(630e) Behavior of Platinum Nanotubes in the Methanol Oxidation Reaction

Platinum supported by amorphous carbon (Pt/C) is often the commercial material used as an electrocatalyst in both the methanol oxidation reaction (MOR) as an anode in direct methanol fuel cells (DMFCs) and the oxygen reduction reaction (ORR) as a cathode in proton exchange membrane fuel cells (PEMFCs). Small platinum particles are used due to the high surface area to volume ratio. The carbon support spaces the particles to prevent agglomeration and increase specific surface area and mass activity. A decrease in particle size, however, causes the specific activity in ORR and organic molecule oxidation to drop due to alterations in the coordination number and crystal planes of the surface platinum atoms. Low durability of commercial catalysts in PEMFCs and DMFCs hinders the commercialization of these devices. Slow kinetics and intermediate adsorption at the anode during MOR, notably of carbon monoxide, further limit the capabilities of DMFCs.

Platinum nanotubes have been synthesized to improve the activity, durability, and carbon monoxide adsorption characteristics of conventional DMFC catalysts. Platinum nanotubes of 5 nm thickness were synthesized by the galvanic replacement of silver nanowires, which were formed by the ethylene glycol reduction of silver nitrate.[1] The catalytic properties of platinum nanotubes were evaluated to demonstrate the improvement in activity and durability of the material to conventional catalysts. MOR, ORR, and durability experiments were conducted to study the activity of platinum nanotubes, platinum nanoparticles, and bulk platinum electrocatalysts. Catalyst activity for MOR was characterized through cyclic voltammetry and chronoamperometry techniques. Bulk platinum electrodes have been previously found to have a higher degree of carbon monoxide adsorption and poisoning when compared to electrodispersed platinum. While platinum nanotubes do not utilize a carbon support, the catalyst exhibits carbon monoxide adsorption characteristics similar to Pt/C. When compared to conventional materials, platinum nanotubes offer significant catalyst improvement in DMFCs.

[1] Z. W. Chen, M. Waje, W. Z. Li, Y. S. Yan, Angewandte Chemie-International Edition 2007, 46, 4060.