Synthesis On Fabrication Of Multi-structured Metal Organic Framework Materials For Electrocatalytic Water Splitting

In the contemporary word,it is of great significance for scientists to develop environmentally friendly,clean and sustainable renewable energy.Renewable energy development,thus,has gained great popularity.Electrolytic water technology is based on the principle of electrochemical or photolysis of water.Decomposing water into hydrogen?hydrogen decomposition reaction HER?and oxygen?oxygen decomposition reaction OER?using renewable electricity or solar energy is considered to be one of the most hopeful and promising methods for industrial production.Currently,Pt/C?HER?and Ru O₂?OER?,have been recognized as state-of-the-art electrocatalysts.The scarcity and high cost hinder the large-scale application of precious metals,which also makes electrolytic water have the disadvantages of high energy consumption and small scale.Therefore,the search for metals with high activity,stable performance,low price,and abundant reserves to replace precious metals has always been the unremitting goal of scientists.In recent years,emerging organic-inorganic hybrid functional materials,metal-organic framework?MOF?,are formed by coordination bonds between organic ligands and metal atom nodes with periodic structural units.It not only possess well-defined chemical structures and readily accessible active sites,but also have large specific surface area,high porosity,and easy functionalization.Although great progress has been made in energy storage and conversion,there are still many problems to be solved.Therefore,based on the multiple advantages of MOFs,we design a variety of multi-structured MOFs material catalysts for HER,OER,or dual-function electrocatalytic water splitting,respectively.The main achievements of this dissertation are as follows:1.The mixed solvent method was used for the first time to prepare the metal-organic framework by self-assembly with a transition metal?Co,Ni?,2,6-naphthalene dicarboxylate acid?NDC?ligand.Based on the two-dimensional?2D?nanosheets with the same structure,the electronic structure of the MOF catalytic center was adjusted and optimized,and its electrocatalytic oxygen generation performance?OER?was studied.The Co₈Ni₁-NDC exhibits excellent OER activity with a lower overpotential of 298 m V at a current density of 10 m A·cm^-2 in 1.0 M KOH electrolyte and it is far superior to the OER performance of Ni-NDC two-dimensional nanosheets.Through the innovation of this MOFs synthesis method,the structure of the material does not change,but different crystal planes are exposed,thereby improving the electrocatalytic performance.The design of the metal nodes further optimizes the electronic structure of the intrinsic catalytic center in MOFs and improves the electrocatalytic performance for OER.2.Herein,a universal one-pot hydrothermal reaction method is reported to grow well-aligned 2D Ni Fe-metal-organic framework?Ni Fe-BPDC?array grown directly on a nickel foam substrate.Through the design of the MOF metal node,the electronic structure of the catalytic active center is adjusted to improve the electrocatalytic performance.It is demonstrated that the optimized catalyst?Ni₅Fe₁-BPDC?is a highly efficient electrocatalytic performance toward the oxygen evolution reaction?OER?and hydrogen evolution reaction?HER?,with a lower overpotentials of 239 m V(at a current density of 25 m A·cm^-2)and 120 m V(at a current density of 10 m A·cm^-2)in alkaline medium,respectively.The overall water splitting using these 2D Ni₅Fe₁-BPDC based catalysts shows 100 h stability at 1.64 V,suggesting a promising pathway forward for the commercial realization of complete water-splitting systems.The high-performance activity is the result of abundant surface coordinatively unsaturated metal atoms,as well as the addition of Fe that is also crucial to enhance the activity.3.We introduced a controllable in-situ vulcanization strategy,using 3D Co Fe-MOF-74 as a self-sacrifice template to partially generate highly conductive ultra-small nanosheet Co Sx species from Co ions,the resulting Co Sx@MOF-74hybrid exhibit enhanced electrocatalytic activity and long-term stability.The optimal Co₃S₄@Co₂Fe₁-MOF-74 electrocatalyst can effectively catalyze water oxidation at a low overpotential of 232 m V at 10 m A·cm^-2 in 1.0 M KOH alkaline solution.The current density is almost maintained even after a long period of 100 hours.It provides a new way to design highly ordered MOF-based surface-active materials?instead of being used as templates and/or precursors for high-temperature calcination?to efficiently produce oxygen and stable electrocatalysts.