Preparation And Electrocatalytic Performance Of High-melting Metal-doped Pt Base Alloy Nanocrystals

Polymer electrolyte membrane fuel cells?PEMFCs?feature high energy densities,low operating temperatures,and low environmental impact,which make it a promising technology for power applications.As a key component of PEMFCs,Pt-based catalysts are still under widespread investigation and have shown exciting performance;however,to move towards their successful commercialization,focusing solely on their catalytic activity is not sufficient.Instead,more effort is required to improve their stability and to decrease their costs.In this thesis,the electrocatalytic properties of Pt-based nanocrystals doped with the high-melting-point metal elements,which have been consider as stabilizing elements,are investigated.The research is focused on the following aspects:1).For PtCuNi alloy nanocrystal catalysts,which are synthesized with monodispersity in size through facile solvothermal approach,a unique acid treatment protocol is employed to remove organic capping agents and obtain clean surface as well as the hollow structure.The surface W doping was further carried out in order to drastically achieve the enhancement of activity and durability towards oxygen reduction reaction?ORR?.The ORR electrochemical measurements reveal that as-synthesized 111-PtCuNi-W/C catalysts show drastically enhanced ORR performance compared with 111-PtCuNi/C catalyst.They display a mass activity?MA?of 2.42 A/mg_Pt and specific activity?SA?of 2.22 mA/cm²,with15.1-and 9.25-fold enhancements,respectively,compared with the commercial Pt/C(0.16 A/mg_Pt of MA and 0.24 mA/cm² of SA).Their electrochemical stabilities have also been greatly improved.After 20000 cycles of accelerated durability test?ADT?test,the MA and SA decreased only by 36%and 44%.2).Based on results on surface doping,bulk doping?or alloying?is further studied to reveal the role of W atoms.Nanocube PtW_x,PtCu_xW_y,truncated octahedral poly-PtNi_xW_y and multi-branched hyper-PtNi_xW_y are synthesized by simple one-pot method.The PtCu_xW_y/C catalysts exhibit high ORR electrocatalytic stability.After20000 cycles of ADT test,the ECSA increases from 76.69 to 105.08 m²/g_Pt with a 37%increase,and SA decreases by only 27%,while the MA does not show any decline.The MA and SA values of poly-PtNi_xW_y/C are 9.7 times and 11.0 times those of the commercial Pt/C catalysts.By comparing the doping effects of nanocrystals with different compositions which are synthesis by different synthetic routes,it is found that the doping of W element could significantly improve the catalytic activity and stability of nanocrystalline catalyst,which may be related to the electronic vacancies and the thermodynamic stability of the high melting point metal.In this thesis,the effect of W-doping is systematically evaluated in the form of surface and bulk doping,which provides a new strategy for improving the electro-catalytic performance of Pt-based alloy catalysts.