New Fuel Cell Electrocatalysts Based on Mesoporous Precious Metals

摘要

A new technique is presented for quickly measuring the electrocatalytic performance of electrocatalysts at the solid polymer electrolyte interface without the need to produce a complicated membrane electrode unit. Mesoporous platinum and platinum-ruthenium has been developed as potential electrocatalysts for use in fuel cells. We have examined these materials for the oxygen reduction reaction, the oxidation of hydrogen, and the oxidation of methanol in both aqueous electrolytes and at the solid polymer electrolyte interface. We show how our technique can be used to elucidate both the transport properties of the membrane material and the electrokinetic performance of electrocatalyst. The mesoporous catalysts show good activity, and electrochemical access to the internal pore surface is not limited by the small pore size as shown by the large surface areas possible when Nafion is used as the solid polymer electrolyte. Mesoporous platinum provides high intrinsic activity to oxygen reduction and hydrogen oxidation, although there is a subtle change of mechanism when moving from sulfuric acid to Nafion as electrolyte. The exchange current density for hydrogen oxidation on the mesoporous platinum catalyst at the Nafion interface is only about half of that seen in sulfuric acid under he same conditions. When compared to sulfuric acid electrolytes, the rate of methanol oxidation is improved at the Nafion interface on mesoporous PtRu, although at higher potentials the performance becomes similar in both electrolytes.