The Syntheses And Application In Electrocatalysis Of Polyoxometalate-Based Metal-Orgnic Frameworks Based On Nitro-Imidazole Derivative Ligand

The rapid development of social economy has caused serious environmental pollution and energy crisis,and researchers are constantly striving to find renewable and eco-friendly energy sources as alternatives to fossil fuels.The hot research issue of electrolyzed water to produce hydrogen and oxygen,the essential question at present is that the high over-potential makes the low electrolysis efficiency.Therefore,the development of high-efficiency,low-cost and durable multifunctional electrocatalysts is crucial.In this study,four nitroimidazole derivative ligands of L_1-4 were obtained through N-alkylation reactions.By hydrothermal synthesis methods and introducing transition metal Cu ions,six new coordination polymers were successfully synthesized,namely,Cu₂(Mo₆O₁₉)（L₁）₂（1）,Cu₄(Si W₁₂O₄₀)（L₁）₄（2）,Cu₄(PW₁₂O₄₀)（L₂）₄（3）,Cu₄(PMo₁₂O₄₀)（L₂）₄（4）,Cu₂(Mo₆O₁₉)（L₃）₂（5）,and Cu₂(Mo₆O₁₉)（L₄）₂（6）,which were analyzed by single crystal X-ray diffractions and infrared spectrum.In compound 1,each L₁ ligand molecule connects two Cu（II）ions to form a wave L₁-Cu-L₁ chain,and[Mo₆O₁₉]^2-ions are surrounded by the L₁-Cu-L₁ long chains.Compound 2 displays a 2D layered structure,four Cu（I）ion centers are connected with four ligands L₁ to form a cyclic[Cu₄（L₁）₄]structural unit,in which the[Si W₁₂O₄₀]^4-ions are surrounded.Further,the[Si W₁₂O₄₀]^4-ion is connected with the[Cu-（L₁）₄]unit to form a1D chain structure.For compound 3,the adjacent ligand L₂ is connected by Cu（I）ions to form a Cu-L₂-Cu chain,and two adjacent chains are connected by PW₁₂O₄₀^4-anion to form a 1D ladder structure.Compound 4 formed a novel ladder-like structure with two chains connected by phosphomolybdic acids.In compound 5,the organic ligand L₄ and Cu（I）are connected to form a long chain,and[Mo₆O₁₉]^2-ion connects two adjacent long chains to expand into a 2D layered structure.In compound 6,the organic ligand L₄ and Cu（I）form a wavy long chain,[Mo₆O₁₉]^2-ion connects two chains side by side to form a cyclic unit,and further expands along the direction of the long chain to form a double chain structure.The single crystal of compounds 1-6 and the calcined material were studied for electrocatalytic hydrogen and oxygen evolutions.The researches show that the performances of the samples are significantly improved after calcination.The overpotential of the samples after calcination at a current density of 10 m A cm^-2 is significantly reduced,and the tafel slopes are significantly reduced.Under acidic conditions,compound 5-550showed a better electrochemical hydrogen evolution activity,with an overpotential of 280m V at a current density of 10 m A cm-2.Under alkaline conditions,compound 4-850 has the best oxygen evolution reactivity,and the overpotential is 1.367V at the current density of10 m A cm-2.Moreover,the polarization curves before and after the CV cycle for 1000cycles almost overlap,which proves that electrochemical stabilities of the calcined compounds are superior to those crystal samples.Compound 1-6 and its calcined sample have excellent performance in electrocatalytic hydrogen evolution and oxygen evolution reactions,and they can be used as non-noble metal catalytic materials,which have a good application prospect in the field of water electrolysis.