Study On The Oxidation Activity Of Formic Acid-Sodium Formate Blended Fuel System

With the increasing global energy crisis, the main energy research topics have been focused on improving the resource utilization efficiency. Due to the environmental friendliness and high efficiency of direct liquid fuel cells (DLFC), it has attracted much attention of researchers. The primary domains of the current researches on DLFCs are fuel systerm and catalyst. For the fuel systerm, the previous researches mostly focused on single fuel, such as direct methanol fuel cells (DMFC), direct formaldehyde fuel cells (DFFC) and direct formic acid fuel cells (DFAFC), etc. For the catalyst, researchers mainly studied the effects of different kinds, morphology of catalysts, and the kind of supports. However, blended fuel system and using anions to improve the oxidation of formic acid have been seldom studied.Our previous work indicated that using formic acid-formate blended solution with sodium formate as electrolyte additive showed better activity than the single fuel systems. However, because the total concentration of HCOOH and HCOONa changed, it was difficult to reveal the mechanism and influential factors for the enhancement. In this dissertation, we attempt to reveal the reasons by keeping the total concentration of formic acid and sodium formate being1mol· dm-3but with different formic acid to sodium formate ratios. In addition, we also carried out researches on the dimension effect of catalysts and the optimal ratio of formic acid to sodium formatet. Finally, we study alloy catalyst in order to find other effective catalysts for oxidation of formic acid-formate blended solution. This research is original for the experimental method and idea. The major results are:(1) The reasons for the oxidation enhancement of formic acid-formate blended solution were studied by keeping the total concentration of the solutions to be1mol9dm-3but with different formic acid-formate ratios. The results showed that the lager the HCOONa concentration was, the better the performance was. The enhanced performance is the mutual effect of many reasons, such as electric conductivity, pH, concentrations of HCOOH and HCOONa, ionic strength of the solution, and oxidation mechanism of HCOOH, with pH and [HCOO-] taking the key roles.(2) The optimal ratio of blended solution was studied by using a Pt disk as the working electrode. The study showed that with increasing the formate ratio, the oxidation activity of blended solutions first increased and then decreased, while the solution containing0.05mol·dm-3HCOOH and0.95mol·dm-3HCOONa showed the best activity.(3) In the paper, we also studied the other catalysts for the blended solutions. The catalyst of Pt/CNTs, PtRu/CNTs and PtSn/CNTs were prepared with their catalytic activity tested in formic acid-formate blended solutions with different formic acid to formate concentration ratios. It was found that, in the blended solutions, PtRu/CNTs showed the best oxidation activity, and in0.2mol·dm-3HCOOH:0.8mol·dm-3HCOONa solution, the catalytic activity of PtRu/CNTs catalyst was best. This improved performance can be ascribed to the bifunctional roles of Pt and Ru, the size of crystal particles and the kind of supporting substrate.