Molecular Nickel Thiolate Complexes for Electrochemical Reduction of CO 2 to C 1-3 Hydrocarbons.

We report the unprecedented electrocatalytic activity of a series of molecular nickel thiolate complexes (1-5) in reducing CO 2 to C 1-3 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 C 3 products from CO 2 for the first time in molecular complex. Compound 5 exhibits Faradaic efficiencies (FEs) of 10.6 %, 7.2 %, 8.2 % for C 1 , C 2 , C 3 hydrocarbons respectively at -1.0 V versus the reversible hydrogen electrode. Addition of CO to the system significantly promotes the FE C1-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 CO 2 reduction.