Enhancement of electrochemical performance of nickel cobalt layered double hydroxide@nickel foam with potassium ferricyanide auxiliary electrolyte

Lamiel, Charmaine,Nguyen, Van Hoa,Hussain, Iftikhar,Shim, Jae-Jin Elsevier 2017 ENERGY Vol.140 No.1

<P><B>Abstract</B></P> <P>Metal oxide nanostructures have been studied widely to overcome the limitations in the capacitance of the carbon-based supercapacitor electrode materials. An electrode with a very porous 3D structure is preferred to facilitate the mass transfer of large electrolyte ions. In this study, highly nanostructured, binder-free Ni-Co-based pseudocapacitive electrodes were synthesized directly on porous 3D structured nickel foam (NF) current collectors using low-power microwave irradiation. The electrochemical performance of the Ni-Co layered double hydroxide (Ni-Co-LDH) showed better performance than Ni-Co oxide (Ni-Co-O) with the further addition of redox additive/active electrolytes, such as K<SUB>3</SUB>Fe(CN)<SUB>6</SUB>. The specific capacitances of 4664 F g<SUP>−1</SUP> for Ni-Co-LDH and 1758 F g<SUP>−1</SUP> for Ni-Co-O at 5 mA cm<SUP>−2</SUP> in the KOH/K<SUB>3</SUB>Fe(CN)<SUB>6</SUB> electrolyte were improved greatly compared to the values of their corresponding materials in the conventional KOH electrolyte (2875 and 250 F g<SUP>−1</SUP>, respectively). Interestingly, the Ni-Co-LDH//AC asymmetric device exhibited a specific capacitance of 108.9 F g<SUP>−1</SUP> and an energy density of 38.7 Wh kg<SUP>−1</SUP> with a stability of 61.9% after 5000 cycles. The facile yet cost-effective synthesis of nanostructured electrodes provides a versatile approach for the design of high-performance pseudocapacitive electrodes for future energy-storage systems.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Binder-free 3D Ni-Co LDH nanoflakes on Ni foam were synthesized under microwave. </LI> <LI> Ni-Co-LDH had a high specific capacitance 2875 F g<SUP>−1</SUP>, while Ni-Co-O had 250 F g<SUP>−1</SUP>. </LI> <LI> The Specific capacitance increased from 2875 to 4664 F g<SUP>−1</SUP> by adding K<SUB>3</SUB>Fe(CN)<SUB>6</SUB>. </LI> <LI> 91.1% of capacitance of Ni-Co-LDH was retained after 3000 cycles in KOH/K<SUB>3</SUB>Fe(CN)<SUB>6</SUB>. </LI> <LI> The Ni-Co-LDH//AC asymmetric device showed an energy density of 38.7 Wh kg<SUP>−1</SUP>. </LI> </UL> </P>

When Anatase Nanoparticles Become Bulklike: Properties of Realistic TiO₂ Nanoparticles in the 1–6 nm Size Range from All Electron Relativistic Density Functional Theory Based Calculations

Lamiel-Garcia, Oriol,Ko, Kyoung Chul,Lee, Jin Yong,Bromley, Stefan T.,Illas, Francesc American Chemical Society 2017 Journal of chemical theory and computation Vol.13 No.4

<P>All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic, and electronic structure of a series of stoichiometric TiO2 anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1-6 nm diameter size range. Initial structures were obtained using the Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces. Final structures were obtained from geometry optimization with full relaxation of all structural parameters using both generalized gradient approximation (GGA) and hybrid density functionals. Results show that, for nanoparticles of a similar size, octahedral and truncated octahedral morphologies have comparable energetic stabilities. The electronic structure properties exhibit a clear trend converging:to the bulk values as the size of the nanoparticles increases but with a marked influence of the density functional employed. Our results suggest that electronic structure properties, and hence reactivity, for the largest anatase nanoparticles considered in this study will be similar to those exhibited by even larger mesoscale particles or by bulk systems. Finally, we present compelling evidence that anatase nanoparticles become effectively bulklike when reaching a size of similar to 20 nm diameter.</P>

