SUPPORTING PLATINUM ON NANO-STRUCTURED METAL OXIDES FOR PROTON EXCHANGE MEMBRANE CATHODES

摘要

The proton exchange membrane (PEM) fuel cell shows tremendous promise and represents a versatile and efficient energy conversion device. However, before the PEM fuel cell can achieve widespread commercial use, improvements in unit cost, fuel cell durability and fuel versatility must be achieved. Key to the PEM fuel cell operation is the catalysis of the oxygen reduction reaction (ORR) on the cathode. A perfect ORR catalyst would very efficiently convert O2, protons, and electrons to water, have no peroxide byproducts, be inexpensive and durable. This, however, represents a significant challenge; the sluggish kinetics of the ORR on precious metals have been the subject of extensive studies in electrocatalysis over the last 8 decades and to date no non-platinum or even non- platinum group metal (PGM) based catalyst has been discovered that is more efficient than a PGM based catalyst. And while Pt and Pt alloys offer acceptable ORR performance, the high cost of Pt severely impacts the future commercial viability of current PEM fuel cell technology. Additionally state of the art fuel cell cathodes are inherently thermodynamically unstable in that the preferred catalyst configuration is well dispersed Pt-nanoparticles on a thermally treated carbon support. Obviously in the presence of air the carbon support is ultimately converted to CO2, a problem exacerbated at high potentials at or above the open circuit potential of the cell. Additionally, under these same conditions, Pt is also susceptible to dissolution and agglomeration through Ostwald ripening.