The Fundão dam collapse occurred on November 2015 in Mariana city (Brazil), provoking a series of ecological impacts over the Doce river basin and its nearshore environment. However many impacts over ...fishery target fauna (fish and shrimp) are still unknown or underestimated due to the lack of baseline data in the region. In the present study we assessed the isotopic niches modeled from δ13C and δ15N signatures of six estuarine fish species before and after the impact to assign potential shifts at the population- and community-level. We showed isotopic niche has altered in all studied species irrespective of its trophic group and habitat use. Niche community metrics indicated a depletion of trophic diversity and basal resources of the whole community after the impact. Food web changes as we reported here can impair the energy transfer through the food chain and put at risk the sustainability of small fisheries that rely upon local resources.
•The Fundão dam collapse in Brazil is known as the worst environmental disaster involving mine ore tailings in the world•The passage of the contaminated mud through the Doce river estuarine environment altered the niche of fish species•Bayesian models indicated that fish species showed low or no niche overlap when comparing before and after impact•Community-wide measures indicated depletion of trophic diversity and basal resources of the food chain
Energy storage technologies are required to make full use of renewable energy sources, and electrochemical cells offer a great deal flexibility in the design of energy systems. For large scale ...electrochemical storage to be viable, the materials employed and device production methods need to be low cost, devices should be long lasting and safety during operation is of utmost importance. Energy and power densities are of lesser concern. For these reasons, battery chemistries that make use of aqueous electrolytes are favorable candidates where large quantities of energy need to be stored. Herein we describe several different aqueous based battery chemistries and identify some of the research challenges currently hindering their wider adoption. Lead acid batteries represent a mature technology that currently dominates the battery market, however there remain challenges that may prevent their future use at the large scale. Nickel–iron batteries have received a resurgence of interest of late and are known for their long cycle lives and robust nature however improvements in efficiency are needed in order to make them competitive. Other technologies that use aqueous electrolytes and have the potential to be useful in future large-scale applications are briefly introduced. Recent investigations in to the design of nickel–iron cells are reported with it being shown that electrolyte decomposition can be virtually eliminated by employing relatively large concentrations of iron sulfide in the electrode mixture, however this is at the expense of capacity and cycle life.
The use of water-in-salt electrolytes (WiSEs) in electrochemical capacitors is an interesting alternative to state-of-the-art electrolytes based on organic solvents. However, making use of their wide ...electrochemical stability in electrochemical capacitors has been challenging, as shown in battery materials. In this work, we used three concentrations of LiTf2N in water (7, 15 and 21 mol kg−1) with activated carbon, and the determination of the maximum operating voltage showed stability up to 2.2, 2.4 and 2.6 V, respectively. This determination suggested positive/negative-electrode mass balances of 2.1, 1.5 and 1.2, but the experiments showed that the cycle life of devices using WiSEs of 15 and 21 mol kg−1 can be improved. Thus, we find that increasing the amount of active material in the positive electrode gave higher capacitance retention over cycling. With the optimization for a longer cycle life, the observed capacitance retentions for the devices with WiSEs of 7, 15 and 21 mol kg−1 were 97%, 70% and near 100%, respectively, after 10000 cycles. The higher amount of active material in the positive electrode penalized the energy-power performance, but the higher electrochemical stability compensated for it, and WiSEs of 7, 15 and 21 mol kg−1 stored 15, 16 and 21 W h kg−1 when they operated at 0.1 A g−1.
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Electrochemical capacitors show high power density but suffer from low energy density. The use of pseudocapacitive material can increase the cell capacitance and therefore increase the device energy ...density. In this work, we show that using microtubular conducting polymers, as polypyrrole (PPy) and poly(3,4-ethylenedioxythiophene) (PEDOT), alongside activated carbon (AC) in asymmetrical devices, and highly concentrated aqueous electrolyte (or water-in-salt electrolyte, WiSE), is possible to maintain the polymers electroactivity at the negative polarization and take advantage of the electrolyte electrochemical stability. The polymers electrochemical behaviours were compared in WiSE and aqueous acidic solution, which hinted that the polymers charge compensation are different in the different electrolytes. PPy-AC and PEDOT-AC cells can reach 2.6 and 2.8 V, respectively, and electrodes mass balance greatly depends on the polymers open circuit potential before and after cycling
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Sodium-ion batteries are a promising alternative to lithium-ion devices, but the development of proper negative electrode materials is still challenging. Here, the properties of a low-voltage sodium ...titanate material are evaluated. Sodium titanate nanotubes (NTO) were produced by an alkalyne alkaline hydrothermal treatment with TiO2 and consisted of a hydrated Na1.4H0.6Ti3O7 with a surface area of 128 m2 g−1. NTO electrode kinetics were studied by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic intermittent titration techniques. The (de)intercalation of Na+ ions involved two redox pairs at 0.3/0.5 V and 1.0/1.2 V, associated with the present mixture of nanotubes and nanosheets. Surface processes had a 95% coulombic efficiency and a high contribution even at low scan rates, accounting for 47% of the total capacity at 0.5 mV s−1. Upon Na+ removal, the electronic resistance and the semiconductor capacitance increased. Battery tests performed on Na|NTO half-cells showed a reversible capacity of 90 mA h g−1 at 10 mA g−1 and near 100% coulombic efficiency at current rates ranging from 10 mA g−1 to 10 A g−1. Additionally, NTO presented a good capacity retention of 92% after 170 cycles at 100 mA g−1.