Microwave-assisted binder-free synthesis of 3D Ni-Co-Mn oxide nanoflakes@Ni foam electrode for supercapacitor applications

Lamiel, Charmaine,Nguyen, Van Hoa,Kumar, Deivasigamani Ranjith,Shim, Jae-Jin Elsevier 2017 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.316 No.-

<P><B>Abstract</B></P> <P>The outstanding performance of nickel foam (NF) as a current collector owing to its better dimensional stability, high electrical conductivity, and less contact resistance has made it a promising candidate for binder-free electrode for supercapacitors. In addition to the current collector, highly stable structures are also favored to facilitate rapid ion insertion and prevent structural collapse of the electrode materials. In this work, a binder-free and controlled structure of Ni-Co-Mn oxide on NF was constructed effectively using microwave irradiation. The structure obtained from the optimal conditions (concentration and holding time) involved hierarchical interconnected nanoflakes with void spaces, forming a stable and conductive network of nanoflakes on the NF. The synergistic effects of three metal (Ni-Co-Mn) oxides resulted in a high specific capacitance of 2536Fg<SUP>−1</SUP> at 5mAcm<SUP>−2</SUP> (6.49Ag<SUP>−1</SUP>) in a mixed KOH/K<SUB>3</SUB>Fe(CN)<SUB>6</SUB> electrolyte. The as-prepared symmetric device also obtained a high capacitance of 298Fg<SUP>−1</SUP>, a high energy density of 41.4Whkg<SUP>−1</SUP>, and a high power density of 5.4kWkg<SUP>−1</SUP>. The highly architectured Ni-Co-Mn oxide nanoflakes improved the pseudocapacitive performance significantly, making it a promising electrode material for high-performance binder-free supercapacitors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hierarchical 3D Ni-Co-Mn oxide@Ni foam was synthesized within 30s under microwave. </LI> <LI> Max. capacitance was 1151Fg<SUP>−1</SUP> in KOH and increased to 106.5% after 5000 cycles. </LI> <LI> Capacitance was 2356Fg<SUP>−1</SUP> with 79.6% retained after 5000 cycles using K<SUB>3</SUB>Fe(CN)<SUB>6</SUB>. </LI> <LI> Symmetrical supercapacitor was with an ED of 43.8Whkg<SUP>−1</SUP> and PD of 5.8kWkg<SUP>−1</SUP>. </LI> <LI> Energy density of 41.4Whkg<SUP>−1</SUP> and power density of 5.4kWkg<SUP>−1</SUP> for supercapacitor. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Enhanced electrochemical performance of nickel-cobalt-oxide@reduced graphene oxide//activated carbon asymmetric supercapacitors by the addition of a redox-active electrolyte

Lamiel, Charmaine,Lee, Yong Rok,Cho, Moo Hwan,Tuma, Dirk,Shim, Jae-Jin Elsevier 2017 JOURNAL OF COLLOID AND INTERFACE SCIENCE - Vol.507 No.-

<P><B>Abstract</B></P> <P>Supercapacitors are an emerging energy-storage system with a wide range of potential applications. In this study, highly porous nickel-cobalt-oxide@reduced graphene oxide (Ni-Co-O@RGO-s) nanosheets were synthesized as an active material for supercapacitors using a surfactant-assisted microwave irradiation technique. The RGO-modified nanocomposite showed a larger specific area, better conductivity, and lower resistivity than the unmodified nanocomposite because the RGO facilitated faster ion diffusion/transport for improved redox activity. The synergistic effect of Ni-Co-O@RGO-s resulted in a high capacitance of 1903Fg<SUP>−1</SUP> (at 0.8Ag<SUP>−1</SUP>) in a mixed KOH/redox active K<SUB>3</SUB>Fe(CN)<SUB>6</SUB> electrolyte. The asymmetric Ni-Co-O@RGO-s//AC supercapacitor device yielded a high energy density and power density of 39Whkg<SUP>−1</SUP> and 7500Wkg<SUP>−1</SUP>, respectively. The porous structure and combination of redox couples from both the electrode and electrolyte provided a highly synergistic effect, which improved the performance of the supercapacitor device.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Hierarchical mesoporous carbon sphereνickel cobalt sulfide core-shell structures and their electrochemical performance

