The Electrochemical Measurement Of MOFs-derived Non-precious Metal-doped Carbon For The Catalysis Of Oxygen Reduction Reaction

The electrochemical reactions in fuel cells include anodic hydrogen oxidation reactions（HOR）and cathodic oxygen reduction reactions（ORR）.The reaction rate of the HOR is normally fast and high current densities can be easily obtained.While the reaction energy barrier of the cathode ORR reaction is often high,the reaction is kinetically controlled and slow at low temperature.Effective catalysts are required to reduce the energy barrier of the reaction.Nowadays,widely used commercialized catalyst is platinum on carbon（Pt/C）.Although its catalytic performance is excellent,since the platinum is a precious metal,the poinsoning problem and its high cost due to the scarcity actually limit the commercial production and widely utilization in fuel cells.Therefore,development and preparation of low cost non-precious metal catalysts with high catalytic activity and stability,good anti-poisoning ability is the most effective way to solve these problems.The transition metals and nitrogen co-doped carbon-based catalysts（TM-N-C）are the most promising alternatives to replace the catalyst of Pt/C due to their rich sources,low cost,high catalytic activity,good stability and resistance to poisoning.Metal organic frameworks（MOFs）are one of the most promising precursors for the preparation of TM-N-C catalysts because of their inherent properties such as highly ordered three-dimensional framework structure,controlled porosity and tunable chemistry.Based on these facts,the TM-N-C catalysts were prepared by adding polymers during the synthesis of Co-MOF and Fe-MOF,and the influence of morphology and elemental composition on the catalytic performance was studied.The dissertation is divided into the following four chapters:In the first chapter,the classical electrochemical research methods are briefly introduced.Then the principle of oxygen reduction reaction and various oxygen reduction catalysts are summarized.The preparation and catalytic effect of TM-N-C catalyst based on MOFs are introduced.Finally,the main application of oxygen reduction reaction-fuel cell is presented.In the second chapter,the polymer nanospheres（PNS）synthesized by3-aminophenol and formaldehyde was added when synthesizing Co-MOF,and then the pyrolysis was carried out at high-temperature to obtain hierarchical porous structure carbon nanocatalyst（Co-N-C-W+E）in which the cobalt particles are embedded in the carbon layers.Comparing the morphology and catalytic performance of the material obtained by using only one ligand or two ligands in the presence of PNS,it was found that the catalytic performance of the material obtained by adding only one ligand was obviously inferior to that of two ligands.The results are the consequence of the unique structure of Co-N-C-W+E obtained by two ligands in the presence of PNS,which is the carbon layers with cobalt metal particles embedded.This type of hierarchical porous structure is favorable for the ORR activity of the catalyst.In the third chapter,in order to further prove that PNS can prevent the carbon skeleton of MOFs from completely decomposition during pyrolysis.We added the PNS and polyvinylpyrrolidone（PVP）when synthesizing Fe-MOF to stabilize the carbon skeleton of MIL-101-Fe and introduce nitrogen atom as a dopant.After pyrolysis at high temperature,Fe-N-C was formed.The morphology and catalytic performance of the materials obtained by adding PNS or PVP individually and both of them were studied.It was found that adding PVP only could change the morphology of MOF,but when carbonized at high temperature,it was completely decomposed into iron and iron oxides.The addition of PNS could stabilize the frame of carbon during carbonization,the agglomeration of Fe particles was more serious.Addition of PNS and PVP at the same time not only introduced the nitrogen dopant,but also improved the dispersion of Fe particles,promoted a uniform distribution of active sites,and enhanced ORR catalytic performance.In the fourth chapter,ZIF-67 synthesized in aqueous solution was coated a layer of polyfurfural by a self-polymerization reaction of furfural,and then pyrolyzed at a high temperature.During this process,ZIF-67 was completely decomposed,the polymerized furfural coated in ZIF-67 formed a hollow spherical structure.The effects of different amounts of furfural on the catalytic performance were investigated.It was found that Co-N-C-800-3 obtained by adding 3 mL of furfural exhibited a positive half-wave potential and a larger current density.It exhibits superior catalytic activity(half-wave potential:0.83 V vs 0.82 V;current density:5.73 mA cm^-22 vs 4.28mA cm^-2),better stability and methanol tolerance than Pt/C in the alkaline media.