Most liquid fuels used in transportation today are derived from petroleum and burned in internal combustion engines. This combination is attractive because of the high energy density of the fuels and current economics, but it remains partially reliant on imported petroleum and is highly carbon intensive. Alternatives to internal combustion engines, such as fuel cells that convert chemical energy to electricity, have shown promise in vehicle powertrains, but are hindered by inefficiencies in fuel transport and storage. Carbon-neutral liquid fuels (CNLFs), such as ammonia, used in conjunction with fuel cells, offer an alternative transportation system that addresses these challenges. These fuels can be produced by converting water and air using chemical or electrochemical processes powered by renewable electricity. The resulting CNLFs can be stored and transported using existing liquid fuels infrastructure to the point-of-use. However, there are technical challenges associated with converting CNLFs to hydrogen for use in conventional fuel cells or directly to electricity. Advanced materials such as membranes and catalysts and new electrochemical processes are required to efficiently generate hydrogen or electricity from energy-dense CNLFs at higher conversion rates and lower costs.
Project Innovation + Advantages:
The University of Delaware (UD) will develop a direct ammonia fuel cell operating near 100°C that will efficiently convert ammonia to electricity for electric vehicles and other applications. The team will develop new materials, including low-cost, high-performance hydroxide exchange membranes (HEMs) that can maintain stability near 100°C and novel ammonia oxidation catalysts. Proton exchange membranes are traditionally used in fuel cell applications, but HEMs have a number of advantages when ammonia is used as the direct fuel source including reduced side-reactions, prevention of ammonia crossover, and enabling of the use of lower cost catalysts. Finally, the team will target new developments in the full membrane electrode assembly structure and metal hardware fuel cell stack design, optimizing the system's operating conditions for effective water management and minimized fuel crossover. The goal is an ammonia-fed, cost-competitive fuel cell generating high power density, with rapid start-up enabled by the low operating temperature.
If successful, developments from REFUEL projects will enable energy generated from domestic, renewable resources to increase fuel diversity in the transportation sector in a cost-effective and efficient way.
The U.S. transportation sector is heavily dependent on petroleum for its energy. Increasing the diversity of energy-dense liquid fuels would bolster energy security and help reduce energy imports.
Liquid fuels created using energy from renewable resources are carbon-neutral, helping reduce transportation sector emissions.
Fuel diversity reduces exposure to price volatility. By storing energy in hydrogen-rich liquid fuels instead of pure hydrogen in liquid or gaseous form, transportation costs can be greatly reduced, helping make CNLFs cost-competitive with traditional fuels.