In Situ Mg/MgO-Embedded Mesoporous Carbon Derived from Magnesium 1,4-Benzenedicarboxylate Metal Organic Framework as Sustainable Li-S Battery Cathode Support.

Development of advanced carbon cathode support with the ability to accommodate high sulfur (S) content as well as effective confinement of the sulfur species during charge-discharge is of great importance for sustenance of Li-S battery. A facile poly(vinylpyrrolidone)-assisted solvothermal method is reported here to prepare Mg-1,4-benzenedicarboxylate metal organic framework (MOF) from which mesoporous carbon is derived by thermal treatment, where the hexagonal sheetlike morphology of the parent MOF is retained. Existence of abundant pores of size 4 and 9 nm extended in three dimensions with zigzag mazelike channels helps trapping of S in the carbon matrix through capillary effect, resulting in high S loading. When tested as a cathode for lithium-sulfur battery, a reversible specific capacity of 1184 mAh g-1 could be achieved at 0.02 C. As evidenced by X-ray photoelectron spectroscopy, in situ generated Mg in the carbon structure enhances the conductivity, whereas MgO provides support to S immobilization through chemical interactions between Mg and sulfur species for surface polarity compensation, restricting the dissolution of polysulfide into the electrolyte, the main cause for the "shuttle phenomenon" and consequent capacity fading. The developed cathode shows good electrochemical stability with reversible capacities of 602 and 328 mAh g-1 at 0.5 and 1.0 C, respectively, with retentions of 64 and 67% after 200 cycles. The simple MOF-derived strategy adopted here would help design new carbon materials for Li-S cathode support.

Core-double shell ZnO/ZnS@Co3O4 heterostructure as high performance pseudocapacitor.

In recent times, a great deal of attention has been paid to the balanced design and fabrication of core-shell heterostructures for enhanced pseudocapacitor (SC) performance. In this paper, we report the synthesis of ZnO@Co3O4 based core-shell heterostructures with controllable shell thickness for the first time by a simple low-temperature solution-based method and their detailed electrode performance as SC wherein a highly enhanced pseudocapacitance of 296 C g(-1) at a current density of 0.5 A g(-1) has been observed. Further, modifying the surface of ZnO by its sulfur analogue (i.e., by creating a ZnO/ZnS heterostructure), an improved capacitance of 317 C g(-1) at a current density of 0.5 A g(-1) for ZnO/ZnS@Co3O4 has been obtained along with a better rate performance. This is attributed to an efficient charge transfer from ZnS to ZnO. Impressively, the core-double shell heterostructure exhibits high energy density of 36 Wh kg(-1) at a power density of 204.3 W kg(-1). Even at a very high power density of 10.9 kW kg(-1), it shows an energy density of 14.7 Wh kg(-1). To the best of our knowledge, this is the first study of the electrochemical properties of ZnO/ZnS@Co3O4 heterostructure.

Electrochemical energy storage in montmorillonite K10 clay based composite as supercapacitor using ionic liquid electrolyte.

Exploring new electrode materials is the key to realize high performance energy storage devices for effective utilization of renewable energy. Natural clays with layered structure and high surface area are prospective materials for electrical double layer capacitors (EDLC). In this work, a novel hybrid composite based on acid-leached montmorillonite (K10), multi-walled carbon nanotube (MWCNT) and manganese dioxide (MnO2) was prepared and its electrochemical properties were investigated by fabricating two-electrode asymmetric supercapacitor cells against activated carbon (AC) using 1.0M tetraethylammonium tetrafluroborate (Et4NBF4) in acetonitrile (AN) as electrolyte. The asymmetric supercapacitors, capable of operating in a wide potential window of 0.0-2.7V, showed a high energy density of 171Whkg(-1) at a power density of ∼1.98kWkg(-1). Such high EDLC performance could possibly be linked to the acid-base interaction of K10 through its surface hydroxyl groups with the tetraethylammonium cation [(C2H5)4N(+) or TEA(+)] of the ionic liquid electrolyte. Even at a very high power density of 96.4kWkg(-1), the cells could still deliver an energy density of 91.1Whkg(-1) exhibiting an outstanding rate capability. The present study demonstrates for the first time, the excellent potential of clay-based composites for high power energy storage device applications.

Reduced graphene oxide anchored Cu(OH)2 as a high performance electrochemical supercapacitor.

Developing new materials for electrochemical supercapacitors with higher energy density has recently gained tremendous impetus in the context of effective utilization of renewable energy. Herein, we report a simple one-pot synthesis of bundled nanorods of Cu(OH)2 embedded in a matrix of reduced graphene oxide (Cu(OH)2@RGO) under mild hydrothermal conditions of 80 °C for 1 h. The synthesized material shows a high BET surface area of 78.7 m(2) g(-1) and a mesoporous nature with a broad pore-size distribution consisting of structural pores as well as inter-particle pores. Raman spectroscopy suggests an intimate interaction between Cu(OH)2 and reduced graphene oxide (RGO) creating more defects by destruction of sp(2) domains which would help the defect-assisted charge transport during electrochemical processes. When investigated as an electrochemical supercapacitor, Cu(OH)2@RGO shows a high capacitance of 602 F g(-1) at 0.2 A g(-1) in 1 M KOH in a three-electrode cell configuration. Detailed electrochemical studies indicate that the Faradic processes are diffusion controlled and follow a quasi-reversible kinetics. Further, a two-electrode symmetric cell shows good energy density and power density (84.5 Wh kg(-1) at 0.55 kW kg(-1) and 20.5 Wh kg(-1) at 5.5 kW kg(-1)) characteristics demonstrating superior application potential of this common low-cost transition metal hydroxide for high performance energy storage devices.