•Surface process contribution is 47% at 0.5 V s−1 with 95% efficiency.•Finite-space diffusion model to fit EIS data considering particle-size distribution.•(Semi)conductive properties of NTO change with (de)sodiation.•Electrode capacity of 93 mA h g−1 at 10 mA g−1•92% capacity retention after 170 cycles at 100 mA g−1
Electrochemical double layer capacitors (EDLCs) employing ionic liquid electrolytes are the subject of much research as they promise increased operating potentials, and hence energy densities, when ...compared with currently available devices. Herein we report on the influence of the particle size distribution of activated carbon material on the performance of ionic liquid based EDLCs. Mesoporous activated carbon was ball-milled for increasing durations and the resultant powders characterized physically (using laser diffraction, nitrogen sorption and SEM) and investigated electrochemically in the form of composite EDLC electrodes. A bi-modal particle size distribution was found for all materials demonstrating an increasing fraction of smaller particles with increased milling duration. In general, cell capacitance decreased with increased milling duration over a wide range of rates using CV and galvanostatic cycling. Reduced coulombic efficiency is observed at low rates (<25 mVs(-1)) and the efficiency decreases as the volume fraction of the smaller particles increases. Efficiency loss was attributed to side reactions, particularly electrolyte decomposition, arising from interactions with the smaller particles. The effect of reduced efficiency is confirmed by cycling for over 15,000 cycles, which has the important implication that diminished performance and reduced cycle life is caused by the presence of submicron-sized particles.
Direct ethanol fuel cells (DEFCs) have the potential to play a valuable role in the conversion of energy from sustainable sources. DEFCs need a support matrix, typically carbon, for the noble metal ...catalyst. In this work, two distinct carbon supports are compared and their electrochemical efficacy is related to their physicochemical characteristics. Specifically, Vulcan (Cv) is compared to Selectivity (Cs) as a support for Pd nanoparticles to catalyze ethanol electrooxidation. Characterisation data show that Cs has potentially favorable properties such as a high surface area. However, Pd/Cv exhibits a superior catalytic performance due to the higher adequacy of Cv texture that meets the particular needs of DEFC support in terms of pore size distribution. Additionally, synthesis of Pd nanoparticles on both carbons has decreased their surface areas and increased their pore sizes.
The search for solid electrolytes for electrochemical devices is an object of intense research due to their benefits compared to the liquids, mainly due to the processability aspects, handling, and ...leak elimination. Although studies involving solid polymeric electrolytes have been reported, the research for materials that combine good mechanical strength, elasticity, chemical, thermal stabilities, and ionic conductivity is still emerging. In this sense, in this study, we show a facile method to fabricate free-standing solid polymer electrolytes using a block copolymer named poly (ether-block-amide) (PEBA) 2533, ionic liquids (IL), and lithium salt bis(trifluoromethylsulfonyl) imide (LiTf2N). These membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analyses (DMA), Fourier transform infrared spectroscopy (FTIR), and complex impedance spectroscopy. Subtle changes in crystallinity, melting temperature (Tm), glass transition temperature (Tg), and thermal stability have been observed when IL and lithium were incorporated in the neat polymer PEBA. Furthermore, the addition of the different ILs in PEBA afforded membranes with conductivity in the order of 10−6–10−5 S cm−1 at 25 °C and the sample containing EMImTf2N showed Li+ transport number of 0.40, which are satisfactory values for solid electrolytes based on elastomers. This is the first report on the preparation of a solid electrolyte based on PEBA for lithium-ion batteries.
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•Solid polymer electrolytes based on elastomers.•Lithium-ion batteries with improved safety performance.•Flexible solid electrolytes for lithium-ion battery.•Commercially available elastomeric block copolymer for solid polymer electrolytes.
In this work, we report on the behavior of ionic liquids (ILs) containing sulfonium cations as electrolytes for electrochemical double layer capacitors (EDLCs). Physical properties such as viscosity ...and ionic conductivity are reported over a range of temperatures for ILs containing the diethylmethyl sulfonium S221, triethyl sulfonium S222, and diethylpropyl sulfonium S223 cations paired with the bis(trifluoromethanesulfonyl) imide Tf2N anion. The size and structure of the cations are shown to influence the physical and electrochemical properties of the ILs, with a significant degree of ionic coordination being evident in S223Tf2N. The electrochemical behavior of these ILs in EDLCs was compared with that of a fairly established IL electrolyte, N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (Pyr14Tf2N), and it is shown that S221Tf2N can perform better in terms of energy and power at room temperature, despite operating at a much reduced potential.
A critical parameter in the design of EDLCs is the determination of electrochemical stability limits for individual combinations of electrode and electrolyte. Using EMImBF4 as an example we ...demonstrate that the physical properties of the activated carbon used in the electrodes influence the permissible operating potential of an EDLC, and also that the binder material employed can have further effects. When EMImBF4 electrolyte is coupled with electrodes containing PTFE binder, operating potentials as wide as 3.8 V can be utilised. Due to the differences in response under opposing polarisations, it is necessary to employ an asymmetric mass loading in EDLC cells in order to make full use of the operating window. By balancing the charge in the cell, the differences in stable potential limits and capacitative behaviour can be overcome, however we also found that this balance can be influenced by the rate at which these parameters are determined. Three-electrode measurements show that using an appropriate mass loading ratio results in each electrode operating within their determined stability limits. Stable cycling of a full cell at an operating potential of 3.8 V was demonstrated over 50,000 cycles.
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