Synthesis of Platinum-based Composite Catalysts and Their Electrocatalytic Properties for Methanol Oxidation
|Course||Physical and chemical|
|Keywords||direct methanol fuel cell platinum and alloy nanoparticles carbon nanotubes platinum nanoflowers electrodeposition energy electrocatalysis oxidation UV illumination titanium oxide|
The lack of energy has done serious damage to hunman’s living environment and the nature environment. The fuel cell as an electricity generated equipment which can convert fuel’s chemical energy to electricity power directly not by burning but by electrochemistry way is hopeful to become the best, clean, and high efficient electricity generate technology. Direct methanol fuel cell （DMFC） as one of the important embranchment of the fuel cell have gained amount of attentions with in the last years due to its high power density, simple, operation, and portability. As a green and renewable fuel, methanol is less toxic and is available from crop ferment. Because of all these advantages, DMFC is hopeful to be used in convenient electrical source, electromotor and so on. However, there is a major problem faced in DMFC: the electrocatalytic activity of methanol at anode is low at low temperature. Transition metal Pt and Pt alloys are the first candidates for anode catalysts of DMFC due to their excellent catalytic activity. It is well known, catalytic activity depends on the size and shape of the metal particles, and therefore the synthesis of well-controlled shapes and sizes of nanocatalysts could be critical for improving catalytic activity.In this thesis, electrocatalysts were prepared by chemistry reduction and electrochemistry methods, respectively. The morphology and composition of the catalysts were characterized by XRD, SEM, TEM and EDX techniques. The electrooxidation of methanol was characterized by electrochemistry measurement. The main cotents and innovations of this thesis are as follows:（1） Pt-Au composite catalysts are prepared on an indium tin oxide （ITO） glass substrate by cyclic voltammetry. Catalyst samples are characterized by scanning electron microscopy （SEM）, X-ray energy dispersive spectroscopy （EDX）, X-ray diffraction （XRD） and electrochemical methods. SEM results reveal that the samples are composed of near-spherical microparticles. Cyclic voltammetry and chronoamperometry results show that the addition of Au into composite catalysts is beneficial to the electro-catalytic oxidation of methanol and the anti-poisoning ability of platinum for methanol oxidation is enhanced. At the same time, the different content of Au in composite catalysts has been studied for methanol electro-oxidation, the results show that Pt1.07Au catalyst has the best catalytic activity for methanol electro-oxidation.（2） Pt-TiO2 nanocomposites prepared by chemistry reduction method are successfully fabricated on ITO glass electrode. As revealed by TEM, Pt nanoparticles with an average size of 2.6 nm are well uniformly dispersed on porous TiO2. XRD structural characterization reveals that Pt presents a face centered cubic crystal structure while TiO2 is in the format of both rutile and anatase phases. The electrochemical performance of as-prepared nanocomposite electrode is evaluated by studying the electro-catalytic oxidation of methanol under various conditions, especially with UV illumination in alkaline medium. Compared to the case of no UV illumination, the electrochemical performance on Pt-TiO2/ITO electrode for methanol oxidation is markedly improved under UV illumination. Moreover, the poisoning resistance of the electrode performance for methanol oxidation is significantly increased under UV illumination, as supported by time-coursed current measurements.（3） The pretreated CNT sample was first dispersed, in an ethanol solution containing 5% Nafion under ultrasonic agitation. The suspension pastes were then applied by micropipette （10μl） onto a glassy carbon electrode. Pt、PtAu、PtAuRu modified CNT/GC electrodes were prepared by potentiostatic electrodeposition. The Pt-based ternary alloy （PtAuRu/CNT） show higher performance for methanol electro-oxidation than Pt-based duality alloy （PtAu/CNT）, PtAu/CNT exhibited higher performance than Pt/CNT electrode, and Pt2.5AuRu catalyst had the highest catalytic activity for methanol electro-oxidation.（4） A facile, one-step and template-free electrodeposition method has been developed to prepare the Pt nanoparticles with different morphologies. As-prepared Pt was characterized by SEM, EDX, XRD and electrochemical methods. The morphologies of Pt nanostructure depended on varying the electrolytes, solution concentration, and deposition time, etc. The Pt nano-catalysts were prepared under different conditions, which exhibit different catalytic activity and poisoning-tolerance for the methanol electrooxidation.