Preparation And Performance Study Of Nitrogen-Doped Carbon-Based Non-Precious Metal Oxygen Electrode Catalysts

The large-scale application of energy storage and conversion technology such as fuel cells and Zn-Air batteries is one of the important approaches to realize the sustainable utilization of energy.However,the slow oxygen electrode reactions in these devices usually depend on precious metal catalysts.The high cost is an important issue that hinders the large-scale application of these technologies.Nitrogen-doped carbon-based non-precious metal catalysts with high catalytic activity,good stability,and low cost,is becoming one of the most promising candidates to replace precious metal catalysts.The aim of this thesis is to develop efficient nitrogen-doped carbon-based non-precious metal catalysts and to study the chemical composition,microstructure and catalytic active sites of catalysts.The main aspects are as follows:（1）Carbon-based single atomic catalysts are widely used in the field of catalysis due to their excellent performance.However,when the traditional high-temperature pyrolysis method is used to synthesize non-precious metal carbon-based catalysts,the metal atoms will inevitably aggregate,and thus difficult to prepare single atomic catalysts.Fe single atom catalyst was prepared by using the polydopamine nanospheres as the precursor with a novel Si O₂ coating strategy.Firstly,a thin Si O₂shell was coated on the polydopamine spheres.The nitrogen-doped carbon-based catalyst with surface anchored Fe single atom was prepared by nanofiltration and limited pyrolysis of Si O₂ shell,which helped to absorb appropriate Fe Cl₃ and prevent the aggregation of Fe atoms.Due to the highly exposed Fe-N₄ active sites on the surface of the carbon-based catalyst,hierarchical porous structure and high graphitization of carbon matrix,the catalyst showed excellent catalytic activity for oxygen reduction in both alkaline and acidic media.The onset and half-wave potentials was 1.00 V and 0.84 V（vs.reversible hydrogen electrode（RHE））respectively in alkaline media.After 20000 s of continuous operation,it still exhibited excellent stability and also excellent tolerance to methanol.The Zn-Air battery based on the Fe single atom catalyst also showed excellent performance,with a peak power density of 107 mWcm^-2 and a specific capacity of 710 m Ah g.（2）High-performance bifunctional catalysts for oxygen reduction reaction and oxygen evolution reaction are essential for the application of rechargeable Zn-Air batteries,but usually the preparation method of carbon-based bifunctional catalyst is complicated and the catalytic performance is poor.Dopamine and transition metal salts were used as raw materials,the carbon-based bifunctional electrocatalyst with Fe Co alloy nanoparticles embedded was prepared by a simple and efficient liquid phase mixing reaction and high temperature pyrolysis method.The co-doping of two metals（Fe and Co）enhanced the N content of the carbon-based catalyst and increased the specific surface area of the catalyst,and the synergistic effect between the Fe Co alloy and the nitrogen-doped carbon matrix improved the bifunctional catalytic performance of the catalyst in alkaline media.The protection of the graphite carbon layer on Fe Co alloy nanoparticles improved the long-term stability of the catalyst.The bifunctional catalytic performance of Fe Co alloy catalyst exceeded that of Fe or Co single metal catalysts.The onset potential and half-wave potential of the oxygen reduction reaction in 0.1 M KOH electrolyte was 0.92 V and 0.80 V（vs.RHE）,respectively.After working for 10000 s,the current retention rate was 91%.The over-potential of oxygen evolution reaction in 0.1 M KOH electrolyte was 386 mV,and it had excellent catalytic stability of oxygen evolution reaction.This work provides inspiration for the development of bifunctional catalysts with high catalytic activity and good stability.