Direct synthesis of thickness-tunable MoS₂ quantum dot thin layers: Optical, structural and electrical properties and their application to hydrogen evolution

Vikraman, Dhanasekaran,Akbar, Kamran,Hussain, Sajjad,Yoo, Geonwook,Jang, Ji-Yun,Chun, Seung-Hyun,Jung, Jongwan,Park, Hui Joon Elsevier 2017 Nano energy Vol.35 No.-

<P><B>Abstract</B></P> <P>We report a layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline molybdenum disulfide (MoS<SUB>2</SUB>) thin layers. For the first time, a facile, cost effective, and mass-scalable direct synthesis approach, based on a chemical bath deposition, is designed for quantum dot(QD)-based MoS<SUB>2</SUB> layers using (NH<SUB>4</SUB>)<SUB>6</SUB>Mo<SUB>7</SUB>O<SUB>24</SUB> and thiourea (CH<SUB>4</SUB>N<SUB>2</SUB>S) as precursors. Using this process, the uniformity of large area thin layer can be retained, and the applicability to various substrates can provide great opportunities in the fabrication of various atomically thin layered structures. The structural and optical properties of the MoS<SUB>2</SUB> QD layers are systematically investigated. Raman, AFM and TEM analyses confirm the formation of continuous and crystalline bi-, tri- and few-layered MoS<SUB>2</SUB>. Their electrical properties are evaluated by bottom-gate FETs, and a field-effect mobility value of ~1.06cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and a current on/off ratio in the order of ~ 10<SUP>5</SUP> are obtained. Particularly, MoS<SUB>2</SUB> prepared as a thin film consisting QD structures of grains shows novel electrocatalytic property. MoS<SUB>2</SUB> QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction, featured by Tafel slope (94mVdecade<SUP>−1</SUP>), exchange current density (1.91×10<SUP>-1</SUP> mAcm<SUP>−2</SUP>) and long-term durability for 20h. Our approach opens new avenues for the design and synthesis of functional MoS<SUB>2</SUB> layers for energy harvesting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A layer thickness-tunable direct synthesis growth method for bi- to few-layer crystalline MoS<SUB>2</SUB> thin layers is reported. </LI> <LI> This approach is applicable to various substrates. </LI> <LI> The structural and optical properties of the synthesized MoS<SUB>2</SUB> layers are systematically investigated. </LI> <LI> The electrical properties of the synthesized MoS<SUB>2</SUB> layers are evaluated by bottom-gate FETs. </LI> <LI> MoS<SUB>2</SUB> QDs on Au/Si are proven to be excellent electrocatalysts for hydrogen evolution reaction. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile and cost-effective methodology to fabricate MoS₂ counter electrode for efficient dye-sensitized solar cells

Vikraman, Dhanasekaran,Patil, Supriya A.,Hussain, Sajjad,Mengal, Naveed,Kim, Hyun-Seok,Jeong, Sung Hoon,Jung, Jongwan,Kim, Hak-Sung,Park, Hui Joon Elsevier 2018 Dyes and pigments Vol.151 No.-

<P><B>Abstract</B></P> <P>Interests in the development of economical and high-efficiency counter electrodes (CEs) of dye-sensitized solar cell (DSSC) to replace the excessively cost and scarce platinum (Pt) CEs have been increased. In this report, we demonstrate a facile chemical bath deposition (CBD) route to prepare layered MoS<SUB>2</SUB>/fluorine-doped tin oxide (FTO) films that directly act as the CEs of DSSCs. A DSSC containing the CBD-synthesized MoS<SUB>2</SUB>/FTO CE (prepared at 0.03 M Mo source concentration, 90 °C bath temperature and 30 min deposition time) exhibits high power conversion efficiency (PCE) of 7.14%, which is approaching that of DSSC with Pt/FTO CE (8.73%). The electrocatalytic activity of the MoS<SUB>2</SUB>/FTO and Pt/FTO CEs are discussed in detail with their cyclic voltammetry (CV), Tafel polarization curves, and electrochemical impedance spectra (EIS). The observed results indicate that our low-cost CE has a high electrocatalytic activity for the reduction of triiodide to iodide and a low charge transfer resistance at the electrolyte–electrode interface with a comparable state to that of a Pt/FTO CE.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Crystalline MoS<SUB>2</SUB> thin layers are grown on FTO using chemical bath deposition (CBD) method. </LI> <LI> The structural and optical properties of the synthesized MoS<SUB>2</SUB> layers are systematically investigated. </LI> <LI> The electrocatalytic activity of the CBD-synthesized MoS<SUB>2</SUB>/FTO is discussed with their CV, Tafel and EIS curves. </LI> <LI> A DSSC containing the MoS<SUB>2</SUB>/FTO CE exhibits high power conversion efficiency of 7.14%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Construction of dye-sensitized solar cells using wet chemical route synthesized MoSe2 counter electrode

