Turning greenhouse gas into fuel in Texas

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Using a renewable energy powered electrolyser, researchers have proposed a way to re-purpose a common greenhouse gas in the production of pure liquid fuels.

The catalytic reactor developed at Rice University, Texas, uses carbon dioxide as its feed-stock. The catalytic reactor then produces a highly purified concentration of formic acid.

Traditionally, formic acid produced using carbon dioxide devices is expensive and require a high level of energy in the purification process.

This method of producing formic acid was designed by Haotian Wang from Rice University’s lab of chemical and bio-molecular engineering.

“Formic acid is an energy carrier…It’s a fuel-cell fuel that can generate electricity and emit carbon dioxide…It’s also fundamental in the chemical engineering industry as a feed-stock 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.”

According to Chuan Xia, post doctoral researcher from Rice University, this new device was made possible by two advances. The first was the development of a robust two-dimensional bismuth catalyst and the second being, 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. “It’s mobility is much lower, particularly under reaction conditions. So that stabilises the catalyst.” Wang highlighted that the reactor is structured to keep water from contacting the catalyst, which also helps preserve it.

Xia makes the nano-materials in bulk. Xia continued: “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.”

Wang continued: “Usually people reduce carbon dioxide in a traditional liquid electrolyte like salty water…You want the electricity to be conducted, but pure water electrolyte is too resistant. You need to add salts like sodium chloride or potassium bicarbonate so that ions can move freely in water.

“But when you generate formic acid that way, it mixes with the salts…For a majority of applications, you have to remove the salts from the end product, which takes a lot of energy and cost. So, we employed solid electrolytes that conduct protons and can be made of insoluble polymers or inorganic compounds, eliminating the need for salts.”

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