Research On Molybdenum Carbide-based Hydrogen Oxidation Catalysts Of Proton Exchange Membrane Fuel Cell

With the merits of zero emission and high efficiency,Proton exchange membrane fuel cells（PEMFCs）are considered to be a promising alternative to fossil fuels and conventional batteries.PEMFCs have already been commercialized and used in many fields.However,with the biggest obstacle of high cost,PEMFCs still cannot be extensive used.Nowadays,PEMFCs cathode catalysts have been reported in a large number of studies,with the accomplishment of reduced Pt loading.Unfortunately,the study on anode catalysts has been shelved for many years,which also affect the total Pt loading in fuel cells especially when the Pt loading on cathode has been reduced to a reasonable level.Therefore,there is an urgent demand on developing anode catalysts with simplified preparation processes,low cost,high catalytic activity and high stability to meet the market requirements.Mo₂C has Pt-like HOR catalytic properties.When combined with a low Pt loading to form a Pt-Mo₂C composite catalyst,it can not only greatly reduce the amount of Pt used,but also maintain high catalytic activity and stability.This thesis introduces the research status and progress of fuel cell anode catalysts.In our work,the stable and feasible synthesis methods of molybdenum carbide-based hydrogen oxidation catalysts of PEMFCs have been established which can greatly reduce the amount of Pt loading,and the reasons and mechanisms of catalytic activity and stability improvement of molybdenum carbide-based anode catalysts also have been explored respectively.Moreover,it provides a new way on the precise design and synthesis of ultra-low platinum loading anode catalysts.Firstly,different synthesis methods of Mo₂C/NC have been explored,the nitrogen doping of BP2000 carbon black support was realized,Mo₂C/NC and 4%Pt-Mo₂C/NC anode catalysts have been synthesized by the suitable synthesis route.Their catalytic activities and stabilities for hydrogen oxidation reaction have been studied.The Pt mass fraction of 4%Pt-Mo₂C/NC anode catalyst was 3.42%,which greatly reduced the loading of Pt,and obtained similar catalytic activity of hydrogen oxidation to that of commercial JM 20%Pt/C catalyst.After 1000 cycles of CV scanning,the current density of the LSV curve decays slightly,showing good catalytic stability and durability.At the same time,the open circuit voltage of 50cm² MEA assembled single cell is 0.956V,its Pt loading of anode is 0.012mg/cm²,and its maximum power density is 700mW/cm².Secondly,different synthesis methods of Mo₂C/NCNT have been explored,the nitrogen doping of carbon nanotube support was realized,Mo₂C/NCNT and 4%Pt-Mo₂C/NCNT anode catalysts have been synthesized by the suitable synthesis route.Their catalytic activities and stabilities for hydrogen oxidation reaction have been studied.The Pt mass fraction of 4%Pt-Mo₂C/NC anode catalyst was 3.26%,which greatly reduced the loading of Pt,and obtained similar catalytic activity of hydrogen oxidation to that of commercial JM 20%Pt/C catalyst.After 1000 cycles of CV scanning,the current density of the LSV curve decays negligibly,showing excellent catalytic stability and durability.At the same time,the open circuit voltage of 50cm² MEA assembled single cell is 0.956V,its Pt loading of anode is 0.012mg/cm²,and its maximum power density is 792mW/cm².Finally,through the precise design of the catalyst morphology and structure,nitrogen-doped HCS@Mo₂C and nitrogen-doped HCS@Mo₂C-4%Pt core-shell hydrogen oxidation anode catalysts have been synthesized for the first time by simple stirring and temperature programmed reduction.The catalytic activities and stabilities of NHCS@Mo₂C and NHCS@Mo₂C-4%Pt have been studied separately.The in-situ nitrogen-doped hollow carbon spheres are evenly distributed and without agglomeration,the particle size is about 200 nm.Mo₂C and Pt particles with a particle size²-5 nm covered on hollow carbon spheres uniformly.The specific surface area of the NHCS@Mo₂C-4%Pt core-shell anode catalyst is>450 m2/g,its Pt mass fraction is 3.80%,which greatly reduced the loading of Pt,and obtained better catalytic activity of hydrogen oxidation than that of commercial JM 20%Pt/C catalyst.After 1000 cycles of CV scanning,the current density of the LSV curve decays negligibly,showing excellent catalytic stability and durability.At the same time,the open circuit voltage of 50cm² MEA assembled single cell is 0.955V,its Pt loading of anode is 0.012mg/cm²（1/4 of DOE anode Pt loading）,and its maximum power density is 877mW/cm².Its MEA performance is comparable to that of high Pt loading anode catalyst reported by DOE.