Redox-Enhanced Electrochemical Capacitors: Electrolyte Design and Device Engineering

Electrochemical energy storage is increasingly important as the world decarbonizes and electrifies. Research in this area requires compromise between properties that are often mutually exclusive, including power, energy, lifetime, efficiency, operating temperature, safety, and cost. Electric double layer capacitors (EDLCs) exhibit high power and outstanding cycle life compared to secondary batteries, but have low specific energy, limiting applications. Redox-enhanced electrochemical capacitors (redox ECs) are a class of augmented electric double-layer capacitors utilizing reversible redox reactions of soluble redox couples in the electrolyte to add faradaic charge storage. These systems offer increased energy density, efficient power delivery, and simple construction. We study a range of redox-active electrolytes to clarify operating mechanisms and formalize design rules for high-performance. Our investigations focus on dual-redox ECs, which attain higher energy density by employing a pair of distinct redox couples, with each operating at a different electrode. Simplicity is important both in terms of the mechanistic aspects of the electrochemical redox chemistry and for system cost considerations. A single ionic molecular entity that intrinsically delivers both distinct redox couples is preferable over two separate redox-active electrolytes. In this context, we have identified specific viologen bromide salts as particularly promising aqueous redox-active electrolytes for dual-redox ECs. While charging, Br– is oxidized to Br3– at the positive electrode and the viologen dication (V2+) is reduced to the stable monocation radical (V+•) at the negative electrode. The reverse processes occur during discharge, providing a high-capacity faradaic discharge plateau and attaining an energy density of ~20 Wh/L. The viologen bromide system shows unusually high Coulombic efficiency and low self-discharge rates for an aqueous redox-EC. This was initially attributed to strong adsorption of the Br3– and V+• to the activated carbon electrodes, but a more detailed analysis confirms that the behavior is due to two electroprecipitation mechanisms. In these mechanisms, each ion acts as a charge-storing redox couple at one electrode and as a complexing agent at the other electrode. The processes are highly reversible and cells show negligible capacity fade even after 20,000 cycles. The devices use conventional activated carbon electrodes, and because crossover is not a concern and self-discharge is suppressed, a simple inexpensive cellulose separator is sufficient and more costly ion-selective membranes are not required. Based on our understanding of solid complexation in redox ECs, we studied in detail the confinement of charged redox species in porous electrodes with liquid-to-solid phase transitions to mitigate self-discharge. We demonstrate that in addition to viologens, tetrabutylammonium cations induce reversible solid complexation of Br2/Br3–. This mechanism slows cross-diffusion of Br3–, stabilizes the reactive bromine generated during charging, and can be broadly used as a positive electrode to balance the capacity of a wide variety of pseudocapacitive or battery-type negative electrodes. In the final component of this work we consider the challenges of scaling up these systems for practical application. We address corrosion of metallic current collectors, which is a common device design challenge for high-power aqueous electrochemical energy storage devices, by designing a bipolar pouch cell using electrochemically stable carbon-polymer composite current collectors. In order to show the versatility of this approach, we construct a high-power redox EC/battery hybrid using a zinc metal anode and an activated carbon cathode with tetrabutylammonium-complexed bromide catholyte. This system achieves excellent power and energy performance, with negligible capacity degradation over more than 3000 cycles.Throughout the dissertation we compare the performance and properties of our dual redox ECs to those of the current state-of-the-art conventional energy storage systems and other redox-enhanced energy storage systems and we close with comments on economic analysis and the future of redox enhanced electrochemical capacitors

Transforming growth factor-b regulation of proteoglycan synthesis in vascular smooth muscle: Contribution to lipid binding and accelerated atherosclerosis in diabetes

Atherosclerosis is accelerated in the setting of diabetes, but the factors driving this phenomenon remain elusive. Hyperglycemia leads to elevated levels of transforming growth factor (TGF)-b and TGF-b has been implicated as a factor in atherosclerosis. Given the established association between hyperglycemia and elevated TGF-b, it is plausible that elevated TGF-b levels in diabetes play a pathogenic role in the development of accelerated atherosclerosis. TGF-b is a potent regulator of extracellular matrix synthesis, including many actions on proteoglycan synthesis that lead to increased binding to low-density lipoprotein and therefore potentially increased lipid retention in the vessel wall and accelerated atherosclerosis. TGF-b signals through the canonical TGF-b receptor I-mediated phosphorylation of Smad transcription factors and TGF-b signaling is also known to involve, positively and negatively, interactions with the mitogen-activated protein kinase pathways. The focus of the present review is on the effects of TGF-b on proteoglycan synthesis in vascular smooth muscle and particularly the signaling pathways through which TGF-b exerts its effects, because those pathways may be therapeutic targets for the prevention of pathological modifications in the proteoglycan component of the vessel wall in the vascular diseases of diabetes

