Scaled-down reactor turns greenhouse gas into fuel

The reactor, which was built by a team at Rice University, recycles CO₂ to produce highly purified versions of formic acid, which is used globally in multiple chemical industries.

Rice University engineer Haotian Wang said: "Currently, people produce catalysts on the milligram or gram scales. We developed a way to produce them at the kilogram scale. That will make our process easier to scale up for industry."

The device uses a two-dimensional bismuth catalyst and a solid-state electrolyte. Bismuth has a much lower mobility than transition metals such as copper or iron, particularly under reaction conditions, which stabilses the catalyst.

The lab followed bismuth’s oxidation states at different potentials and were able to identify the catalyst’s active state during CO₂ reduction. They generated formic acid continuously for 100 hours with low degradation of the reactor’s components. The reactor reached an energy conversion efficiency of about 42%.

Formic acid is used in fuel, preservatives, animal feed additives, cleaning products and leather production. It is also a liquid hydrogen carrier and can hold nearly 1,000 times the energy of the same volume of hydrogen gas, which has given it uses in the hydrogen car industry.

But the production of formic acid currently requires costly and energy-intensive purification steps, which the team at Rice have avoided with their renewable energy-powered prototype.

“The big picture is that carbon dioxide reduction is very important for its effect on global warming as well as for green chemical synthesis,” Wang said.

"If the electricity comes from renewable sources like the sun or wind, we can create a loop that turns carbon dioxide into something important without emitting more of it."

The reactor, which is described further in Nature Energy, could be retooled to produce higher-value products such as acetic acid, ethanol or propanol fuels.