Synthesis Of Single-Atom/Cluster Catalysts For Oxygen Reduction By Metal Chloride Vapour Capture Method

In terms of cost and catalytic performance,the great advantages of single-atom catalysts make them a promising substitute for platinum-based oxygen reduction（ORR）catalyst.The vapour capture method（using the vapour of metal oxides or ammonia complexes）reported in the literatures is a very innovative synthesis method.But there are still some problems,such as lack of universality,using additional corrosive ammonia.Based on the fact that the melting/boiling point of most transition metal chlorides is obviously lower than that of their oxides（polarization effect）,this dissertation directly used them as vapour sources to improve the universality of the method.The lower melting point means that it has a higher vapour pressure at the same temperature,which can effectively increase the metal loading.And there is no need to use extra corrosive gas,which can simplify the experimental process and reduce the experimental cost.The main research contents are as follows:（1）Manganese single-atom catalyst（Mn SAs/N-C）was synthesized by the vapour capture method.Manganese chloride was used as the vapour source and the carbonized ZIF-8 was used as the carrier.The experimental results show that the loading of Mn in Mn SAs/N-C is 3.61 wt.%.The specific surface area of it is as high as 1833 m²·g^-1.In alkaline media,Mn SAs/N-C exhibits high electrocatalytic activity for the oxygen reduction reaction.The half-wave potential reaches 0.904 V（vs.RHE）.After 2000cycles,the polarization curve changes little.And the mass activity is 0.83A·mg_Mn^-1 at overpotential of 0.9 V.When it is applied to the cathode catalyst of zinc-air battery,the output power（311 m W/cm²）is significantly higher than that of commercial platinum carbon（236 m W/cm²）.（2）The above experimental idea was extended to the copper catalyst system.The vapour source was replaced by copper chloride,and the Cu_SA/Cu_AC-N-C catalyst was successfully prepared.A series of characterizations such as AC-HAADF-STEM and XAS have verified that the catalyst was in the form of coexistence of copper single atoms and clusters.Electrocatalytic performance of the catalyst for the ORR was evaluated.In alkaline medium,the half-wave potential and Tafel slope of Cu_SA/Cu_AC-N-C(0.898 V vs.RHE,57.3 m V·dec^-1)are far better than that of commercial platinum carbon(0.867 V vs.RHE,70.9 m V·dec^-1),which exhibit excellent catalytic activity toward ORR.