Nickel complexes as catalysts for the light-driven production of hydrogen from aqueous solutions

Photocatalytic water splitting for hydrogen production with earth-abundant metal complexes as the catalysts becomes one of most effective pathways to solve the problems of energy shortage and environmental pollution. Here, two Ni(II) complexes of Ni(qbz)(hqt)2 (qbz = 2-quinoline benzimidazole, hqt = 8-quinolinethio) (complex 1) and Ni(qbo)(hqt)2 (qbo = 2-quinoline benzothiazole) (complex 2) were synthesized and their performances for H2 generation were explored. A stable reaction system was established with triethanolamine as sacrificial electron donor and fluorescein (Fl) as the photosensitizer. Complex 2 has good hydrogen-production performance, over 25 mg of which 1250 μmol of H2 can be released after irradiation for 3 h under optimal conditions. Density functional theory (DFT) was adopted to unveil the relationship between active site and performance of nickel catalyst, and the hydrogen-production performance of catalysts can be predicted preliminarily by DFT. Meanwhile, the mechanism for H2 generation was discussed by theory and experiment. This work provides a way of experiment combining theory to find excellent catalysts with less time and energy.