▎ 摘　　要

A bio-functional composite of vitamin B-12 with graphene and ionic liquid in chitosan solution was prepared for the first time. The composite was tested for its spectroscopic and electrochemical signatures, which establish the presence of vitamin B-12 in its native structure, with its Co-metal centre accessible for heterogeneous electron transfer. Our electrochemical investigations establish that with 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF(4)) as electrolyte, the Co(III) metal centre of the biocomposite film can be reduced to electrocatalytically active Co(I) at potentials that are significantly less negative than that reported for solution phase vitamin B-12. The biocomposite modified electrode was observed to exhibit excellent electrocatalytic activity toward the electroreduction of halocarbons viz. benzyl bromide, dibromoethane and trichloroacetic acid. The presented investigations indicate that the biocomposite modified electrode minimizes the probability for undesired solution phase reactions of electrogenerated reactive intermediates during electroreduction of dihaloalkanes. This feature is expected to have profound implications on product profile/yield for selective electroreductive reactions of dihaloalkanes. Our comparative electrocatalytic activity investigations for the chosen halocarbons suggest a synergistic activity of the components employed for the fabrication of the biocomposite modified electrode.