Protic ionic liquids are known to form extended hydrogen-bonded networks that can lead to properties different from those encountered in the aprotic analogous liquids, in particular with respect to the structure and transport behavior. In this context, the present paper focuses on a wide series of 1-alkyl-imidazolium bis­(trifluoromethylsulfonyl)­imide ionic liquids, [HC n Im]­[TFSI], with the alkyl chain length (n) on the imidazolium cation varying from ethyl (n = 2) to dodecyl (n = 12). A combination of several methods, such as vibrational spectroscopy, wide-angle X-ray scattering (WAXS), broadband dielectric spectroscopy, and 1H NMR spectroscopy, is used to understand the correlation between local cation–anion coordination, nature of nanosegregation, and transport properties. The results indicate the propensity of the −NH site on the cation to form stronger H-bonds with the anion as the alkyl chain length increases. In addition, the position and width of the scattering peak q1 (or the pre-peak), resolved by WAXS and due to the nanosegregation of the polar from the nonpolar domains, are clearly dependent on the alkyl chain length. However, we find no evidence from pulsed-field gradient NMR of a proton motion decoupled from molecular diffusion, hypothesized to be facilitated by the longer N–H bonds localized in the segregated ionic domains. Finally, for all protic ionic liquids investigated, the ionic conductivity displays a Vogel–Fulcher–Tammann dependence on inverse temperature, with an activation energy E a that also depends on the alkyl chain length, although not strictly linearly.

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In this work, the possibility of using the protic ionic liquids N-ethylimidazolium trifluoromethylsulfonate, [EIm][TfO], and N-ethylimidazolium bis(trifluoromethylsulfonyl)imide, [EIm][TFSI], as charge carriers in appropriately modified Nafion membranes has been investigated. The superior thermal stability of ionic liquids, as compared to that of water-based electrolytes, hypothetically offers a wider temperature range of fuel cell operation as well as an increased electrochemical performance even at low-humidity conditions. The nano-and microstructure of Nafion membranes swollen with these protic ionic liquids has been studied in detail, with focus on the correlation with the observed ionic conductivity. Although the presence of the ionic liquid within the hydrophilic domains of Nafion suppresses the thermomechanical properties of the polymer, satisfactory conductivities are achieved between 90 and 150 °C, namely, in the range 0.2−1.2 × 10 −3 S/cm.

Energy-conversion devices based on the phenomenon of proton conduction, for example, polymer electrolyte membrane fuel cells (PEMFCs), require low cost and sustainable electrolytes with high ionic conductivity and good mechanical properties under anhydrous conditions and at temperatures up to 150 °C. Biopolymers possess an intrinsic thermomechanical stability but an insufficient proton conductivity in the dry state, which however may be imparted by a protic ionic liquid (PIL). This work presents the preparation and properties of composite membranes made of cellulose nanocrystals (CNCs) and a PIL. The membranes are thermally stable and display an ionic conductivity within the range 10–4–10–3 S/cm for temperatures between 120 and 160 °C. Moreover, the analysis of the biopolymer’s apparent dimensions at nanoscale reveals a dependence of the CNCs’ defects, twisting, and aggregation in the presence of the PIL. Preliminary tests using a simple fuel cell setup demonstrate a response of the membranes to the inlet of H2 gas, with a generation of electrical current. These findings provide a solid groundwork for further development and future studies of biopolymer/PIL electrolytes for energy applications.

Manufacturing new electrolytes with high ionic conductivity has been a crucial challenge in the development and large-scale distribution of fuel cell devices. In this work, we present two Nafion composite membranes containing a non-stoichiometric calcium titanate perovskite (CaTiO3−δ) as a filler. These membranes are proposed as a proton exchange electrolyte for Polymer Electrolyte Membrane (PEM) fuel cell devices. More precisely, two different perovskite concentrations of 5 wt% and 10 wt%, with respect to Nafion, are considered. The structural, morphological, and chemical properties of the composite membranes are studied, revealing an inhomogeneous distribution of the filler within the polymer matrix. Direct methanol fuel cell (DMFC) tests, at 110 °C and 2 M methanol concentration, were also performed. It was observed that the membrane containing 5 wt% of the additive allows the highest cell performance in comparison to the other samples, with a maximum power density of about 70 mW cm−2 at 200 mA cm−2. Consequently, the ability of the perovskite structure to support proton carriers is here confirmed, suggesting an interesting strategy to obtain successful materials for electrochemical devices.