Preparation And Study Of Cathode NON-Precious Metal Catalyst Of Polymer Electrolyte Membrane Fuel Cells

Polypropylene (PP), has good mechanical properties, chemical properties and processing performance, which has been widely used in various fields of national economy. But polypropylene easily suffered from thermal/thermo-oxidative degradation, and loss of its performance. Therefore, some antioxidants are required to inhibit thermo-oxidative degradation of PP and then guarantee long-term properties. Hindered phenolic antioxidants (AO) are one of the most used and efficient polypropylene antioxidants. However, these antioxidants are organic compound, which will fast migrate from the PP matrix to the sufance and significantly reduce its antioxidant effects, so it is very important to prepare the novel and efficient resistance migration antioxidant.Layered double hydroxides(LDH) is a kind of widely used anionic inorganic functional materials, which orderly arranged with the two-dimensional layers and interlayer anions. The main plate with positive charge and the interlayer anion distribution and through electrostatic force balance of main layer charge, then make the crystal is electrically neutral. Because LDH are avaible to adjust the composition anions, some function object anions can be intercalated into the interlayer spacing of the LDH to from a class of novel supramolecular structure functional materials, which not only can maintain or even improve the function of the original material, but only improves the application of stability.In this paper, based on the excellent antioxidantof the hindered phenolic compounds and the assembling characteristics of LDH, intercalating hindered phenolic antioxidant into LDH, which prepared a series of supramolecular structure organic-inorganic composite anti-oxidants. The preparaed anti-oxidants are expected to be able to fix the anti-oxidant species and extent their servive life, and further favor to improve thermal/thermo-oxidantive stability of the PP. The details are shown below:1. MgAl-CO3-LDH has been prepared by a method involving separate nucleation and aging step (SNAS). The p-Hydroxybenzoic acid (AO1) and3,5-ditert-butyl-4-hydroxy phenyl propionic acid (AO2) had been intercalated into the interlayer region of LDH to produce MgAl-AO-LDH by one-step synthesis method. The prepare of MgZnAl-AO-LDH through intercalating AO2anions into the interlayer spacing of LDH. In the preparation process, the Zn element was introduced into the Mg, Al host sheet by adjusting the molar ratio of Mg, Zn, Al. The AO-LDH was characterized by XRD、FT-IR、SEM and ICP. The obtained results show that the successful preparation of supemolecular intercalation structure of antioxidant AO-LDH, and the TG-DTA curve show that after intercalation, the thermal stability of AO anion improved.2. By using the method of organic solvent washing to modify LDH. Different loading of LDH/PP nanocomposites were prepared by direct mixing of the modified LDH slurry with the PP in xylene at140℃under a N2flow. Charaterization of LDH/PP composite by XRD、SEM、TG、FT-IR and other means, research results show that the addition of the MgAl-AO-LDH in PP did not change the crystal structure of PP, and they all were shown a spherical configuration, with the increase of loading of AO-LDHwill gradually decrease the radius of the spherical, and the spherical structure even will be destroyed. TG curve indicate that the addition of AO-LDH enhances the thermal stability of the nanocomposites, and when the mass loading is4.0wt%, achieve the best effectiveness. The AO-LDH exhibits heterogeneous distribution in the PP matrix when the mass loading is more than4.0wt%, which cause the decrease of the thermal stability. After accelerated thermal aging at150℃under air, showed thatthe addition of AO-LDH delay the aging process of nanocomposites materials. With the mass loading is increase, the carbonyl peak area becomes smaller, and the mass loading is4.0wt%, has the best against thermal-oxidative performance. The results also suggest that the antioxidative mechanism of AO-LDH is different from that of CO3-LDH for PP, and the AO-LDH have significant positive effect on the improvement of antioxidative performance for PP. Universal testing machine have been used to examine the mechanical properties and the thermal stability of LDH/PP. The investigated result show that they not only improve the mechanical properties, but also improve the thermal stability for PP.3. XRD、SEM、TG、UV、FT-IR and other characterization results indicate that making Zn element introduce into the Mg、Al main board did not change the crystal structure of the LDH/PP nanocomposites. Compared to the thermal stability of composites without the addition of Zn increase, and thermal oxidative aging process also delays. However, when the Mg:Zn:Al ratio was1:1:1, the thermal degradation decreases, which is due to excessive Zn, then lead to the "zinc fever" phenomenon. Mechanical test results show that after joining Zn, the mechanical properties of MgZnAl-AO-LDH/PP nanocomposites increased comparing with no Zn, and brittleness, toughness has been greatly improved.