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 NiCl 2 ·6H 2 O, Na 2 (mnt) and [BzPyN(CH 3 ) 2 ]Br or [4-ClBzPyN(CH 3 ) 2 ]Br (BzPyN(CH 3 ) 2  = 1-benzyl-4-(dimethylamino)pyridinium, mnt = 2.2-dicyanoethylene-1.1-dithiolate, and 4-ClBzPyN(CH 3 ) 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 504.25 mol of hydrogen per mole of catalyst per hour at an overpotential (OP) of 0.848 V from a neutral buffer, respectively, indicating that the nickel(III) complex constitutes the better active catalyst than the nickel(II) species.