Metallic nanoparticle on micro ring resonator for bio optical detection and sensing

We have investigated the unique effects of metallic nanoparticle on the ring resonator, especially multiple Au nanoparticles on the micro ring resonator with the 4-port configuration on chip. For the Au nanoparticle, because it has smaller real refractive index than air and large absorption refractive index, we found that there is a blue shift for the ring resonance wavelength, instead of red shift normally observed for dielectric nanoparticles. The drop port intensity is strongly dependent on both number and size of nanoparticles, while relatively independent on position of nanoparticles. The correlation between the penetration depth of Au and the resonance mode evanescent tail is also discussed to reveal the unique properties of Au nanoparticle to be used for detection, sensing and nano medicine.Comment: Accepte

G1 Domain of Versican Regulates Hyaluronan Organization and the Phenotype of Cultured Human Dermal Fibroblasts

Variants of versican have wide-ranging effects on cell and tissue phenotype, impacting proliferation, adhesion, pericellular matrix composition, and elastogenesis. The G1 domain of versican, which contains two Link modules that bind to hyaluronan (HA), may be central to these effects. Recombinant human G1 (rhG1) with an N-terminal 8 amino acid histidine (His) tag, produced in Nicotiana benthamiana, was applied to cultures of dermal fibroblasts, and effects on proliferation and pericellular HA organization determined. rhG1 located to individual strands of cell surface HA which aggregated into structures resembling HA cables. On both individual and aggregated strands, the spacing of attached rhG1 was similar (~120 nm), suggesting interaction between rhG1 molecules. Endogenous V0/V1, present on HA between attached rhG1, did not prevent cable formation, while treatment with V0/V1 alone, which also bound to HA, did not induce cables. A single treatment with rhG1 suppressed cell proliferation for an extended period. Treating cells for 4 weeks with rhG1 resulted in condensed layers of elongated, differentiated α actin-positive fibroblasts, with rhG1 localized to cell surfaces, and a compact extracellular matrix including both collagen and elastin. These results demonstrate that the G1 domain of versican can regulate the organization of pericellular HA and affect phenotype

Hyaluronan is crucial for stem cell differentiation into smooth muscle lineage

Deciphering the extracellular signals that regulate SMC differentiation from stem cells is vital to further our understanding of the pathogenesis of vascular disease and for development of cell-based therapies and tissue engineering. Hyaluronan (HA) has emerged as an important component of the stem cell niche, however its role during stem cell differentiation is a complicated and inadequately defined process. This study aimed to investigate the role of HA in embryonic stem cell (ESC) differentiation toward a SMC lineage. ESCs were seeded on collagen-IV in differentiation medium to generate ESC-derived SMCs (esSMCs). Differentiation coincided with increased HA synthase (HAS) 2 expression, accumulation of extracellular HA and its assembly into pericellular matrices. Inhibition of HA synthesis by 4-methylumbelliferone (4MU), removal of the HA coat by hyaluronidase (HYAL) or HAS2 knockdown led to abrogation of SMC gene expression. HA activates ERK1/2 and suppresses EGFR signaling pathways via its principle receptor, CD44. EGFR inactivation coincided with increased binding to CD44, which was further augmented by addition of high molecular weight (HMW)-HA either exogenously or via HAS2 overexpression through adenoviral gene transfer. HMW-HA-stimulated esSMCs displayed a functional role in vascular tissue engineering ex vivo, vasculogenesis in a matrigel plug model and SMC accumulation in neointimal lesions of vein grafts in mice. These findings demonstrate that HAS2-induced HA synthesis and organization drives ESC-SMC differentiation. Thus, remodeling of the HA microenvironment is a critical step in directing stem cell differentiation toward a vascular lineage, highlighting HA as a potential target for treatment of vascular diseases

