Carbon Effect on the Synthesis and MEA Performances of L10 CoPt Intermetallic Catalysts

Abstract

Incorporation of base metals to carbon supported Pt catalysts is known to enhance oxygen reduction reaction (ORR) activity. Therefore, Pt-base metals random alloys, such as Pt-Co, are often applied as cathode catalysts in proton exchange membrane fuel cells (PEMFCs). However, poor stability of Co under oxidative and acidic conditions makes the enhancement limited during long-term fuel cell testing. Recently, we have developed a robust method to prepare L10 ordered CoPt catalysts that exhibit superior fuel cell performances compared with the random alloy counterpart. In this systematic study, we observed that carbon supports impose strong effects not only on the growth of CoPt L10 intermetallic nanoparticles but also on the fuel cell performances. Solid carbons, including Vulcan other highly graphitized carbons, have moderate surface areas and relatively higher degree of graphitization. CoPt L10 intermetallic particles prepared such type of carbons usually have a large size distribution. But their fuel cell performances are still desirable, showing high current densities at low voltages and less carbon corrosion. Moreover, we found that surface functionalization can improve the size distribution and dispersion of nanoparticles, thus improving the fuel cell performances. In parallel, porous carbons of high surface areas were also applied as the supports for depositing CoPt L10 intermetallic nanoparticles. Different from the particles on surface of solid carbons, a large number of nanoparticles are located in the micropores of porous carbons. These nanoparticles can maintain their small particle size and a narrow size distribution after heat treatment. CoPt L10 intermetallic nanoparticles on porous supports exhibit excellent performances at high voltage end in fuel cell testing.