Alkaline Membrane-Based Ammonia Electrosynthesis
Most liquid fuels used in transportation today are derived from petroleum and burned in internal combustion engines. These fuels are attractive because of their high energy density and current economics, but they remain partially reliant on imported petroleum and are highly carbon intensive. Domestically produced carbon-neutral liquid fuels (CNLFs), such as ammonia (NH3), can address both of these challenges. Chemical manufacturers commonly use the Haber-Bosch (HB) process to produce NH3 for use in agriculture or the chemical industry. The HB process involves first separating nitrogen (N2) from air, then breaking the very stable nitrogen-nitrogen bond, and finally combining the nitrogen atoms with hydrogen to form NH3. The HB process requires huge capital investments for reactors to operate at high pressure and temperature, large amounts of base-load power to keep the process running continuously (HB uses 1-2% of global energy), and distribution infrastructure to ship the resulting ammonia around the world. Technology enabling the small- and medium-scale synthesis of ammonia can move the production of the fuels closer to the consumer, and - if renewable sources are used - the fuels can be produced in a carbon neutral manner. However, significant technical challenges remain in either adapting the HB process for smaller scale use or developing alternative electrochemical processes for fuel development. New methods would also have to employ variable rates of production to match the intermittent generation of renewable sources. Improvements in these areas could dramatically reduce the energy and carbon intensity of liquid fuel production. By taking better advantage of intermittent renewable resources in low-population areas and transporting that energy as a liquid fuel to urban centers, we can more fully utilize domestically available resources.
Project Innovation + Advantages:
Wichita State University will develop a renewable energy-powered electrochemical device for ammonia production at ambient temperature. This allows the unit to consume less energy but maintain high productivity. The goal is an alternative path for ammonia electrochemical synthesis from water and air without the need for the high temperature and pressure required by the Haber-Bosch process. The key innovation is the use of a hydroxide-exchange membrane (HEM) polymer electrolyte. The more commonly used proton exchange membranes (PEM) present major challenges leading to low efficiency for PEM-based ammonia electrosynthesis. Switching to HEMs will reduce side-reactions, allow the use of non-precious metal catalysts, and eliminate ammonia crossover and electrolyte contamination. As such, HEM-supported ammonia electrosynthesis may offer high coulombic efficiency and high ammonia productivity, without losing the key advantages of PEM-based electrosynthesis - operating under ambient conditions and using air and water as reactants. Unlike the Haber-Bosch process, electrochemical synthesis of ammonia can be made much smaller and can operate intermittently which allows better integration with renewable electricity.
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.