Design,Synthesis and Study of Nickel and Cobalt Complexes with the Property of Catalytic Water Reduction for Hydrogen Production

Author:Lei Jia Mei

Supervisor:zhan shu zhong

Database:Doctor

Degree Year:2019

Download:46

Pages:186

Size:9269K

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As we know,hydrogen is a renewable carbon-free energy,the efficiency of hydrogen generation and the storage of hydrogen are main problems to be solved.Hydrogen generation from water by electrocatalytic or photocatalytic method is an effective way to solve it.Therefore,how to design a cheap and effective catalyst,such as transition complex has become a hot topic in this field.At present,the reported catalysts based on transition complexes often show a performance for electrocatalytic or photocatalytic hydrogen production,in particular,the homogeneous photocatalytic systems for hydrogen evolution are unstable.To solve these problems,based on properties of metal centers and organic ligands,seven complexes with both electrochemical and photochemical driven hydrogen production via water reduction are synthesized in this paper.Works are following:(1)Synthesis and studies of a water-soluble cobalt complex,[(bpy)2Co(CN)2]·NO3 1(bpy=2,2-bipyridine).Electrochemical studies show that complex 1 can electrocatalyze hydrogen generation from a neutral buffer with a turnover frequency(TOF)of 1365 mol H2(mol cat)-1 h-1 under an overpotential(OP)of 837.6 mV.In a homogeneous photocatalytic system together with ascorbic acid as a sacrificial electron donor and[Ru(bpy)3]Cl2 as a photosensitizer,complex 1 can photo-catalyze hydrogen production from water and can sustain for about 16 h,and the turn over number(TON)is 7.3×105 mol H2(mol cat)-1 during12 h irradiation.Comparing with other cobalt complexes,complex 1 exhibits higher efficiency for both electrochemical and photochemical hydrogen production via water reduction.(2)Synthesis and studies of three nickel and cobalt complexes,([(bpte)NiCl2]2,[(bpte)CoCl2]3 and[Ni(bpte)(SCN)2]4(bpte=S,S’-bis(2-pyridylmethyl)-1,2-thioethane).Electrochemical studies show that:All three complexes 2,3 and 4 can electrocatalyze hydrogen generation from a neutral water with a TOF of 555.78,244.01 and 52.23 mol H2(mol cat)-1 h-1 under an overpotential(OP)of 837.6 mV,respectively.The results also show that the introduction of SCN-into the nickel center leads to a significant decrease for the efficiency of electrocatalytic hydrogen production.Together with CdS as a photosensitizer and ascorbic acid as a sacrificial electron donor,complex 2 can photocatalyze hydrogen e volution with a TON of 20981 mol H2(mol cat)-1 during 60 h irradiation and 24900 mol H2(mol cat)-1 during 83 h irradiation.Complex 3 can afford 9810 mol H2(mol cat)-1 during 95 h irradiation.The photocatalytic system with complex 4 can work for about 60 h and provide23800 mol H2(mol cat)-1.Comparing 2 with 3,the nickel complex has better catalytic efficiency than the cobalt complex.Comparing complexes 2 and 4,the introduction of SCN-into the nickel center leads to a increase for the efficiency of photocatalytic hydrogen production.(3)Synthesis and properties of a nickel complex,[Bz-4-MePy]2[Ni(i-mnt)2]5(i-mnt2-=iso-maleonitriledithiolate,Bz-4-MePy+=1-benzyl-4′-methylpyridinium ion).Electrochemical in vestigations show that complex 5 can electrocatalyze hydrogen generation from a neutral buffer with a TOF of 959.2 mol H2(mol cat)-1 h-1 under an overpotential of 837.6 mV.Together with CdS as a photosensitizer and ascorbic acid as a sacrificial electron donor,complex 5 can photocatalyze hydrogen evolution with a TON of 58900 mol H2(mol cat)-1during 60 h irradiation.Comparing 4 with 5,the nickel complex 5 with planar structure has better catalytic efficiency for hydrogen generation from water reduction.(4)Synthesis and properties of nickel complexes with different oxidation states,[TBA]2[NiII(mnt)2]6 and[TBA][NiIII(mnt)2]7(TBA+=[n-Bu4N]+).Electrochemical and photochemical studies exhibit that the nickel(III)complex 7 has much higher efficiency than the nickel(II)complex 6 for hydrogen generation via water reduction under the identical conditions.The results indicate that the oxidation state of metal has obvious influence on the properties of their complexes.(5)Characteristics of homogeneous and heterogeneous photocatalytic systems:The efficiency for hydrogen evolution of homogeneous photocatalytic system is high,but the duration is short and the stability is poor,while heterogeneous photocatalytic system can work for longer time.