Hydrogen Production in Aromatic and Aliphatic Ionic Liquids

Abstract

The radiolytic production of molecular hydrogen in the ionic liquids N-trimethyl-N-butylammonium bis(trifluoromethanesulfonyl)imide ([N1114][Tf2N]) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([emim][Tf2N]) has been examined with γ-rays, 2-10 MeV protons, and 5-20 MeV helium ions to determine the functional dependence of the yield on particle track structure. Molecular hydrogen is the dominant gaseous radiolysis product from these ionic liquids, and the yields with γ-rays are 0.73 and 0.098 molecules per 100 eV of energy absorbed for [N1114][Tf2N] and [emim][Tf2N], respectively. These low yields are consistent with the relative insensitivity of most aromatic compounds to radiation. However, the molecular hydrogen yields increase considerably on going from γ-rays to protons to helium ions with [emim][Tf2N] while they remain essentially constant for [N1114][Tf2N]. FTIR and UV-vis spectroscopic studies show slight degradation of the ionic liquids with radiation.

γ-Radiolysis of Room-Temperature Ionic Liquids: An EPR Spin-Trapping Study

“…The protons recombine with electrons to give H atoms, and these will in turn abstract H atoms from pyrrolidinium cations. The large yield of H 2 measured in this system is consistent with this mechanism at room temperature. , …”

“…Finite lifetime of CF 3 SO 2 • radicals is proven by observation of the recombination product CF 3 SO 2 CF 3 in γ-radiolysis, though CF 3 SO 2 • was not observed in cryogenic EPR experiments . (It seems likely that CF 3 SO 2 CF 3 is formed very promptly (nanoseconds) in a radiolysis spur recombination because if CF 3 SO 2 • lives long enough (milliseconds) to randomly recombine by second order in a room-temperature γ-radiolysis experiment, it should be observed at 77 K.) The relatively long-lived • CF 3 radical has been observed and studied by pulse radiolysis/transient absorption, as well as low-temperature EPR. ,,, There is also evidence for dissociative electron attachment: F – product is certainly observed as corrosive hydrofluoric acid, and the radical is observed in low-temperature EPR …”

“…There are numerous investigations of changes in the physical properties of ILs during radiolysis, such as viscosity, density, conductivity, and optical absorbance. − Mass spectroscopy and nuclear magnetic resonance (NMR) have been used to identify products and degradation of the starting IL after irradiation with large doses. ,,, Radiation-induced degradation of ILs at lower dose can be quickly assessed by an analysis of the yields of gas generated in radiolysis, among which hydrogen is the main product. − In our previous study, we analyzed the yields of gaseous hydrogen formed during radiolysis of several RTILs with bis­(trifluoromethylsulfonyl)­imide anion and identified that aromatic imidazolium and pyridinium ILs gave the smallest G (H 2 ) yield . The radiolytic free-radical mechanism in ILs is mainly quantified by measuring the yields of the transients formed in pulse radiolysis with transient optical absorbance. − A large number of papers are devoted to studies of solvated electron yields and kinetics in a wide range of ILs. − Shkrob and co-workers used continuous wave electron paramagnetic resonance (cw-EPR) spectroscopy to detect radical intermediates generated from frozen ILs upon exposure to ionizing radiation at low temperature. ,− They found that ILs consisting of aromatic heterocyclic ions exhibit better radiation and electrochemical stability because of their extended conjugated bonds.…”

Stability studies of ionic liquid [EMIm][NTf2] under short-term thermal exposure

“…This IL is widely available and features high thermal stability, low vapour pressure and low melting point. 13 We have recently established the application of ionic liquids in the process of metallic component hardening. Energy storage, densities and thermal conductivities are quite favourable according to Liu and Fox.…”

Gamma and heavy ion radiolysis of ionic liquids: A comparative study

“…A few studies have been reported on the production of H 2 in the -radiolysis of ILs. [25,29,32,48] However, no systematic examination of the production of H 2 on the specific type of IL has been performed. Furthermore, used nuclear fuel is primarily composed of uranium along with minor amounts of transuranic fission product elements (e.g.…”