posted on 2014-12-04, 00:00authored byMuhammed Shah Miran, Tomohiro Yasuda, Md. Abu Bin Hasan Susan, Kaoru Dokko, Masayoshi Watanabe
Binary mixtures of two protic ionic
liquids (PILs), namely, diethylmethylammonium hydrogensulfate ([dema]HSO4) and diethylmethylammonium bis(trifluoromethanesulfonyl)amide
([dema][NTf2]), were prepared by mixing in various weight
ratios for prospective use as fuel cell electrolytes. The binary mixtures
showed significantly higher electrochemical activity compared with
the constituent pure PILs, and the activity changed depending on the
composition of the mixtures. Specifically, the open circuit potential
(OCP) for a H2 | O2 cell using a binary electrolyte
consisting of 56 wt % [dema][NTf2] was 1.03 V vs a reversible
hydrogen electrode (RHE), whereas the values were 0.90 and 0.77 V
for pure [dema]HSO4 and [dema][NTf2], respectively,
under similar conditions. The electrochemical activity of the binary
mixtures was interpreted by comparing their molecular characteristics
inferred from Fourier transform infrared (FT-IR) and 1H
NMR spectroscopy with those of the constituent PILs. The binary systems
showed enhanced electrochemical activity, possibly due to anion/proton
exchange through the formation of hydrogen bonds of varying strengths
via the N–H bond. The anion/proton exchange appears to average
the N–H bond strength to render it suitable for fuel cell reactions.
Bulk physicochemical properties such as thermal properties, viscosity,
ionic conductivity, and ionicity were also measured precisely. The
results of the pulsed gradient spin echo (PGSE) NMR and Walden plot
collectively suggest that the Grotthuss mechanism in addition to the
vehicle mechanism contributes to proton transport in the binary systems,
possibly due to the coexistence of [dema] cation and HSO4– anion, whereas the vehicle mechanism is dominant
for pure [dema][NTf2].