The Design Of Two-dimensional MOFs Materials And Their Catalysis For Energy Conversion Reactions

In recent years,as global warming and energy problems become increasingly serious,it has become imperative to accelerate the development of clean energy and achieve efficient conversion and storage of sustainable energy.Oxygen reduction reaction（ORR）,nitrogen reduction reaction（NRR）and hydrodeoxygenation reaction（HDO）are significant reactions in fuel cell,ammonia technology and value-added lignin conversion processes,respectively.The increase in efficiency of these catalytic reactions is crucial for alleviating environmental pollution and energy shortage.The exploration of new catalysts with high efficiency,durability and low cost will greatly facilitate the replacement of fossil fuels by renewable energy sources.In this dissertation,we designed a new class of two-dimensional metal-organic frameworks（2D-MOFs）materials:M₃（C₆X₆）₂（M is transition metal,X is NH,S,O）based on density functional theory.Their structures,properties and cataytic performances in different energy conversion reactions have also been systematically investigated.Firstly,we explored the catalytic performance of two-dimensional M₃（C₆O₆）₂（M=Cr,Mn,Fe,Co,Ni,Cu,Ru,Rh and Pd）materials as oxygen reduction electrocatalysts and screened the optimal catalysts among these nine different 2D-MOFs.Owing to the sufficientπ-electron conjugation and effective interaction between the metal and the organic linkers,the studied 2D M₃（C₆O₆）₂are all metallic with good conductivity for electron transfer.Interestingly,the catalytic activity of M₃（C₆O₆）₂can be modified by changing the metal atoms with different d-electron occupations.Remarkably,while Mn₃（C₆O₆）₂,Fe₃（C₆O₆）₂,Rh₃（C₆O₆）₂and Co₃（C₆O₆）₂show a rather good ORR activity rivaling that of Pt,Co₃（C₆O₆）₂presents a much higher onset potential than that of Pt and becomes the best ORR catalyst among the studied two-dimensional M₃（C₆O₆）₂.Based on the previous study of 2D M₃（C₆O₆）₂materials,we investigated the potentials of using Mo₃（C₆X₆）₂（X=NH,S,O）monolayers as effective NRR electrocatalysts.Similar to 2D M₃（C₆O₆）₂,the Mo-based MOFs show the porous planar structures and can be regarded as single-atom catalysts.As we expected,this type of material also possesses good electrical conductivity.The Mo atom is found to be highly effective for nitrogen adsorption and activation.Our thermodynamic computations reveal that all three catalysts have good NRR catalytic performance.In addition,Mo₃（C₆S₆）₂monolayer is a promising NRR electrocatalyst due to its smallest limiting potential（-0.37 e V）and effective inhibition of the HER competition reaction.We further studied the ability to catalyze HDO of lignin-containing derivatives（phenol）using the same Mo₃（C₆X₆）₂（X=NH,S,O）monolayer.Through first principles calculations,we found that phenol can be spontaneously adsorbed on the catalyst surface in a vertical configuration.For the deoxygenation reaction of phenol,the Mo₃（C₆X₆）₂prefer to follow the hydrogenation pathway for catalysis.Among these three catalysts,Mo₃（C₆S₆）₂and Mo₃（C₆O₆）₂have better HDO catalytic performance than Mo₃（C₆（NH）₆）₂.These results provide new ideas for the design of value-added catalysts for deoxygenation of lignin-containing derivatives and promote the development of biomass energy conversion.