A New Catalyst Splits Apart CO2

Researchers at Ecole Polytechnique Federale de Lausanne (EPFL) have developed a new catalyst that does the electrolysis of carbon dioxide into oxygen and carbon monoxide. The scientists have developed an Earth-abundant catalyst based on copper-oxide nanowires modified with tin oxide. This is a step into the future of clean energy by storing it in the form of carbon-based fuels produced from renewable sources, effectively enabling the clean use of liquid fuels such as gasoline.

Current CO-forming catalysts are either not selective enough or too expensive to be industrially viable. This and the stability of the CO2 molecule pose difficult problems for a carbon cycling renewable fuel plan.

The solar-driven system setup using this catalyst was able to split CO2 with an efficiency of 13.4%. The work paper has been published in Nature Energy, and is expected to help worldwide efforts to synthetically produce carbon-based fuels from CO2 and water.

The research was carried out by the lab of Michael Grätzel at EPFL. Grätzel is known worldwide for the invention of dye-sensitized solar cells (“Grätzel cells”). The new catalyst, developed by PhD student Marcel Schreier, postdoc Jingshan Luo, and several co-workers, is made by depositing atomic layers of tin oxide on copper oxide nanowires. Tin oxide suppresses the generation of side-products, which are commonly observed from copper oxide catalysts, leading to the sole production of CO in the electroreduction of CO2.

The catalyst was integrated into a CO2 electrolysis system and linked to a triple-junction solar cell (GaInP/GaInAs/Ge) to make a CO2 photo-electrolyzer. Importantly, the system uses the same catalyst as the cathode that reduces CO2 to CO and the anode that oxidizes water to oxygen through what is known as the “oxygen evolution reaction.” The gases are separated with a bipolar membrane. Using only Earth-abundant materials to catalyze both reactions, this design keeps the cost of the system low.

The system was able to selectively convert CO2 to CO with an efficiency of 13.4% using solar energy. The catalyst also reached a Faradaic efficiency of up to 90%, which describes how efficiently electrical charge is transferred to the desired product in an electrocatalysis system like the one developed here. “The work sets a new benchmark for solar-driven CO2 reduction,” says Luo.

“This is the first time that such a bi-functional and low-cost catalyst is demonstrated,” adds Schreier. “Very few catalysts – except expensive ones, like gold and silver – can selectively transform CO2 to CO in water, which is crucial for industrial applications.”

The work was carried out in a collaboration with Jeremy Luterbacher’s Laboratory of Sustainable and Catalytic Processing at EPFL. It was funded by Siemens AG, and a Marie Skłodowska-Curie Fellowship from the European Union’s Seventh Framework Programme. It included a contribution from Abengoa Research in Spain.

This is an astonishingly good result for a new catalyst concept. The 13.4% efficiency using solar for power is a strong indicator that refinements and further innovation can take the efficiency further. For the next most likely step in energy and fuel supplies, hydrocarbons look like they may well be in the hunt for keeping market share. This is a massive step forward, remaking fuels instead of drilling them out of the ground could be the future, and an easy market transition, too.