside-out Ostwald ripening process to construct a yolk–shell-like configuration with porous properties. In aqueous electrolyte solution, the corresponding material exhibited a high specific capacitance (211.36 F g<SUP>−1</SUP> at a current density of 0.5 A g<SUP>−1</SUP>), a good rate capability (79.4% at 10 A g<SUP>−1</SUP>) and an excellent cycling stability (92% after 2000 cycles) compared to its solid counterparts. Meanwhile, a low-cost material based on biomass-derived activated carbon with a honeycomb-like structure is also prepared using waste corrugated boxes, which exhibits a reliable electrochemical performance for use as a negative electrode material. Moreover, the fabricated asymmetric SC using both electrode materials offers a maximum potential window of 2 V with higher energy density (19.47 W h kg<SUP>−1</SUP>) and power density (2263.89 W kg<SUP>−1</SUP>) values, which can effectively power up commercial light-emitting diodes for practical applications.</P></▼2>

Hydrothermal synthesis of MoS₂ and WS₂ nanoparticles for high-performance supercapacitor applications

Nagaraju, Chandu,V. V. Muralee Gopi, Chandu,Ahn, Jin-Woo,Kim, Hee-Je The Royal Society of Chemistry 2018 NEW JOURNAL OF CHEMISTRY Vol.42 No.15

<P>Nanoparticle-featured MoS2 and WS2 have been synthesized using a facile one-step hydrothermal approach and their application as electroactive materials for high-performance supercapacitors has been investigated. The electrochemical results of the MoS2 electrode exhibit a higher specific capacitance (<I>C</I>s) of 1531.2 F g<SUP>−1</SUP> at 5 mA cm<SUP>−2</SUP> with good cycling stability (up to 81.6% retention over 3000 cycles). The WS2 electrode delivers a high <I>C</I>s of 1439.5 F g<SUP>−1</SUP> at 5 mA cm<SUP>−2</SUP> and excellent cycling stability with 77.4% retention after 3000 cycles. The outstanding performance of the MoS2 and WS2 electrodes indicates their potential in next-generation high-performance supercapacitor applications.</P>

Metallic Layered Polyester Fabric Enabled Nickel Selenide Nanostructures as Highly Conductive and Binderless Electrode with Superior Energy Storage Performance

Nagaraju, Goli,Cha, Sung Min,Sekhar, S. Chandra,Yu, Jae Su Wiley Blackwell (John Wiley Sons) 2017 Advanced energy materials Vol.7 No.4

<P>Highly flexible and conductive fabric (CF)-supported cauliflower-like nickel selenide nanostructures (Ni3Se2 NSs) are facilely synthesized by a singlestep chronoamperometry voltage-assisted electrochemical deposition (ECD) method and used as a positive electrode in supercapacitors (SCs). The CF substrate composed of multi-layered metallic films on the surface of polyester fibers enables to provide high electrical conductivity as a working electrode in ECD process. Owing to good electrical conductivity, high porosity and intertwined fibrous framework of CF, cauliflower-like Ni3Se2 NSs are densely integrated onto the entire surface of CF (Ni3Se2 NSs@CF) substrate with reliable adhesion by applying a chronoamperometry voltage of -1.0 V for 240 s. The electrochemical performance of the synthesized cauliflower-like Ni3Se2 NSs@CF electrode exhibits a maximum specific capacity (CSC) of 119.6 mA h g(-1) at a discharge current density of 2 A g(-1) in aqueous 1 m KOH electrolyte solution. Remarkably, the specific capacity of the same electrode is greatly enhanced by introducing a small quantity of redox-additive electrolyte into the aqueous KOH solution, indicating the CSC approximate to 251.82 mA h g(-1) at 2 A g(-1) with good capacity retention. Furthermore, the assembled textile-based asymmetric SCs achieve remarkable electrochemical performance such as higher energy and power densities, which are able to light up different colored lightemitting diodes.</P>