| Catalyst and membrane electrode assembly are the crucial parts and materials of proton exchange membrane fuel cell(PEMFC). They are so important for improving performance and promoting the commecialization of fuel cell. To solve the problems existing in the supported catalysts of carrier corrosion and high amount of noble mental loading. We firstly prepared PtO2colloidal solution. It was found that when reaction temperature was above110℃, an unsupported Pt catalyst would be produced by the reduction of PtO2colloidal solution. And then we prepared cathode of membrane electrode assembly(MEA) with Buckypaper as catalyst layer via electrophoretic deposition(EDP) of PtO2colloidal solution to reduce particle size and loading of catalyst. The microstructure and morphology of samples were characterized by scanning electron microscope(SEM) and transmission electron microscopy(TEM), the elemental valence and content were tested by X-ray diffraction photoelectron spectroscopy(XPS) and energy dispersive X-ray(EDX) analysis. The electrocatalytic performances of samples were measured by cyclic voltammetry(CV), linear sweep voltammetry(LSV) techniques and polarization curve.Resulting product was yellow PtO2colloidal solution under the conditions of reaction time for9h and temperature of between70-100℃. TEM results show that average size of PtO2particles is2nm in uniformly dispersed colloidal solution. Particle shape is not standard spherical, they overlapped each other and bonded together to form network structure. When the colloidal solution changed from yellow to black with the change of electrochemically active area(ECA) from0to35.90m2·g-1. After treatment at50℃for1h in H2and N2mixture (VH2:VN2=1:9), the ECA increased to43.15m2·g-1. It has high oxygen reduction reaction(ORR) onset reduction potential(0.98V) and small number of active molecules.When the temperature was above110℃during the preparation of PtO2colloidal solution, it would be destroyed and then became black two-phase solution. We had examined the effects of dispersant, dried method, grinding, reduction time, temperature and pH value(when added H2O2) on catalytic performance of the unsupported Pt nanoparticles. CV results show that it is better for samples not to grind and one after vacuum freeze drying which dispersed in high purity water had higher ECA. When reduction time was30min, reaction temperature was110℃, pH value(when added H2O2) was7, the as-prepared unsupported Pt achieved the best ECA of37.96m2·g-1and it was found that it’s onset reduction potential for ORR was0.98V, about50mV higher than that of commercial20%Pt/C. SEM result shows that the unsupported Pt nanoparticles were easy to gather together and to form larger secondary particles. TEM results indicate that the unsupported Pt nanoparticles also bonded together to form network structure and overlapped each other. It has a smaller average particle size(2.46nm), and also agglomerated after treatment in H2and N2mixture(VH2:VN2=1:9). Buckypaper is a freestanding, self-supported and well defined membrane-like black film. We developed a two-layer Buckypaper film containing a multi-walled nanotubes(MWNTs) rich surface and a carbon nanofibers(CNFs) rich surface by a self-assembly and filter process. It is feasible to control or adjust the microstructure and surface conduction of Buckypaper with certain preparation procedures. Electrochemical tests show Buckyapper had higher ORR activity than that of XC-72. And the use of Buckyapper carrier layer could improve MEA performance. We deposited PtO2colloidal solution into Buckyapper carrier via electrophoretic depositon and eventually found that PtOx gradiently distributed along the cross side and significantly agglomerted. |
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