Ionic clathrate hydrates for energy devices

Abstract

Ionic clathrate hydrates are known to be formed by the enclathration of hydrophobic cations or anions into confined cages and the incorporation of counterions into the water framework. As the ionic clathrate hydrates are considered for their potential applicability in various fields, including those that involve solid electrolytes, gas separation, and gas storage, numerous studies of the ionic clathrate hydrates have been reported. In this study, some notable features for energy devices in ionic clathrate hydrates were investigated. One notable phenomenon occurring in the ionic clathrate hydrate is structural transformation arising from co-host inclusion. It was found that the $NH_{3}$ molecule can serve as a co-host in the $Me_{4}NOH$ clathrate hydrate system. The neutral $NH_{3}%$ has been considered less in clathrate hydrate fields because its ability to form strong hydrogen bonds prevents enclathration into a water cage and because its three hydrogen atoms prevent incorporation into a water host network having two hydrogen atoms and two unshared electron pairs. However, the proton deficient site, induced by incorporated $OH^{-}$ in the $Me_{4}NOH$ hydrate, allows one additional hydrogen atom of $NH_{3}$ to incorporate into the host framework. It is accompanied by a structural transformation of the orthorhombic $\It{Pnma}$ $(Me_{4}NOH\cdot10H_{2}O)$ to cubic $\It{Fd3m}$ $(Me_{4}NOH-xNH_{3}\cdot16H_{2}O)$. $Me_{4}NOH-xNH_{3}\cdot16H_{2}O$ has two $5^{12}$ cages per $Me_{4}N^{+}$, whereas $Me_{4}NOH \cdot 10H_{2}O$ has only a very small $4^{3}5^{6}$ cage per $Me_{4}N^{+}$; thus, the restructuring of the host water framework caused by co-host inclusion can be considered as one method of tuning the cage dimensions. As a new approach to ionic clathrate hydrates, the magnetic property of $Me_{4}NOH$ clathrate hydrates was investigated. It was attempted to obtain the isothermal M-H curves of $Me_{4}NOH+H_{2}$ and $Me_{4}NOH+N_{2}$ clathrate hydrates at 1.9 K c...