Reversible Lithium Storage in Manganese 1,3,5-Benzenetricarboxylate Metal-Organic Framework with High Capacity and Rate Performance.

Metal organic frameworks (MOFs) with diverse structural chemistry are being projected as futuristic electrode materials for Li-ion batteries. In this work, we report synthesis of Mn-1,3,5-benzenetricarboxylate MOF by a simple solvothermal method and its application as an anode material for the first time. Scanning electron microscopy of the synthesized MOF shows a bar shaped morphology where these bars, about 1 µm wide and of varied lengths between 2 and 20 µm, are made of porous sheets containing mesoporous walls and macroporous channels. The MOF anode, when examined in the potential window of 0.01-2.0 V versus Li/Li(+), shows high specific capacities of 694 and 400 mAh g(-1) at current densities of 0.1 and 1.0 A g(-1) along with good cyclability, retention of capacity, and sustenance of the MOF network. Ex situ X-ray diffraction, Fourier transform infrared, and X-ray photoelectron spectroscopy studies on the electrode material at different states of charge suggest that the usual conversion reaction for Li storage might not be applicable in this case. Conjugated carboxylates being weakly electron withdrawing ligands with a stronger π-π interaction, a probable alternative Li storage mechanism has been proposed that involves the organic moiety. The present results show promise for applying Mn-1,3,5-benzenetricarboxylate MOF as high performance <2 V anode.

Extraordinarily high pseudocapacitance of metal organic framework derived nanostructured cerium oxide.

MOF derived CeO2 showed a pseudocapacitance of 1204 F g(-1) at 0.2 A g(-1), far exceeding its theoretical capacitance (560 F g(-1)). The present study demonstrates that combination of a two-way strategy, controlled nano-architecture and redox active electrolyte additive, could potentially alleviate both low energy density and capacitance fading issues plaguing the current metal oxide pseudocapacitors.

Interconnected network of MnO2 nanowires with a "cocoonlike" morphology: redox couple-mediated performance enhancement in symmetric aqueous supercapacitor.

Low electronic conductivity and slow faradic processes limit the performance of MnO2 as an electrochemical pseudocapacitor with respect to cycling and power density. Herein, we report preparation of single-phase α-MnO2, composed of an interconnected nanowire network with "cocoonlike" morphology, and its application as electrode in a symmetric aqueous supercapacitor. Increased "effective" surface area, coexistence of micropores and mesopores, and enhanced electron transport in these nanowire networks result in a specific pseudocapacitance (CS) of 775 F·g(-1) in 3 M KOH, derived from cyclic voltammetry in the potential window of -1 to +1 V at a scan rate of 2 mV·s(-1), the highest reported for two-electrode symmetric configuration. Furthermore, introduction of K4Fe(CN)6 as a redox-active additive to KOH results in ∼7 times increase in energy density at a power density of ∼6000 W·kg(-1). The presence of the Fe(CN)6(4-)/Fe(CN)6(3-) redox couple provides an electron buffer source compensating for the slow faradic reactions. The results demonstrate that this simple approach might be an effective way to enhance the redox kinetics and reversibility of transition metal oxide-based pseudocapacitors.

Tungsten disulfide-multiwalled carbon nanotube hybrid anode for lithium-ion battery.

The present work is focused on the preparation of tungsten disulfide-multiwalled carbon nanotube (WS2-MWCNT) hybrids by simple dry grinding of WS2 and MWCNT in different proportion by weight (1:3, 1:1, 3:1). The as prepared hybrids have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM) and Raman analyses. XRD results indicated complete exfoliation of MWCNT among WS2 particles in WS2-MWCNT (3:1) and (1:1) hybrids. FESEM images showed the formation of a 3-D network in WS2-MWCNT (1:1) hybrid with uniform dispersion of MWCNT being evident from HRTEM images. Raman analysis also suggested significant interaction between WS2 and MWCNT. WS2-MWCNT (1:1) hybrid, when used as anode material in lithium ion battery, exhibited a high initial charge capacity (483 mA h g(-1)) and an improved cycling stability with over 80% retention of the first cycle capacity after 20 cycles compared to only 40% capacity retention in pristine WS2. Such enhanced electrochemical performance of WS2-MWCNT (1:1) hybrid has been attributed to synergistic effect of WS2 and MWCNT.

MoS2-MWCNT hybrids as a superior anode in lithium-ion batteries.

Molybdenum disulfide (MoS(2))-multiwalled carbon nanotube (MWCNT) hybrids have been prepared by simple dry grinding. Excellent initial charge capacity (1214 mA h g(-1)) and ~85% retention after 60 discharge-charge cycles at different current densities (100-500 mA g(-1)) make MoS(2)-MWCNT (1 : 1) hybrids a superior anode in Li-ion batteries.