Design,Synthesis And Studies Of Cobalt,Nickel Complexes With Properties For Hydrogen Production

Using non-precious metal molecular catalysts to driving water splitting into hydrogen is considered an ideal way to create clean and storable energy,which is great benefit for solving energy shortages and environmental pollution.Considering that energy acquisition is limited by environment and terrain,it is still a challenge to solve the energy required for human survival and development completely.Converting solar energy into clean and high-heat hydrogen energy is considered one of the most ideal solutions to the energy crisis which is inspired by photosynthesis from plant.Although many non-noble metal-based molecular catalysts were synthesized with excellent catalytic activity for H₂ generation,it has been rarely reported to elucidate the interaction characteristics between photosensitizers and catalysts,and the reasons for the hydrogen evolution of the catalysts by the theory.In this work,four Schiff base complexes were synthesized and used for photocatalytic hydrogen evolution reaction under visible light irradiation.Among them,the complex 3 with the benzene ring in the axial position shows the best catalytic activity.Density functional theory（DFT）calculations show that the formed hydrogen bonds between the catalyst3 and Fl are greatly shortened after excitation,which contributes to the rapid electron transfer（ET）.Meanwhile,the fast ET favors a large number of electrons to stay on complex 3.Therefore,a large amount of H⁺in the solution around 3 can easily capture electrons,thereby releasing the most H₂.This work provides detailed theoretical guidance for the catalytic mechanism,sufficient theoretical support for the electron transfer pathway and the combination of photosensitizers in the photocatalytic system.In addition,we find that the"trial and error method"is still the mainstream method for the design of novel and efficient photocatalysts,in which the cumbersome cycle and unsatisfactory time have brought great waste of material and financial resources.Metallic nickel can bind to many ligands by coordination bonds,making the synthesis process of Ni complexes easier.Besides,the formed complexes can adsorb H⁺or H₂O via hydrogen bonds or van der Waals forces,and the excited electrons can be driven to the central Ni of the complex causing electrons accumulation.Furthermore,the unique editable and controllable properties of the active site enable the catalyst to purposefully split water to generate H₂.Here,a series of nickel-based catalysts have been synthesized according to the properties predicted by DFT,and a new three-component system with excellent performance for H₂ generation in aqueous solution was established,including the organic dye fluorescein as a photosensitizer,Ni（dpi）（pys）₂（dpi=2,2’-Dipyridyl,pys=2-Mercaptopyridine）as catalyst and TEOA as electron sacrificial agent.Under optimal conditions,about 1613.51μmol of hydrogen was obtained after 3 hours of illumination for Ni（dpi）（pys）₂ with the best performance.In order to simplify the tedious design again,taking benzothiazole-based ligands as an example,three nickel-based molecular complexes were synthesized and exhibited catalytic hydrogen production performance in aqueous solution.Among them,the smooth planar structure and large electronic capacity of benzothiazole make the final complex exhibit the best activity in aqueous solution.The structure determines the performance,and the performance is reflected in the structure.The prediction of the performance of the whole catalyst from the ligand provides a more convenient method for the design of new catalysts.Finally,the photochemical pathways and possible hydrogen production mechanisms have been proposed according to the test of fluorescence quenching and proton transfer.This work will help to design new catalysts and facilitate continuous innovation of photocatalysts form light energy to hydrogen energy.