Oxygen Reduction Reaction (ORR) Activities of Pt-Ni Alloy Nanoparticles Supported on Graphene

Abstract

Polymer electrolyte membrane fuel cell (PEMFC) has been studied widely due to its higher energy efficiency than a conventional internal combustion engine by generates electrical energy directly from chemical energy. However, the fuel cells faces lots of challenges to commercialization. Cost reduction and improvement of catalysts activities are two major problems impedes the commercialization. Since costly platinum has been used as a catalyst at both anode and cathode of fuel cells, it is required to decrease amounts of Pt. Alloying Pt with secondary transition metals such as Fe, Co, and Ni can reduce the amount of Pt and leading to the cost reduction. In terms of activities, not only Pt-M (M=Fe, Co, Ni, etc.) alloys but carbon support materials should be considered. Graphite materials such as Valcan carbon XC-72 (VXC) and carbon nanotubes (CNT) have been utilized as a carbon support materials for fuel cells. Moreover, since it discovered, graphene has been widely used as a support for electrocatalysts with different metal nanoparticles because of its specific features like high electro-conductivity, surface area and thermal stability. In an attempt to develop low cost and highly active oxygen reduction reaction (ORR) catalysts, graphene supported Pt-Ni alloy catalyst was synthesized, and the electrochemical ORR performance was evaluated. Due to the ORR sluggish on cathode side plays an important role in fuel cells performance, it is necessary to improve the ORR activities of electrocatalysts. The ORR activity of Pt-Ni supported on graphene was compared with commercial Pt/C catalyst, and Pt-Ni alloy supported on other carbon support materials such as carbon black (VXC) and carbon nanotube (CNT). Among three different electrocatalysts, Pt-Ni alloy catalyst supported on graphene showed highest ORR activity. All Pt-Ni alloy catalysts were followed the direct 4 electron pathway. Among three catalysts, Pt-Ni/graphene catalyst was observed lowest hydrogen peroxide production. Moreover, Pt-Ni/graphene catalysts showed highest methanol resistance. Pt-Ni alloy catalysts were characterized using various physical-chemical techniques, such as scanning electron microscopy, transmission electron microscope, X-ray diffraction, and X-ray photoelectron spectroscopy. The electrocatalytic activity and stability of Pt-Ni alloy catalysts were studied using CV, LSV, RDE and RRDE techniques. Thus, developing Pt-Ni alloy supported on various carbon materials with desired properties of ORR activities will be discussed. ⓒ 2013 DGIST