Advanced Catalysts for Fuel-Flexible Fuel Cells

Advanced Catalysts for Fuel-Flexible Fuel Cells

Su Ha^a, Byeong Wan Kwon^a, Christian Martin Cuba Torres^a, Shreya Shah^a, Kale Warren Herrison^b, Qian He^b, M. Grant Norton^b

^a The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164

^bSchool of Mechanical and Materials Engineering, Washington State University Pullman, WA, 99164-2920

Fuel cells offer a number of advantages as an alternative energy production technology for both stationary and mobile applications. In commercial aviation, a concept called the more electric airplane (MEA) will allow greater fuel efficiency by substituting hydraulically and pneumatically driven systems by those based on electrical energy. The increased electrical power demand in a MEA can be met by decentralizing the power-producing units using small individual devices such as fuel cells. Furthermore, existing commercial aircraft use a low efficiency gas turbine auxiliary power unit (APU) to provide electrical power for operating navigation systems and various other electronic devices. By replacing the conventional APU with a solid oxide fuel cell (SOFC) APU improvements can be made in providing a means to obtain auxiliary power without consuming excessive amounts of fuel when the airplane is on the ground or when the load is increased on the main engines during flight. Thus, fuel cells may become the primary electrical power source with engine-driven generators serving a backup role on future airplanes.

An important practical requirement for the use of fuel cells on commercial and military airplanes is that they must operate using kerosene-based aviation fuels (such as Jet-A and JP-8), which are already on board. The existing approach for fuel cell systems operating on Jet-A fuel (the standard kerosene-based commercial aviation fuel) requires a fuel reformation process in which the Jet-A is mostly converted to hydrogen and carbon monoxide. This syngas mixture is fed into SOFCs where it is electrochemically converted to H₂O and CO₂, and produces electrical power. To develop a high performance fuel reforming system that can operate with Jet-A fuel, a catalyst with the following attributes is required: (1) High oxidation activity toward Jet-A fuel; (2) High resistance to coking; (3) Stability at high operating temperatures (i.e., higher than 700^oC); (4) High sulfur tolerance (e.g., aviation fuels typically contain 500 ppm of sulfur).

Conventional nickel-based catalysts quickly deactivate under reforming environments due to coke formation and sulfur poisoning. However, we have developed a fuel-flexible molybdenum dioxide (MoO₂) based catalyst that has been shown to display high catalytic activity for various processes involving long-chain hydrocarbons and bio-based aviation fuels. In this presentation, we will discuss the performance of MoO₂ based catalysts in a number of reforming environments and also the potential to incorporate MoO₂ into an active anode for a SOFC that can operate directly on a range of hydrocarbon fuels from both fossil and bio-based sources. Although on-board applications for fuel cells may be some way off, there are near term applications for this technology including alternative-fuel fuel cells as range extenders or battery powered airport ground support equipment (GSE). The airport GSE market includes various types of specialty vehicles used to service aircraft during ground operations and fuel cells have the potential to provide significant lifecycle cost savings over lead acid battery and combustion engine systems.