Study On The Electrodes Of Direct Alcohol Fuel Cells And Enzyme-based Biofuel Cells

Direct alcohol fuel cells (DAFC) have been attracting more and more attention and interest due to their simplicity, the easy handle, low pollution, high power density, easy storage and transportation of the liquid alcohol fuels. However, along with DAFC's development, the low electrocatalytic activity and high cost of the catalysts are the key problems hindering its commercial application. Thus, it is of great scientific and practical importance to exploit relative highly active and inexpensive catalysts for alcohol oxidation and oxygen reduction.Enzyme-based biofuel cells (EBFC) are one kind of fuel cells which could convert chemical energy into electrical energy directly with enzymes as electrode catalysts. Recently, EBFC have attracted considerable research attention because of their unique advantages such as corrosion-free electrolyte, low cost, good biocompatibility and more moderate temperature. In the case of EBFC, the major barriers to their practical application are short lifetime and low power density, both of which are related to enzyme immobilization. Therefore, immobilization of enzymes on suitable electrochemical materials plays a crucial role in the construction of EBFC.In this dissertation, in order to solve the problems of DAFC and EBFC mentioned above, new anodic catalysts for DAFC and novel enzyme electrodes for EBFC were prepared, respectively. Their electrocatalytic activity and stability were studied by typical electrochemical methods in detail. The main points are summarized as follows:(1)Ru-doped SnO₂ nanoparticles were prepared by chemical precipitation and calcinations at 550℃, and then selected as the catalyst support and second catalyst of for methanol electrooxidation. The micrograph, elemental composition and structural analysis of the Ru-doped SnO₂ nanoparticles were characterized by scanning electron microscopy, energy disperse X-ray spectroscopy and X-ray diffraction, respectively. The electrocatalytic properties of the Ru-doped SnO₂ supported Pt catalyst (Pt/Ru-doped SnO₂) for methanol oxidation have been investigated by cyclic voltammetry in acidic solution. Under the same loading mass of Pt, the Pt/Ru-doped SnO₂ catalyst shows better electrocatalytic performance than Pt/SnO₂ catalyst and the best atomic ratio of Ru to Sn in Ru-doped SnO₂ is 1/75. Additionally, Pt/Ru-doped SnO₂ catalyst possesses good long-term cycle stability.(2)Polyaniline-tin dioxide (PANI-SnO₂) composites were prepared by chemical polymerization method, and then characterized by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction. Due to the good stability in diluted acidic solution, PANI-SnO₂ composites were selected as the catalyst support and second catalyst for methanol oxidation. The electrocatalytic properties of the PANI-SnO₂ supported Pt catalyst (Pt/PANI-SnO₂) for methanol oxidation have been investigated by cyclic voltammetry, chronoamperometry and chronopotentiometry in acidic solution. For the same loading mass of Pt, the Pt/PANI-SnO₂ catalyst shows higher electrocatalytic activity towards methanol electrooxidation and better anti-poisoning ability than Pt/SnO₂ catalyst.(3)The electrooxidation of ethanol on Pt/ZSM-5-C catalyst was investigated in acid aqueous solution. Due to high stability in general acidic solution, ZSM-5 zeolite particles were selected as the support and second catalyst. The micrograph and elemental composition of Pt/ZSM-5-C catalyst were characterized by scanning electron microscopy and energy disperses X-ray spectroscopy. The electrocatalytic properties of Pt/ZSM-5-C catalyst for ethanol oxidation have been investigated by cyclic voltammetry in acidic solution. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt/ZSM-5-C catalyst shows higher activity than Pt/C catalyst. Additionally, Pt/ZSM-5-C catalyst possesses good long-term cycle stability.(4)SnO₂-carbon nanotubes (SnO₂-CNTs) composites were prepared and selected as the catalyst support and second catalyst for ethanol electrooxidation. The micrograph and structural analysis of the SnO₂-CNTs composites were characterized by scanning electron microscopy and X-ray diffraction. The electrocatalytic properties of the SnO₂-CNTs supported platinum (Pt) catalyst (Pt/SnO₂-CNTs) for ethanol oxidation have been investigated by typical electrochemical methods in acidic solution. For the same mass loading of Pt, the Pt/SnO₂-CNTs catalyst shows higher electrocatalytic activity and better long-term cycle stability than Pt/SnO₂ catalyst. Additionally, the effect of the mass ratio of CNTs to SnO₂ on the electrocatalytic activity of the electrode for ethanol oxidation was investigated.(5)CNTs were noncovalent-functionalized with 1-aminopyrene (1-AP) and used to immobilize Laccase (Lac) with the aid of glutaraldehyde (GA). The results of Fourier transform infrared (FTIR) spectra confirmed the successful modification of CNTs with 1-AP. The electrocatalytic properties of the Lac immobilized on the 1-AP functionalized CNTs (Lac/AP-CNTs) for oxygen reduction have been investigated by cyclic voltammetry in the presence of 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS) in the Britton-Robinson (B-R) buffer solution (pH 3.0). Under the same experimental condition, the Lac/AP-CNTs catalyst shows higher electrocatalytic activity and better stability than the Lac immobilized on the pristine CNTs (Lac/CNTs). Additionally, effects of the mass ratio of 1-AP to CNTs in the AP-CNTs composites, the loading mass of the Lac/AP-CNTs catalyst and the pH value of the electrolyte on the electrocatalytic activity of the Lac/AP-CNTs electrode for oxygen reduction were also optimized.(6)Glucose oxidase (GOD) and ferrocenylamine (Fc) were co-immobilized onto the noncovalent-functionalized CNTs by covalent bond via different routes. The electrocatalytic properties of the different kinds of GOD-Fc/CNTs electrodes for glucose oxidation have been investigated by cyclic voltammetry in the presence of glucose in 0.1 M PBS buffer solution (pH 7.0). The results indicate that the immobilized routes of GOD and Fc on electrode is closely related with the electrocatalytic activity of the GOD-Fc/CNTs electrode, and the best electrocatalytic behavior is observed while Fc and GOD is immobilized on CNTs with the aid of 1-AP and 1-AP/glutaraldehyde, respectively.