A modified imidazole, namely guanidimidazole (Gim) was designed and synthesized as a novel quaternizing- and cross-linking agent for alkaline polymer electrolyte membrane fabrication. The resulting membrane was more alkali tolerant and swelling resistant than that quaternized purely by 1-methylimidazole owing to the enhanced resonance and cross-linking ability of Gim, the former confirmed by a LUMO (lowest unoccupied molecular orbital) energy calculation. The membrane also showed good ionic conductivity, mechanical strength and thermal stability. A H-2/O-2 fuel cell using the synthesized membrane showed a peak power density of 39 mW cm(-2) at 50 degrees C. This work preliminarily demonstrates the beneficial effect of imidazole modification by both experimental and computational investigation; it provides a new cation design strategy that may potentially achieve simultaneous improvement of alkali stability and swelling resistance of alkaline electrolyte membranes. (C) 2015 Elsevier B.V. All rights reserved.