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We have successfully prepared composite membranes consisting of the ionic liquid N‐ethyl‐N‐methylpyrrolidinium fluorohydrogenate and the polymer 2‐hydroxyethylmethacrylate and have secured them on a polyimide (PI) membrane support. The resulting EMPyr(FH)1.7F–HEMA (9:1 molar ratio) composite possesses ionic conductivity of 75 mS cm−1 at 120 °C when a 16‐µm support is employed, showing improved performance with elevated temperature; this marks a significant difference from devices using conventional polytetrafluoroethylene supports. In the single cell test, a maximum power density of 31 mW cm−2 is observed at 120 °C. Cross‐sectional SEM images of the corresponding membrane electrode assemblies reveal no significant difference in membrane thickness before and after cell testing, implying that this support does not suffer from membrane softening issues.

Oxygen reduction reaction (ORR) rate constants (k) on Pt and Pt-M (M = Fe, Co, Ni) electrodes were evaluated in N-ethyl-N-methylpyrrolidinium fluorohydrogenate (EMPyr(FH) 1.7 F) ionic liquid at 298-333 K. The Pt-Fe electrode exhibited the best catalytic activity in EMPyr(FH) 1.7 F, because of the large surface area of its nanoporous structure after Fe dissolution. X-ray photoelectron spectroscopy and field-emission scanning electron microscopy showed that Co and Ni barely dissolved in EMPyr(FH) 1.7 F. The observed ORR activities of Pt-Co and Pt-Ni alloys were lower than that of Pt in EMPyr(FH) 1.7 F.

Composite membranes consisting of N-ethyl-N-methylpyrrolidiniumfluoro-hydrogenate (EMPyr(FH)1.7F) ionic liquid and poly(vinylidene fluoride hexafluoropropylene) (PVdF-HFP) copolymer were successfully prepared in weight ratios of 5:5, 6:4, and 7:3 using a casting method. The prepared membranes possessed rough surfaces, which potentially enlarged the three-phase boundary area. The EMPyr(FH)1.7F/PVdF-HFP (7:3 weight ratio) composite membrane had an ionic conductivity of 41 mS·cm 1 at 120 °C. For a single cell using this membrane, a maximum power density of 103 mW·cm 2 was observed at 50 °C under non-humidified conditions; this is the highest power output that has ever been reported for fluorohydrogenate fuel cells. However, the cell performance decreased at 80 °C, which was explained by penetration of the softened composite membrane into gas diffusion electrodes to partially plug gas channels in the gas diffusion layers; this was verified by in situ a.c. impedance analysis and cross-sectional SEM images of the membrane electrode assembly.