Synthesis Of Transition Metal-carbon Catalysts And Electrocatalytic Ammonia Oxidation Performance

Ammonia is gaining interest in hydrogen storage,hydrogen production,and fuel cells due to its advantages as an excellent hydrogen carrier and carbon-free fuel,as well as its excellent infrastructure and supply chain that can be put into production directly.The key to employing ammonia is the ammonia oxidation reaction（AOR）,and the three factors of high oxidation overpotential,low current,and easy to poison the catalyst surface have restricted the development of AOR,which is especially evident in AOR transition metal catalysts,while the better performing Pt-based catalysts have the limitations of high cost and low storage capacity.In recent years,many transition metal-based catalysts with excellent AOR catalytic performance have emerged,providing new solutions to the above problems.Thus,with reference to previous authors and combined with practical research,the specific research of this thesis is as follows.（1）Firstly,the catalysts were synthesized by a one-step solvothermal method by combining Ni,Cu and Co nitrates with single-walled carbon nanotubes（SWCNTs）already homogeneously dispersed in ethanol solution with the aim of obtaining high currents,and two sets of comparison experiments were set up without the addition of Co and without the addition of SWCNTs.the best performance of Ni-Cu-Co/CNT catalyst was obtained with a ratio of 2:1:1.The physical characterization suggested that the metal salts were all present in the catalyst as hydroxides and hydroxyl oxides,and cyclic voltammetry（CV）tests showed that the best catalyst had an onset potential of 0.3 V vs.Ag/Ag Cl and a peak current of 96m A cm^-2.Density flooding theory（DFT）indicated that Cu as the adsorption center would preferentially adsorb NH₃,and the addition of Co and CNT led to a decrease in the energy barrier of the critical the addition of Co and CNT leads to a reduction of the energy barrier of the key AOR reaction step thus exhibiting high activity for AOR catalysis.In conclusion,the high activity of the catalysts is attributed to the metal-to-metal synergy formed by the ternary metal system and the metal-carrier interaction due to SWCNTs,which provides an idea for the research of new AOR catalysts.（2）Further,a copper phthalocyanine（Cu Pc）catalyst grown on carbon fiber cloth（CFC）by seeding method assisted by solvothermal method was investigated by using Cu as the main metal of the catalyst in order to achieve low potential in conjunction with the conclusion of DFT in the previous chapter,and the sample with ethanol content of 10 m L was experimented as the best performance（Cu Pc@CFC）.The Cu Pc loading on CFC was confirmed by physical characterization.In electrochemical tests,the peak potential of Cu Pc-CFC in AOR was-0.29 V vs.Hg/Hg O,outperformed the reported Pt/C.And copper pyridyl azide(C₁₀H₁₀Cu N₈)was found in the samples after AOR.DFT calculations showed that Cu-N4 is the reaction center of AOR and the LUMO of Cu Pc is distributed on the Cu site,which facilitates the adsorption of Cu Pc from NH₃ gaining electrons and thus adsorbing NH₃;on the contrary,the HOMO of C₁₀H₁₀Cu N₈ is distributed on the Cu site and tends to give electrons,which is not favorable for NH₃ adsorption.In conclusion,from this part of the experiment,it was learned that changing the ethanol content has the effect of changing the d-energy center and Fermi energy level as well as inhibiting the generation of C₁₀H₁₀Cu N₈,and the difference between 2 different Cu-N₄ type catalysts in AOR,which provides a new idea of catalyst making for the future use of phthalocyanine type catalysts in various fields of AOR.