Electrical double layer capacitors (EDC) store energy using accumulation of ions of opposite charge in a nano-thick layer at high surface area electrodes. They can complement batteries in energy storage and harvesting, when high power density and fast delivery or uptake is needed. A notable improvement of EDCs has been achieved due to advances in nano-structured materials. Experimental results of the Gogotsi group that show that desolvation of electrolyte ions in pores smaller than the size of solvated ions. leads to higher capacitance, opened the door to improved devices using a variety of electrolytes. In the absence of faradic reactions across the interface, which degrade electrodes in batteries during charge/discharge cycles, EDCs can sustain millions of cycles, while batteries survive a few thousand at best. But EDCs suffer from a limited energy density. This is why EDC research is largely focused on increasing their energy performance and widening the temperature limits into the range where batteries experience thermal runaway (explosion). Energy density is proportional to capacitance and is roughly quadratic in voltage. Thus, the larger voltage window (determined by the electrolyte decomposition and Faraday processes at high potentials) and the larger capacitance are the targets in EDC research. Both are provided by room-temperature Ionic liquids (RTIL) --solvent-free liquid electrolytes; their voltage stability is thus only driven by the electrochemical stability of the ions. As was recently understood, RTILs made a revolution in solution chemistry, because RTILs and their mixtures are the 'designer solvents/electrolytes' of high fidelity, as they are non-volatile under a wide range of conditions. Many of them are environmentally friendly. These features present a world of advantages, but also a challenge: how to choose the best RTIL for a given application from hundreds available and thousands possible? In EDC-research, this is impossible without deep understanding of the properties of electrical double layer in ionic liquids on flat electrodes, for a start, and electrodes with nano-templated surfaces, as 'designer electrodes' must match the 'designer electrolytes'. Achieving this understanding through the interaction of theory, simulations and experiments is the task of this proposal. We will perform modelling and simulation of equilibrium properties, such as capacitance, and transport-dynamics to determine how ions diffuse to and from flat carbon and in and out of nano-porous (pore size <2 nm) and mesoporous (2 nm - 10 nm) carbon electrodes. The results will be compared with experimental data obtained on planar graphite, graphite with nano-trenches and nano-templated electrodes built of assemblies of carbon nanotubes. This will be done in a series of RTILs, with systematic variation of asymmetry in the size of cations and anions, and their anisotropy. Of particular interest will be understanding and implementation of the phenomenon recently discovered by Gogotsi: the maximum of capacitance as function of the average pore size, detected in the nano-porous regime. According to preliminary estimates of A. Kornyshev, the latter may be related with the screening of ion-ion interactions in the metallic nano-pores due to image forces. The latter will be incorporated in the simulation force-fields of ion-ion interactions. Of special interest will be the effects of polarity of EDCs caused by the interplay between different pore sizes on the two electrodes and different sizes of cations and anions. The project is conducted in collaboration between researchers from Drexel University in Philadelphia, US, (experiments) and Imperial College, London, UK (modelling). Its completion will bring a new level of understanding of the optimal nano-scale carbon structures and RTILs for optimization of energy storage, charging and power delivery.