Search

Hydrogen-oxygen fuel cell technology is a critical component for crewed space exploration mission beyond low earth orbit. While lowering platinum loading is of paramount importance for automotive fuel cells, it is not a significant constraint for MEAs used for space applications. As such, support-less platinum black catalysts is a viable choice. Historically, surfactant-stabilized polytetrafluoroethylene (PTFE) emulsion is used as the binder for platinum black electrode. High temperature treatment steps needed for the PTFE emulsion prevents the direct deposition of the electrocatalysts onto the Nafion® membrane. In this study, two alternative materials have been used to replace PTFE emulsion. These include surfactant-free PTFE fine particles and functionalized carbon nanotube with Nafion®. An ultrasonic spray deposition technique was applied to directly deposit support-less Pt black catalyst ink onto the Nafion® membrane. The fabrication process was optimized to produce high performance membrane electrode assemblies that approaching NASA performance target.

The performances of ruthenium oxide-based oxygen evolution catalysts fabricated by various techniques have been studied. A thermal processing technique has been identified that can produce viable iridium and lead-doped ruthenium oxide catalyst. The best oxygen evolution performance was obtained with an iridium-doped ruthenium oxide catalyst with nine molar percent iridium. The cell voltage of the Ir(9)-d-RuO2 catalyst at an applied current density of 200 mA/cm2 was 1.45 volts at 70 oC. The oxygen evolution Tafel slope for doped ruthenium oxide catalysts are in the range of 40 to 55 mV/decade, a minimum of 10 mV/decade lower than what was found for ruthenium oxide.