The electrocatalysts in proton exchange membrane (PEM) and direct methanol (DMFC) fuel cells, also known as low temperature fuel cells, typically consist of metal nanoparticles dispersed onto a conducting (often carbon) support. In this research group we seek to relate the activity and durability of the catalyst nanoparticles to their structure and electronic properties. Much of the research focuses on the study of platinum and platinum-based binary or ternary alloy particles.
The PEM fuel cell utilizes hydrogen as the fuel, whilst the DMFC uses methanol. Both use oxygen or air as the oxidant. Commercialisation of both types of low temperature fuel cell is being limited by the performance of the cathode. There are three main difficulties, the slow kinetics of the oxygen reduction reaction at Pt (meaning more Pt must be used to obtain the desired activity), the durability of the catalysts, and methanol cross-over from the anode in the case of the DMFC. Alloying Pt with first row transition metals usually addresses the first of these problems; with the most promising bimetallic catalysts being Pt3Cr, Pt3Ni, and Pt3Co. Various structural investigations have indicated that improvements in activity are related to a combination of electronic effects, contraction of the Pt-Pt bond distance within the particle, and modification of the adsorption of oxygen species at either Pt or alloy element sites. We are currently exploring new catalyst formulations and specific nanoparticle structures in the search for more active catalysts as well as providing increased understanding of the structure/property relationships. Once a promising catalyst has been identified, durability becomes the primary concern and recently we have been focussing on methods that enable rapid screening of the stability and degradation mechanisms of the catalysts.
For DMFCs the anode needs to be a selective catalyst, promoting the full 6-electron oxidation of methanol all the way to CO2, thereby avoiding poisoning of the catalyst surface by carbon monoxide. PtRu bimetallic alloy particles have, thus far, been shown to be the most active catalysts. We are investigating their durability and degradation mechanisms.