Sdudy On Oxygen Reduction Reaction Of Low Temperature Fuel Cells And Electrocatalyst For Formic Acid Oxidation

To solve the problems of energy shortage and environmental pollution in the world, low temperature fuel cell possesses the wide application in the portable equipment, electric car and field power etc. due to the low-pollution, abundant sources, high energy efficiency, the easy storge and transportation of the fuel. However, the poor long-term durability and high cost of the electrocatalysts are still the key issues hindering the commercial application of fuel cells. Therefore, to improve the long-term durability of the electrocatalysts and to decrease the loading mass of noble metals are effective routes to the commercial application of fuel cells. In this dissertation, electrocatalysts or catalyst supports noncovalently functionalized by polysiloxane and a new non-noble metal catalyst have been evaluated. Their micrographs, structure, properties and applications have been investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction spectroscopy (XRD), energy dispersive spectroscopy (EDS), cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometry, etc. The main points of this dissertation are summarized as follows:(1) Based on the polysiloxane noncovalent functionalization, Au@SiO₂@Pt catalyst was prepared by layer-by-layer assembly technique and used as the electrocatalyst for oxygen reduction reaction (ORR). The electrocatalytic properties of the Au@SiO₂@Pt catalyst for ORR have been evaluated by typical electrochemical methods such as CV and LSV. With the same Pt mass loading, the current density of ORR on the Au@SiO₂@Pt/GC electrode is about 2.3 times as high as that on the ETK 20wt.% Pt/C/GC electrode. The long-term durability of Au@SiO₂@Pt catalyst is also better than that of ETK 20wt.% Pt/C. The rotating ring-disk electrode (RRDE) investigation demonstrates that the number of electrons involved in ORR is close to the theoretical value for four-electron-reduction of O₂.(2) Polyaniline (PANI) hollow nanospheres were successfully synthesized using polystyrene (PS) gel particle as the templates. The morphology of PANI hollow nanospheres was characterized by TEM. The good electrocatalytic property of the PANI hollow nanospheres for ORR was characterized by CV. The electron number (n) involved in the O₂ reduction was calculated to be 3.37, which is close to the theoretical value for four-electron-reduction of O₂. PANI hollow nanosphere is a good non-noble metals catalyst.(3) PtPd electrocatalysts for catalytic oxidation of formic acid were supported on the cabon nanotubes noncovalently modified with polysiloxane. The SiO₂-CNTs were characterized by FTIR. The morphology and crystal form of the PtPd/SiO₂-CNTs catalyst were characterized by SEM, TEM and XRD, respectively. The results demonstrate that SiO₂-CNTs are beneficial to loading PtPd electrocatalysts with well dispersion and small particle size (4.7 nm). The electrocatalytic properties of the PtPd/SiO₂-CNTs electrode for catalytic oxidation of formic acid have been investigated by CV and chronoamperometry. The results demonstrate that the main peak current of formic acid oxidation on the PtPd/SiO₂-CNTs/GC electrode is 3.0 times as high as that on the PtPd/CNTs/GC electrode and PtPd/SiO₂-CNTs catalyst shows superior long-term cycle stability.