Novel Dithiolene Nickel Complex Catalysts for Electrochemical Hydrogen Evolution Reaction for Hydrogen Production in Nonaqueous and Aqueous Solutions

Abstract

Abstract Three molecular catalysts based on mononuclear nickel(II) complexes with square planar geometries, [BzPy] 2 [Ni(mnt) 2 ] ( 1 ), [BzPy] 2 [Ni(i-mnt) 2 ] ( 2 ), and [BzPy] 2 [Ni(tdas) 2 ] ( 3 ) (BzPy = benzyl pyridinium) are synthesized by the reaction of NiCl 2 ∙6H 2 O, [BzPy]Br, and Na 2 (mnt)/Na 2 (i-mnt)/Na 2 (tdas) (mnt = 1,2-dicyanoethylene-1,2-dithiolate for ( 1 ), i-mnt = 2,2-dicyanoethylene-1,1-dithiolate for ( 2 ), and tdas = 1,2,5-thiadiazole-3,4-dithiolate for ( 3 )), respectively. The structures and compositions of these three catalysts are characterized by XRD, elemental analysis, FT-IR, and ESI-MS. The electrochemical properties and the corresponding catalytic activities of these three catalysts are studied by cyclic voltammetry. The controlled-potential electrolysis with gas chromatography analysis confirms the hydrogen production with a turnover frequency (TOF) of 116.89, 165.51, and 189.16 moles of H 2 per mole of catalyst per hour at a potential of − 0.99 V (versus SHE) in acetonitrile solutions containing the catalysts, respectively. In a neutral buffer solution, these three molecular catalysts exhibit a TOF of 411.85, 488.76, and 555.06 mol of H 2 per mole of catalyst per hour at a potential of − 0.49 V (versus SHE), respectively, indicating that Complex 3 constitutes the better active catalyst than Complexes 1 and 2 . For fundamental understanding, a catalytic HER mechanism is also proposed. Graphical abstract