The production, transport and use of carbon-neutral liquid fuels for energy delivery. Areas of interest within Category 2 are shown in bold. Click to enlarge.

REFUEL seeks to develop technologies that convert water and air into CNLFs using chemical or electrochemical processes powered by renewable electricity sources, such as wind and solar. By transforming renewable resources into liquid fuels, renewable power can be stored for longer periods and transported efficiently and inexpensively as liquids via existing infrastructure to consumers. REFUEL also targets technologies that convert CNLFs into electricity or into hydrogen to power zero-emission vehicles.

The program’s overall goal is a competitive total cost (including production, transportation, storage, and conversion costs) of delivered (source-to-use) energy (e.g. converted to motive power for transportation) as opposed to the primary energy stored in chemical form below $0.3/kWh—the price needed to be competitive with other carbon-free delivery methods

ARPA-E defines source-to-use energy cost as the sum of the fuel production cost (CF), the cost of transportation or transmission from production to the user (CT), and the cost of any storage (CS), divided by the conversion efficiency (η) to account for any losses during the conversion steps.

Chemicals, such as hydrocarbons, are effective energy carriers and return the largest fraction of their energy density when delivered via a pipeline. However, fossil fuels are major CO₂ emitters and also drive energy imports. … Because of the inherent difficulties in achieving zero-carbon emissions with fossil fuels in the transportation sector, we must consider new options. The REFUEL program seeks to address these challenges by developing CNLFs that provide a new set of technology options for storing renewable energy in CNLFs, and delivering it economically and effectively when and where it is needed.

—DE-FOA-0001562

ARPA-E provided some representative examples of the types of hydrogen-rich liquid fuels that would be responsive to the FOA (only as examples, not as an exhaustive list). These include:

• Ammonia (NH₃). Modern Haber-Bosch plants, using hydrogen generation by SMR, release about 1.6 – 1.8 ton CO₂ per ton of NH₃ of which only 0.95 ton comes from the SMR process and the rest from heating and pressurization needs. Energy consumption for NH₃ production using SMR varies from 7.8 to 10.5 MWh per ton of NH₃ (including feedstock, which accounts for 80% of energy).

  A potentially greener technology option of using hydrogen from water electrolysis requires 9.5 MWh to make 1 metric ton NH₃ (of which 8.9 MWh comes from hydrogen production, assuming 50.2 kWh/kg H₂). Solid-state electrochemical ammonia synthesis, a possible alternative to the Haber-Bosch process, has potentially lower energy input and operational pressure and temperature thus simplifying the balance of plant, and could be cost competitive as long as the reaction rate is significantly increased.

• Hydrazine hydrate (N₂H₄·H₂O). This is currently produced by oxidation of ammonia at a large scale (80,000 ton/year globally) and is therefore more expensive than ammonia. However, it has a high energy density (3.56 kWh/L), is easy to handle (freezing point -51.7 °C, flash point 74 °C) and, if low-cost synthetic methods are developed, may fit the technical targets of the FOA.

  To accomplish wide-scale implementation of CNLFs, technological advances in both the production and conversion of this fuel would need to be achieved. An example of a non-toxic substitute for hydrazine with low carbon footprint is carbohydrazide (CH₆N₄O). Carbohydrazide has been used as a fuel in a fuel cell with an OCV 1.65V.

• Carbon-containing CNLFs. There are numerous examples of carbon-containing CNLFs that would fit APRA-E’s targets synthetic gasoline or diesel fuel, alcohols, and dimethyl ether. The requirements are that the carbon is directly taken from the atmosphere or another sustainable CO₂ source and that the fuel is produced in a one-pot chemical or electrochemical process.

  Current processes for production of synthetic fuels such as Fischer- Tropsch process are multi-step, very capital intensive and eventually not economical. Reducing the process complexity may allow increased efficiency and lower costs.

SBIR/STTR. Under REFUEL, ARPA-E will allocate up to $5 million to small businesses through its Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) program, with up to $25 million made available to all applicants.