Dhanasekaran Vikraman,Supriya A. Patil,Sajjad Hussain,Naveed Mengal,정성훈,정종완,박휘준,김학성,김현석 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.69 No.-

This paper presents a simple and large area wet chemical preparation route for molybdenum diselenide (MoSe2) atomic layers. MoSe2 was synthesized onto fluorine doped tin oxide substrates and could be directly used as a counter electrode (CE) for dye-sensitized solar cells (DSSCs). The role of deposition time on the growth of MoSe2 CE was elaborately discussed using Raman, X-ray diffraction and photoluminescence studies. Influence of wet chemical growth time on the surface modification of MoSe2 CE was evidently demonstrated by scanning electron microscopy and atomic force microscopy studies. The MoSe2 CE electrode has lower charge transfer resistance and superior electrocatalytic activity towards triiodide/iodide redox behavior, comparable to conventional Pt CEs. High power conversion efficiency of 7.28% was achieved, equivalent to scarce noble metal Pt CE (7.40%). Uniform surface morphology with active edge sites highly dominated to promote the superior electrocatalytic activity. This work opens a way to use an economical wet chemical method to fabricate the layered MoSe2 CE as a replacement for high cost Pt based CE for DSSCs.

Facile fabrication of n-ZnO nanorods/p-Cu₂O heterojunction and its photodiode property

Kathalingam, A.,Vikraman, Dhanasekaran,Kim, Hyun-Seok,Park, Hui Joon North-Holland 2017 Optical materials Vol.66 No.-

<P><B>Abstract</B></P> <P>This report presents the fabrication and characterization of n-ZnO nanorods/p-Cu<SUB>2</SUB>O hetrojunction photo-diode. The ZnO nanorods (NRs) were deposited onto electrodeposited Cu<SUB>2</SUB>O thin film by hydrothermal method. The structural, morphological and optical properties of ZnO NRs and Cu<SUB>2</SUB>O films were studied by X-ray diffraction, scanning electronic microscopy, UV–Vis spectrophotometer, respectively. XRD patterns revealed that the as-grown films were highly crystalline nature with strong predominant orientation of (111) and (002) lattices corresponding to Cu<SUB>2</SUB>O and ZnO NRs, respectively. Current–voltage (I–V) characteristic of n-ZnONRs/p-Cu<SUB>2</SUB>O structure confirmed the formation of heterojunction exhibiting diode-like rectifying nature. It showed enhanced conversion of UV light, which indicates the suitability of the simple and low-cost n-ZnO NRs/p-Cu<SUB>2</SUB>O heterojunction device for optoelectronic applications. The sandwich type ITO/n-ZnO NRs/p-Cu<SUB>2</SUB>O/ITO structure is quite novel approach for the efficient and complete collection of carriers in nanorods incorporated devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Successfully fabricated ZnO NRs/Cu<SUB>2</SUB>O heterojunction by facile solution routes. </LI> <LI> Shown good photodiode response. </LI> <LI> Showed excellent UV light response suitable for UV light sensor. </LI> <LI> Sandwich type device using ITO as a transparent conductor is a novel approach for Nanorods structure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile and cost-effective growth of MoS₂ on 3D porous graphene-coated Ni foam for robust and stable hydrogen evolution reaction

Hussain, Sajjad,Vikraman, Dhanasekaran,Truong, Linh,Akbar, Kamran,Rabani, Iqra,Kim, Hyun-Seok,Chun, Seung-Hyun,Jung, Jongwan Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.788 No.-

<P><B>Abstract</B></P> <P>To replace the costly, noble platinum electrocatalyst, the inexpensive, earth abundant and highly efficient electrocatalysts of layered transition metal dichalcogenides (TMDs) are explored for the hydrogen evolution reaction (HER). This paper describes cost-effective synthesis of 1T-MoS<SUB>2</SUB> on 3D-graphene/Ni foam (NF) via a facile solution bath approach as an electrocatalyst for HER. The improved HER performances were observed due to the 3D-structure of MoS<SUB>2</SUB>/graphene. HER performance of MoS<SUB>2</SUB>/graphene/NF electrocatalyst exposed a superior catalytic performance with the low overpotential (−89 mV vs RHE) to drive the 10 mA cm<SUP>−2</SUP>, steep Tafel slope (45 mV dec<SUP>−1</SUP>), large exchange current density (4.16 × 10<SUP>−1</SUP> mA cm<SUP>−2</SUP>), and robust stability over 18 h. Density functional theory (DFT) calculations also confirmed the reduced Gibbs free energy for H-adsorption (ΔG<SUB>H</SUB>) for MoS<SUB>2</SUB>/graphene compared to MoS<SUB>2</SUB>. The observed results suggest that the 1T-MoS<SUB>2</SUB>/graphene/NF is an interesting alternative to platinum-based catalyst for boosting HER efficiency.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Active electrocatalyst of MoS<SUB>2</SUB> decorated on graphene/NF by chemical route. </LI> <LI> Raman and XRD results confirmed the observation of 1T-MoS<SUB>2</SUB>. </LI> <LI> The robust stability over 18 h with over potential of 89 mV vs RHE was observed. </LI> <LI> DFT calculations explained in terms of density of states for high HER performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electrochemical performance of MWCNT/GO/NiCo₂O₄ decorated hybrid nanocomposite for supercapacitor electrode materials

