Facile electrochemical synthesis of three dimensional flowerlike gold microstructure for electrochemical oxidation of hydrogen peroxide

Muthurasu, Alagan,Kim, Hak Yong Elsevier 2018 ELECTROCHIMICA ACTA Vol.283 No.-

<P><B>Abstract</B></P> <P>In the present work, we report a simple and facile templateless electrodeposition of hierarchical flowerlike gold microstructure which was synthesized by using a chronoamperometric (CA) i–t curve technique at a constant applied potential of <I>E</I> = 0.5 V with respect to sat Ag/AgCl (KCl) on indium tin oxide electrode (ITO) substrate. The surface morphology, elemental composition and the preferred orientation of gold microflowers (AuMFs) were characterized using scanning electron microscopy (SEM) and X–ray photoelectron spectroscopy (XPS) analyses. The SEM images of the as-prepared AuMFs resembled nanoflakes which are building block for the formation of a three dimensional hierarchical flower–like morphology. Surface elemental composition and valence state of AuMFs is further examined by X–ray photoelectron spectroscopy (XPS). The electrochemical oxidation behavior of AuMFs was investigated by using Cyclic Voltammetry (CV) and chronoamperometric CA techniques with the H<SUB>2</SUB>O<SUB>2</SUB> analyst in 0.1 M phosphate buffer solution (pH 7.4). The AuMFs deposited ITO electrodes exhibited excellent electrocatalytic reactivity towards H<SUB>2</SUB>O<SUB>2</SUB> oxidation due to the increase of in adsorption of H<SUB>2</SUB>O<SUB>2</SUB> on gold–oxide surfaces and it was enhancing the amperometric sensing of H<SUB>2</SUB>O<SUB>2</SUB> in neutral solutions.</P>

Metal-organic framework derived Co₃O₄/MoS₂ heterostructure for efficient bifunctional electrocatalysts for oxygen evolution reaction and hydrogen evolution reaction

Muthurasu, Alagan,Maruthapandian, Viruthasalam,Kim, Hak Yong Elsevier 2019 Applied Catalysis B Vol.248 No.-

<P><B>Abstract</B></P> <P>Fabrication of highly efficient, sustainable and low-cost nonprecious metal oxide for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is exceedingly challenging and warranted for overall water splitting. Herein, we synthesized cobalt nanoleaves metal-organic framed work (MOF) on nickel foam substrate with uniform growth. After calcination of Co-MOF, molybdenum disulfide nanosheets is grown by a facial hydrothermal method. The as-prepared heterostructure (Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB>) can act as bifunctional electrocatalysts for overall water splitting. Under optimized condition, synthesized Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB> heterostructure catalyst exhibited excellent catalytic activity for both OER and HER in 1 M KOH solution with a current density of 20 mA cm<SUP>−2</SUP> at overpotential of 230 mV for OER and 205 mV for HER (@ j = 10 mA cm<SUP>−2</SUP>) and Tafel slopes of 45 and 98 mV dec<SUP>-1</SUP>, respectively. The superior catalytic activity for both OER and HER arises from the unique heterostructure of Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB> and the synergistic effects of Co<SUB>3</SUB>O<SUB>4</SUB> and MoS<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical structures of MoS<SUB>2</SUB>nanosheets wrapped MOF based Co<SUB>3</SUB>O<SUB>4</SUB> nanoleaves heterostructures on nickel foam was successfully synthesized (Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB>) by a facile hydrothermal process. </LI> <LI> The Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB> heterostructure catalyst exhibits remarkable activities towards HER and OER. </LI> <LI> The superior catalytic activity as both OER and HER arise from the unique heterostructure of Co<SUB>3</SUB>O<SUB>4</SUB>/MoS<SUB>2</SUB> and the synergistic effects of Co<SUB>3</SUB>O<SUB>4</SUB> and MoS<SUB>2</SUB>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Optimization and analysis of microstructural friction stir welded AA5083 grade aluminium alloy

