Innovative Sodium Fuel Cell Offers New Hope for Electric Aviation

Researchers at the Massachusetts Institute of Technology (MIT) have developed a sodium-based fuel cell that could serve as an alternative to lithium-ion batteries and hydrogen fuel cells. This innovative technology is aimed at advancing clean energy solutions in sectors where replacing fossil fuels has proven challenging.

The sodium-air fuel cell, led by Professor Yet-Ming Chiang, boasts a higher energy density than traditional lithium-ion batteries and eliminates the need for the extreme low temperatures or high pressures associated with hydrogen systems. This makes it particularly promising for electrifying rail transport, regional aviation, and short-distance travel.

Chiang and his team drew on experience from Form Energy, a company known for its iron-air batteries designed for large-scale energy storage, such as those used to harness wind and solar energy for the grid. While the design of the new fuel cell resembles hydrogen fuel cell vehicles, it operates on a fundamentally different principle.

One of the significant advantages of this fuel cell technology is its refueling mechanism, which allows the device to take in chemicals that produce electricity and then remove the byproducts, enabling the fresh fuel to be added without the need for electrical recharging. This approach is similar to the hydrogen fuel cell systems used in vehicles like the Toyota Mirai.

The research team successfully built small test cells to demonstrate the viability of sodium as a fuel source for electricity generation. The sodium becomes liquid at approximately 98 degrees Celsius, and the fuel cells operate at moderate temperatures between 110 and 130 degrees Celsius, making them suitable for use in aircraft and ships.

Initial assessments indicate that this sodium-based system could achieve an energy density of around 1,200 watt-hours per kilogram (Wh/kg), significantly surpassing the approximately 300 Wh/kg typical of commercial lithium-ion batteries. Although hydrogen fuel cells also offer high energy density, they require hydrogen to be stored under high pressure and often at very low temperatures.

Experts in the field have expressed interest in this new cell concept, noting that while sodium-air batteries have been researched previously, applying this chemistry in a fuel cell context is a novel approach. However, safety concerns are paramount, as sodium can react vigorously with water. The design of the cell aims to continuously remove water produced during reactions, minimizing the risk of hazardous interactions. Additionally, a solid electrolyte made from ceramic materials further helps to prevent undesired reactions.

The researchers also addressed the issue of sodium hydroxide, a byproduct of the process. They proposed diluting it before releasing it into the atmosphere or ocean, where it could react with carbon dioxide, potentially helping to sequester CO2 and mitigate its contribution to global warming. Some groups are already conducting field trials using sodium hydroxide for carbon removal in marine environments, although this has sparked some controversies.

On the economic front, sodium presents a viable alternative, as it can be extracted from sodium chloride, commonly known as table salt. Historically, sodium was produced in large quantities for use in leaded gasoline, indicating that a supply chain for sodium could be established. Expanding sodium metal production could make it affordable for use in fuel cell systems.

Chiang is also a co-founder of Propel Aero, a company that aims to commercialize the research findings. The project has received support through the ARPA-E Propel-1K program, which focuses on developing new high-performance energy storage solutions for aircraft, trains, and ships.

The next steps involve further research to enhance the performance and energy density of the cells, with initial applications potentially targeting drones. Chiang expressed enthusiasm for bringing a prototype to flight within the next year, emphasizing that groundbreaking ideas often seem unconventional at first.