Electrochemical double layer capacitors (EDLCs) are investigated with activated carbon electrodes and a lithium-ion electrolyte, in anticipation of potential future applications in hybridised battery-supercapacitor devices and lithium ion capacitors. An experimental study of a symmetric electrochemical double layer capacitor (EDLC) with activated carbon (AC) electrodes on aluminium foil current collectors and electrolyte 1 M LiPF6 in EC:EMC 50:50 v/v concludes a stability window to a maximum potential of 3 V, an equivalent in series resistance of 48 ohm for 1 cm 2 cell area (including the contact resistance between electrode and current collector) and an average specific electrode capacitance of 50.5 F g -1 . Three AC electrode materials are assessed via computer simulations based on a continuum ion and charge transport model with volumeaveraged equations, considering the pore size distribution for each electrode material and, depending on pore size, transport of tetrahedral solvated or flat solvated Li + ions and solvated or desolvated PF6ions. The computer simulations demonstrate that the best electrode material is an AC coating electrode with a hierarchical pore size distribution measured in the range of 0.5-180 nm and bimodal shape, and specific surface area BET = 808 m 2 g -1 .

[1] Measurements have been made of the effect of compaction on water retention, saturated hydraulic conductivity, and porosity of two English soils: North Wyke (NW) grassland clay topsoil and Broadbalk silty topsoil, fertilized inorganically (PKMg) or with farmyard manure (FYM). As expected, the FYM topsoil had greater porosity and greater water retention than PKMg topsoil, and the NW clay topsoil retained more water at each matric potential than the silty topsoils. Compaction had a clear effect on water retention at matric potentials wetter than −10 kPa for the PKMg and FYM soils, corresponding to voids greater than 30 mm cylindrical diameter, whereas smaller voids appeared to be unaffected. The Pore-Cor void network model has been improved by including a Euler beta distribution to describe the sizes of the narrow interconnections, termed throats. The model revealed a change from bimodal to unimodal throat size distributions on compaction, as well as a reduction in sizes overall. It also matched the water retention curves more closely than van Genuchten fits and correctly predicted changes in saturated hydraulic conductivity better than those predicted by a prior statistical approach. However, the changes in hydraulic conductivity were masked by the stochastic variability of the model. Also, an artifact of the model, namely its inability to pack small features close together, caused incorrect increases in pore sizes on compaction. These deficiencies in the model demonstrate the need for an explicitly dual porous network model to account for the effects of compaction in soil.

Coated paper for high-quality printing comprises a fine particulate mineral coating, applied as an aqueous suspension and fixed to the fibrous paper substrate with a binder. The shrinkage occurring while the coating layer dries onto the substrate has been measured by observing the deflection of strips of a synthetic substrate coated with ground calcium carbonate with different binders. The force acting on the surface of the strips to cause a given deflection has been calculated using the elementary beam theory. The porosities of the dry structures were measured by compression-corrected mercury porosimetry. We show that the shrinkage occurring during the drying of the coating layer is mainly due to capillary forces acting as the water recedes in the porous structure, while the binder can act to retain the stress resulting from such forces. Starch produced much higher stresses than latex.

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Porometry, porosimetry, image analysis and void network modelling in the study of the pore-level properties of filters Gribble, CM

The challenge of optimizing the pore size distribution of porous electrodes for different electrolytes is encountered in supercapacitors, lithium-ion capacitors and hybridized battery-supercapacitor devices. A volume-averaged continuum model of ion transport, taking into account the pore size distribution, is employed for the design of porous electrodes for electrochemical double-layer capacitors (EDLCs) in this study. After validation against experimental data, computer simulations investigate two types of porous electrodes, an activated carbon coating and an activated carbon fabric, and three electrolytes: 1.5 M TEABF4 in acetonitrile (AN), 1.5 M TEABF4 in propylene carbonate (PC), and 1 M LiPF6 in ethylene carbonate:ethyl methyl carbonate (EC:EMC) 1:1 v/v. The design exercise concluded that it is important that the porous electrode has a large specific area in terms of micropores larger than the largest desolvated ion, to achieve high specific capacity, and a good proportion of mesopores larger than the largest solvated ion to ensure fast ion transport and accessibility of the micropores.

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