Study On The Electrocatalytic Properties Of Bimetallic Organic Frameworks Constructed With Flexible Ligands

Metal-organic frameworks（MOFs）have rich chemical activity and porous structure,which can be used for multifunctional heterogeneous catalysis.The combination of polyoxometalates（POMs）and MOFs improves the disadvantages of MOFs and POMs as electrode materials alone,so this cross-field has been widely studied.The two can be combined in many ways,among which POMs,as an inorganic building unit,participates in the construction of structure to form POMOFs,which is a popular branch of research.In this paper,five new POMOFs were synthesized by a variety of POMs and transition metals with a flexible chain containing ligand btbu=1,4-bis（1,2,4-triazole-1-yl）butane,and their electrocatalytic properties were studied.1.Hydrothermal synthesis of two kinds of POMOF crystals by selecting classic Keggin type[SiW₁₂O₄₀]^4-,transition metal Ni²⁺,Co²⁺,and btbu ligands,[Ni₂（btbu）₄（H₂O）₂(SiW₁₂O₄₀)]（CUST-631）and[Co₂（btbu）₄（H₂O）₂(SiW₁₂O₄₀)]（CUST-632）.The crystal structure analysis shows that CUST-631 and CUST-632 are isomorphic.The electrocatalytic reduction of KBr O₃and KNO₂and the oxidation of AA were tested,and the catalytic efficiency of the two electrodes was compared.The results show that the catalytic efficiency of CUST-632 on 8 m M KBr O₃and AA is 167.7%and 243.3%,respectively,and the electrocatalytic redox reduction effect is better.In addition,POMOF derived nanomaterials were prepared by pyrolysis,and their hydrogen evolution properties were tested.The results showed that both CUST-631 and CUST-632 have certain electrocatalytic activity for hydrogen evolution,and the overpotential of CUST-631 and CUST-632 in acidic solution is 349 m V and 417 m V,respectively,which is stronger than that in alkaline solution.2.Two kinds of three-dimensional POMOF crystals were synthesized by the reaction between[PW₁₂O₄₀]^3-and[PMo₁₂O₄₀]^3-with Cu²⁺and btbu ligand,respectively,[Cu₃（btbu）₄（H₂O）₂(PW₁₂O₄₀)]（CUST-633）and[Cu₃（btbu）₄（H₂O）₂(PMo₁₂O₄₀)]（CUST-634）.The crystal structures of CUST-633 and CUST-634 are similar to each other.The electrocatalytic reduction of KBr O₃and KNO₂and the oxidation of AA were tested.The catalytic efficiency of CUST-633 and CUST-634 for 8 m M KBr O₃is 81.4%and 115.5%,respectively.CUST-634 has better electrocatalytic reduction performance.In addition,CUST-634 was also found to have a good electrocatalytic reduction of Cr（VI）.Using CUST-633 derived nanomaterials as electrocatalysts for hydrogen evolution experiments,the results show that the overpotential of CUST-633 derived electrocatalyst in acidic and alkaline electrolyte is 376 m V and 366 m V,respectively,and both of them have certain electrocatalytic activity of hydrogen evolution.3.A two-dimensional POMOF based on[Mo₈O₂₆]^4-,Zn²⁺and btbu ligand was prepared by simple hydrothermal method,[Zn（btbu）₂（H₂O）₃(β-Mo₈O₂₆)_0.5]·3H₂O（CUST-635）.The structural analysis of CUST-635 showed that metal ions and POM clusters were connected to each other through btbu to construct a two-dimensional framework.Using CUST-635 directly as electrode material,it was found that the electrocatalytic reduction of KBr O₃,KNO₂and H₂O₂is great.In addition,hydrogen evolution experiments were conducted on the nanomaterials obtained from pyrolysis at850℃.The overpotential was 338 m V in acidic electrolyte and 242 m V in alkaline solution,which had the lowest overpotential among the above POMOFs derived materials and the best catalytic effect.