Ion sieving effects in the electrical double layer of porous carbon electrodes: Estimating effective ion size in electrolytic solutions

TLDR: In this paper, the size-calibrated porous carbons were used as an electrode in electrolytic solutions to estimate effective ion sizes, and the results indicated that all the cations that are employed are electroadsorbed in the electrode pores in hydrated states.

Abstract: Certain microporous carbons have pores of molecular dimensions, the size of which can be adjusted over a wide range to fit the dimensions of a large variety of molecules. With knowing the dimensions of these molecules, size-calibrated porous carbons can be produced. In this work, we took advantage of the electronic conductivity of carbon in using it as an electrode in electrolytic solutions. By changing the electrode potential, we could induce electroadsorption and electrodesorption of ions of different dimensions into pore-calibrated carbons, thus enabling us to estimate effective ion sizes. A few fundamental questions such as whether ions accommodated in the electrodes' pores are in a solvated state, which is important for novel electrochemical energy storage devices and for microbiological systems, could be addressed. Analysis of the results indicates that all the cations that are employed are electroadsorbed in the electrode pores in hydrated states. Compared with the monovalent cations, the bivalent ...