Conducting gel-fibres based on carrageenan, chitosan and carbon nanotubes

A simple continuous flow wet-spinning method for assembling fibres consisting of two oppositely charged biopolymers (chitosan and carrageenan) and carbon nanotubes is reported. It was observed that the order in which the biopolymers are added, i.e. spinning chitosan into one of the carrageenans (or vice versa), affects the fibre composition as well as the resulting electrical and mechanical properties. The addition of carbon nanotubes into the fibres was found to improve Young's modulus values coupled with a significant improvement in the electrical conductivity by up to 6 orders of magnitude.

Spinning Carbon Nanotube-Gel Fibers Using Polyelectrolyte Complexation

Biopolymer-single walled carbon nanotube (SWNT)-biopolymer fibers were prepared using a continuous flow spinning approach. Polyelectrolyte complexation was facilitated by injecting a SWNT-biopolymer dispersion into a coagulation bath containing a biopolymer of opposite charge. We showed that the ability to spin fibers and their properties depend on processing conditions such as polyelectrolyte pH, sonolysis regime (conditions employed to disperse SWNT) and the order of adding the anionic and cationic biopolymer solutions. Maximizing the ionic nature through changes in the pH increased spin-ability, while combining a sonicated dispersion with an as-prepared (non-sonicated) polyelectrolyte solution allowed us to optimize sonolysis conditions while retaining spin-ability of fibers with smooth surface morphology. Addition of the cationic biopolymer-SWNT dispersion to the anionic biopolymer solution resulted in mechanical reinforcement with the increase in SWNT loading fraction. All fibers decreased their electrical resistance upon exposure to water vapor.

On choosing a reference redox system for electrochemical measurements: A cautionary tale

The potential of a quasi-reference electrode can be determined by introducing an internal reference redox system (IRRS) which comprises either the oxidizable or reducible form of a reversible (and, ideally, outer-sphere) redox couple and then observing the cyclic voltammetric responses. The objective is to choose the IRRS so that the cyclic voltammetric response for the simultaneously present electroactive analyte system (ANS) can be observed independently of the IRRS response. We identify three fundamental paradigms describing the relative positioning of the IRRS and ANS on the potential scale, the operative redox components for the IRRS and ANS, and the starting potential (E start), reversing potential (E rev), and ending potential (E end) for the cyclic voltammetric scan as follows: paradigm A, an optimal paradigm which can produce completely independent cyclic voltammetric responses for the IRRS or for ANS; paradigm B, a less-than-optimal paradigm which can produce an independent cyclic voltammetry (CV) response for the ANS or a mixed response for the IRRS with that response on top of the ANS response; paradigm C, a problematic paradigm that can produce an independent CV response for the IRRS or a mixed response for the ANS with that response on top of the IRRS response; and any mixed response produces a thermodynamically favored redox cross-reaction which couples the IRRS and ANS systems and which can complicate the analysis of the ANS and IRRS responses. The conclusion is that paradigm C is to be avoided.

Empowering the smart grid : can redox batteries be matched to renewable energy systems for energy storage?

The charging of an undivided cerium–zinc redox battery by various current waveforms some of which mimic the output of renewable energy (solar, wind, tidal, biofuel burning) to electricity transducers is considered in this work, where the battery operates through diffusion-only conditions, and is discharged galvanostatically. Under reasonable assumption, the mathematical model developed enables the observation that the performance characteristic of the cells charged with a constant power input differentiates between the various current–charge waveforms, with cell geometry and electrode kinetics playing subtle, but significant, roles; in particular, high efficiency is observed for sunlight-charged batteries which are thin and suffer no corrosion of the sacrificial electrode, and which have already experienced a charge–discharge cycle. The performance characteristics of the systems are interpreted in the light of consequences for smart grid realisation, and indicate that, for a constant power input, the most matched renewable is biofuel burning with a current output that linearly increases with time.

Altering the redox state of skeletal muscle by glutathione depletion increases the exercise-activation of PGC-1α

We investigated the relationship between markers of mitochondrial biogenesis, cell signaling, and antioxidant enzymes by depleting skeletal muscle glutathione with diethyl maleate (DEM) which resulted in a demonstrable increase in oxidative stress during exercise. Animals were divided into six groups: (1) sedentary control rats; (2) sedentary rats + DEM; (3) exercise control rats euthanized immediately after exercise; (4) exercise rats + DEM; (5) exercise control rats euthanized 4 h after exercise; and (6) exercise rats + DEM euthanized 4 h after exercise. Exercising animals ran on the treadmill at a 10% gradient at 20 m/min for the first 30 min. The speed was then increased every 10 min by 1.6 m/min until exhaustion. There was a reduction in total glutathione in the skeletal muscle of DEM treated animals compared to the control animals (P < 0.05). Within the control group, total glutathione was higher in the sedentary group compared to after exercise (P < 0.05). DEM treatment also significantly increased oxidative stress, as measured by increased plasma F2-isoprostanes (P < 0.05). Exercising animals given DEM showed a significantly greater increase in peroxisome proliferator activated receptor γ coactivator-1α (PGC-1α) mRNA compared to the control animals that were exercised (P < 0.05). This study provides novel evidence that by lowering the endogenous antioxidant glutathione in skeletal muscle and inducing oxidative stress through exercise, PGC-1α gene expression was augmented. These findings further highlight the important role of exercise induced oxidative stress in the regulation of mitochondrial biogenesis.

Enhanced thermo-electrochemical power using carbon nanotube additives in ionic liquid redox electrolytes

Waste heat recovery with thermo-electrochemical cells is limited by their low power and conversion efficiencies. Here we explore ionic liquid electrolytes mixed with multiwall carbon nanotubes (MWCNTs) as alternative electrolytes for thermo-electrochemical cells. The results show that, upon addition of MWCNTs, the combination of interfacial polarization and ion pair dissociation reduces mass transfer resistances and enhances the power of thermo-electrochemical cells at low weight percentage of MWCNTs by up to 30%. This occurs in spite of reduced open circuit voltage due to percolated networks.

Excellent electrochemical performance of LiFe0.4Mn0.6PO4 microspheres produced using a double carbon coating process

Composite LiFe0.4Mn0.6PO4/C microspheres are considered advanced cathode materials for electric vehicles and other high-energy density applications due to their advantages of high energy density and excellent cycling stability. LiFe0.4Mn0.6PO4/C microspheres have been produced using a double carbon coating process employing traditional industrial techniques (ball milling, spray-drying and annealing). The obtained LiFe0.4Mn0.6PO4 microspheres exhibit a high discharge capacity of around 166 mA h g-1 at 0.1 C and excellent rate capabilities of 132, 103, and 72 mA h g-1 at 5, 10, and 20 C, respectively. A reversible capacity of about 152 mA h g-1 after 500 cycles at a current density of 1 C indicates an outstanding cycling stability. The excellent electrochemical performance is attributed to the micrometer-sized spheres of double carbon-coated LiFe0.4Mn0.6PO4 nanoparticles with improved electric conductivity and higher Li ion diffusion coefficients, ensuring full redox reactions of all nanoparticles. The results show that the advanced high-energy density cathode materials can be produced using existing industry techniques.