| The adsorption and reaction of CH3OH on transition metal surfaces has its great significance to both the practical application and fundamental researches. The extensive investigation in this field have been carried out and great progress has been made. However, due to the differences in electrode materials, surface pretreatment procedures, solution compositions and the detection techniques, especially the complexity of the system during the reaction process, at least at present, the detailed mechanism on the reaction process is still in controversy, some very important problem, such as the influence of methanol concentration, temperature and electrolyte in methanol oxidation. Among the various techniques in investigating the adsorption and reaction behavior of small organic molecules, infrared (IR) spectroscopy is the most widely used in-situ spectroscopic method, and has made tremendous contributions to provide a better understanding of this field. But the most widely used systems in IR, are those electrodes with very high surface reflectivity, such single crystal electrodes or smooth polycrystalline electrodes or surfaces of mild roughness. This is distinctively different from practical systems where electrodes with high surface roughness are used. On the other hand, surface enhanced Raman spectroscopy is applicable to rough electrode surfaces, which is complimentary to IR. Furthermore, SERS can provide a wider spectral window, which is quite convenient to obtain the vibrational information reflecting the interaction of the adsorbates and the substrates located under 600 cm-1. Thus,Raman spectroscope is used to study methanol electrocatalytic system to provide importantly spectral evidence for electrocatalytic mechanism of methanol.In this thesis , based on the purpose of studying the reaction and adsorption process of methanol molecules on Pt-Ru/GC and Pt/GC electrodes, two parts of work have been performed, and the main results of which are listed as follows:(1) Cyclic voltammetry (CV) and in-situ surface enhanced Raman spectroscope (in-situ SERS) were used to investigate electrochemical behavior of methanol on platinum nanoparticle modified glassy carbon substrate(Pt/GC). The influence of methanol concentration, temperature and electrolyte was studied. The results indicate electrocatalytic oxidation activity of methanol is relatively higher on the Pt/GC electrode, especially in the alkaline medium. Methanol can dissociate spontaneously on the Pt/GC electrode and produce strongly absorbed intermediates CO, the increasing of experimental temperature can improve electrocatalytic activity of the Pt/GC electrode for methanol oxidation. At the same time, the concentration of methanol is higher, the electrode is poisoned more severely. It is indicated by in-situ SERS that COL which methanol dissociate spontaneously on the Pt/GC electrode is detected in the acidic, neutral media and alkaline media. And it is found that the peak potentials of methanol oxidation shift 400～600mV negatively in the acidic and neutral media than in the alkaline medium. It was confirmed at the molecular level that methanol can be oxidized more easily in the alkaline medium.(2) The electrooxidation behavior of methanol on the Pt-Ru/GC electrode was investigated by conventional electrochemical methods ,such as cyclic voltammetry , chronoamperometry and so on. The influence of ratio of Pt and Ru, methanol concentration and electrolyte for methanol oxidation was studied. The results show that the peak potential of methanol oxidation on the Pt-Ru/GC electrode shifts 200mV negatively than that of the Pt /GC electrode, and the peak potential shifts less negatively with the increase of Ru% in Pt-Ru alloy. Methanol can also dissociate spontaneously on the Pt-Ru/GC electrode and produce strongly absorbed intermediates CO, the oxidation peak potential of which shifts 80mV negatively than that of the Pt /GC electrode. The above experimental results indicate that electrocatalytic activity of Pt-Ru for methanol oxidation is higher than Pt. In-situ SERS technique was used to study behavior of methanol oxidation in the acidic, neutral and alkaline media on the Pt-Ru/GC electrode. It is observed in the first time that the oxidation of methanol produces CO2 in the neutral medium but CO32- or HCO3- in the alkaline medium. The results indicate that the electrocatalytic activity of the Pt-Ru/GC electrode for methanol oxidation in the alkaline medium is higher than that in the acidic and neutral media and the oxidation of methanol to CO2 proceeds via the parallel reaction mechanism: both strong or weak intermediate could be detected both in the acidic medium and in the alkaline medium.
|
PDF Full Text Request