Pt-Co Bimetallic Catalysts for PEM Fuel Cell Cathodes
Microscopy and Microanalysis
Polymer electrolyte membrane fuel cells (PEMFCs) are being developed for future use as efficient, zero-emission power sources. However, the performance of PEMFCs degrades rapidly as a function of time at temperature (≤ 80°C), potential cycling, and a corrosive operating environment, during electrochemical aging. Much of the performance degradation can be attributed directly to the limited durability of the electrocatalyst, especially on the cathode side where the catalysts are subjected to
... e subjected to extremely harsh oxidative conditions. Pt nanoparticles supported on carbon black (CB) continue to be the most used cathode catalyst, but bimetallic catalysts are being investigated to replace Pt. The most important reasons to replace Pt are cost and a limited supply of Pt, but improved activity for the oxygen reduction reaction (ORR) and enhanced durability are also desired. Pt alloyed with transition metals (M=Co,Cr,Ni, etc.) have shown enhanced activity compared with Pt-only catalysts, which may be attributed to changes in the atomic nature of the nanoparticles, including Pt-Pt and Pt-M bond lengths, the atomic coordination, a change in the electron density of states in the Pt-5d orbital, the nature of the particle morphology and surface, and ordering of the atoms within the particle [1-4]. Thus, it is important to characterize the nature and uniformity of the atomic-scale crystalline structure of catalyst nanoparticles in order to determine the effects of catalyst microstructure, morphology, and composition on performance.