The 3-triethylammonium propane sulfonic (TEA-PS+) cation associated with the anion tetrafluoroborate, hydrogen sulfate or trifluoromethanesulfonate leads to the formation of the new protic ionic liquids (ILs) 3-triethylammonium propane sulfonic acid tetrafluoroborate (TEA-PS center dot BF4), 3-triethylammonium propane sulfonic acid hydrogen sulfate (TEA-PS center dot HSO4) and 3-triethylammonium propane sulfonic acid trifluoromethanesulfonate (TEA-PS center dot CF3SO3), respectively. These ILs are used to produce Nafion/IL composite membranes with 2.5, 5 or 10 wt% of IL. The results show that the IL addition improves the thermal stability, hydrophilicity and conductivity. Experiments performed with the Nafion/IL membranes in a single proton exchange membrane fuel cell at 100 degrees C indicate that the membrane containing 5 wt% of TEA-PS center dot HSO4 is the most efficient one producing an increase of the maximum current density of approximately 230% when compared to the pristine membrane.