Influence of imidazolium-based ionic liquid electrolytes on the performance of nano-structured MnO2 hollow spheres as electrochemical supercapacitor

Use of room temperature ionic liquids (ILs) as electrolytes with a wider potential window offers scope for developing high energy density supercapacitors for efficient energy storage. In this work, a comparative study on the performance of nanostructured MnO2 hollow spheres as electrochemical supercapacitor was made by fabricating activated carbon (AC)//MnO2 asymmetric supercapacitor cells using imidazolium-based ILs as electrolytes. Mesoporous MnO2 hollow spheres were synthesized through a simple low temperature (80 degrees C) solvothermal method by reduction of KMnO4 under acidic condition in presence of Cu-3(1,3,5-benzenetricarboxylate)(2) metal organic framework (MOF) in the precursor solution, which acts as the source of Cu2+ playing a crucial role for the formation of the hollow spheres. Four different ILs were investigated from combinations of two different cations 1-ethyl-3-methylimidazolium (EMI+) and 1-butyl-3-methylimidazolium (BMI+)] and four different anions hexaflurophosphate (PF6(-)), tetrafluoroborate (BF4(-)), trifluromethanesulfonate (Otf(-)) and bis(trifluromethylsulfonyl) imide (TFSI-)]. Influences of the physico-chemical properties such as ionic size, nucleophilicity, viscosity of the IL on the electrochemical properties are discussed. A high energy density of 163 W h kg(-1), which is comparable to the energy density of a lithium-ion battery, could be achieved with EMIMBF4 as electrolyte. The present findings would help in further research for developing IL-based supercapacitors

Membrane-Bound IL-21 Promotes Sustained Ex Vivo Proliferation of Human Natural Killer Cells

NK cells have therapeutic potential for a wide variety of human malignancies. However, because NK cells expand poorly in vitro, have limited life spans in vivo, and represent a small fraction of peripheral white blood cells, obtaining sufficient cell numbers is the major obstacle for NK-cell immunotherapy. Genetically-engineered artificial antigen-presenting cells (aAPCs) expressing membrane-bound IL-15 (mbIL15) have been used to propagate clinical-grade NK cells for human trials of adoptive immunotherapy, but ex vivo proliferation has been limited by telomere shortening. We developed K562-based aAPCs with membrane-bound IL-21 (mbIL21) and assessed their ability to support human NK-cell proliferation. In contrast to mbIL15, mbIL21-expressing aAPCs promoted log-phase NK cell expansion without evidence of senescence for up to 6 weeks of culture. By day 21, parallel expansion of NK cells from 22 donors demonstrated a mean 47,967-fold expansion (median 31,747) when co-cultured with aAPCs expressing mbIL21 compared to 825-fold expansion (median 325) with mbIL15. Despite the significant increase in proliferation, mbIL21-expanded NK cells also showed a significant increase in telomere length compared to freshly obtained NK cells, suggesting a possible mechanism for their sustained proliferation. NK cells expanded with mbIL21 were similar in phenotype and cytotoxicity to those expanded with mbIL15, with retained donor KIR repertoires and high expression of NCRs, CD16, and NKG2D, but had superior cytokine secretion. The mbIL21-expanded NK cells showed increased transcription of the activating receptor CD160, but otherwise had remarkably similar mRNA expression profiles of the 96 genes assessed. mbIL21-expanded NK cells had significant cytotoxicity against all tumor cell lines tested, retained responsiveness to inhibitory KIR ligands, and demonstrated enhanced killing via antibody-dependent cell cytotoxicity. Thus, aAPCs expressing mbIL21 promote improved proliferation of human NK cells with longer telomeres and less senescence, supporting their clinical use in propagating NK cells for adoptive immunotherapy

Metal hydroxides as a conversion electrode for lithium-ion batteries: a case study with a Cu(OH)(2) nanoflower array

Conversion electrodes, the materials of choice for the next generation lithium-ion battery (LIB), are mainly limited to metal oxides. In this work, we have investigated the electrochemical performance of chemically synthesized Cu(OH)(2) nanoflower arrays. A 50 : 50 composite of Cu(OH)(2) and multiwalled carbon nanotubes (MWCNTs) showed a reversible capacity of 522 mA h g(-1) at a current density of 0.1 mA cm(-2) with 95% retention of capacity after 50 cycles. The results demonstrate that it can be a competitive choice over the corresponding oxides as an anode for LIB

Superior lithium storage properties of Fe-2(MoO4)(3)/MWCNT composite with a nanoparticle (0D)-nanorod (1D) hetero-dimensional morphology

