Hypercross-linked microporous polymeric ionic liquid membranes: synthesis, properties and their application in H2 generation

Abstract

This work focuses on hydrogen (H₂) generation from the hydrolysis of sodium borohydride (NaBH₄) by using high performance microporous polymeric ionic liquid membranes. Microporous organic polymers are broadly recognized for gas separation and gas storage. In this study, we synthesized hypercross-linked microporous polystyrene (PS) ionic liquid (IL) membranes via in situ cross-linking by the Friedel–Crafts alkylation method. The BET surface area of microporous PS/IL membranes after cross-linking is as high as 852 m² g⁻¹ compared to non-porous PS/IL membranes before cross-linking (2.7 m² g⁻¹) and pure PS membranes (2.5 m² g⁻¹). The as-prepared microporous membranes are tested for H₂ generation. The results show that the microporous PS/IL membranes increase the H₂ rate as compared to non-porous membranes. This is due to the dominant factor of hierarchical porosity and high surface area of the membranes. There is no leach or loss of the ionic liquid; it is well attached to the cross-linked membranes. The highest rate of H₂ generation (3621 mL H₂ g⁻¹ min⁻¹) was observed for 8 wt% of NaBH₄ solution, which is comparable to that of noble metal-based catalysts reported in the literature for a similar kind of this reaction. The catalyst provided 17 290 total turnovers before they are deactivated.