SYNTHESIS AND CHARACTERIZATION OF AuPd/CeO2/MWCNTS HYBRID MATERIALS FOR DIRECT FORMIC FUEL CELLS

摘要

Direct formic acid fuel cells (DFAFCs) are expected to be the first commercial application as a portable power supply among various fuel cells [1-3]. The advances in DFAFCs have been reviewed recently [4]: (i) DFAFCs have higher power density, higher energy efficiency, and higher electromotive force than that of direct methanol fuel cells; (ii) the crossover flux of formic acid (FA) through Nafion membrane is several times smaller than that of methanol [5]; (iii) FA is less toxic and has no risk of producing hazardous byproducts during oxidation, while methanol can produce formaldehyde; (iv) the DFAFCs can use more concentrated fuel up to 15M compared to 3M for methanol; and (v) palladium alloys, used as catalysts in DFAFC, are cheaper and more available than platinum ones. The main drawback of FA as a fuel is its low energy density; however it can be compensated by the high-energy efficiency ofDFAFCs. Palladium has been demonstrated to be a good catalyst for low temperature electrooxidation of FA [6], However, the activity and stability of Pd catalyst still need improvements. Previous results indicate the activity of Pd catalyst can be enhanced by the addition of metal or metal oxide promoters [7]. Another effective method of enhancing catalytic activity is forming bimetallic catalysts. The introduction of a second metal as a promoter attracts both scientific and technological interests because it can modify the physical and chemical properties of catalyst due to geometric and electronic effects [8-13]. The metal promoters can improve both activity and stability of the original single-metal catalysts. It also has been demonstrated that the structure of bimetallic nanoparticles significantly depends on the degree of alloying [14]. Bimetallic nanoparticles have also been valuable for in-depth investigation of the relationship between catalytic activity and the structure of catalyst.