The Direct Methanol Fuel Cell Carbon Contained Study Of The Cathode Catalyst

Direct methanol fuel cell (DMFC) is attracting much more attention for their usage as the clean and mobile power source in the future. It is because the use of methanol as fuel has several advantages comparing with hydrogen. For example, the source of methanol is abundant, methanol is cheap and it is easy to be transported and stored. In addition, methanol has the high theoretical energy density. Although a lot of progress has been obtained in the development of DMFC for about 20 years, several problems are still existed. For example, the poor kinetics of both anodic and cathodic reactions and the crossover of methanol from the anode to the cathode side through the proton-exchange membrane. In order to commercialize DMFC rapidly, these problems should be solved.In this paper, the cathodic Pt-Fe/C and Pt-P/C catalyst was investigated. The effects of the several preparation variables on the alloying extent, the average size of the metal particles in the catalysts, the relative crystallinity and the distribution of the metal particles on the electrocatalytic activity of the cathodic catalysts were studied. The main results obtained are as follows:1 The Pt-Fe/C and Pt/C catalysts were prepared with predeposited method. It was found that the electrocatalytic activity of the Pt-Fe/C catalyst for the oxygen reduction is higher than that of the Pt/C catalyst. However, the electrocatalytic activity of the Pt-Fe/C catalyst for the methanol oxidation is lower than that of the Pt/C catalyst. Even in the presence of methanol in the electrolyte solution, the electrocatalytic activity of the Pt-Fe/C catalyst for the oxygen reduction is still higher than that of the Pt/C catalyst.2 It was found that most of Fe in the Pt-Fe/C catalyst prepared does not enter the crystal lattice of Pt, but they exist as Fe and Fe₂O₃. Fe out of the crystal lattice of Pt can be dissolved in the acid, but Fe in the crystal lattice of Pt can be not dissolved in the acid. Fe out of the crystal lattice of Pt does not increase the electrocatalytic activity of Pt for the oxygen reduction, but it would decrease the exposure surface area of Pt and then reduces the electrocatalytic activity of Pt for the oxygen reduction. Thus, after the acid treatment, the electrochemically active specific surface area of the Pt-Fe/C catalyst would be increased by about 30% comparing with that of the Pt-Fe/C catalyst before the acid treatment, leading that the electrocatalytic activity of the Pt-Fe/C catalyst for the oxygen reduction is much better than that of the Pt-Fe/C catalyst before the acid treatment.3 The XRD and EDS results indicated that the heat treatment of the Pt-Fe/C catalyst in the temperature range of 200-800℃can make Fe to enter into the crystal lattice of Pt. The amount of Fe entered into the crystal lattice of Pt increases with increasing the temperature.4 It was studied for the first time that nonmetal element, P and Pt consist the Pt-P/C cathodic catalyst. It was found that although the average size and the relative crystallinity of the Pt-P particles in the Pt-P/C catalyst prepared is similar to that of the commercial E-TEK Pt /C catalyst, the electrocatalytic activity of the Pt-P/C catalyst for the oxygen reduction is much higher than that of the commercial E-TEK Pt /C catalyst, indicating that P can promote the oxygen reduction at Pt.