Lamiel, C.,Nguyen, V.H.,Baynosa, M.,Huynh, D.C.,Shim, J.J. Elsevier Sequoia 2016 Journal of Electroanalytical Chemistry Vol.771 No.-

<P>The pursuit for renewable sources of energy has increased rapidly due to the continuous depletion of nonrenewable sources. Supercapacitors have attracted considerable attention because they can store electrical energy. In this study, a hierarchical mesoporous carbon sphere@nickel cobalt sulfide (CS@Ni-Co-S) core-shell was synthesized using a facile hydrothermal method. The reaction involved green synthesis without further sulfurization or post-heat treatment. The CS@Ni-Co-S core-shell microstructures exhibited a high capacitance of 724.4 F g(-1) at 2 A g(-1) in a 6 M KOH electrolyte. Good specific retention of 86.1% and high Coulombic efficiency of 97.9% were obtained after 2000 charge-discharge cycles. High energy density (58.0 Wh kg(-1) at 1440 W kg(-1)) and high power density (34.2 Wh kg(-1) at 7200W kg(-1)) were observed. Through this study, a cost-effective and simple synthesis of CS@Ni-Co-S as an active electrode showed favorable electrochemical performance. (C) 2016 Elsevier B.V. All rights reserved.</P>

Synthesis of mesoporous RGO@(Co,Mn)₃O₄ nanocomposite by microwave-assisted method for supercapacitor application

Lamiel, Charmaine,Nguyen, Van Hoa,Roh, Changhyun,Kang, ChanKyu,Shim, Jae-Jin Elsevier 2016 ELECTROCHIMICA ACTA Vol.210 No.-

<P><B>Abstract</B></P> <P>Supercapacitors have attracted considerable attention because they can store more energy than conventional capacitors and can have higher power densities than batteries. In this study, microwave irradiation was used for the rapid and facile synthesis of mesoporous RGO@(Co,Mn)<SUB>3</SUB>O<SUB>4</SUB> oxide nanosheets as an electrode material for supercapacitor applications. The as-prepared electrode exhibited a high capacitance of 1004Fg<SUP>−1</SUP> at 3mVs<SUP>−1</SUP> in a 6M KOH electrolyte solution. Moreover, the electrode showed good specific retention and high Coulombic efficiency of 81.6% and 96.9%, respectively, after 3000 charge-discharge cycles. The electrode also exhibited a high energy density of 53Whkg<SUP>−1</SUP> (at power density of 500Wkg<SUP>−1</SUP>) and high power density 5000Wkg<SUP>−1</SUP> (at energy density of 27Whkg<SUP>−1</SUP>). Overall, the RGO@(Co,Mn)<SUB>3</SUB>O<SUB>4</SUB> electrode showed very promising results for supercapacitor applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Mesoporous RGO@(Co,Mn)<SUB>3</SUB>O<SUB>4</SUB> nanosheets were prepared by microwave-assisted method. </LI> <LI> The as-prepared electrode exhibited a high capacitance of 1004Fg<SUP>−1</SUP> at 3mVs<SUP>−1</SUP> in a 6M KOH. </LI> <LI> It exhibited an energy density of 53Whkg<SUP>−1</SUP> at a power density of 500Wkg<SUP>−1</SUP>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Controlled synthesis and growth mechanism of zinc cobalt sulfide rods on Ni-foam for high-performance supercapacitors

Iftikhar Hussain,Charmaine Lamiel,Saad Gomaa Mohamed,수부칼라이비자야쿠마르,Awais Ali,심재진 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.71 No.-

Rod-like zinc cobalt sulfide (ZCS) with controlled uniform structure was synthesized using a single-stephydrothermal method and its growth mechanism was investigated. A ZCS-based electrode showed anultrahigh capacitance of 2,418 F g 1 (967 C g 1) at 1 A g 1 with a good cycling stability of 83% after 10,000cycles. Moreover, an asymmetric ZCS-12//activated carbon supercapacitor, exhibited a high capacitanceof 142 F g 1 (227 C g 1) at 0.5 A g 1 and a high energy density of 51 Wh kg 1 and a high power density of8 kW kg 1, highlighting the next generation high performance supercapacitors.

