Carbon neutral electrochemical conversion of carbon dioxide mediated by [Mn+(cyclam)Cln] (M = Ni2+ and Co3+) on mercury free electrodes and ionic liquids as reaction media

Abstract

In this work, the electrochemical reduction of carbon dioxide using [M+n(cyclam)Cln] (M= Ni+2 y Co+3) as electrocatalysts has been studied in 1-Butyl-3-methylimidazolium tetrafluoroborate and 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMImBF4 and BMImNTf2 respectively) ionic liquids as reaction media. Complexes were characterized electrochemically in these salts and relevant parameters, such as an heterogeneous electron transfer rate were calculated. Results indicate a faster M(II)/M(I) redox process in BMImBF4 despite its higher viscosity compared to BMImNTF2. Cyclic voltammetry experiments demonstrated that [Ni(cyclam)Cl2] is the most active macrocycle, towards the reaction under survey. For this compound, potential controlled electrolysis was carried out at -1.4V vs Ag/AgCl in BMImBF4 as solvent, yielding only CO as a reaction product, with a turn over frequency (TOF) of 0.73 h-1. NMR spectra for the ionic liquids, after electrolysis, shows that applied potential does not affect the chemical structure of the salts. FT-IR thin layer spectroelectrochemical experiments in CO2 saturated solution in BMImBF4 at -1,4V vs Ag/AgCl, show the formation of [Ni(cyclam)CO]+ as precursor species, and also the most stable [Ni(CO)4]