Preparation And Properties Of Transition Metal Carbon-Supported Oxygen Reduction Catalysts

With the increasing energy crisis and environmental issues,there is an increasing demand for efficient,clean and sustainable energy conversion and storage devices.Proton exchange membrane fuel cells?PEMFCs?and zinc-air batteries?Zn-air?have attracted much attention in recent years due to their safety,pollution-free and high energy density.However,whether it is PEMFCs or Zn-air battery,the slow electrochemical process in which the cathode oxygen reduction reaction?ORR?seriously hinders its further development.At present,platinum-based catalysts are widely used on the market,but their high cost and ease of being deactivated by the reaction intermediate occupying the active site affect the stability and further affect the large-scale application.In this paper,a series of transition metal type ORR catalysts were prepared on the basis of summarizing the research results of ORR electrocatalyst in recent years,which were summarized as follows:1.Preparation of high catalytic activity Co-N-C catalyst and application in electrocatalytic oxygen reduction reactionIn this work,a metal-organic complex synthesized by using p-phenylenediamine and cobalt nitrate was reported for the first time.And metal cobalt nanoparticle loaded on porous carbon with high graphitization degree was prepared by high-temperature carbonization treatment,and the influence of preparation temperature on catalytic activity of the material was discussed.Due to the characteristics of the complex,a certain amount of nitrogen is also doped during the carbonization process.The catalytic performance of the material is greatly improved by removing the large metal cobalt particles with no catalytic activity by the acid washing process.The effect of acid washing process on the catalytic performance of the material was further discussed,and the catalytic active site was further determined to be Co-N-C structure.The catalyst was applied to the Zn-air battery and also showed excellent performance.2.Synthesis of Fe,N Co-doped carbon materials and application in oxygen reduction reactionWe first reported a preparation method of a cadmium metal organic complex,and thus a porous carbon material was prepared at a lower temperature?400??.At the same time,catalytically active metal iron ions were introduced in the synthesis process,and the influence of different molar ratios of cadmium ions and iron ions on the structure of the prepared complex was explored.The effect on the properties of the catalyst and material at different carbonization temperatures were further discussed.At the same time,because the organic ligand used in the prepared material is p-phenylenediamine,which is rich in amino groups,which can be introduced a amount of nitrogen in the process of carbonization.After optimization,3-5 nm Fe nanoparticles were uniformly loaded on porous,ultra-thin two-dimensional nitrogen doped graphene-like carbon material and exhibited excellent catalytic activity.At the same time,it was applied to the Zn-air battery and showed excellent performance.3.Exploring the effect of doping type in carbon supported Mn based catalysts on their oxygen reduction performanceThe performance of the catalyst depends mainly on the type and content of the active sites.Based on summarizing the previous work,in this work we introduced Mn²⁺ions in the process of preparing cadmium metal organic complexes,and prepared cadmium manganese bimetallic organic complexes?CdMn-PPD?.The prepared complexes are carbonized under different atmosphere conditions,such as Ar,H₂/Ar mixed gas and NH₃to obtain materials with different catalytic active sites.At the same time,all of them contain 3-5 nm Mn-based nanoparticles.The particles are uniformly loaded on the porous carbon material.Meanwhile,the active site of the Mn-N_x structure was confirmed by XPS under NH₃ conditions.As oxygen reduction reaction catalysts,their performance were estimated and their active sites were discussed in detail.We found that the performance of the catalyst obtained under NH₃ conditions is much higher than that formed under H₂conditions.It is main due to in the alkaline test environment,the active site of Mn-N_x is easier to react with oxygen.Furthermore,applied in the Zn-air battery,the test resusts were consistent with above results,further demonstrating that Mn-N_x has excellent catalytic activity.