A New and Improved Carbon Dioxide Conversion Method

Teams of researchers from MIT and Harvard have developed an efficient process that can convert carbon dioxide into formate – a material that can be used like hydrogen or methanol to power a fuel cell and generate electricity. 

Most techniques for converting carbon dioxide into fuel involve a two-stage process, where the gas is first chemically captured and turned into a solid form as calcium carbonate, then heated in order to drive off the carbon dioxide and convert it to a fuel feedstock, such as carbon monoxide. The second step has very low efficiency, typically converting less than 20% of the gaseous carbon dioxide into the desired product.

This new process achieves a conversion of well over 90% and eliminates the need for the inefficient heating step. It first converts the carbon dioxide into an intermediate form, liquid metal bicarbonate. That liquid is then electrochemically converted into liquid potassium or sodium formate in an electrolyzer that uses low-carbon electricity, from a renewable energy source. The highly concentrated liquid potassium or sodium formate solution produced can then be dried to produce a solid powder that is highly stable and can be stored in ordinary steel tanks for up to years or even decades.

The team also built a fuel cell specifically optimized for the use of this formate fuel to produce electricity. The stored formate particles are dissolved in water and pumped into the fuel cell as needed. 

The new process has been demonstrated at a small, laboratory scale, but the researchers expect it to be scalable so that it could provide emissions-free heat and power to individual homes, and also be used in industrial or grid-scale applications. 

“The formate economy is an intriguing concept because metal formate salts are very benign and stable, and a compelling energy carrier,” said Ted Sargent, a professor of chemistry and of electrical and computer engineering at Northwestern University, who was not associated with this work. “The authors have demonstrated enhanced efficiency in liquid-to-liquid conversion from bicarbonate feedstock to formate, and have demonstrated these fuels can be used later to produce electricity.”