Highly efficient photocatalytic hydrogen evolution from nickel quinolinethiolate complexes under visible light irradiation

Earth-abundant metal complexes have emerged as promising surrogates of platinum for catalyzing the hydrogen evolution reaction (HER). In this study, we report the design and synthesis of two novel nickel quinolinethiolate complexes, namely [Ni(Hqt)(2)(4, 4'-Z-2, 2'-bpy)] (Hqt = 8-quinolinethiol, Z = -H [1] or -CH3 [2], bpy = bipyridine). An efficient three-component photocatalytic homogeneous system for hydrogen generation working under visible light irradiation was constructed by using the target complexes as catalysts, triethylamine (TEA) as sacrificial electron donor and xanthene dyes as photosensitizes. We obtain turnover numbers (TON, vs. catalyst) for H-2 evolution of 5923/7634 under the optimal conditions with 5.0 x 10(-6) M complex 1/2 respectively, 1.0 x 10(-3) M fluorescein and 5% (v/v) TEA at pH 12.3 in EtOH/H2O (1:1, v/v) mixture after 8 h irradiation (lambda > 420 nm). We discuss the mechanism of H-2 evolution in the homogeneous photocatalytic system based on fluorescence spectrum and cyclic voltammetry data. (C) 2016 Elsevier B.V. All rights reserved.