Nickel Schiff Base Complexes for Light Driven Hydrogen Production

Abstract

Over the next century, the world's population is expected to increase at a drastic rate; therefore it is essential to consider new and more efficient sources of energy such as the use of artificial photosynthesis to generate hydrogen gas. Hence, the development of more active and robust catalysts is necessary in order to make artificial photosynthesis a viable method of hydrogen generation. Recent studies have shown that cobalt complexes with polypyridyl groups are highly active and thus lead to a lower overpotential and higher turnover rate of hydrogen gas. Using 1,1'-(pyridine-2,6-diyl)bis(2-(pyridin-2-yl)ethyl)ethan-1-imine is a promising ligand to study due to its electronic similarity to previously used ligands for cobalt catalyzed hydrogen production. However, the two pyridine substituents may act as pendant bases, enhancing its activity. Nickel complexes were synthesized with this ligand and were spectroscopically and electrochemically characterized. X-ray diffraction revealed an octahedral geometry for [Ni(EtPyPDI)NO3]NO3 comprising pentadentate chelation of the EtPyPDI ligand and nitrate coordination. Cyclic voltammetry experiments showed reversible redox waves at -0.92 and -1.77 V vs Fc/Fc+. In the presence of acetic acid, a catalytic wave corresponding to hydrogen formation was observed at - 2.26 V vs Fc/Fc+. Hydrogen production was observed under electrocatalytic and light-driven conditions.