The Hierarchical Structure of Nanoporous Carbon Electrode Materials Elucidated by Water Sorption: a Comparison of Multiple Structural Models

The total amount of energy that an electrical double layer capacitor (EDLC) can store depends on the voltage and the accessible surface area for ion electrosorption. Nanoporous carbon materials with a high specific surface area, such as carbide derived carbon (CDC), make ideal electrodes for EDLC devices. Recent reports of water's diffusional dynamics dependence on CDC pore size indicate confinement effects similar to that observed in pores of 16 Å. Small-angle neutron scattering (SANS) was used to find to what degree pores are filled with water (D2O) at intermediate stages of loading for four TiC-CDC powders, each with different pore size distributions. We present models to reproduce the SANS data, consisting of subnanometer pores as well as mesopores. In addition, the structure of the room temperature ionic liquid (RTIL) [C4mim]+[Tf2N]- and water confined inside the micropores (< 2 nm) of carbide derived carbon (CDC) were investigated using small angle x-ray scattering (SAXS). This study provides information on the length scales of the CDC porosity, the extent to which RTIL enters micropores, and how confinement affects the charge-ordered structure of the RTIL.