Ramesh, Sivalingam,Vikraman, Dhanasekaran,Kim, Hyun-Seok,Kim, Heung Soo,Kim, Joo-Hyung Elsevier 2018 Journal of alloys and compounds Vol.765 No.-

<P><B>Abstract</B></P> <P>In the present study, GO/MWCNT/NiCo<SUB>2</SUB>O<SUB>4</SUB> decoration of a hybrid nanocomposite was synthesized by a hydrothermal process, with nickel and cobalt nitrate precursors. The electrochemical performance of the hybrid composite was investigated as a supercapacitor electrode material through cyclic voltammetry (CV), galvano static charge–discharge and electrochemical impedance analysis. The cyclic voltammetry result showed that the excellent capacitive behaviour of the MWCNT/GO/NiCo<SUB>2</SUB>O<SUB>4</SUB> hybrid composite had a specific capacitance of 707 F g<SUP>−1</SUP> at a current density of 2.5 A/g and a 88% specific capacitance retention after 5000 continuous charge–discharge cycles, indicating their high potentials for high-performance supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanocrystalline Morphology of Nico<SUB>2</SUB>O<SUB>4</SUB> materials. </LI> <LI> GO/MWCNT materials with hybrid nanocomposite. </LI> <LI> Increased specific capacitance with good cyclic stability. </LI> <LI> Controlled morphology of ceramic nanoparticles of Nico<SUB>2</SUB>O<SUB>4</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Maskless patterned growth of ZnO nanorod arrays using tip based electrolithography

Kathalingam, A.,Vikraman, Dhanasekaran,Karuppasamy, K.,Kim, Hyun-Seok,Park, Hyun-Chang,Shanmugam, Kumaran Elsevier 2018 Materials science in semiconductor processing Vol.77 No.-

<P><B>Abstract</B></P> <P>We report patterned growth of ZnO nanorods based on electrochemical driven writing on a PMMA layer using a metal tip. Electric field induced breaking of the PMMA layer was used for pattern formation. ZnO nanorods were grown on the patterned PMMA layer using two step hydrothermal synthesis. After etching the unaffected PMMA using the conventional lift-off process, patterned growth of vertically aligned ZnO nanorods was produced. This strategy provides an easy and innovative solution for submicron lithographic patterning without requiring complex mask alignment, and allows micro-level semiconductor patterns to be easily formed. The process of pattern formation and ZnO nanorods growth are reported.</P>

Optical and Structural Properties of Solvent Free Synthesized Starch/Chitosan-ZnO Nanocomposites

Sanmugam, Anandhavelu,Vikraman, Dhanasekaran,Venkatesan, Sethuraman,Park, Hui Joon Hindawi Limited 2017 Journal of nanomaterials Vol.2017 No.-

<P>The objective of this work is to develop an environmentally friendly method for preparation of ZnO nanocomposites. ZnO nanocomposites were prepared by three natural fibers such as coir, sawdust, and chitosan using aqueous solution of zinc chloride and sodium hydroxide. The functional groups of ZnO, C=O for polysaccharide, and N-H bending vibration of amine were confirmed by FTIR spectroscopy. A new high intensity absorption band has been observed at 424 cm<SUP>−1</SUP> which corresponds to the E2 mode of hexagonal ZnO. The crystallinity and phase formation of coir, chitosan, and sawdust combined ZnO nanocomposites were confirmed by X-ray diffraction patterns. XRD patterns revealed the polycrystalline nature of ZnO composites belonging to the hexagonal phase with (101) preferential lattice orientation. The microstructural parameters were calculated for coir, chitosan, and saw wood combined ZnO composites. Also texture coefficients were estimated for all the diffraction lines of ZnO based nanocomposites. SEM and TEM analyses confirmed evenly distributed nanosized grains in the ZnO composites. The UV-Vis absorption spectra were observed where the blue shift absorption peak was at 334 nm. The optical band gap values were estimated in the range of 3.18-3.26 eV. The emission peak was observed at ~388 nm and ~463 nm by photoluminescence spectroscopy.</P>

