Layered catalyst selectively generates two-carbon compounds from CO2

Copper-catalyzed electrochemical reduction offers a path for making valuable chemicals, such as ethanol or ethylene, from CO₂. However, selectively generating sufficient yields of two-carbon products requires precise manipulation of the microenvironment near the surface to control reaction activity and product selectivity.

Recent research from the Lawrence Berkeley National Laboratory (LBL; Berkeley, Calif.; www.lbl.gov) has demonstrated progress toward a catalyst system capable of activity and selectivity for C2 products that vastly outstrips those of copper alone. The LBL approach relies on layering two ion-conducting polymers — one a perfluorosulfonic acid, cation-conducting ionomer (Nafion); the other a polystyrene-based, anion-conducting ionomer (Sustainion) — onto a copper surface to catalyze the electrochemical reduction.

“The Sustainion layer boosts the concentration of CO₂ relative to that of H₂O at the catalyst surface because the CO₂ affinity and hydrophobicity of this ionomer, make it more likely that carbon-carbon coupling will occur,” explains Alexis Bell, senior scientist at LBL and professor of chemical engineering at the University of California at Berkeley (www.berkeley.edu). “Meanwhile, the Nafion raises pH near the copper surface by trapping hydroxyl ions, thereby suppressing the formation of H ₂ and C1 products.”

Further enhancement of the surface effects of the bilayer ionomer films is achieved by altering the cathode voltage by applying five-second pulses, generating Faraday efficiencies of over 90% for C2 products, and only 4% for hydrogen formation.

In the future, Bell and his team plan to investigate methods to coat copper nanoparticles with the bilayer ionomers. The concept of layering ionomers can also be applied to other catalyst systems.