Ionic liquids are composed of equal quantities of positive and negative ions. In the bulk, electrical neutrality occurs in these liquids due to Coulombic ordering, in which ion shells of alternating charge form around a central ion. Their structure under confinement is far less well understood. This hinders the widespread application of ionic liquids in technological applications. Here we use scattering experiments to resolve the structure of the widely used ionic liquid (EMI-TFSI) when it is confined inside nanoporous carbons. We show that Coulombic ordering reduces when the pores can only accommodate a single layer of ions. Instead, equally-charged ion pairs are formed due to the induction of an electric potential of opposite sign in the carbon pore walls. This non-Coulombic ordering is further enhanced in the presence of an applied external electric potential. This finding opens the door for the design of better materials for electrochemical applications.

(11)B NMR spectroscopy has been used to investigate the sorption of BF(4)(-) anions on a highly porous, high surface area carbon, and different binding sites have been identified. By implementing in situ NMR approaches, the migration of ions between the electrodes of the supercapacitors and changes in the nature of ion binding to the surface have been observed in real time.

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Microporous carbon materials are widely used in gas storage, sorbents, supercapacitor electrodes, water desalination, and catalyst supports. While these microporous carbons usually have a particle size in the 1–100 μm range, here the synthesis of porous carbide‐derived carbon (CDC) with particle diameters around 30 nm by extraction of titanium from nanometer‐sized titanium carbide (TiC) powder at temperatures of 200 °C and above is reported. Nanometer‐sized CDCs prepared at 200–400 °C show a disordered structure and the presence of CN sp1 bonds. Above 400 °C, the CN bond disappears with the structure transition to disordered carbon similar to that observed after synthesis from carbide micropowders. Compared to CDCs produced from micrometer‐sized TiC, nano‐CDC has a broader pore size distribution due to interparticle porosity and a large contribution from the surface layers. The material shows excellent electrochemical performance due to its easily accessible pores and a large specific surface area.

a b s t r a c tIon adsorption onto high surface area microporous Carbide Derived Carbons (CDCs) with pore sizes in the sub-nanometer range was studied by means of the Electrochemical Impedance Spectroscopy (EIS) technique in two electrolytes, Tetraethylammonium Tetrafluoroborate (NEt 4 BF 4 ) in Acetonitrile (AN) and in Propylene Carbonate (PC). Polarization at two bias voltages (0.5 V/Ref and −1 V/Ref) for EIS measurements enabled comparing the capacitive behaviors resulting from anions and cations adsorption, respectively, it was confirmed that the effective size of NEt 4 + is bigger than the one of BF 4 − . Higher transport limitation was then observed for cations and was exalted in PC-based electrolyte. Although slow ion transport kinetics, it was found that the low frequency vertical line observed on the Nyquist plots was preserved meaning that carbon electrodes were fully charged. This study confirmed the importance of choosing an electrode carbon pore size adapted to the effective ion size. Finally, the best performances would be got in 1.5 M NEt 4 BF 4 AN-based electrolyte with a 0.76 nm pore size negative electrode and a 0.68 nm pore size positive electrode.

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International audienceWith the goal to improve the capacitance in electrochemical double-layer capacitors (EDLCs) many studies on pore size/ion size relationship have been undertaken to achieve a better understanding of the charge storage mechanism in the electrochemical double-layer in confinement. A significant capacitance increase was achieved by using carbon electrodes with micropores (b1 nm), when the carbon pore size was close to the ion size. In this paper, the accessibility of narrow pores is investigated by selecting a carbon with a small pore size (b0.7 nm) and electrolyte mixtures with different ion sizes. It has been shown that the adsorption capacitance limitation observed for large cations and anions could be overcome by adding ions with a smaller effective size. This result demonstrates that the pores are accessible when their size matches the effective ion size and contradicts the surface saturation assumption; effective ion size which exceeds the pore size leads to current limitation. This work confirms that the steric effect is involved when ions are adsorbed into pores and highlights the importance of controlling ion size/pore size relationship for optimisation of the capacitive performance of EDLC devices