Direct Formic Acid Fuel Cell Of Carbon Supported Pd And Pd-based Composite Catalysts

At present, it was found that the direct methanol fuel cell (DMFC) has some disadvanges. For example, the electrocataltic activity of the catalysts is low and is easy to be poisoned. Methol is easy to penetrate the Nafion membrane. Methanol is toxic. Thus, DMFC can not be commercialized in the near future. Recently, it was found that formic acid is an excellent liquid fuel and the performance of the direct formic acid fuel cell (DFAFC) is better than that of DMFC. In DMFCs, Pt-based composite catalysts are usually used as the anodic catalyst. It was found that the Pd catalyst is much better than the Pt catalyst in DFAFC. Therefore, this thesis mainly investigated the new Pd-based composite catalysts and new preparation methods of the catalysts. The effect of the composition and structure of Pd-based composite catalysts on the electrocatalytic activity and stability of the catalysts for the formic acid oxidation was investigated.The main results obtained are as follows:1. It is reported for the first time that the carbon supported Pd (Pd/C) catalyst was prepared with the improved organic sol method for the oxidation of formic acid in the direct formic acid fuel cell.(1) The electrocatalytic activity and stability of Pd/C catalyst prepared with the improved organic sol method for the oxidation of formic acid in DFAFC is better than that of the Pd/C catalyst prepared with the general reduction method. It is mainly due to that the average size and the relative crystallinity of the Pd particles in the Pd/C catalyst prepared with the improved organic sol method are smaller than these prepared with the the general reduction method.(2) It was found that when the Pd/C catalyst is prepared with the improved organic sol method controlling the evaporation temperature of the solvent could control the average size and relative crystallinity of the Pd particles in the Pd/C catalyst. The evaporation temperature is not proportional to the average size and relative crystallinity of the Pd particles in the Pd/C catalyst. When the suitable evaporation temperature is selected, the Pd/C catalyst with the small average size and the low relative crystallinity of the Pd particles could be obtained. Thus, this Pd/C catalyst shows the high electrocatalytic performance for the oxidation of formic acid.2. The anodic Pd/C catalyst and Pd-P/C catalyst using the complex reduction method were prepared and their electrocatalytic activities for the formic acid oxidation were investigated.(1) It was reported for the first time that the Pd/C catalyst as the anodic catalyst in DFAFC was prepared using the complex reduction method with NH4F and H3BO3 as the complexing agents and its electrocatalytic performance for the oxidation of formic acid was evaluated. The results demonstrated that the average size of the Pd particles in the Pd/C catalyst prepared with the complex reduction method is only 3.2nm, while it is 15.5 nm for the Pd/C catalyst prepared with the general reduction method. Thus, the electrocatalytic activity and stability of Pd/C catalyst prepared with the complex reduction method for the oxidation of formic acid are better than that of the Pd/C catalyst prepared with the general reduction method.(2) It was reported for the first time that the carbon supported Pd-P (Pd-P/C) catalyst as the anodic catalyst in DFAFC was prepared and its electrocatalytic performance for the oxidation of formic acid was evaluated. The results demonstrated that the electrocatalytic activity of the Pd-P/C catalyst for the oxidation of formic acid are better than that of the Pd/C catalyst. It is mainly because the addtion of P as a nonmetal element increases the density of the electron clound on Pd and leads to that Pd is not easy to be oxidized. Thus, the electrocatalytic performance of the Pd/C catalyst for the oxidation of formic acid is increased.