Engineering Phase And Surface Composition Of Supported PtM Alloy Electrocatalysts

Proton exchange membrane fuel cell(PEMFC)have many advantages such as high energy efficiency,environmental friendliness and convenient.It is considered as the uppermost power supply for transportation vehicles and electronic products in the future.At present,The problem of CO poisoning in reforming hydrogen at the anode and the sluggish kinetics and the poor durability of the ORR at the cathode are bottlenecks restricting the development of PEMFC.Herein,this work aims to provide theoretical guidance for the design and preparation of Pt based alloy catalysts which can be used in PEMFC.The main works include the following several parts:(1)Engineering phase and surface composition of Pt3Co model nanocatalysts via adsorbate-driven segregation.We prepared Pt3Co catalysts supported in the space-confined porous graphitic carbon,and then tuned the surface composition by controlling the thermal treatment conditions under different atmospheres(Air,Ar,10 vol%H2/N2).We obtained three Pt3Co catalysts with the same bulk composition but different surface composition,namely:PtCo4.4i(Co-increased),Pt3Co(Intermetallic)and Pt4.39Co(Pt-increased),respectively.Electrochemical method in combination with XRD,XPS and atomic-resolution HAADF-STEM characterizations demonstrated that the magnitudes of electronic effect increased in the order Pt-increased>Intermetallic>Co-increased.Correspongingly,the value of oxophilic effect decreased in the order of Pt-increased<intermetallic<Co-increased.(2)Exploring the intrinsic relationship between the CO electro-oxidation activity of Pt3Co model nanocatalysts and their electronic effect/oxophilic effect at a molecular level.The activity of the COad oxidation increases in the order of Co-increased>Intermetallic>Pt-increased>Pt/C.CO stripping voltammetry and in-situ Fourier transform infrared spectroscopy(FTIRS)were used together to investigate the origin of varied CO poisoning tolerance on three Pt3Co catalysts.The results illustrated that electronic effect plays a major role in weakening CO adsorption on Pt3Co nanocatalysts and thus promoting CO oxidation to form COOHad intermediate consistent with Langmuir-Hinselwood mechanism.Oxophilic effect promotes the oxidation of COOHad intermediate into the final products CO2/CO32-.(3)Surface reconstruction of Pt3Co/PC(M=Co,Ni)nanocatalysts under the reaction conditions.We characterize the surface structural reconstruction and durability of PtM/PC(M=Co,Ni)nanocatalysts via CV,CO stripping and RDE technical means under the reaction conditions,such as ORR and ethanol electro-oxidation.The non-noble M atoms of PtM NPs will segregate to the surface under the oxidizing reaction conditions in typical fuel cell cathode application.Subsequently,the non-noble M atoms segregate to the surface immediately dissolves into the electrolyte in the acidic environment.(4)The experimental assume of preparing bifunctional structures MoCxNy supports.To solve the problem of stability for Pt-alloy catalysts due to the non-noble M atoms was dissolved in acid,this work last puts forward the experimental assume of preparing bifunctional structures MoCxNy supports.Herein,we successfully prepared the porous bifunctional structures MoCxNy supports with high specific surface area and uniform pore size via using the SB A-15 as hard templet.It is expected to be a new type of bifunctional carrier which can enhance the activity and stability of electrocatalytic activity of Pt nanoparticles.