The redox flow battery (RFB) has been the subject of state-of-the-art research by several groups around the world. Most work commonly involves the application of various low-cost carbon-polymer ...composites, carbon felts, cloth, paper and their different variations for the electrode materials of the RFB. Usually, the carbon-polymer composite electrode has relatively high bulk resistivity and can be easily corroded when the polarised potential on the anode is more positive than that of oxygen evolution and this kind of heterogeneous corrosion may lead to battery failure due to electrolyte leakage. Therefore, carbon electrodes with high electrical conductivity, acid-resistance and electrochemical stability are highly desirable. This review discusses such issues in depth and presents an overview on future research directions that may help commercialise RFB technology. A comprehensive discussion is provided on the advances made using nanotechnology and it is envisaged that if this is combined with ionic liquid technology, major advantages could be realised. In addition the identification of RFB failure mechanisms by means of X-ray computed nano tomography is expected to bring added benefits to the technology.
•A comprehensive coverage on carbon materials used in redox flow batteries is given.•The influence of nanotechnology and graphene is discussed in detail.•The importance of studying RFB degradation mechanisms is emphasised.
Graphene (GN) has many beneficial properties that encourage wide applications. Various manufacturing procedures are detailed in the literature but most are unable to produce GN flakes in bulk and ...usually result in toxic discharges. These techniques are also time-consuming and involve operations at high temperatures. A ‘greener’, simpler and a one-step synthesis of the material may be realised by electrochemical oxidation (or reduction) of the graphite host leading to intercalation of ions from the electrolyte (which may be aqueous, organic or an ionic liquid) followed by electrochemical exfoliation. Single- or multi-layered GN flakes can easily be produced in short periods of time, typically within 30min. This paper reviews the state-of-the-art methods reported in the literature regarding electrochemical synthesis of GN flakes as well as their properties (determined via sophisticated analytical methods such as AFM, TEM, SEM or Raman spectroscopy). This is followed by a discussion on the applications of electrochemically prepared GN flakes. Challenges and opportunities are briefly considered leading to the conclusion that the cathodic intercalation of lithium ions into graphite can produce the highest yield (>70%) of pristine GN flakes in organic electrolytes. Future work is recommended with ternary eutectic melts as electrolytes.
Production of biohydrogen has the potential to be a renewable alternative to current technologies. There are varieties of technologies for biological hydrogen production mechanisms including ...biophotolysis, photo fermentation, dark fermentation and hybrid biohydrogen production by electrochemical processes. In these studies, a review on the recent developments of biohydrogen production is presented. First, the theoretical principles of biophotolysis by cyanobacteria and green micro algae, as well as direct and indirect of biophotolysis process on hydrogen production are described. Secondly, practical aspects and fundamental of biological hydrogen production processes by photo and dark fermentation are reviewed. This work also involved comparison of the maximum H2 yield, bacterial strains, operating condition, suitable substrates, and mathematical models for fermentative hydrogen production. A new hybrid biological hydrogen production processes by using the electrochemical process is then proposed. This study can also be used to improve the basic and current knowledge about the performance of the biophotolysis, fermentative and electrochemical process in producing hydrogen gas as the alternate fuel.
In SOFC (solid oxide fuel cell) systems operating at high temperatures, temperature fluctuation induces a thermal stress in the electrodes and electrolyte ceramics; therefore, the cell temperature ...distribution is recommended to be kept as constant as possible. In the present work, a mathematical model based on first principles is presented to avert such temperature fluctuations. The fuel cell running on ammonia is divided into five subsystems and factors such as mass/energy/momentum transfer, diffusion through porous media, electrochemical reactions, and polarization losses inside the subsystems are presented. Dynamic cell-tube temperature responses of the cell to step changes in conditions of the feed streams is investigated. The results of simulation indicate that the transient response of the SOFC is mainly influenced by the temperature dynamics. It is also shown that the inlet stream temperatures are associated with the highest long term start-up time (467 s) among other parameters in terms of step changes. In contrast the step change in fuel velocity has the lowest influence on the start-up time (about 190 s from initial steady state to the new steady state) among other parameters. A NNPC (neural network predictive controller) is then implemented for thermal stress management by controlling the cell tube temperature to avoid performance degradation by manipulating the temperature of the inlet air stream. The regulatory performance of the NNPC is compared with a PI (proportional–integral) controller. The performance of the control system confirms that NNPC is a non-linear-model-based strategy which can assure less oscillating control responses with shorter settling times in comparison to the PI controller.
