Quantum Chemical Design And The Catalytic Performance Prediction Of M-N-C Catalysts

With the development of modern civilization,the problems of energy shortage and environmental pollution caused by energy use are attracting more and more attentions.Fuel cell is a device that can directly convert chemical energy into electrical energy,which has attracted widespread attention due to its clean,efficient,and quiet characteristics.Volatile organic compounds（VOCs）are seriously harmful to both the environment and human.Conversion of VOC by fuel cell has the advantages of clean,efficient,and pollution-free,which is a promising approach for the VOC treatment,but the slow kinetics of cathodic oxygen reduction reaction（ORR）limits the development of fuel cells.The slow kinetics of ORR requires the application of catalysts to accelerate it,of which M-N-C catalysts are one of the most promising ORR catalysts.Some of the catalysts can remove VOC by direct catalytic oxidation,but only if the VOC are capture and activated.In this thesis,density functional theory（DFT）we used to investigate the ORR activity and VOC capturing and activation ability of M-N-C catalysts,which are important for both fuel cell development and environmental protection.Theoretically designed M-N-C catalysts,Zn-N-C,Ni-N-C,and Co-N-C catalysts were built and optimized based on ZIF-8 materials.Four Ni-N-C and Co-N-C catalysts including（C₃N₂H₃）₂Ni,（C₃N₂H₃）₄Ni,（C₃N₂H₃）₃Co,and（C₃N₂H₃）₆Co₂ were selected by calculating and analyzing quantum chemical properties such as frontline molecular orbitals and Fukui index,and ORR activity studies were performed.The Gibbs free energy changes of the ORR pathways of（C₃N₂H₃）₂Ni,（C₃N₂H₃）₄Ni,（C₃N₂H₃）₃Co,and（C₃N₂H₃）₆Co₂ catalysts were calculated,and it was found that the highest reaction energy barrier of ORR can be reduced by 0.02e V on（C3N2H3）2Ni compared with the catalyst-free system,and reduced on 0.19e V on（C3N2H3）3Co.Indicate that both（C3N2H3）2Ni and（C3N2H3）3Co are possible ORR catalysts.In order to improve the ORR activity of the catalysts,S-doped was introduced on（C3N2H3）2Ni and（C3N2H3）3Co,and the structure of the doped catalysts was optimized,it was found that the stability of the catalysts decreased with the increase of S content by calculating the binding energy.The quantum chemical properties and Gibbs free energy of the catalysts were calculated and analyzed,and it was found that（C3N2H3）2Ni-2S,2,3S,-2,5S,-3,5S,-2,3,5S,（C3N2H3）3Co-2S,-3S,-14S,-2,3S,-12,16S,-2,3,5S,-2,8S,-2,9S,-2,11S,-3,8S,-3,9S,-3,11S,-12,5S,-14,3S may be used as ORR catalysts.Among them,（C3N2H3）3Co-2,3,5S,-2,8S,-12,5S,and-14,3S are most likely to be used as ORR catalysts.The ability of M-N-C catalysts to capture and activate VOC was investigated,the VOC model was optimized,the adsorption energy of VOC on the surface of M-N-C catalysts was calculated,and the changes of VOC bond lengths before and after adsorption were analyzed.The results show that（C3N2H3）2Ni,（C3N2H3）3Co,（C3N2H3）2Ni-2S,2,3S,-2,5S,-3,5S,-2,3,5S and（C3N2H3）3Co-2S,-12,16S,-2,8S,-12,5S,-14,3S are capable of VOC capturing and activation and are expected to be used for VOC removal.