Studies On The Electrocatalysis Of Layered Double Hydroxides And Their Composites Toward Methanol Oxidation In Alkaline Medium

The electrochemical oxidation of methanol and other small organic molecules is widely involved in different types of fuel cells research. At present, the extensive investigations of the corresponding catalysis in methanol electrooxidation are being carried out on Pt, Au, Pd and other related noble eletrode materials. However, the direct methanol fuel cell application is restricted in the lab scale due to its poisonous charateristics and high cost. Layered double hydroxides (LDHs), also known as anionic clays or hydrotalcite-like compounds, are a class of inorganic materials with potential applications in wide areas. LDHs constitute a versatile material for modifying an electrode surface because they possess special structure and excellent properties.In this dissertation, according to the corresponding properties of LDHs,several types of LDHs and their composites with noble metals were prepared through different methods. Various modified electrodes were fabricated based on the aboved materials, whose electrocatalytic activities were investigated in detail for methanol oxidation in alkaline medium. The focus of this dissertation has been listed as follows:(1) Based on the lamellar structure and anion exchange properties of LDHs, MgAl-Au LDHs were prepared via hydrothermal treatment followed by a reduction procedure. The obtained products were characterized by XRD and TEM. In the following, LDHs were spread on the surface of GC electrode in order to construct MgAl-Au LDH film modified electrode. Under the same conditions, the obtained modified electrode exhibits higher electrocatalytic activity than that of both the pure AuNPs-modified electrode and LDH-modified electrode for methanol oxidation in alkaline medium. This work indicates that LDHs is expected to be a good supporting material in the development of methanol anode catalysts.(2) Based on the strong stability and adsorbability of LDHs, MgAl LDH/Pt was fabricated by high temperature heat reduction. The electrocatalytic activities of Pt/LDH-modified glassy carbon electrode for methanol oxidation in alkaline medium were investigated in detail. The results showed that the presence of the LDHs significantly enhanced the catalytic activity of Pt for the oxidation of methanol. Meanwhile, further studies about the effects of the presence of the LDHs were investigated in other aspects, such as the effects of different ratios of Mg/Al and different electrolytes.(3) NiAl LDHs with different Ni/Al radios and Ni(OH)2 were deposited on the glassy carbon electrodes by electrosynthesis and characterized through XRD, SEM and cyclic voltammetry. Moreover, the electrocatalytic activities of the corresponding modified electrodes toward methanol oxidation were studied in detail by cyclic voltammetry, chronoamperometry and repeated cyclic voltammetry cycles, respectively. Under the same conditions, the LDH/GCE exhibites higher electrocatalytic activity and stability than Ni(OH)2/GCE. Further studies were carried out to explore the mechanism of methanol oxidation on the LDH/GCE by investigating the effects of methanol concentration and scan rates.(4) The uniform and stable NiAl LDH/Au films were deposited on the GCE with different sequence by electrosynthesis. At the same time, the electrocatalytic activities of the corresponding modified electrodes toward methanol oxidation were studied in detail both by cyclic voltammetry and chronoamperometry. The results show that the presence of the Au significantly enhanced the catalytic activity of LDHs for the oxidation of methanol. Further studies were carried out to explain the mechanism of methanol oxidation on the NiAl LDH/Au/GCE.