Preparation And Electrocatalytic Performance Of Manganese-rich MOF-derived Catalyst

Fuel cell has the advantages of high efficiency,high environmental protection and low pollution,and it is one of the most promising energy technology in contemporary society.However,the oxygen reduction reaction（ORR）with slow kinetics during the cathode reaction inhibits the rapid development of fuel cells.As a catalyst,platinum（Pt）-based electrocatalyst has low initial potential and high current density in ORR reaction,which can greatly improve efficiency.It is widely used as ORR electrocatalyst,but its scarce reserves,high price and poor stability seriously hinder the further development of fuel cells.Therefore,it is necessary to study other low-cost and high-performance materials and design new catalysts with high oxygen reduction reaction activity to replace Pt-based precious metal catalysts.The transition metal element manganese（Mn）is rich in reserves,low in price,and variety of chemical valences.Research has found that the catalyst containing Mn has good catalytic performance.（1）By using the co-precipitation method,Mn was doped into Co MOF（ZIF 67）.Through controlling the ratio of different metals Mn and Co and the heat treatment temperature,Mn-ZIF 67 samples were obtained.XRD,SEM and other physical characterization methods and electrochemical workstation tests were carried out to confirm the best Mn:Co ratio is 1:2 and carbonization temperature is 600°C.The MnCo-1:2-600 sample still maintains the same dodecahedral structure as that of the original of ZIF 67.And BET results show that the specific surface area is 195 m²g^-1,and the pore diameter is between 3-4 nm,indicating a loose and porous,which is beneficial to the exposure of active sites.The electrochemical test results indicate the starting potential and the half-wave potentials for oxygen reduction are 0.89 V and 0.80 V,respectively,indicating that its catalytic activity is equivalent to that of commercially available Pt/C.After 10,000 cycles of cyclic voltammetry test in a 0.1 M KOH solution saturated with O₂,the half-wave potential has only a negative shift of 8 mV,indicating good stability.（2）Mn MOF and Mn MOF/carbon materials were prepared by solvothermal method.First,different metal Mn salts were used to prepare Mn MOF materials.By comparing its morphological characteristics and electrochemical properties,it is determined that the best metal source for the preparation of MOF materials is manganese chloride.Carbon black and graphene were compounded to form MOFs/carbon composite catalysts.Through characterization and comparison of electrochemical performance,the best Mn MOF@rGO sample was obtained.Then N doping was performed to further improve its performance.The best N doping amount is confirmed when the mass ratio of Mn MOF@rGO and melamine is 1:1,named N-Mn MOF@rGO-1:1.The electrochemical test results show that the initial potential and half-wave potential are 0.88 and 0.76 V,respectively.After a long cycle test of 10,000 cycles,the half-wave potential was negatively shifted by 20 mV.