Preparation And Investigation Of The Highly Stable Anode Catalysts In Direct Methanol Fuel Cells

Among varieties of fuel cells,direct methanol fuel cells(DMFCs)are promising in mobile electric devices due to their high energy density,abundant reserves of fuel and wally potability.Unfortunately,improving the durability for methanol oxidation of catalysts is one of the most important challenges to the commercialization of DMFCs.Pt is widely used as a catalyst for fuel cell,but pure Pt is easily poisoned by CO and CHx when designing an effective methanol oxidation.Common strategy to alleviate deactivation of pure Pt is alloying Pt with other metals,such as Ru,Sn and Co.Among them,the PtRu system displays the best performance for methanol oxidation,because the oxidation of CO on Pt is promoted by Ru atoms at lower potential via a bi-functional mechanism.However,Ru dissolution at high potential remains major problems for the invalidation of fuel cells.Thus,it's of great urgency to reduce Ru dissolution in PtRu system.This article aims to reduce Ru dissolution and slow the process of metal migration and coalescence.By two different strategies of the carrier effect and the component effect,we designed highly stable anode catalysts in DMFCs.And main research contents were listed below.On the one hand,we have synthesized the graphene(G)by microwave exfoliation of graphitic oxide,and nitrogen-doped graphene(NG)was then synthesized by microwave-heating of graphene in deoxy NH3 atmosphere.The XPS analysis showed that a negative shift was seen in the binding energy of N 1 s after loading with PtRu NPs,which should be attributed to the electrons transfer from Pt and Ru to N-based groups.And the EDS mapping could prove that Pt and Ru NPs are clustering around N sites of N-containing carbon,rather than showing a random distribution on carbon.As seen in TEM images,we directly observed that PtRu NPs of PtRu/NG showed less migration and coalescence trails after methanol oxidation operation because of increased metal-support interaction caused by N-doping.After accelerated aging CV test,the peak current density in the forward sweep at the PtRu/NG showed a decrease of only 33%.As a comparison,the peak current density in the forward sweep at the commercial PtRu/C and PtRu/G were 43%and 45%,respectively.Meanwhile,the decrease of onset potential at commercial PtRu/G and PtRu/G were 190 mV and 210 mV,while the decrease of onset potential at PtRu/NG was only 20 mV.The accelerated aging CV results indicated that PtRu/NG showed better long-term catalytic stability than PtRu/G and commercial PtRu/C.In particular,N-doping slows the decrease of onset potential,proving that N-doping has a positive impact on reducing Ru dissolution.On the other hand,we have synthesized PtRuAu/C catalysts from commercial PtRu/C by an easy impregnation method.And the content of Au-doping was controlled by adjusting concentration of the impregnation solution.As seen in electrochemical testing results,we can find that Au-doping has a positive impact on enhanceing stability of the catalysts.The XPS analysis showed that a positive shift was seen in the binding energy of Pt 4f and Ru 3p after doping with Au element,which should be attributed to the electrons transfer from Pt to Au.And the same procedure was happened on Ru.As seen in TEM images,we directly observed that Metal NPs of PtRuAu/C-0.5 showed less migration and coalescence trails after methanol oxidation operation because of increased interaction caused by Au-doping.After accelerated aging CV test,the peak current density in the forward sweep at the PtRuAu/C-0.5 showed merely no decrease,while the peak current density in the forward sweep at the commercial PtRu/C were 43%.Meanwhile,the decrease of onset potential at commercial PtRu/C was 190 mV,while the decrease of onset potential at PtRuAu/C-0.5 was only 10 mV.The accelerated aging CV results indicated that Au-doping is beneficial for the minimization of metal migration and coalescence,and it slows Ru dissolution meanwhile.