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A numerical simulation method is hereby adopted in this paper to calculate and analyze the thermal dispersion influence factors of three particle-shaped porous mediums of two-dimensional porous medium with different skeleton structures. Result shows that the thermal dispersion influence factors include fluid thermal properties, Darcy velocity, porosity and skeleton structure, etc. Under the same condition, the thermal dispersion coefficient of a circular particle model is maximum, and it increases with the rise of Pednumber; with the increase of the porosity or the reduction of Darcy velocity, the thermal dispersion coefficient reduces increasingly. When considering the thermal dispersion effect, the axial temperature variation of fluid is more applicable for numerical simulation, which proves that it shall consider the thermal dispersion during researches on porous medium models.

Dynamic response performance of PEMFC affects its durability and reliability significantly. So improving on dynamic performance of PEMFC has become the key for prolonging PEMFC life in fuel cell vehicles application. In this study, in order to promote the PEMFC dynamic response performance, RuO2·xH2O was prepared by solgel method and then sprayed onto catalyst layers. The RuO2·xH2O prepared was characterized by TEM, which shows the average particle size of RuO2·xH2O was 8 nm and particulates were well distributed. A 10-cell stack using MEAs with and without RuO2·xH2O was assembled and studied under different relative humidity. It was found that added with RuO2·xH2O dramatically improves the dynamic response performance, which revealing that RuO2·xH2O can buffer the voltage undershoot and improve the stability and lifetime of PEMFC stack.

Fe3O4 modified Pt/C electro-catalyst was synthesized and studied. Fe3O4 and Fe3O4 with carbon coating (designated as Fe3O4/C) were prepared by co-precipitation method and ethyl acetate pretreatment. Fe3O4 and Fe3O4/C were sprayed onto the Pt/C cathode surface. X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) results show that Fe3O4 and Fe3O4 with carbon coating nano-particles (Fe3O4/C) are distributed evenly and c.a. 11.2 nm and 14.3 nm, respectively. TEM images show that electrode surfaces with Fe3O4 and Fe3O4/C are of little difference from that with Pt/C only; Fe3O4/C is much more evenly distributed on the electrode surface than Fe3O4 because of the adaptability of carbon coating. Cathodic curves of Rotating Disk Electrode (RDE) tests shows that the adding of Fe3O4 (7 wt %) improves oxygen reduction reaction (ORR) activity about 30 mV in both cases. The adding of Fe3O4/C (Fe3O4: 7 wt %) to the Pt/C catalysts demonstrates the highest peak current of about 13.8 mA•cm-2 in all cases. The promotion of Fe3O4 in O2 enrichment and dispersion of Pt particles are confirmed in the study. The paramagnetism of Fe3O4 and its promotion in 4-electron oxygen reduction reaction (ORR) are the possible reasons for the promotion.his template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.