Multidimensional physical activity: An opportunity not a problem

Our research shows that no single metric will adequately reflect an individual’s physical activity because multiple biologically-important dimensions are independent and unrelated. We propose that there is an opportunity to exploit this multidimensional characteristic of physical activity in order to improve personalised feedback and offer physical activity options and choices that are tailored to an individual’s needs and preferences

Design of aqueous redox-enhanced electrochemical capacitors with high specific energies and slow self-discharge

Electrochemical double-layer capacitors exhibit high power and long cycle life but have low specific energy compared with batteries, limiting applications. Redox-enhanced capacitors increase specific energy by using redox-active electrolytes that are oxidized at the positive electrode and reduced at the negative electrode during charging. Here we report characteristics of several redox electrolytes to illustrate operational/self-discharge mechanisms and the design rules for high performance. We discover a methyl viologen (MV)/bromide electrolyte that delivers a high specific energy of ~14 Wh kg⁻¹ based on the mass of electrodes and electrolyte, without the use of an ion-selective membrane separator. Substituting heptyl viologen for MV increases stability, with no degradation over 20,000 cycles. Self-discharge is low, due to adsorption of the redox couples in the charged state to the activated carbon, and comparable to cells with inert electrolyte. An electrochemical model reproduces experiments and predicts that 30–50 Wh kg⁻¹ is possible with optimization.This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Nature Publishing Group. The published article can be found at: http://www.nature.com/ncomms/2015/150804/ncomms8818/full/ncomms8818.htm

Two-site diamond-like point defects as new single-photon emitters

In this small review, we recall two promising candidates for biomarker nanosystems, in which a two-site defect embedded in a diamond-like lattice makes a single-photon source. The two candidates are the silicon-vacancy defect in diamond, and the carbon antisite-vacancy pair in 4H silicon carbide. These defects, which by symmetry resemble to the famous nitrogen-vacancy defect in diamond, bear an exact or nearly exact C3v symmetry, giving them selection rules which lead their important magnetooptical properties. The embedding diamond-like crystal lattice not only determines the symmetry of two-site defects, but also ensure a nontoxic vehicle on which they reside; a definitive requirement against biomarker nanosystems. In the silicon-vacancy case, the size of the biomarker system is also an important feature. Nanoparticles of the embedding crystal do not exceed the size of molecular clusters, in order to be able to aid measuring all types of relevant biomolecular processes

Versican-A Critical Extracellular Matrix Regulator of Immunity and Inflammation.

The extracellular matrix (ECM) proteoglycan, versican increases along with other ECM versican binding molecules such as hyaluronan, tumor necrosis factor stimulated gene-6 (TSG-6), and inter alpha trypsin inhibitor (IαI) during inflammation in a number of different diseases such as cardiovascular and lung disease, autoimmune diseases, and several different cancers. These interactions form stable scaffolds which can act as "landing strips" for inflammatory cells as they invade tissue from the circulation. The increase in versican is often coincident with the invasion of leukocytes early in the inflammatory process. Versican interacts with inflammatory cells either indirectly via hyaluronan or directly via receptors such as CD44, P-selectin glycoprotein ligand-1 (PSGL-1), and toll-like receptors (TLRs) present on the surface of immune and non-immune cells. These interactions activate signaling pathways that promote the synthesis and secretion of inflammatory cytokines such as TNFα, IL-6, and NFκB. Versican also influences inflammation by interacting with a variety of growth factors and cytokines involved in regulating inflammation thereby influencing their bioavailability and bioactivity. Versican is produced by multiple cell types involved in the inflammatory process. Conditional total knockout of versican in a mouse model of lung inflammation demonstrated significant reduction in leukocyte invasion into the lung and reduced inflammatory cytokine expression. While versican produced by stromal cells tends to be pro-inflammatory, versican expressed by myeloid cells can create anti-inflammatory and immunosuppressive microenvironments. Inflammation in the tumor microenvironment often contains elevated levels of versican. Perturbing the accumulation of versican in tumors can inhibit inflammation and tumor progression in some cancers. Thus versican, as a component of the ECM impacts immunity and inflammation through regulating immune cell trafficking and activation. Versican is emerging as a potential target in the control of inflammation in a number of different diseases