Synthesis of benzimidazolium hydrochloride. The synthesis of benzimidazolium hydrochloride (bImCl) followed the method described by Peppel et al. . Benzimidazole (8.671 g, 73.4 mmol) was dissolved in 25 mL demineralized water in a beaker, followed by the addition of 37% hydrochloric acid (7.95 g, 81.2 mmol) with stirring. The solutions were heated to 110℃ in an oil bath until all liquid had evaporated, resulting in the formation of white crystalline powder. The powder was dried in a vacuum environment at 110 ℃ for 24 h before being subjected to X-ray diffraction analysis as presented in Supplementary Fig. .