Electrochemical Behaviour of Hydrogen in Low-Viscosity Phosphonium Ionic Liquids

Abstract

The electrochemical and diffusive properties of hydrogen in low-viscosity phosphonium ionic liquids were investigated by the electrochemical methods such as cyclic voltammetry and chronoamperometry. The hydrogen redox reactions were concluded to be a quasi-reversible system in phosphonium-based ionic liquids. The diffusion coefficients of hydrogen in these ionic liquids were of the order of 10-10 m2 s-1 at 25 ° C. Additionally, the obtained activation energy of the diffusion process for hydrogen was 11.2 - 15:9 kJ mol-1 estimated from the temperature dependence of the diffusion coefficients. A new type of proton conducting medium such as triethylphosphonium bis(trifluoromethylsulfonyl) amide was synthesized by the neutralization reaction, because the trialkylphosphine-based ionic liquids with good stability at higher temperature and high conductivity were appropriate candidates. This proton conducting membrane containing the ionic liquids with trialkylphosphine-based cations and the polyvinylidenefluoride-co-hexafluoropropylene has been fabricated in the present study. The proton conducting membrane exhibits relatively high ionic conductivity along with good mechanical stability.