Synthesis Of Co-based Nitrogen-doped Carbon Electrocatalysts And Investigation Of Their Oxygen Reduction Reaction Performance

The transition metal-based electrocatalysts（M-N-C）with nitrogen-doped carbon as supports haves high electrocatalytic activity for oxygen reduction reaction（ORR）.They have great potential in proton exchange membrane fuel cell（PEMFC）and metal-air cell.Considering the growing commercial demand for renewable energy,it is critical to prepare catalysts with high catalytic efficiency and stability through simple and efficient strategies.Porous materials have the structural advantage of large specific surface area and chemical stability.The porous structure enables the electrolyte to enter the active site within the electrocatalyst more quickly,ensuring effective contact between the electrolyte and the electrode surface,thus facilitating the charge transfer between the electrolyte-electrode interface.In this thesis,a series of porous material electrocatalysts were prepared by template method.The structure and morphology of the catalysts were characterized by XRD,XPS,HR-TEM,AC HAADF-STEM and XAFS.ORR activity of catalysts was evaluated by cyclic voltammetry（CV）and Linear Sweep Voltammetry（LSV）.The main research contents of this paper are as follows:1)In this paper,a three-dimensional N-doped mesoporous carbon（NC）supported Co-N-C catalyst Co Clusters/NC was developed by using sodium EDTA-Na₂ as the soft template,and the mixture of metal salt and 2-methylimidazole as the precursor of Co,N,and C.XRD,BET,TEM,AC HAADF-STEM and XPS characterization confirmed abundant mesoporous structures and active sites in the carbon framework.The Co clusters/NC exhibits a remarkable ORR performance with excellent activity(onset and half-wave potentials of 0.99 V vs.RHE and 0.89 V vs.RHE,a Tafel slope of 59.2 m V dec^-1 and J_k of 25.48 m A cm^-2 at 0.85 V)and stability（10 m V activity decay after 20000 cycles）.In addition,the catalyst demonstrates great promise in substituting for a traditional Pt/C catalyst in zinc-air batteries while maintaining high performance in terms of high specific capacity of(822.5 m Ah/g _Zn),power density（181.3m W/cm²）,and long-term cycling stability（80 h）.The preparation methodsheds light on the construction of stable and efficient electrocatalysts.2)Here,we report an efficient approach combining dopamine-mediated synthesis,annealing,metal anchoring,and NH₃ activation to create a single atom cobalt electrocatalyst Co SAs/NC.A dopamine-mediated method was employed to slow down the nucleation rate of zeolitic imidazolate framework-8（ZIF-8）in water to form monodispersed ZIF-8 nanocrystals.Then,a thermal treatment was conducted,with the evaporation of zinc atoms,to yield a nitrogen-doped carbon（NC）support.Co SAs/NC exhibits a remarkable ORR performance with excellent activity(onset and half-wave potentials of 1.04 V vs.RHE and 0.90 V vs.RHE,a Tafel slope of 69.8 m V dec^-1 and J_k of 18.8 m A cm^-2 at 0.85 V vs.RHE)and stability（7 m V activity decay after 10000 cycles）.In addition,the catalyst demonstrates great promise in substituting for a traditional Pt/C catalyst in zinc-air batteries while maintaining high performance in terms of high specific capacity of(796.1 m Ah/g _Zn),power density（175.4m W/cm²）,and long-term cycling stability（140 h）.The work provides ideas for rational design of MOFs derived metal monatomic catalysts with ultra-high specific surface area to improve the performance of oxygen reduction in fuel cells or metal air cells.