Preparation And Performance Of Transition Metal And Nitrogen Co-Doped Porous Carbon For Oxygen Reduction Reaction

As one of the green energy technologies,proton exchange membrane fuel cell?PEMFC?has broad application prospect.Cathode oxygen reduction reaction?ORR?is the key process of PEMFC.At present,the expensiveness and scarcity of Pt/C catalyst hinder the widespread commercial application of PEMFC.The key step to reduce the cost of PEMFC for commercial production is to prepare an alternative catalyst that has properties of inexpensiveness,high performance and stability.Among them,transition metal and nitrogen co-doped carbon material is one of the non-precious metal materials that has received extensive attention,and possesses many advantages,such as widely available precursors,environmentally friendly,strong resistance to CO poisoning and high immunity to fuel crossover.However,the performance and stability of the prepared catalysts still cannot meet the requirements of commercial application,and the complicated preparation process and high cost prevent PEMFC from large-scale production and application.This thesis develops a simple synthesis scheme of inexpensive transition metal and nitrogen co-doped carbon material catalysts.A series of effective characterization and electrochemical performance tests were implemented to analyze the influence of structural composition on the performance of the catalysts.The research provides a theoretical support for the ORR mechanism study and catalyst preparation process,and provides a substitute for the precious metal Pt/C catalyst.The contents of this thesis are as follows:?1?Crystalline Co nanoparticles encapsulated by sp²-C rich nitrogen-doped sheet-like carbons was facilely synthesized with the aid of melamine-containing hydrogen-bonded organic frameworks?HOF?which were precoated with a thin layer of in-situ polymerized dopamine coordinated with Co²⁺cations?Co@DA-HOF?.After pyrolyzing the Co@DA-HOF precursor,irregular sheet-like Co@MPC-T samples comprising a large number of Co nanoparticles as well as abundant mesopores were obtained,attributing to the decomposition of thermally volatile HOF microrods that helped generate porous structures in the resulting catalyst samples.Thus-synthesized nitrogen-doped 2D carbon composites encapsulating Co nanoparticles at 800? were found to display the highest ORR catalytic activity among the series,characterizing with a half-wave potential of +0.796 V,a limiting current density of 5.492 mA cm^-2 at +0.200 V,and a kinetic current of 51.40 mA cm^-2 that is even markedly higher that the 20.10 mA cm^-2 for commercial Pt/C catalyst.Moreover,benefiting from the protection of sp²-C rich carbon layer,Co@MPC-800 showed substantially higher operation stability and superior tolerance to fuel crossover,as compared with commercial Pt/C catalyst.?2?The metal organic framework UiO-66 was used as a template on which dopamine was polymerized in situ to form a thin film polymer layer which was subsequently coordinated with the Co²⁺cation.In the pyrolysis process,Co-coordinated polydopamine was carbonized under the support of UiO-66 template,and the cobalt-nitrogen co-doped carbon nanoparticles?Co@NP-T?were obtained,which have abundant mesopores and large specific surface area(947.78 m²g^-1).Co nanoparticles and nitrogen co-doped carbon nanoparticles exhibit excellent ORR catalytic activity,and it is determined that the material pyrolyzed at 700? shows the highest ORR catalytic activity in the series,characterizing with a half-wave potential of +0.863 V,a limiting current density of 5.918 mA cm^-2 at +0.200 V,which can be attributed to large specific surface area and rich mesoporous,three-dimensional nanoparticle structure,which facilitates oxygen adsorption and changes electron distribution of nitrogen-doped carbon.