Converting CO2 into pure liquid fuel just got a lot greener using new reactor

3 Sep 2019

An electrocatalysis reactor built at Rice University recycles CO2 to produce pure liquid fuel solutions using electricity. Image: Jeff Fitlow/Rice University

Questions are often raised about how green CO2 conversion tech really is, but a new reactor design claims to do it using renewable electricity.

The demand for sustainable fuels is only increasing as nations strive for the goal of becoming carbon neutral, and now a team of researchers at Rice University has unveiled a production system that makes substantial promises using CO2.

Writing in Nature Energy, the team said that it has found a way to repurpose CO2 into highly purified and high concentrations of formic acid, which is commonly used in fuel cells to produce electricity. While not the first device of its kind, the team led by Haotian Wang said that typically these are both costly and energy intensive.

By contrast, the team’s new electrocatalyst system reached an energy conversion efficiency of approximately 42pc. That means nearly half of the electrical energy can be stored in formic acid as liquid fuel.

“Formic acid is an energy carrier. It’s a fuel-cell fuel that can generate electricity and emit CO2 – which you can grab and recycle again,” Wang said.

“It’s also fundamental in the chemical engineering industry as a feedstock for other chemicals, and a storage material for hydrogen that can hold nearly 1,000 times the energy of the same volume of hydrogen gas, which is difficult to compress. That’s currently a big challenge for hydrogen fuel-cell cars.”

Creating a greener loop

Two major advances were behind this latest breakthrough. The first being the development of a robust, 2D bismuth catalyst and the second being a solid-state electrolyte that eliminates the need for salt as part of the reaction.

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

The big energy drain and cost of a typical system is that CO2 is typically reduced in salty water, which means the salt has to eventually be removed to prevent it from mixing with the formic acid. The team’s system, however, uses solid electrolytes that conduct protons and can be made of insoluble polymers or inorganic compounds, eliminating the need for salts.

With its current reactor, the lab generated formic acid continuously for 100 hours with negligible degradation of the reactor’s components, including the nanoscale catalysts.

“The big picture is that CO2 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 CO2 into something important without emitting more of it.”

Colm Gorey was a senior journalist with Silicon Republic