Performance of a modified hybrid functional in the simultaneous description of stoichiometric and reduced TiO₂ polymorphs

Ko, Kyoung Chul,Lamiel-Garcí,a, Oriol,Lee, Jin Yong,Illas, Francesc The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.17

<P>Conventional density functionals with either the local density approximation (LDA) or the generalized gradient approximation (GGA) form of the exchange-correlation potential fail to describe the electronic structure of a large number of metal oxides. Both the LDA and the GGA grossly underestimate the band gaps of these materials which severely affect the description of oxygen vacancy point defect states in reduced samples. To find a pragmatic approach to simultaneously and accurately describe the atomic and electronic structures of the most common TiO2 polymorphs, we explore the effect of the percentage of exact, non-local, Fock exchange on the electronic structure of stoichiometric rutile and anatase. From these results, a modified hybrid functional is proposed to properly describe the atomic structures, formation enthalpies and electronic structures of rutile and anatase and, at the same time, the results of reduced samples are also in good agreement with the available experimental results. The present approach can be safely used to accurately describe numerous TiO2 based materials containing defects or realistic nanoparticles for which the required large unit cells or system sizes hinder the use of GW related techniques.</P>

3D hierarchical mesoporous NiCo₂S₄@Ni(OH)₂ core–shell nanosheet arrays for high performance supercapacitors

Nguyen, Van Hoa,Lamiel, Charmaine,Shim, Jae-Jin The Royal Society of Chemistry 2016 NEW JOURNAL OF CHEMISTRY Vol.40 No.5

<P>Hierarchical mesoporous NiCo2S4@Ni(OH)(2) core-shell nanosheet arrays on conductive carbon substrates were prepared using a facile electrochemical deposition method and used as electrodes for supercapacitors. These electrodes exhibited rapid electron and ion transport, and excellent structural stability due to the highly conductive and mesoporous nature of the carbon substrates and NiCo2S4@Ni(OH)(2) nanosheets, as well as due to the open framework of the three-dimensional nanoarchitectures. The capacity of the obtained electrodes was as high as 15.7 mA h cm(-2) at a high current density of 100 mA cm(-1), highlighting their promising applications as efficient positive electrodes for electrochemical capacitors.</P>

A 3D walking palm-like core-shell CoMoO₄@NiCo₂S₄@nickel foam composite for high-performance supercapacitors

Hussain, Iftikhar,Ali, Awais,Lamiel, Charmaine,Mohamed, Saad Gomaa,Sahoo, Sumanta,Shim, Jae-Jin The Royal Society of Chemistry 2019 Dalton Transactions Vol.48 No.12

<P>Supercapacitors are one of the most promising renewable-energy storage systems. In this study, a three-dimensional walking palm-like core-shell CoMoO4@NiCo2S4@nickel foam (NF) nanostructure was synthesized using a two-step hydrothermal method for high electrochemical performance. The as-prepared composite exhibited a high areal capacitance of 17.0 F cm<SUP>−2</SUP> (2433 F g<SUP>−1</SUP>) at a current density of 5 mA cm<SUP>−2</SUP> in a three-electrode system. The results revealed outstanding cycling stability of 114% after 10 000 charge-discharge cycles. An aqueous asymmetric supercapacitor device assembled with CoMoO4@NiCo2S4@NF and activated carbon (AC)@NF as the positive and negative electrodes, respectively, showed a high capacitance of 4.19 F cm<SUP>−2</SUP> (182 F g<SUP>−1</SUP>) and delivered a high energy density of 60.2 W h kg<SUP>−1</SUP> at a power density of 188 W kg<SUP>−1</SUP> and a high power density of 1.5 kW kg<SUP>−1</SUP> at an energy density 29.2 W h kg<SUP>−1</SUP>, lighting 22 parallel-connected red light emitting diodes for over 60 s. The synergistic effects of the core-shell CoMoO4@NiCo2S4@NF electrode material highlight the potential of this composite as an effective active material for supercapacitor applications.</P>