•Effect of the operating parameters on the fuel cell temperature is analysed.•A neural network predictive controller (NNPC) is implemented.•The performance of NNPC is compared with the PI controller.•A detailed model is used for the NNPC for the first time in the literature.
•Six means of functionalizing graphene electrochemically is reviewed.•Electrochemical functionalization is relatively new to other standard methods.•The technique is expected to improve graphene's ...application range considerably.
Graphene is a 2D allotrope of carbon with exciting properties such as extremely high electronic conductivity and superior mechanical strength. It has considerable potential for applications in fields such as bio-sensors, electrochemical energy storage and electronics. In most cases, graphene has been functionalized and modified with other materials to prepare composites. This work reviews the electrochemical modification of graphene. Commencing with a brief history, a summary of several different means of modifying graphene to effect diverse applications is provided. This is followed by a discussion on different composite materials that have been prepared with reduced graphene oxide prior to moving onto a detailed consideration of six different methods of electrochemically modifying graphene to prepare composite materials. These methods involve cathodic reduction of graphene oxide, electrophoretic deposition, electro-deposition techniques, electrospinning, electrochemical doping and electrochemical polymerization. Finally a consideration on the applications of electrochemically modified graphene composite materials in various fields is presented prior to discussing some prospects in enhancing the electrochemical process to realize excellent and economic composite materials in bulk.
Growth of plants is severely reduced due to water stress by affecting photosynthesis including photosystem II (PSII) activity and electron transport. This study emphasised on comparative and priority ...targeted changes in PSII activity due to progressive drought in seven populations of Panicum antidotale (P. antidotale) collected from Cholistan Desert and non-Cholistan regions. Tillers of equal growth of seven populations of P. antidotale grown in plastic pots filled with soil were subjected progressive drought by withholding water irrigation for three weeks. Progressive drought reduced the soil moisture content, leaf relative water content, photosynthetic pigments and fresh and dry biomass of shoots in all seven populations. Populations from Dingarh Fort, Dingarh Grassland and Haiderwali had higher growth than those of other populations. Cholistani populations especially in Dingarh Grassland and Haiderwali had greater ability of osmotic adjustment as reflected by osmotic potential and greater accumulation of total soluble proteins. Maximum H2O2 under water stress was observed in populations from Muzaffargarh and Khanewal but these were intermediate in MDA content. Under water stress, populations from Muzaffargarh and Dingarh Fort had greater K+ accumulation in their leaves. During progressive drought, non-Cholistani populations showed complete leaf rolling after 23 days of drought, and these populations could not withstand with more water stress condition while Cholistani populations tolerated more water stress condition for 31 days. Moreover, progressive drought caused PSII damages after 19 days and it became severe after 23 days in non-Cholistani populations of P. antidotale than in Cholistani populations.
