Synthesis And Oxygen Reduction Reaction Performance Of Cobalt Nitrogen Doped Carbon And Composite Materials Derived From MOFs

In recent years,fuel cells have attracted extensive attention as the clean,efficient and sustainable energy devices.Yet,the sluggish kinetics of oxygen reduction reaction is an important factor affecting the performance of the fuel cells.Up to date,Pt-based catalysts are still the outstanding ORR catalysts,whereas they are susceptible to methanol poisoning leading to catalytic performance degradation.At the same time,the high price and limited resources restrict their large-scale commercial production.Therefore,it is an effective way to develop non-precious metal materials with low cost,highly efficient catalytic activity and stability to replace the platinum base catalysts for application of commercial fuel cells.MOF-derived metal nitrogen doped carbon and its composite materials are the potential substitute for platinum based catalysts in ORR.MOFs have the advantages of high chemical stability,thermal stability,large specific surface area,adjustable pore structure and high carbon content.The metal nitrogen doped carbon materials were prepared by high temperature pyrolysis can maintain the porous structure of the MOFs precursors.And,the active sites of the materials are distributed uniformly in the carbon layer.In this paper,we use the Co-MOF crystal as precursor,and investigated the effect of calcination temperature of MOF-derived cobalt nitrogen-doped porous carbon materials on ORR performance.The cobalt nitrogen doped carbon/carbon nanotube composites were prepared by mixing Co-MOF and other nitrogen source followed by high temperature calcination in inert atmosphere,and were further investigated on ORR performance.Then,the effects of different calcination temperature,different nitrogen content of the ligand and composite materials on electrocatalytic performance were studied.The research content is as follows:1.The 3D[Co?INA?₂]·0.5EtOH were prepared by a facile solvothermal reaction,using Co?NO₃?₂·6H₂O and isonicotinic acid as raw material.A series of Co-N/C catalysts were prepared by carbonization of[Co?INA?₂]·0.5EtOH precursor at different temperatures?700,800 and 900°C?.The Co-N/C materials were tested using the standard three electrode system for ORR,and the influence of calcination temperature on the catalytic performance was investigated.The results show that the Co-N/C-800 has higher catalytic activity compared with Co-N/C-700 and Co-N/C-900,with a positive onset potential of-0.13 V?Ag/AgCl?and a large limiting current density of 3.9 mA/cm^-2.The stability and tolerance to methanol crossover properties of the material are tested used chronoamperometry measurements.After the reaction 12000 s,Co-N/C-800 retained 86.8%of its initial current density.Whereas Pt/C exhibits only 69.5%retention.In short,Co-N/C-800 catalyst exhibits higher stability in alkaline solution than Pt/C.2.The 3D[Co₂?u-OH₂??pyc?₄]?DMF?were prepared by a facile solvothermal reaction,using Co?NO₃?₂·6H₂O and pyrimidine-5-carboxylic acid as raw material.The cobalt nitrogen doped carbon materials were prepared by carbonization of[Co₂?u-OH₂??pyc?₄]?DMF?precursor in the inert atmosphere at high temperature.We fabricated catalysts by using different nitrogen containing MOFs precursors and explored the influence of the MOFs-derived materials on ORR performance.The results show that electrocatalytic activity of cobalt nitrogen doped carbon material obtained by pyrolysising[Co₂?u-OH₂??pyc?₄]?DMF?at 800°C exhibits onset potential of-0.13 V?Ag/Ag Cl?and a limiting current density of 4.2 mA/cm^-2,which are better than the[Co?INA?₂]·0.5EtOH derived material at the same condition,its electric catalytic performance close to commercial Pt/C material.3.The Co nanoparticles N-doped carbon encased CNT?Co-N/C@CNT?composites was prepared by one step carbonization of the[Co?INA?₂]·0.5EtOH and melamine.The[Co?INA?₂]·0.5EtOH as precursor,melamine as a secondary source of nitrogen and carbon source.The composition,phase and chemical structure of the Co-N/C@CNT were tested and analyzed.The ORR electrochemical properties of Co-N/C@CNT show a larger limiting current density of 4.8 mA cm^-2 than commercial Pt/C(4.1 mA cm^-2).The tolerance to methanol crossover and stability of composite materials were tested using chronoamperometry.The results showed that the Co-N/C@CNT catalyst exhibited higher stability and tolerance to the methanol crossover effect in alkaline solution than those of Pt/C.The excellent ORR catalytic performance of Co-N/C@CNT materials is due to bamboo-like carbon nanotube structure with higher conductivity as well as the synergistic effect of different types of component facilitating fast electron and proton transfer.