The effect of oxidation state of metal on hydrogen production electro-catalyzed by nickel complexes supported by maleonitriledithiolate ligand

Abstract

Two molecular electro-catalysts based on nickel complexes, [Ni(mnt)2]n− (n=2 (1) and 1 (2)) are formed by the reactions of NiCl2·6H2O, Na2(mnt) and [BzPyN(CH3)2]Br or [4-ClBzPyN(CH3)2]Br (BzPyN(CH3)2=1-benzyl-4-(dimethylamino)pyridinium, mnt=2.2-dicyanoethylene-1.1-dithiolate, and 4-ClBzPyN(CH3)2=4-Cl-benzyl-4-dimethylaminopyridinium). Electrochemical investigations show 1 and 2 can electrocatalyze hydrogen generation both from acetic acid and aqueous buffer solution. And complexes 1 and 2 afford a turnover frequency (TOF) of 282.95 and 504.25mol of hydrogen per mole of catalyst per hour at an overpotential (OP) of 0.848V from a neutral buffer, respectively, indicating that the nickel(III) complex constitutes the better active catalyst than the nickel(II) species.