Controlled synthesis of SnO₂@NiCo₂O₄/nitrogen doped multiwalled carbon nanotube hybrids as an active electrode material for supercapacitors

Ramesh, Sivalingam,Vikraman, Dhanasekaran,Karuppasamy, K.,Yadav, Hemraj M.,Sivasamy, Arumugam,Kim, Hyun-Seok,Kim, Joo-Hyung,Kim, Heung-Soo Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.794 No.-

<P><B>Abstract</B></P> <P>A thermal reduction process was successfully employed to construct novel hybrid composites of SnO<SUB>2</SUB>@NiCo<SUB>2</SUB>O<SUB>4</SUB>/N-doped multiwalled carbon nanotubes (N-MWCNTs) for supercapacitors. The hybrid confirmation studies were performed using X-ray diffraction, Raman and X-ray photoelectron spectroscopy analyses. Cyclic voltammetry performance confirmed their suitability for use as an active electrode material for supercapacitors. SnO<SUB>2</SUB>@NiCo<SUB>2</SUB>O<SUB>4</SUB>/N-MWCNTs showed the high specific capacitance of ∼728 Fg<SUP>−1</SUP> at 4 A/g in 6 M KOH electrolyte. After 5000 cycles, the hybrid composite produced excellent capacitance retention property with ∼92% of its primary value. Consequently, this SnO<SUB>2</SUB>@NiCo<SUB>2</SUB>O<SUB>4</SUB>/N-MWCNTs hybrid composite promising electrode for high-performance supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Controlled synthesis of SnO<SUB>2</SUB>@NiCo<SUB>2</SUB>O<SUB>4</SUB>/N-MWCNT hybrid materials via thermal reduction process. </LI> <LI> The hybrid composite shows the specific capacitance ∼728 Fg<SUP>−1</SUP> at 4 A/g. </LI> <LI> The excellent capacitance retention 92% with 5000 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>A thermal reduction process was successfully employed to construct novel hybrid composites of SnO<SUB>2</SUB>@ NiCo<SUB>2</SUB>O<SUB>4</SUB>/N-doped multiwalled carbon nanotubes (N-MWCNTs) of well-defined nanostructured for supercapacitor applications.</P> <P>[DISPLAY OMISSION]</P>

WS₂/CoSe₂ heterostructure: A designed structure as catalysts for enhanced hydrogen evolution performance

Hussain, Sajjad,Akbar, Kamran,Vikraman, Dhanasekaran,Liu, Hailiang,Chun, Seung-Hyun,Jung, Jongwan THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.65 No.-

<P><B>Abstract</B></P> <P>The development of hydrogen-evolving catalysts based on transition metal dichalchogenides (TMDs) is receiving a great attention for practical application of water-splitting devices and fuel cells due to their high electrocatalytic activity. Herein, we synthesized tungsten disulfide (WS<SUB>2</SUB>)/cobalt diselenide (CoSe<SUB>2</SUB>) hybrid catalyst for hydrogen evolution reaction (HER). CoSe<SUB>2</SUB> films were first deposited via electrodeposition of Co and followed by selenization process. And, the surface of the synthesized CoSe<SUB>2</SUB> films was covered with WS<SUB>2</SUB> via combined process of sputtering and sulfurization. In acidic media, the WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure catalyst exhibited fast hydrogen evolution kinetics of onset potential and Tafel slope were at 95mV and 44mVdecade<SUP>−1</SUP>, respectively with the excellent electrocatalytic stability over 20h. WS<SUB>2</SUB>/CoSe<SUB>2</SUB> heterostructure electrode demonstrates an excellent HER activity and long-term stability owing to their abundant active edge sites, and the strong chemical and electronic coupling between the CoSe<SUB>2</SUB> and WS<SUB>2</SUB>.</P> <P><B>Graphical abstract</B></P> <P>WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid structure was implemented to enhance HER electrocatalytic activity. The WS<SUB>2</SUB>/CoSe<SUB>2</SUB> catalyst exhibited low overpotentials of 95mV (@1mAcm<SUP>−2</SUP>) and 160mV (@ 10mAcm<SUP>−2</SUP>), a high exchange current density of ∼1.0×10<SUP>−2</SUP> mAcm<SUP>−2</SUP>, and a small Tafel slope of 44mVdecade<SUP>−1</SUP>. In addition, WS<SUB>2</SUB>/CoSe<SUB>2</SUB> hybrid electrode was stable over 20h of sustained hydrogen production in 0.5M H<SUB>2</SUB>SO<SUB>4</SUB> acidic medium.</P> <P>[DISPLAY OMISSION]</P>