P. Muthurasu,M. Kathiresan 한양대학교 세라믹연구소 2021 Journal of Ceramic Processing Research Vol.22 No.6

The present work is the novel approach to optimize the friction stir welding process of aluminium AA5083 alloy by utilizingTaguchi L9 orthogonal array technique. The present work also investigated the mechanical and metallurgical characteristicsof the weld joint. The present work involved three input friction stir welding parameters that were varied in the investigationunder the Taguchi L9 orthogonal array experimental methodology. The experimental methodology was utilized to predict theoptimal input parameters to obtain peak tensile strength and hardness values of the welded joint and the signal to noise (S/N) ratio and results of the Analysis of variance (ANOVA) were also investigated. The optimal tool rotational speed, weldingspeed and tool tilt angle were 560 rpm, 60 mm/minute and 1 degree respectively for the peak joint tensile strength and 560rpm, 80 mm/minute and 1 degree for peak joint hardness. The results from ANOVA indicated that the highest influencinginput factor of the weld joint was tool tilt angle followed by the welding speed and tool rotational speed. Metallurgical analysisof the joint revealed fine grain structure within the stir zone which directly resulted in the enhancement of the weld jointproperties.

Three-dimensionally assembled manganese oxide ultrathin nanowires: Prospective electrode material for asymmetric supercapacitors

Ojha, Gunendra Prasad,Pant, Bishweshwar,Muthurasu, Alagan,Chae, Su-Hyeong,Park, Soo-Jin,Kim, Taewoo,Kim, Hak-Yong Pergamon Press 2019 Energy Vol.188 No.-

<P><B>Abstract</B></P> <P>In this report, we have forwarded a noble synthesis route for the fabrication of self-supported three-dimensional networks of manganese oxide ultrathin nanowires (3D MnO<SUB>2</SUB>-UTNWs) via a simple and cost-effective process for the first time. The formation of ultrathin nanowires (5 nm in diameter with several micrometer lengths) and their 3D assembly was achieved via a slow-reduction of potassium permanganate by oleylamine under constant stirring at 80 °C for 50 h. The resultant material was characterized using FE-SEM, TEM, XRD, FTIR, BET, XPS and Raman techniques. As-fabricated 3D MnO<SUB>2</SUB>-UTNWs network was used as the electrode material for supercapacitor. The electrochemical studies of the material revealed an excellent electrochemical performance with a high specific capacitance of 544.7 Fg<SUP>-1</SUP> at 1 Ag<SUP>-1</SUP> and excellent life span of 86.3% after 5000 cycles. An asymmetric supercapacitor was assembled using 3D-MnO<SUB>2</SUB> UTNWs and nitrogen-doped graphene hydrogels (NGHs) as the positive and negative electrodes; respectively. The 3D-MnO<SUB>2</SUB> UTNWs//NGHs device delivered an admirable specific capacitance of 56.5 Fg<SUP>-1</SUP> at 1 Ag<SUP>-1</SUP>, energy density of 21 Whkg<SUP>−1</SUP> at 840 Wkg<SUP>-1</SUP>, and extraordinary cyclic stability of 81.3% after 5000 cycles. This method provides a novel green synthetic route to prepare 3D MnO<SUB>2</SUB>-UTNWs without utilizing non-ambient reaction parameters.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D-networks of MnO<SUB>2</SUB> ultrathin nanowires were prepared. </LI> <LI> The mechanism of 3D-network formation is discussed. </LI> <LI> It showed high specific capacitance of 544.7 F/g at 1 A/g. </LI> <LI> The nanowires were used as electrode material for asymmetric supercapacitor. </LI> <LI> The synthesis process is simple, effective, and can be scaled up. </LI> </UL> </P>

In-built fabrication of MOF assimilated B/N co-doped 3D porous carbon nanofiber network as a binder-free electrode for supercapacitors

Dahal, Bipeen,Mukhiya, Tanka,Ojha, Gunendra Prasad,Muthurasu, Alagan,Chae, Su-Hyeong,Kim, Taewoo,Kang, Dawon,Kim, Hak Yong Pergamon Press 2019 Electrochimica Acta Vol. No.

