Preparation Of M-N-C Oxygen Catalysts And The Research On Their Electrocatalytic Activity

In recent years,with people’s attention to key issues such as sustainable development,the demand for clean energy equipment in various countries is also increasing.Metal-air batteries have the advantages of high theoretical energy density,low discharge product pollution and relatively low price.More and more attention has been paid by countries.As a key material in metal-air batteries,the air electrode plays a crucial role in the performance of the battery,but considering the slow kinetics of oxygen reduction and oxygen evolution,the development of an inexpensive and efficient catalyst is important for metal-air batteries.Among the numerous candidate electrocatalysts,metal-nitrogen-carbon catalysts have received extensive attention due to their relatively low cost and activity comparable to noble metal catalysts.In this study,two strategies for regulating active sites of metal-nitrogen-carbon materials were investigated to comprehensively improve the discharge performance of metal-air batteries,and elucidate the catalytic mechanism of oxygen reduction.The specific research work of this paper is as follows:（1）High-temperature pyrolysis of melamine and ethylenediamine with Co²⁺,Fe³⁺,and Zn²⁺chelates was performed to synthesize a nanoparticle with Co Fe nanoparticles coexisting with Co/Fe-N_x sites without using a hard template.A carbon-supported transition metal material with a hierarchical porous structure（high macropore ratio）at the same time.The unique organizational structure is beneficial to expose more catalytically active sites and accelerate the transport of reaction intermediates.It exhibits excellent oxygen reduction activity in both 0.1 M KOH and 3.5 wt.%Na Cl solutions,with half-wave potentials of 0.91 V（vs.RHE）and 0.61 V（vs.RHE）,respectively.By assembling the catalyst into an Al/Mg-air battery,it was found that it outperformed the commercial Pt/C assembled battery in all aspects,with peak powers of 271.2 m W cm^-2 and 24.5 m W cm^-2 for Al-air battery and Mg-air battery,respectively.The catalyst plateau voltage of 1.4 V for Al-air batteries at a current density of100 m A cm^-2 is much higher than 1.3 V for Pt/C.（2）The citric acid and Co²⁺/Zn²⁺are formed into a gel,and melamine is filled between the Co Zn-citric acid chains.After calcination,a porous carbon material with Co₃Zn C nanoparticles and fluffy carbon nanotubes uniformly distributed on the surface is obtained.The half-wave potential of 0.88 V（vs.RHE）in 0.1 M KOH is similar to that of Pt/C,and the Zn-air peak power of 140 m A cm^-2 assembled into Zn-air is much higher than that of Pt/C,and the cyclic charge-discharge 350 h no significant increase in process polarization for hours.Through characterization and analysis,Co₃Zn C nanoparticles play a very important role,and the electronic structure of cobalt carbide doped with zinc is changed,which improves the oxygen reduction activity of the material.At the same time,the porous structure and carbon nanotubes covering the surface of the substrate play a positive role in improving the oxygen reduction activity.