Novel poly(1-vinyl imidazole) p(VI) cryogels were synthesized via cryopolymerization technique where simultaneous polymerization and crosslinking occur around ice crystals under freezing conditions. The superporous p(VI) cryogels were modified with various alkyl bromides possessing different chain lengths such as 1.2-Dibromoethane (1,2-BE), 1.4-Dibromobutane (1,2-BB) and 1.6-Dibromohexane (1,6-BH), and used as template for in situ metal nanoparticle (M) synthesis (M: Co-0 or Ni-0). The prepared p(VI)-M cryogel composites were used in hydrogen (H-2) generation from the hydrolysis of sodium borohydride (NaBH4). Very high turnover frequency (TOP) and H-2 generation rate (HGR) values, of 34.4 (mol H-2) (mol catalyst min)(-1) and 14566.9 (mL H-2) (min)(-1) (g of M)(-1), respectively, were obtained at 70 degrees C for 3rd time Co (II) loaded and reduced 1.2-BE modified p(VI)-Co composite catalyst system compared with other imidazole-based catalyst systems reported in the literature. Moreover, modified p(VI) cryogels possess inherently magnetic behavior even after a single Co(II) loading-reduction step. Due to their superior properties, such as being recoverable via external applied magnetic field, fast HGR, and reusability, 1.2-BE-p(VI)-Co metal composites were found to be a highly attractive catalyst system for catalytic hydrolysis of NaBH4. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.