Design, Synthesis And Studies Of Molecular Catalysts Based On Transition Metal Complexes For Hydrogen Evolution

Nowadays,people are facing with two serious global problems:energy scarcity and environmental pollution.To overcome these issues,many efforts are being made to develop and use clean energy systems such as hydrogen.Up to now,there are various methods to get hydrogen,splitting water is an important and easy way for hydrogen generation with high purity and large quantities.While this method needs too much energy.Inspired by hydrogenase catalyzed hydrogen production performance,a variety of transition metal-based molecular catalysts have been designed and synthesized to decrease the reactive energy and improve energy utilization.The mainly works:1、Seven kinds of transition metal-based molecular catalysts are designed and synthesized:[Ni^II（HL）₂Cl₂]1、[Co^II（HL）₂Br₂]2、[NiL]3、[Ni L（TCNQ）]4、[Cu₄^I（L）₄]5、[Ni^II（L）₂]6、[NiA₂（H₂O）₂]7.2、Catalytic mechanism and performance of transition metal-based molecular catalysts（1）Different metal complexes with N-phenylpyridin-2-yimethanimineA ligand,N-phenylpyridin-2-yimethanimine（HL）was synthesized by the reaction between p-aminobenzoic acid and pyridine-2-carboxaldehyde.HL reacted with Ni Cl₂?6H₂O and CoBr₂ in a molar of 2:1 to afford complexes[Ni^II（HL）₂Cl₂]1 and[Co^II（HL）₂Br₂]2.Complexes 1 and 2 are used as homogeneous electrocatalysts for hydrogen generation from a neutral buffer solution with TOF of 970.45 h^-1and 875.17 h^-1 at an overpotential of 837.6 mV,respectively.This discussion indicates that the catalytic effects of nickel complex is better compared with cobalt complex with the same ligand.（2）Molecular catalyst based on Ni-TCNQA ligand,N,N’-benzene bis（salicylidenimine）（H₂L）was synthesized by the reaction of salicylaldehyde and o-phenylenediamine.H₂L reacted with NiCl₂?6H₂O in a molar of 1:1 to obtain complex 3.Complex 4 was getted from a mixture of H₂L、NiCl₂?6H₂O and TCNQ in a molar of 1:1:1.Complexes 3 and 4 act as molecular electrocatalysts for hydrogen evolution from a neutral buffer solution with TOF of 462.33 h^-11 and 909.58 h^-11 at an overpotential of837.6 mV,respectively.Above researches show that TCNQ is the key factor for eliciting proton and water reduction catalysis,which can stabilize a low oxidation state of nickel in complex 4,thus making complex 4 has higher catalytic activity.（3）triazenido-metal complexesTwo different triazenido-metal complexes 5 and 6 have been designed and synthesized.Their catalytic mechanism and electrochemical hydrogen production are mainly studied.Electrochemical studies show that complexes 5 and 6 are used as electrocatalysts for hydrogen evolution from a neutral aqueous with TOF of 970.45 h^-1and 875.17 h^-1 at an overpotential of 837.6 mV,respectively.In the process of splitting water,hydrogen is formed via ligand-centered and metal-centered proton-transfer.Above results reveal that proton-transfer process of hydrogen production by transition metal-based molecular catalysts is not a single existence.Both central metal and ligand can function as the catalytic active center for water splitting.（4）Molecular catalyst based on metal saltComplex 7 was synthesized by pyridine-2-carboxylic acid and NiCl₂?6H₂O in a molar of2:1.Compared with nickel acetate,Complex 7 electrocatalyzes for hydrogen generation from a neutral buffer solution with TOF of 646.31 h^-11 at an overpotential of 837.6 mV.While the TOF of nickel acetate is only 233.48 h^-1.From above analysis,we can know that the metal salt complexes can stably exist in aqueous solution,which will result in a better catalytic effect compared with common metal salts.