Preparation And Application Of Composite Supports And Pt-based Electrocatalysts For Fuel Cells

Polymer electrolyte membrane fuel cell(PEMFC)is a device which can convert chemical energy into electrical energy directly.Advantages for PEMFCs include high energy conversion efficiency,wide fuel resource,zero pollution,quick start,and so on.H2-fueled PEMFCs are particularly suitable for automobile power sources,the application of this sort of PEMFC can solve the environment and energy issues,and bring about new opportunities for the future development of the automotive industry.However,the high cost of fuel cells remains a huge challenge for large-scale industrialization and commercialization.At present,although platinum-based catalysts offer the best fuel cell performance,the limited resource and high cost of platinum restrict its large-scale commercialization.Therefore,it is vitally important to improve the utilization efficiency of platinum and enhance the catalytic activity.Aiming at improving the activity and utilization of Pt,electrocatalysts were tailordesigned and prepared by optimizing the structure of the support materials and the active components in this thesis.Firstly,Ni-P/CNT was prepared on the surface of carbon nanotubes(CNT)by electrolessly-plated nickel-phosphorus(Ni-P)alloy.Then,carbon nanofibers(CNF)were grown on Ni-P/CNT by chemical vapor deposition to yield a new composite Ni-P/CNTCNF.This composite combines the merits of CNT with high electronic conductivity and the merits of CNF with rich defect sites.The composite materials were characterized by scanning electron microscope(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD),Brunauer–Emmett–Teller(BET),and hydrophilicity analysis.The composites were used as non-noble metal catalysts in the alkaline oxygen reduction reaction(ORR)to evaluate their electrochemical performance.It was found that this composite material with a random orientation structure exhibits satisfactory ORR activities and excellent methanol tolerance in alkaline solutions.Secondly,platinum-based catalyst supported on the composite(Ni3P/CNT-CNF)was prepared by microwave-assisted ethylene glycol reduction method as an electrocatalyst(Pt/Ni3P/CNT-CNF).Ni3P/CNT-CNF composite and Pt/Ni3P/CNT-CNF catalysts were characterized by SEM,TEM,XRD and TGA.The electrocatalytic properties of the catalysts were evaluated by methanol oxidation reaction(MOR)and oxygen reduction reaction(ORR).It was found that the electrochemical surface area(ECSA)of Pt/Ni3P/CNT-CNF measured by hydrogen adsorption cyclic voltammetrywas 95 m2·g-1,and the ECSA measured by CO stripping voltammetry was 106 m2·g-1,Pt/Ni3P/CNT-CNF showed an enhanced catalytic activity of MOR and ORR when compared with commercial Pt/C-JM and Pt/CNT catalysts,which can be attributed to the excellent electronic conductivity of Ni3P/CNT-CNF composite support and facilitated mass transportation.Thirdly,polyhedral copper nanoparticles were prepared by hydrothermal method,followed by galvanic replacement with platinum precursor to prepare bimetallic Cu-Pt electrocatalysts.The electrochemical properties of the resulted Cu-Pt electrocatalysts with different compositions were investigated for MOR and ORR.It was found that the bimetallic Cu-Pt electrocatalyst with low platinum loading demonstrated high Pt utilization efficiency in fuel cell reactions.