<P><B>Abstract</B></P> <P>Polyacrylonitrile (PAN) based carbon nanofibers (CNFs) show enormous potential as a high performance and cost-effective supercapacitor electrode material. However, there are two intrinsic limitations that prevent their deployment in this field, namely their low surface area and limited transporting channels for ion diffusion. Here, we design an approach that concurrently addresses both problems. We employ electrospinning of PAN and zeolitic imidazolate framework (ZIF-8) nanoparticles to fabricate highly porous CNFs, followed by a sodium borohydride treatment and freeze-drying to maintain the three-dimensionalities of carbon nanofibers networks. Nitrogen and boron co-doping could be achieved together by controlling the conditions for stabilization and carbonization after the ammonium borate tri-hydrate treatment. The novel ZIF-8 incorporated 3D nitrogen and boron co-doped carbon nanofiber electrode was tested as a binder-free supercapacitor electrode and delivered a high specific capacitance of 295 F g<SUP>−1</SUP> at a 0.5 A g<SUP>−1</SUP> current density, exceeding that of PAN-based carbon nanofiber supercapacitor electrodes. Indeed, the novel electrode also maintained a high rate capability and remarkable cyclic stability of 94.5% capacitance retention even after 10 000 charge-discharge cycles. This superior electrochemical performance is attributed to the large surface area, mesoporous nature and high wettability of the B and N doped carbon nanofiber electrode. This study will inspire the development of new 3D PAN and metal organic framework based porous electrode materials for high performance energy storage devices.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Engineering nanohaired 3D cobalt hydroxide wheels in electrospun carbon nanofibers for high-performance supercapacitors

Mukhiya, Tanka,Dahal, Bipeen,Ojha, Gunendra Prasad,Kang, Dawon,Kim, Taewoo,Chae, Su-Hyeong,Muthurasu, Alagan,Kim, Hak Yong Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.361 No.-

<P><B>Abstract</B></P> <P>Engineering nanostructures in the desired design and suitable size is one of the key issues for persuading high-performance supercapacitors (SCs). In this work, we report a successful synthesis of a new type of nanohaired three-dimensional cobalt hydroxide wheels/carbon nanofibers (3D Co(OH)<SUB>2</SUB>/CNFs) composite by a cost-effective electrospinning cum hydrothermal method. The 3D Co(OH)<SUB>2</SUB> wheels are composed of many partially-fused, nanohaired and serrated sheet-like nanoleaflets furnishing abundant active sites. This novel architecture is quite significant for the stability of the composite since the wheels encircle one or more conductive CNFs firmly rather than the simple attachment on the surface of substrate. The growth process of 3D Co(OH)<SUB>2</SUB> wheels on CNFs has been studied by synthesizing other two novel Co(OH)<SUB>2</SUB>/CNFs composites. The as-prepared material exhibits a specific capacitance of 1186 F g<SUP>−1</SUP> at a current density of 1 A g<SUP>−1</SUP> with excellent cyclic stability which is the highest reported value for Co(OH)<SUB>2</SUB>/CNFs composites. The asymmetric supercapacitor (ASC) device assembled using 3D Co(OH)<SUB>2</SUB>/CNFs as a positive electrode and nitrogen doped graphene hydrogel (NGH) as a negative electrode exhibits a high energy density of 60.31 W h kg<SUP>−1</SUP> at power density of 740.8 W kg<SUP>−1</SUP> which still remains 37 W h kg<SUP>−1</SUP> even at a higher power density of 7500 W kg<SUP>−1</SUP> with remarkable cycle life. Therefore, the composite stands as a promising candidate for SCs electrode material. This unique nanoengineering gives an insight into the synthesis of other stable nanocomposites for diverse applications like sensors, catalysis, etc.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel nanohaired 3D cobalt hydroxide wheels have been uniformly inserted in CNFs. </LI> <LI> Growth process of 3D cobalt hydroxide wheels in CNFs has been proposed. </LI> <LI> 3D Co(OH)<SUB>2</SUB>/CNFs//NGH ASC exhibits high energy density with remarkable cycle life. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>