Preparation And Performance Reaserch Of PtRh Alloys Catalysts For Ethonal Electro-oxidation

Recently,direct alchohl fuel cells(DAFCs)have been more and more applied for portable devices owing to their high power density and environmental benignity.Among these,the use of ethanol in direct ethanol fuel cells(DEFCs)offers high energy density(8.0 kWh kg-1),low toxicity,easy storage and transport,and can be mass produced from agricultural biomass.As such,ethanol affords a promising alternative to the traditional fossil fuels of coal,natural gas,petroleum etc.Catalysts play a key role to energy conversion efficiency in DEFCs applications.Currently,Pt/C is widely used as a catalyst for ethanol electro-oxidation in DEFCs.However,it is difficult to break the C-C bond in ethonal for Pt/C catalyst duo to its poor catalytic activity.And the high cost and easy poisoning of Pt/C catalyst hinder the commercialization of DEFCs.Consequently,it is urgent to develop more efficient catalysts and increase the utilization of platinum.Presently,alloying Pt with other metals is an effective method to improve the catalytic activity of Pt-based catalysts due to the synergistic effect bettwen them.Besides,improving the catalytic activity and stability of Pt-based catalysts by the interaction between metals and supports is another foucus in reaserch.In this thesis,we prepared different PtRh alloys nanoscale materials from two aspcets,and investigated their physic-chemical performance as DEFCs anode catalysts.The main contents and conclusions are as follows:(1)The catalytic performance reaserch for ethanol electro-oxidation of PtRh alloy catalysts decorated with TiO2Firstly,the TiO2-C hybrid materials were prepared by the thermal decomposition method.Then,the Pt and Rh nanoparticles were reduced on the surface of TiO2-C hybrid by using NaBH4.Finally,the obtained powder was annealed at 300? under N2 atmosphere at ambient pressure for 2 h.As previously reported,catalysts produce the best catalytic performance when atomic ratio of Pt/Rh is 9:1.Therefore,we prepared the catalyst with the atomic ratio of Pt/Rh is 9:1,which denoted as Pt9Rh/TiO2-C.XRD and STEM results demonstrate that PtRh alloy nanoparticles are uniformly distributed on the TiO2-C hybrid supports.And the electrochemical characterization results display that the peak current density of Pt9Rh/TiO2-C catalyst achive 1039.5 mA mgpt-1,which is 8.31 times higher than that of Pt/C catalyst.Meanwhile,the onset potential of Pt9Rh/TiO2-C catalyst is more nagertive than that of other compared catalysts,which exhibt an amazing resistance to CO-poisoning.(2)The catalytic performance reaserch for ethanol electro-oxidation of PtRh alloy catalysts supported by WN-CNTs hybrid materialsFirstly,the post-treated carbon nanotubes(CNTs)were mixed with ammonium tungstate(AMT)under vigorous stirring,then the dried powders were annealed under NH3 atmosphere at 800 0C for 2 h,the resulting products were WN-CNTs hybrid materials.Next,the Pt and Rh nanoparticles are reduced on the surface of WN-CNTs support by NaBH4.Finally,the obtained powder are annealed at 300? under N2 atmosphere at ambient pressure for 2 h to form alloys,which is denoted as Pt9Rh/WN-CNTs.XRD and SEM show that the PtRh alloys particles are distributed uniformly on WN-CNTs support,and TEM results show that the average particle size of Pt9Rh/WN-CNTs is 5.36 nm.And the electrochemical test results show that the peak current density of Pt9Rh/WN-CNTs is 484.8 mA mgPt-1,which is 3.59 times higher than that of Pt/WN-CNTs catalyst.More importantly,the onset potential of Pt9Rh/WN-CNTs catalyst is 0.27 V,130 mV more negative than that of Pt/CNTs catalyst,which shows excellent CO anti-poisoning performance.(3)The preparation of Pt9RhFex/C ternary alloys catalysts and their catalytic performance reaserch for ethanol electro-oxidationWe prepar the catalysts via one-pot process as following:the Pt,Rh and Fe particles are reduced on the carbon surface by NaBH4,then the product is annealed at 300? under N2 atmosphere at ambient pressure for 2 h to form ternary Pt9RhFex alloys.Different catalysts maintained the atomic ratio of Pt to Rh at 9:1,with different Fe contents(x = 1,3,5,7 and 9).The electrochemical test results indicate that the catalyst of atomic ratio composition 9:1:3(Pt/Rh/Fe)has the best catalytic performance.From STEM,we can observe that the ternary Pt9RhFe3 alloy particles uniformly distributed on the support with fine particle size.From XPS and STEM-EDX line scan,we can see there is a Pt-rich property on the surface of the particle,which ensure that the catalyst stable in acidic electrolyte.The results of CV accelerated test and chronoamperometry test demonstrate that Pt9RhFe3/C catalyst has high stability.Moreover,the catalyst with such atomic ratio shows excellent CO-poisoning tolerance in CO-stripping test,and more stable than commercial PtRu/C catalyst.