Theoretical Study On Catalytic Performance Of Some Graphene-based Materials

With the rapid development of industrial technology and the consumption of fossil energy,energy and environmental issues have been increasingly prominent.The clean energy conversion device is an effective way to solve the relevant problems.The fuel cell is one of energy conversion devices with high energy efficiency and no pollution to the environment.The Pt-based catalysts used in the cathode of traditional fuel cells have hindered the rapid development of commercialization due to their high price,low abundance,low durability and CO poisoning.The related experimental and theoretical studies have found that the metal-free doped graphene materials can be used as a potential electrode catalyst for the substitution of Pt-based catalysts.Based on the dispersion-corrected density function theory（DFT-D）calculations,this article studies Sulfur doped graphene（SGV）as a metal-free electrocatalyst for oxygen reduction reaction and the mechanisms of the direct synthesis of hydrogen peroxide（DSHP）on silicon and phosphorus dual doped graphene（Si-P-G）.The main research work and results are shown,as below:1.The detailed kinetic and thermodynamic behaviors of the entire ORR process on SGV,as well as the original mechanism are investigated by DFT-D calculations.It is found that the SGV is rather stable and the sulfur dopant is probably the active center.There are two proposed ORR pathways by kinetic process: the dissociation of OOH and the hydrogenation of OOH with the rate-determining steps of 0.75 eV and 0.62 eV,respectively.And the Gibbs free energy diagram of the entire ORR indicates that the hydrogenation of HOOH is the most favorable pathway even at high potential of 0.86 V.Our DFT-D simulation reveal that the SGV have the novel catalytic activity for ORR.2.The mechanisms of DSHP on the metal-free Si-P-G catalyst,based on DFT-D,are systematically investigated.The most stable Si-P-G is presented and the local region with dopants displays an important role for the adsorption and reduction of oxygen.The two-electron pathway is probable for DSHP on Si-P-G according to the analysis of the kinetics and thermodynamics.The hydrogenation of O₂ to OOH is the rate-limiting step with the small barrier energy of 0.66 eV and the potential energy surface is downhill by Gibbs free energy calculations.All results indicate that Si-P-G as a novel catalyst has the high activity and good selectivity for DSHP.