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Advanced energy materials: ordered Pt Zn nanoparticles with biaxial stress modulation structure -- efficient and stable cathode catalyst for proton exchange membrane fuel cell

wallpapers News 2020-07-10
As a clean efficient environment-friendly energy conversion device

proton exchange membrane fuel cell (PEMFC) has been widely concerned studied by researchers. At present carbon supported platinum nanoparticles (Pt / C) are commercially used as electrode catalysts but their activity stability are still low which has not yet reached the goal of DOE. Platinum based alloys such as platinum nickel (PT Ni) platinum cobalt (PT CO) platinum iron (PT FE) alloys have high catalytic activity can reduce the amount of platinum to a great extent. They have become star catalysts in this field. However transition metals such as Fe CO Ni are easy to be oxidized dissolved lost under the high temperature high voltage conditions of fuel cell operation resulting in the decline of catalyst activity; in addition these transition metal ions may catalyze the Fenton reaction produce free radicals to attack the proton exchange membrane catalytic layer also lead to the failure of fuel cell. In view of this the research group of Professor Li Qing School of materials Huazhong University of science technology has carried out targeted research on this problem designed a platinum zinc (L10 ptzn) nanoparticle catalyst with ordered intermetallic phase which shows excellent fuel cell performance long-term operation stability.

firstly the research team developed a "Self-protection" method to solve the problem of generally large size of platinum based intermetallic phase using zinc oxide as a physical protective layer to prevent the size growth of nanoparticles successfully prepared monodisperse L10 ptzn / Pt nanoparticles catalyst with the size of 4 nm (Fig. a). On the one h ZnO can be used as a zinc source to provide Zn Pt alloying oxygen vacancies in the reduction process of ZnO can accelerate the phase transformation process improve the order degree. Further studies on the properties mechanism show that: (1) after the phase transition from disordered A1 ptzn to ordered L10 ptzn biaxial stress is introduced at the coherent interface between the inner ptzn core the outer Pt shell (Fig. b) including the tensile stress along < 110 > direction the compressive stress along < 011 > direction. Both of them regulate the stress state of the PT shell to achieve a moderate compressive stress so as to improve the oxygen content Reduction / fuel cell activity; (2) after the phase transition from disordered A1 ptzn to ordered L10 ptzn the vacancy formation energy of zinc atoms in the lattice is greatly improved which improves the stability of materials in fuel cell test (Fig. C); moreover compared with the vacancy formation energy of 3d transition metals in L10 PtNi L10 PTFE L10 PtcO systems the vacancy formation energy of Zn is higher which may be related to L10 PtNi -The results show that the formation energy of ptzn system is more negative (Fig. d); (3) Zn element shows higher resistance to Fenton reaction which reduces the yield of free radicals the damage to the catalytic layer proton exchange membrane improves the operation stability of the fuel cell to a certain extent. The results of

have certain significance for the structure design of cathode catalyst of PEMFC which is helpful to further improve the activity of oxygen reduction catalyst the stability of operation under fuel cell conditions. The related work is supported by the National Natural Science Foundation of China the State Key Laboratory of material forming mold technology of Huazhong University of science technology.

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