Theoretical Investigations Of Transition Metal Atoms Incorporated In 2D Materials As Single Atom Catalysts

Transition metal particles supported on the two-dimensional(2D)materials have been widely investigated in many important heterogeneous catalytic reactions.When reducing the size of the transition metal particles to single atoms,the performance of the catalysts can be greatly improved due to the electronic structure and unsaturated coordination envronment of the single metal atom[1-3].At the same time,the two-dimensional materials as substrates provide a large specific surface area,and the metal atoms are uniformly dispersed on such substrates to form a rich collection of active sites,and thus greatly improves the utilization efficiency.However,there are significant challenges in designing and preparing stable single atom catalysts(SACs).Transition metal atoms would easily diffuse and agglomerate due to their high mobility on the substrates.Therefore,the suitable two-dimensional materials as substrates of SACs are of great importance.With the development of computers and density functional theory,it is easier to design and explore new high-efficiency catalysts.We applied adsorption energy,charge density analysis,density of states,d-band center theory,transition state search,reaction pathway analysis and other methods to systematically study the process of three types of two-dimensional materials loading transition metal single atoms as SACs.The main content of our thesis is as follows:(1)The 2D N-doped carbon materials:The 2D phthalocyanine(Pc)loading with a series of transition metal atoms(TM-Pc)are investigated as the SACs for propane dehydrogenation(PDH).Considering density of states and Br(?)nsted-Evans-Polanyi theory,the 2D Ru-Pc with the lowest reaction energy for C-H activation(1.01 eV)and a suitable propylene adsorption energy(-0.55 eV)is ranked as the potential PDH catalyst.The 2D pyridine-N2(N2/C-a,N2/C-b)adopted by a series of transition metal atoms(TM-N2/C)are studied as bi-functional catalysts for HER and OER.The H adsorption free energy(△GH)and free energy of the water dissociation(△GHzO)are regarded as essential factors to realize high catalytic activity for HER in the acidic/alkaline medium.The overpotential in the PDS(potential-determining step)is the evaluation standard of the OER performance.The result turns out that Ni-N2/C-a exhibiting the outstanding activity for HER and OER for a wide pH range.(2)The 2D Si-doped carbon materialsThe 2D Siligraphene(SiC,SiC2,SiC3,SiC5,SiC7 with different Si/C doping ratios anchored by a series of transition metal atoms(TM-SiCx)are studied as SACs.For SiC,Pt-SiC acts as a stable and efficient HER catalyst.For SiC2,SiC3,SiC5,SiC7,TMs are easily agglomerated on the surfaces forming different types of magic clusters.(3)The 2D metal sulfide materialsThe 2D VS2 embedded by single atom Cu(Cu-VS2)as SAC for the ORR.The single atom Cu adsorbed firmly on the top of the V atom serves as an independent and highly efficient catalytically active site for the ORR.The 2 e-ORR path:(1)O2(g)+H++e-→OOH+,(2)OOH*+H++e-→HOOH becomes the optimal with the overpotential of 0.49 V.