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:
Molecule Works will develop an electrochemical membrane reactor to produce ammonia from air, water, and renewable electricity. The team proposes a solid-state, thin-film alkaline electrochemical cell that has the potential to enhance ammonia synthesis productivity and energy efficiency, while lowering the cell material and fabrication costs. Current systems for ammonia production all have several challenges. Some use acidic membranes that can react with ammonia, resulting in lower conductivity and reduced membrane life. Others that operate at low temperatures (<100°C) may have low rates of reactions, while those that operate at high temperatures (>500°C) have long-heating processes that make them less practical for intermittent operation using renewable energy. Alkaline electrolytes have a number of advantages over traditional cells. Notably, alkaline electrolytes allow a larger area of the catalyst for nitrogen activation, increasing the rate of ammonia production. The team's system operates at a much lower temperature and pressure than the traditional ammonia production process. The modular nature of the system will also allow it to be deployed near the point of use.
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.