Design Of Non-Precious Metal ORR Catalysts And CO-tolerant HOR Catalyst For Proton-Exchange Membrane Fuel Cells

Fuel cells are electrochemical devices capable of converting chemical energy into electrical energy directly,have attracted great attention owing to their high efficiency and low emissions in recent years.Currently,some problems still exist that hindered their large-scale commercialized application.In the cathode region of the fuel cell,a large amount of Pt need to be used due to the relatively slow kinetic process of oxygen reduction reaction.However,the precious and resource scarcity of Pt greatly increased the cost of fuel cells,it is an urgent need to develop a cheap non-precious oxygen reduction catalyst to replace Pt.While in the anode region of the fuel cells,the existing Pt based catalyst is easily poisoned by CO,making the reforming gas which contains contaminated CO can not be used directly.Therefore,it is of great significance to develop a HOR catalyst with high CO tolerance.In this paper,we focus our research on the two issues discussed above:for the cathode region of the fuel cell,we designed a highly activite Co-N/C oxygen reduction catalyst and discussed the active site of carbon-based ORR catalyst.While for the cathode region,we designed a RuSn/TiO2 catalyst with high CO tolerance and discussed the coating effects of titanium oxide on the surface of Pt and it's influence on HOR activity and CO tolerance.The results are as follows:(1)We reported the preparation of a highly active Co-N/C catalyst through pyrolysis the precursor which made by in situ growth a layer of Zif-8 and Zif-67 film on the surface of carbon black with high specific surface and electrical conductivity.The as-prepared Co-N/C catalyst exhibited a half-wave potential of 0.77 V vs.RHE in acidic media and power density of 0.92 W cm-2 in the H2/O2 fuei cell test.After 20 hours of test under 0.77 V,the Co-N/C catalyst still maintained 73%of the initial activity,showing good stability.(2)We have prepared a series of Co-N/C catalysts with different contents of Co nanoparticles.The results of XPS,TEM,SEM and XRD show that the metal-nitrogen is the active center of the catalyst.Co nanoparticles have no activity for ORR,but can enhance the activity of metal-nitrogen structure.For the catalysts which content a lot of Co nanoparticles,removing Co nanoparticles can improve the activity by increasing the exposed metal-nitrogen active sites.However,when the content of Co nanoparticles in the catalyst is low,the removal of nanoparticles will reduce the ORR activity of catalyst.(3)We have designed a model catalyst with MLG covered FePc by using structured monolayer graphene and FePc molecular.The results have shown that the FePc molecules can influence the electric property of graphene through electronic interaction,making the inert graphene layer with ORR activity.Which means that the active center of ORR catalyst can still catalyze oxygen reduction after it was covered by a monolayer graphene.(4)The high CO tolerance HOR catalyst RuSn/TiO2 was prepared by a SnCl2 reduction and NaOH treatment process.The catalyst was able to maintain 80%of the original activity after 16 hours of test under 0.1 V in 1000 PPM CO+H2 saturated 0.1 M H2SO4 solution.We have founded that the surface modified oxides can great influence the CO tolerance ability.(5)We designed a metal-metal oxide model catalyst by modifying a layer of porous TiO2 on the surface of Pt sheet.It was found that the modification of TiO2 can create a HOR active region on the surface of Pt which would not be poisoned by CO.this region would highly improve the CO tolerance of Pt.