EPFL scientists have developed an Earth-abundant and low-cost catalytic system for splitting CO2 into CO and oxygen—an important step towards achieving the conversion of renewable energy into hydrocarbon fuels. A solar-driven system set up using this catalyst was able to split CO2 with an efficiency of 13.4%. A paper on the work appears in the journal Nature Energy.
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 the atomic layer deposition (ALD) of tin oxide (SnO2) on copper oxide (CuO) 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. The system uses the same catalyst for the cathode that reduces CO2 to CO and for the anode that oxidizes water to oxygen through 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. Accounting for all reduction products, the total solar-to-fuel efficiency peaks at 14.4%. 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.—Jingshan Luo
This is the first time that such a bi-functional and low-cost catalyst is demonstrated. Very few catalysts—except expensive ones, like gold and silver—can selectively transform CO2 to CO in water, which is crucial for industrial applications.—Marcel Schreier
This work was carried out in 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.
Marcel Schreier, Florent Héroguel, Ludmilla Steier, Shahzada Ahmad, Jeremy S. Luterbacher, Matthew T. Mayer, Jingshan Luo, Michael Grätzel (2017) “Solar conversion of CO2 to CO using Earth-abundant electrocatalysts prepared by atomic layer modification of CuO” Nature Energy 2, 17087 doi: 10.1038/nenergy.2017.87