Design Principles And Catalytic Mechanism Research Of Transition Metal Contained Electrocatalysts For Oxygen Evolution And Reduction Reaction

Due to the limited of the fossil energy and pollution from its combustion,clean energy is urgently needed to change status.Clean energy technologies such as fuel cells,metal-air batteries,and water-splitting devices are effective means to solve the energy problems.In the process of energy conversion and storage,two key reaction processes are involved:oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Because the rates of the two reactions are relatively slow under standard conditions,traditional platinumgroup metals(PGM)catalysts are commonly used to catalyze those reactions.To facilitate the reaction process,the state-of-the-art catalysts,Pt is used to catalyze ORR while Ir/IrO2,RuO2,etc.to catalyze OER processes.The scarcity and high cost of precious metal resources have greatly restricted the large-scale commercialization of PGM catalysts.Therefore,scientific researchers are committed to finding cheap and easy-to-obtain platinum-group metal free(PGMF)catalysts to replace the PGM.For some PGM catalysts still have no definite reaction path and design principles in the experiment.Therefore,in this paper,a new novel of transition metal atoms(TM)contained catalyst structures were built.Based on density functional theory(DFT),studied the theoretical catalytic activity and mechenaism of each catalytic structure,discussed the catalytic mechanism of the catalyst,and explored the descriptors to predict and screen the outstanding structures,and provided a series of design principles for the rational design of catalysts in the experiments.The main research contents and innovations of the full text are as follows:(1)A new hybrid heterostructure of SAC was built which combined the stability of graphene with the properties of transition metal halide salts.Four groups of graphene-covered divalent transition metal halide salts were designed,namely G/TMF2,G/TMC12,G/TMBr2,G/TMI2(TM=Sc,Ti,V,Cr,Mn,Fe,Co,Ni,Cu,Zn).The electron transfer between graphene and halide salts molecules changes the electronic structure of graphene,while the metal ions still exert their metallic properties,enhancing the catalytic activity of the structure.This type of material separates the active metal part and the acidic or alkaline reaction medium,which can improve the long-term durability of the material to a certain extent.DFT was used to calculate the adsorption energy,electronic structure distribution and elementary reaction of the intermediates on the G/TMX2 surface during the OER/ORR reaction.The Gibbs free energy of each step in the process was also calculated;the adsorption energy of the intermediate product was used as the descriptor to plot the relationship between structures and its catalytic activity.Among them,G/CrBr2 exhibits excellent bifunctional catalytic activity in the 4-electron transfer process,with the overpotential of OER is 0.36V,ORR is 0.35V;G/CoF2 exhibits the best catalytic activity in the process of generating clean energy H2O2 during the 2-electron transfer process,with the overpotential is 0.03V.At the same time,it was proposed that the electric field force induced by metal ions may affect the catalytic activity of G/TMX2 and used it as an intrinsic descriptor to express the catalytic activity of the structures.Meanwhile,the catalytic activity was also related to the d-band center of the spin-down d electrons.(2)Synergistic effect of the metal atoms pairs in DACs further promote the catalytic performance.Collaborators synthesized the NiFeNC DAC in the experiment.Since the structure-activity relationship between structure and catalytic performance was not clear,by DFT calculation,the order of catalytic activity in the ORR catalytic process was Fe-NiNC?FeNC>FeNC-NiNC>NiNC.Computational results showed that Fe-Ni metallic pair could facilitate the break of the O-O band after O2 absorbed on the activity site,which is beneficial to the ORR process.(3)The synergistic effect of NiFe pair in the NiFe DAC effected the catalttic activity in OER/ORR process.Thus there will be a flash of the combination of different bimetals may exist a series of catalysts with excellent catalytic activity.Single TM atom,double TM atoms,triple TM atoms and nitrogen coordinated graphene catalysts were built to compare their catalytic properties.According to the DFT calculation,the catalytic activity of DACs performed preeminent catalytic activity than SACs and TACs.Importantly,some catalytic structures showed excellent bifunctional catalytic performance for OER/ORR process.Among them ZnCoNC performs outstanding bifunctional catalytic activity with the overpotential of OER is 0.13 V and ORR is 0.12V.DACs breaks the linear relationship between the adsorption energy in SAC,moving the catalytic activity of DACs closer to the ideal catalyst.Through analysis,the catalytic mechanism of the OER/ORR reaction process on the surface of the catalyst in the 4-electron reaction pathways is generated,and an internal electric field force induced between the bimetallic atoms is explored to describe the catalytic activity and the catalytic activity of DACs,and proposed a design principle of DAC as bifunction catalysts.(4)Since the defects of the structure and the synergistic effect of metal atoms pairs have great effect on the catalytic activity,the combination of those two will be surely affected the catalytic activity in somehow.Among PGMF catalysts,2-D layered double hydroxides(LDHs)has the potential to replace the commercial PGM catalysts due to their unique electronic structure.Ultrathin NiFe-LDHs(Nano Sheets,NSs)expose more metal active sites than LDHs,thereby improving OER catalytic activity.Through DFT calcution investgated the OER process on NiFe-LDH NDs and found that electron transfer between Ni and Fe metal atoms caused by defects affected the catalytic activity.Additionly,edge defects and H vacancy on the surface of NiFe-LDH NDs also have influence on catalytic activity.What's more.The calculation results showed that the overpotential of the defect structure of NiFe-LDH NDs in OER process could as low as 0.22V.Innovations of this paper:Four groups of novel heterogeneous catalyst structures G/TMX2 and three groups of bimetallic atom catalyst DACs were built.By DFT calculations,the catalytic mechanism process on each structure were systematically analyzed,and two new intrinsic descriptors were eatablished to predict the catalytic activity and define the design principles of this type of catalytic structure in OER/ORR process;determined the catalytic mechanism and the structure-activity relationship between the catalytic activity and Ni-Fe LDH NDs with abundant edge defects in the OER process.Provided new design principles and strategies for the construction and design of catalysts for oxygen reduction and oxygen evolution reaction processes in energy conversion and storage.