Molecular Nickel Thiolate Complexes for Electrochemical Reduction of CO2 to C1–3 Hydrocarbons

Abstract

We report the unprecedented electrocatalytic activity of a series of molecular nickel thiolate complexes (1–5) in reducing CO2 to C1–3 hydrocarbons on carbon paper in pH-neutral aqueous solutions. Ni(mpo)2 (3, mpo=2-mercaptopyridyl-N-oxide), Ni(pyS)3− (4, pyS=2-mercaptopyridine), and Ni(mp)2− (5, mp=2-mercaptophenolate) were found to generate C3 products from CO2 for the first time in molecular complex. Compound 5 exhibits Faradaic efficiencies (FEs) of 10.6 %, 7.2 %, 8.2 % for C1, C2, C3 hydrocarbons respectively at −1.0 V versus the reversible hydrogen electrode. Addition of CO to the system significantly promotes the FEC1–C3 to 41.1 %, suggesting that a key Ni−CO intermediate is associated with catalysis. A variety of spectroscopies have been performed to show that the structures of nickel complexes remain intact during CO2 reduction.