Advanced BioFuels USA

by Robert F. Service (Science Magazine) As windmills and solar panels multiply, the supply of renewable electricity sometimes exceeds demand. Chemists would like to put the excess to work making commodity chemicals, such as the raw materials for fertilizer and plastics, which are now produced with heat, pressure, and copious fossil fuels. The electrochemical cells that can harness renewable electricity to make these compounds have been too slow to be practical. Now, two groups report redesigning the cells to achieve a dramatic speedup—perhaps enough to put green industrial chemistry within reach.

“In the future, electrons to molecules will be a major part of how we do chemical synthesis,” says Etosha Cave, chief scientific officer of Opus 12, a startup aiming to turn renewable energy into chemicals. “These two papers help push that vision forward.”

One research group uses carbon dioxide (CO₂) as its starting material to make ethanol, a fuel, and ethylene, a starting point for plastics; the other turns nitrogen (N₂) into ammonia (NH₃), a key component in fertilizer. Both owe their progress to advances in the catalyst-coated electrodes that drive chemical reactions between gases and liquids.

In theory, turning CO₂ into hydrocarbons such as ethanol and ethylene is simple: Just add energy to the CO₂ so it can steal hydrogen atoms from water. But the reactions are tricky. They take place in electrolyzers, which consist of two electrodes separated by a liquid electrolyte. At one electrode, the anode, water splits into oxygen, electrons, and hydrogen ions, or protons. The protons then migrate through the electrolyte to the cathode, where they react with CO₂, which is fed in separately, to make the hydrocarbons.

In current electrolyzers, the cathode typically consists of a 3D carbon mesh dotted with tiny copper catalyst particles. Their “gas diffusion” design allows CO₂ gas that infiltrates the mesh to interact with all the catalyst particles simultaneously. One side of the mesh is also in contact with the liquid electrolyte, which helps ferry protons over from the anode. But water in the electrolyte can also infiltrate the pores, blocking CO₂ gas from reaching the catalyst particles.

Coating the electrode with a water-repellent, fluorine-rich polymer can help. That and other improvements have resulted in electrolyzers that efficiently convert a modest input of electricity into hydrocarbons. But only about 40% of the product compounds have two carbon atoms, as ethylene and ethanol do. Much of the rest is methane, which has one carbon and is less valuable.

Now, researchers led by Ye Wang, a chemist at Xiamen University, report that adding fluorine to the standard copper catalyst on their gas diffusion electrode changes the pathway of the reactions, making them more likely to produce two-carbon compounds. Up to 85% of the resulting products are valuable two-carbon compounds, and the setup can handle 1600 milliamps of current per square centimeter of catalyst, twice the throughput of the previous record holder, the researchers reported on 20 April in Nature Catalysis. “[It’s] definitely in the range where someone will be interested in commercializing the technology,” says Karthish Manthiram, a chemical engineer at the Massachusetts Institute of Technology.

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With oil prices crashing because of price wars and the coronavirus pandemic, companies will likely continue to rely on fossil fuels to produce ammonia, ethanol, and other commodity chemicals in the near future. But as researchers continue to improve electricity-based production methods, even cheap fossil fuels may ultimately prove no match for surplus green energy.  READ MORE

Electrocatalytic reduction of CO2 to ethylene and ethanol through hydrogen-assisted C–C coupling over fluorine-modified copper (Nature Catalysis)

NOVA Chemicals and Enerkem collaborate to close the loop on plastics recycling (Canadian Packaging)

Nova Chemicals, Enerkem partner on advanced recycling technology for plastics (Recycling Today)