Considering the high potential of hydrogen (H 2 ) as a clean energy carrier, the implementation of high performance and cost-effective biohydrogen (bioH 2 ) purification techniques is of vital importance, particularly in fuel cell applications. As membrane technology is a potentially energy-saving solution to obtain high-quality biohydrogen, the most promising poly(ionic liquid) (PIL)-ionic liquid (IL) composite membranes that had previously been studied by our group for CO 2 /N 2 separation, containing pyrrolidinium-based PILs with fluorinated or cyano-functionalized anions, were chosen as the starting point to explore the potential of PIL-IL membranes for CO 2 /H 2 separation. The CO 2 and H 2 permeation properties at the typical conditions of biohydrogen production (T = 308 K and 100 kPa of feed pressure) were measured and discussed. PIL-IL composites prepared with the [C(CN) 3 ]- anion showed higher CO 2 /H 2 selectivity than those containing the [NTf 2 ]- anion. All the membranes revealed CO 2 /H 2 separation performances above the upper bound for this specific separation, highlighting the composite incorporating 60 wt% of [C 2 mim][C(CN) 3 ] IL. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.