Synthesis of nanostructures with pre-designed morphology has recently gained tremendous research attention for achieving enhanced performance. Herein, we report synthesis of hetero-dimensional hybrid nanostructure of Fe-2(MoO4)(3) consisting of nanorods (length 90-170 nm, dia similar to 30 nm) in which spherical nanoparticles (dia 5-10 nm) are embedded. We also report the electrochemical properties of synergic Fe-2(MoO4)(3)/MWCNT composites as lithium-ion battery anode for the first time. Here, 1D Fe-2(MoO4)(3) nanorods serve as a strain accommodative matrix imparting stability while the entrenched OD Fe-2(MoO4)(3) nanoparticles offer a large number of active sites yielding high capacity. Due to high surface to volume ratio of the composites, the Li+ ion diffusion length is shortened leading to a faster kinetics and improved the rate performance. Moreover, MWCNT provides an effective conduction network for electron transport during lithiation/delithiation process and at the same time, serves as a strain-buffer preserving mechanical integrity of the composite electrode. This three-way strategy results in a specific capacity of 1321 mAh g(-1) for a 50:50 wt% composite of Fe-2(MoO4)(3) and MWCNT. Even at a high current density of 1.0 mA cm(-2) (1200 mA g(-1)), capacity of 600 mAh g(-1) could be obtained. Further, 82% retention of capacity is observed after 200 cycles at 0.1 mA cm(-2). Importantly, no appreciable change in morphology is observed with discharge-charge cycling. (C) 2016 Elsevier B.V. All rights reserved

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 alpha-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 (C-S) 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 similar to 7 times increase in energy density at a power density of similar to 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

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 degrees 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

Electrochemical energy storage in Mn2O3 porous nanobars derived from morphology-conserved transformation of benzenetricarboxylate-bridged metal-organic framework

Tailoring the morphology of mesoporous nanostructures toward performance enhancement plays a key role in developing efficient energy storage devices. Herein, we report the formation of well crystallized Mn2O3 mesoporous nanobars through simple exo-templating of a manganese 1,3,5-benzenetricarboxylate metal-organic framework (Mn-BTC MOF) by thermal treatment whereby the general morphology of the parent MOF is conserved, but with more voids and spaces. The parent Mn-BTC MOF was synthesized by solvothermal reaction of trimesic acid with manganese nitrate in alcoholic solution. The MOF-derived Mn2O3 was characterized by XRD, field-emission SEM, high-resolution TEM, and N-2 adsorption/desorption isotherm measurements. When examined as an anode material for lithium-ion batteries in the potential windows of 0.01-3.0 V and 0.01-2.0 V, high reversible specific capacities of 849 and 778 mAh g(-1) were obtained. It was found that the electrochemical processes are more reversible when cycled in the 2 V window. A steady capacity of similar to 410 mAh g(-1) was observed after 300 continuous cycles at similar to C/5.5 exhibiting good cycling stability in the 2 V window. When tested as a pseudocapacitor electrode in a three-electrode configuration, a specific capacitance of 250 F g(-1) at 0.2 A g(-1) could be achieved. Further, to demonstrate practical applicability, two-electrode asymmetric supercapacitor pouch cells were assembled with Mn2O3 as the positive electrode and commercial activated carbon as the negative electrode which showed an ultrahigh energy density of 147.4 W h kg(-1) at a power density of 1004 W kg(-1). The present work shows the potential of a MOF derived route for obtaining metal oxides with desired nano-architectures for electrochemical applications with high performance

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

Cu-3(1,3,5-benzenetricarboxylate)(2) metal-organic framework: A promising anode material for lithium-ion battery

Versatility and diversity in the nature of bonding between metal ions and polyfunctional organic molecules render metal organic frameworks (MOFs) as interesting materials for a variety of applications. In this work, we have examined the electrochemical properties of solvothermally synthesized Cu-1,3,5-benzenetricarboxylate MOF as a novel anode material for lithium-ion battery (LIB). At a current density of 96 mAg(-1), reversible capacity of 740 mAhg(-1) is achieved, the highest ever reported for a MOF. Even at a high current density of 383 mAg(-1), specific capacity of 474 mAg(-1) is observed with no apparent fading up to 50 cycles. Ex-situ studies on the electrode material in the charged and discharged state by X-ray diffraction, Fourier transformed infra-red spectroscopy and X-ray photoelectron spectroscopy suggest that Li storage in Cu-3(BTC)(2) MOF might not be fully explained by the conventional conversion mechanism that involves reduction into corresponding metal and subsequent oxidation. Rather, redox participation of the organic moiety is indicated. The present results would help in designing new MOFs for LIB applications. (C) 2016 Elsevier Inc. All rights reserved

Redox-active organic molecular salt of 1,2,4-benzenetricarboxylic acid as lithium-ion battery anode

Hybrid organic–inorganic materials, particularly with a framework structure, have recently attracted much attention as redox electrode. In this work, we report for the first time, the electrochemical properties of redox-active organic molecular Li-salt derived from 1,2,4-benzenetricarboxylic acid (1,2,4-H3BTC) as lithium-ion battery (LIB) anode. The organic molecular salt (1,2,4-Li-BTC), prepared by a simple low temperature (80 °C) solvothermal process, delivers a first cycle charge capacity of 162 mAhg−1. Further, it is shown that preparing a composite electrode with 8 wt% MWCNT improves charge transport and alleviates the dissolution problem, resulting in steady cycling behaviour and good rate performance. The results show promise for this new class of anode with flat charge discharge profiles and a convenient working potential of ∼1.2 V vs. Li+/Li