Turning Greenhouse Gas into Pure Liquid Fuel

Lab’s ‘green’ invention reduces carbon dioxide into valuable fuels

Rice University / Science Daily / September 3, 2019

Summary:

An electrocatalysis reactor built at Rice University recycles carbon dioxide to produce pure liquid fuel solutions using electricity. The scientists behind the invention hope it will become an efficient and profitable way to reuse the greenhouse gas and keep it out of the atmosphere.

A common greenhouse gas could be repurposed in an efficient and environmentally friendly way with an electrolyzer that uses renewable electricity to produce pure liquid fuels.

The catalytic reactor developed by the Rice University lab of chemical and biomolecular engineer Haotian Wang uses carbon dioxide as its feedstock and, in its latest prototype, produces highly purified and high concentrations of formic acid.

Formic acid produced by traditional carbon dioxide devices needs costly and energy-intensive purification steps, Wang said. The direct production of pure formic acid solutions will help to promote commercial carbon dioxide conversion technologies.

The method is detailed in Nature Energy.

Wang, who joined Rice’s Brown School of Engineering in January, and his group pursue technologies that turn greenhouse gases into useful products. In tests, the new electrocatalyst reached an energy conversion efficiency of about 42%. That means nearly half of the electrical energy can be stored in formic acid as liquid fuel.

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

“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,” he said. “That’s currently a big challenge for hydrogen fuel-cell cars.”

Two advances made the new device possible, said lead author and Rice postdoctoral researcher Chuan Xia. The first was his development of a robust, two-dimensional bismuth catalyst and the second a solid-state electrolyte that eliminates the need for salt as part of the reaction.

“Bismuth is a very heavy atom, compared to transition metals like copper, iron or cobalt,” Wang said. “Its mobility is much lower, particularly under reaction conditions. So that stabilizes the catalyst.” He noted the reactor is structured to keep water from contacting the catalyst, which also helps preserve it.

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

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