(Invited) Investigation of Pt-Alloy and Strained Pt As Electrocatalysts

Abstract

The need to replace conventional sources of energy has driven the development of fuel cell technology. The polymer electrolyte membrane fuel cells (PEMFCs) show high performance and are important power sources for hydrogen fuel cell vehicles due to the fact that the cells can operate at relatively low temperatures (50 - 90 oC) , has high energy efficiency and only emits water as a byproduct. Furthermore, the direct methanol fuel cell emerge as an important technology for the green energy transition with the use methanol fuel. The most important electrocatalyst for the fuel cells is platinum and efforts are made to enhance its performance and reduce its requirement by alloying with other metals. Therefore, novel approaches are required to develop electrocatalysts for the oxygen reduction reaction (ORR) and methanol oxidation using reduced amounts of Pt for use at PEMFC cathodes with high electrocatalytic activity.Investigation of alloying Pt with transition metals (Ni, Co, Fe) has demonstrated increased electrocatalytic activity and is attributed to changes in the Pt-Pt atomic interaction distances. The electrocatalytic activity is linked to the adsorption of molecular oxygen to the electrocatalytic sites, which is a process enhanced by creating favorable Pt-Pt distances at the electrocatalyst. It is also understood that Pt-alloys have an increased density of d-band vacancies, resulting in stronger binding of OH species to catalyst surfaces. Furthermore, the use of alloying metals causes distortions in the atomic lattice, resulting in compressive strain in the lattice, which increases orbital overlap, widens the d-band, lowers the d-band centre and affects electrocatalytic performance. In addition, enhanced methanol oxidation on strained pure Pt platinum was recently demonstrated and is associated with the preferential absorption of reactant at optimum Pt-Pt interatomic distances.Here, we show results of electrocatalytic activity for oxygen reduction reaction of Fe-Pt alloy with a range of iron content (0 to 80%), the electrocatalytic activity of highly ordered array of Pt nanotubes for methanol oxidation and the effect of strained Pt on methanol oxidation. Structural and electrochemical data of the catalysts will be presented including rotating disk electrode (RDE) voltammetry and SEM images.