Direct Formic Acid Fuel Cell Anode Catalyst

Direct methanol fuel cell (DMFC) use cheap methanol as the fuel. It does not need the fuel reforming equipment. Its operating temperature is low. The fuel source is abundant and is easy to store and to transport. Therefore, it is an ideal power for mobile electronic equipments and electric automobiles. Recently, many countries invest lot of the enormous manpower and material resource to carry out its fundamental and applied research. However, due to the high toxicity of methanol, it is necessary to find a new liquid fuel to displace methanol in order to realize the application of DMFC as the mobile power for the mobile phone, mobile computer and electric automobiles. Among methanol-alternative fuels, formic acid is easy to obtain on the large scale and its toxicity is low. Thus, it is possible to use formic acid as the methanol-alternative fuel in DMFC.In this thesis, the effects of the preparation methods of Pt/C and Pt-Ru/C catalysts on their electrocatalytic performance for the formic acid oxidation were investigated using the electrochemical methods, XRD, TEM and EDS techniques. The main results obtained are as follows:1. The electrocatalytic activity of the Pt/C catalyst prepared with the solid phase reaction method for the formic acid oxidation is investigated. It was found that the electrocatalytic activity of the Pt/C catalyst with 20(wt)% Pt prepared with the solid phase reaction method for the formic acid oxidation is much better than that of the Pt/C catalyst prepared with the traditional liquid phase reaction method. For example, in the cyclic voltammogram of the Pt/C catalyst electrode prepared with the solid phase reaction method in the 0.5mol/L HCOOH+ 0.5mol/L H₂SO₄ solution, the current densities of the two anodic peaks during the potential scan in the positive direction are about 4.70 and 10.96 mA/cm², respectively. However, under the same conditions, for the Pt/C catalyst electrode prepared with the traditional liquid phase reaction method, the current densities of the corresponding anodic peaks are only 2.43 and 6.79 mA/cm², respectively. It is mainly due to that the average diameter of the Pt particles in the Pt/C catalyst prepared with the solid phase reaction method is small, about 3.7nm. Thus, its utilization ratio and the electrochemical active surface area of Pt are high, about 15.2% and 31.6m²/g. However, the average diameter ofthe Pt particles in the Pt/C catalyst prepared with the traditional liquid phase reaction method is large, about 9.0nm, Its utilization ratio of Pt and the electrochemical active surface area are low, about 3.62% and 8.60m2/g.2. The electrocatalytic activity of the Pt-Ru/C catalyst prepared with the solid phase reaction method for the formic acid oxidation is investigated. It is found that the electrocatalytic activity of the Pt-Ru/C catalyst with 30(wt)% Pt-Ru and the atom ratio of Pt:Ru=l:l prepared with the solid phase reaction method for the formic acid oxidation are much better than that of the Pt-Ru/C catalyst with 30% Pt-Ru and the atom ratio of Pt:Ru = 1:1 prepared with the traditional liquid phase reaction method. For example, in the cyclic voltammogram of the Pt-Ru/C catalyst electrode prepared with the solid phase reaction method in the 0.5mol/L HCOOH + 0.5mol/L H2SO4 solution, the anodic peak potential is about 0.50V and its current density is about 52.36 mA/cm2. However, for the Pt-Ru/C catalyst prepared with the traditional liquid phase reaction method, the corresponding peak is located at about 0.53V and the peak current density is only 35.72 mA/cm2. The TEM and EDS measurements indicated that it is mainly due to the high dispersibility and small average diameter of the Pt-Ru particles in the Pt-Ru/C catalyst prepared with the solid phase reaction method.3. The performance of formic acid used as the methanol-alternative fuel in DMFC was studied. It was found that although the energy density of formic acid is lower than 1/3 of methanol, the peak potential and onset potential of the oxidation of formic acid at the Pt-Ru/C electrode are 120 and 300mV more negative than that of methanol, respectively. The permeability of formic acid through the Nafion membrane is only 1/5 of methanol. In addition, the toxicity and volatility of formic acid are much lower than that of methanol. Therefore, formic acid is a preferentially considerable methanol-alternative fuel.4. It is reported for the first time that the Pt-Ru/C catalyst is prepared in the THF/H2O mixture solvent. It was found that the alloying extent of the Pt-Ru/C catalyst prepared with this preparation method is much higher than that of the commercial E-TEK Pt-Ru/C catalist, resulting in a high electrocatalytic activity for the oxidation of formic acid. Itillustrates that the alloying extent of Pt-Ru in the Pt-Ru/C catalyst could significantly affect the electrocatalytic activity of the Pt-Ru/C catalyst for the oxidation of formic acid.