The rapid advancement of nanotechnology has created a vast array of engineered nanomaterials (ENMs) which have unique physical (size, shape, crystallinity, surface charge) and chemical (surface ...coating, elemental composition and solubility) attributes. These physicochemical properties of ENMs can produce chemical conditions to induce a pro-oxidant environment in the cells, causing an imbalanced cellular energy system dependent on redox potential and thereby leading to adverse biological consequences, ranging from the initiation of inflammatory pathways through to cell death. The present study was designed to evaluate size-dependent cellular interactions of known biologically active silver nanoparticles (NPs, Ag-15nm, Ag-30nm, and Ag-55nm). Alveolar macrophages provide the first defense and were studied for their potential role in initiating oxidative stress. Cell exposure produced morphologically abnormal sizes and adherence characteristics with significant NP uptake at high doses after 24 h. Toxicity evaluations using mitochondrial and cell membrane viability along with reactive oxygen species (ROS) were performed. After 24 h of exposure, viability metrics significantly decreased with increasing dose (10−75 μg/mL) of Ag-15nm and Ag-30nm NPs. A more than 10-fold increase of ROS levels in cells exposed to 50 μg/mL Ag-15nm suggests that the cytotoxicity of Ag-15nm is likely to be mediated through oxidative stress. In addition, activation of the release of traditional inflammatory mediators were examined by measuring levels of cytokines/chemokines, including tumor necrosis factor (TNF-α), macrophage inhibitory protein (MIP-2), and interleukin-6 (IL-6), released into the culture media. After 24 h of exposure to Ag-15nm nanoparticles, a significant inflammatory response was observed by the release of TNF-α, MIP-2, and IL-1β. However, there was no detectable level of IL-6 upon exposure to silver nanoparticles. In summary, a size-dependent toxicity was produced by silver nanoparticles, and one predominant mechanism of toxicity was found to be largely mediated through oxidative stress.
This highlight summarises electrochemical approaches for the generation and utilization of alkoxy radicals, predominantly focusing on recent advances (2012-present). The application of ...electrochemically generated alkoxy radicals in a diverse range of transformations is described, including discussion on reaction mechanisms, scope and limitations, in addition to highlighting future challenges in this burgeoning area of sustainable synthesis.
This highlight summarises electrochemical approaches for the generation and utilization of alkoxy radicals, predominantly focusing on recent advances (2012-present).
Context. Magnetospheric accretion has been thoroughly studied in young stellar systems with full non-evolved accretion disks, but it is poorly documented for transition disk objects with large inner ...cavities. Aims. We aim at characterizing the star-disk interaction and the accretion process onto the central star of LkCa 15, a prototypical transition disk system with an inner dust cavity that is 50 au wide. Methods. We obtained quasi-simultaneous photometric and spectropolarimetric observations of the system over several rotational periods. We analyzed the system light curve and associated color variations, as well as changes in spectral continuum and line profile to derive the properties of the accretion flow from the edge of the inner disk to the central star. We also derived magnetic field measurements at the stellar surface. Results. We find that the system exhibits magnetic, photometric, and spectroscopic variability with a period of about 5.70 days. The light curve reveals a periodic dip, which suggests the presence of an inner disk warp that is located at the corotation radius at about 0.06 au from the star. Line profile variations and veiling variability are consistent with a magnetospheric accretion model where the funnel flows reach the star at high latitudes. This leads to the development of an accretion shock close to the magnetic poles. All diagnostics point to a highly inclined inner disk that interacts with the stellar magnetosphere. Conclusions. The spectroscopic and photometric variability on a timescale of days to weeks of LkCa 15 is remarkably similar to that of AA Tau, the prototype of periodic dippers. We therefore suggest that the origin of the variability is a rotating disk warp that is located at the inner edge of a highly inclined disk close to the star. This contrasts with the moderate inclination of the outer transition disk seen on the large scale and thus provides evidence for a significant misalignment between the inner and outer disks of this planet-forming transition disk system.
An integrated economic/ecological model is built to address tradeoffs between biodiversity conservation and two marketable rangeland ecosystem services: cattle grazing and elk hunting. The ecology is ...represented by an eleven species food web in which individual optimizing plants and animals engage in competitive and predator/prey relationships. The ecological model defines a steady-state set of sustainable grazing and hunting options, and for each option, biodiversity is measured using an index defined over the eleven species. In linking the ecology to the economics, social welfare depends on grazing profits and hunter net benefits. The problem can be stated as maximizing economic welfare over two ecosystem services, subject to their sustainable use and subject to a target level of biodiversity. A numerical application with economic and biological data from the Western United States is used to determine sustainable grazing and hunting options for alternative biodiversity levels, and to select the option that maximizes welfare.
•An 11-species food web yields two ecosystem services: elk harvests and cattle grazing.•Elk growth curves are used to derive a sustainability frontier.•An economic optimum over harvests and grazing is constrained by the frontier.•Conservation of biodiversity may place further constraints on the optimum.•Real data from the Western United States illustrates the model's potential.
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