Electric double-layer capacitors are a family of electrochemical energy storage devices that offer a number of advantages, such as high power density and long cyclability. In recent years, research and development of electric double-layer capacitor technology has been growing rapidly, in response to the increasing demand for energy storage devices from emerging industries, such as hybrid and electric vehicles, renewable energy, and smart grid management. The past few years have witnessed a number of significant research breakthroughs in terms of novel electrodes, new electrolytes, and fabrication of devices, thanks to the discovery of innovative materials (e.g. graphene, carbide-derived carbon, and templated carbon) and the availability of advanced experimental and computational tools. However, some experimental observations could not be clearly understood and interpreted due to limitations of traditional theories, some of which were developed more than one hundred years ago. This has led to significant research efforts in computational simulation and modelling, aimed at developing new theories, or improving the existing ones to help interpret experimental results. This review article provides a summary of research progress in molecular modelling of the physical phenomena taking place in electric double-layer capacitors. An introduction to electric double-layer capacitors and their applications, alongside a brief description of electric double layer theories, is presented first. Second, molecular modelling of ion behaviours of various electrolytes interacting with electrodes under different conditions is reviewed. Finally, key conclusions and outlooks are given. Simulations on comparing electric double-layer structure at planar and porous electrode surfaces under equilibrium conditions have revealed significant structural differences between the two electrode types, and porous electrodes have been shown to store charge more efficiently. Accurate electrolyte and electrode models which account for polarisation effects are critical for future simulations which will consider more complex electrode geometries, particularly for the study of dynamics of electrolyte transport, where the exclusion of electrode polarisation leads to significant artefacts.

Measurements of S-shaped adsorption isotherm as evidence of ZIF-7 gate opening in the presence of CH4 at 1245 kPa.

Nanoporous carbon-based supercapacitors store electricity through adsorption of ions from the electrolyte at the surface of the electrodes. Room temperature ionic liquids, which show the largest ion concentrations among organic liquid electrolytes, should in principle yield larger capacitances. Here we show by using electrochemical measurements that the capacitance is not significantly affected when switching from a pure ionic liquid to a conventional organic electrolyte using the same ionic species. By performing additional molecular dynamics simulations, we interpret this result as an increasing difficulty of separating ions of opposite charges when they are more concentrated, i.e. in the absence of a solvent which screens the Coulombic interactions. The charging mechanism consistently changes with ion concentration, switching from counter-ion adsorption in the diluted organic electrolyte to ion exchange in the pure ionic liquid. Contrarily to the capacitance, in-pore diffusion coefficients largely depend on the composition, with a noticeable slowing of the dynamics in the pure ionic liquid.Supercapacitors are a promising electrochemical energy storage technology. They may be separated into two families of devices, depending on the electricity storage mechanism, i.e. the electric double-layer capacitors (EDLCs) and pseudocapacitors. 1 . In EDLCs, the charge is stored by a simple process of ion adsorption at the surface of the electrodes, even if at the microscopic scale complex mechanisms are at play. The most prominently employed electrode materials are porous carbons with high accessible surface area. Research and development of such EDLCs is being driven by demand from emerging applications which require efficient energy storage, notably renewable energy, 2 electric vehicles, 3 and smartgrid management. 4,5 Currently, commercial supercapacitors have energy densities on the order of 5 W h kg −1 . 5 There is a large ongoing interest in the design of electrolytes with improved performance over the traditional organic liquids, such as acetonitrile-based electrolytes. Room temperature ionic liquids (RTILs) have raised a lot of interest due to their high window of electrochemical stability, 6 high thermal stability, 7 and low toxicity. 8 RTILs are also highly tunable, and there are many possible combinations available which is beneficial as they can be selected to match specific electrodes. 9 However, when used as a pure electrolyte in EDLCs with highly microporous carbon electrodes, they suffer from high viscosity and poor conductivity. 10 Superconcentrated electrolytes, which are highly-concentrated mixtures of RTILs and organic solvents, may offer a good compromise for these target properties, while keeping most of the RTIL benefits. They are therefore considered as promising alternatives in EDLCs.A difficulty for choosing the optimal electrolyte is that the ions they contain adsorb inside electrified nanoporous carbon electrodes, in which the structure changes significantly due to strong electric field and co...

Interfacial gas enrichment (IGE) covering the entire area of hydrophobic solid-water interface has recently been detected by atomic force microscopy (AFM) and hypothesized to be responsible for the unexpected stability and anomalous contact angle of gaseous nanobubbles, and the significant change from DLVO to non-DLVO forces. In this paper, we provide further proof of the existence of IGE in the form of a dense gas layer (DGL) by molecular dynamic simulation.Nitrogen gas adsorption at the water-graphite interface is investigated using molecular dynamic simulation at 300 K and 1 atm normal pressure. The results show that a DGL with a density equivalent to a gas at pressure of 500 atm is formed and equilibrated with a normal pressure of 1 atm. By varying the number of gas molecules in the system, we observe several types of dense gas domains: aggregates, cylindrical cap gas domains and DGLs. Spherical cap gas domains form during the simulation but are unstable and always revert to another type of the gas domains.Furthermore, the calculated surface potential of the DGL-water interface, -17.5 mV, is significantly closer to 0 than the surface potential, -65 mV, of normal gas bubble-water interface. This result supports our previously stated hypothesis that the change in surface potential causes the switch from repulsion to attraction for an AFM tip when the graphite surface is covered by an IGE layer. The change in surface potential comes from the structure change of water molecules at the DGL-water interface as compared with the normal gas-water interface. In addition, the contact angle of the cylindrical cap high density nitrogen gas domains is 141degrees. This contact angle is far greater 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 than 85 degrees observed for water on graphite at ambient conditions and much closer to the 150 degrees contact angle observed for nanobubbles in experiments.

, Techno-economic assessment of poly-3-hydroxybutyrate (PHB) production from methane-The case for thermophilic bioprocessing, Journal of Environmental Chemical Engineering http://dx.doi.org/10.1016/j.jece. 2016.07.033 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractA major obstacle preventing the large scale production of polyhydroxyalkanoates (PHAs) has been the lack of a reliable, low cost, large volume feedstock. The abundance and relatively low price of methane therefore marks it as a substrate of interest. This paper presents a technoeconomic assessment of the production of poly-3-hydroxybutyrate (PHB) from methane.ASPEN Plus was used for process design and simulation. The design and economic evaluation is presented for production of 100,000 t/a PHB through methanotrophic fermentation and acetone-water solvent extraction. Production costs were estimated at $4.1-$6.8/kg PHA, which compares against a median price of $7.5/kg from other studies. Raw material costs are reduced from 30-50% of production for sugar feedstocks, to 22% of production for methane. A feature of the work is the revelation that heat removal from the two-stage bioreactor process contributes 28% of the operating cost. Thermophilic methanotrophs could allow the use of cooling water instead of refrigerant, reducing production costs to $3.2-5.4/kg PHA; it is noted that PHB producing thermophilic methanotrophs are yet to be isolated. Energy consumption for air compression and biomass drying were also identified as significant capital and operating costs and therefore optimisation of bioreactor height and pressure and biomass moisture content should be considered in future research.3