Bi-Functional Oxygen Electrocatalysis Of Manganese-based Composites

For the further development of new energy devices such as fuel cells and metal-air batteries,the high price and low stability of noble metal-based electrocatalysts are the bottlenecks.Therefore,it is of great significance to develop new bifunctional oxygen electrocatalysts that is both efficient and cheap.Non-precious transition metal-based electrocatalysts are one of the alternate for their abundant reserves and high catalytic activity.In particular,manganese-based electrocatalysts have received much attention due to the low cost,hypotoxicity and competitive oxygen evolution reaction?OER?activity.However,the low oxygen reduction reaction?ORR?activity of manganese-based catalysts restricts its application to bifunctional oxygen catalysts.Based on the above problems,the purpose of this dissertation is to improve the oxygen reduction catalytic activity of manganese-based electrocatalysts by constructing different composite forms of materials,and also preliminary study the principle of performance enhancing.In addition,this dissertation also provides new research ideas for the design and development of other non-precious transition metal-based bifunctional oxygen electrocatalysts.The main research content of the entire dissertation is as follows:?1?A manganese-based catalyst precursor was first prepared by wet ball milling with citric acid as a ligand and a carbon source,and after calcination,the composite material of M/MnO/C?M=Co,Ni,Cu?obtained.The ORR catalytic activity of composite materia are tested,and the electrocatalyst materials are also tested for bifunctional oxygen electrocatalysis based on the optimal conditions.It is found that when the ratio of Co/Mn was 1:8,the sample shows the best oxygen reduction activity with the half-wave potential of0.819 V.After a preliminary discussion of the principle of performance improvement,the results obtained can also provide research ideas for the design of other composite catalysts.?2?As the ORR properties of materials obtained in the previous chapter still have a large gap compared with the Pt/C catalysts,and the stability of materials are also not very satisfactory,a new composite of Co/MnO/N-C is prepared by solvothermal method and subsequent calcination process with the using of N-Methyl-D-glucamine as nitrogen and carbon source.The ORR activity and stability of the complexes are further enhanced by the presence of nitrogen-doped carbon,and the as-prepared hybrid also displayed high efficient electrocatalytic activity of OER.The half-wave oxygen reduction potential is 0.822 V and the oxygen evolution overpotential is only 379 mV.This synthesis method can also be extended to the synthesis of other non-precious transition metal-based catalysts and thus has a certain significance.?3?The manganese oxides have not always been the most desirable manganese-based electrocatalysts,and the solvothermal heat used in the previous chapter is also a extreme synthetic method.Based on the above problems,a new composite of Co/Mn₄N/N-CNTs is prepared by ball milling and subsequent calcination process with the using of dicyandiamide.The nitrogen-doped carbon nanotubes which are catalyzed by cobalt,entangled Mn₄N to form a special structural composite,further enhancing the oxygen reduction electrocatalytic activity?half-wave potential is 0.825 V?compared to manganese oxides.After exploring the calcination temperature and adding metal species on the effect of phase and morphology for the electrocatalysts,the optimum synthesis conditions are determined.The results show that the Co/Mn₄N/N-CNTs hybrid is an efficient bifunctional oxygen electrocatalyst.