(285b) Rational Design of a Metallic Electrocatalyst for the Selective Reduction of CO2 to C2+ Oxygenates

Authors: 
Clark, E. L., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Kwon, Y., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Cheng, M. J., Joint Center for Artificial Photosynthesis, Lawerence Berkeley National Lab
Lobaccaro, P., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Lum, Y., Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Lab
Singh, M. R., Lawrence Berkeley National Laboratory
Bell, A. T., University of California, Berkeley

The promise of utilizing solar energy to promote the electrochemical or photoelectrochemical reduction of CO2 to transportation fuels has motivated extensive research efforts aimed at identifying highly active and selective  CO2 reduction (CO2R) electrocatalysts.1–4  These efforts have revealed that copper is the only metallic electrocatalyst capable of reducing CO2 to hydrocarbons and alcohols.5–7  Unfortunately, the reaction requires an overpotential of approximately -1 V, resulting in a cathodic CO2R energy efficiency of roughly 25%.8–11  Furthermore, CO2R over metallic copper can produce up to 16 different products depending on the surface morphology and the applied potential.10,11  As a consequence, there is considerable motivation to discover novel electrocatalysts that can reduce CO2 to fuels with higher efficiency and selectivity than metallic copper.

Highly disordered metallic electrocatalysts have been shown to dramatically reduce the overpotential requirement of CO2R over Sn,12 Cu,13 Au,14 and Ag15 electrodes.  The enhanced activity of these electrocatalysts is presumably due to the presence of stepped facets and grain boundaries at the electrode surface.16  Unfortunately these highly activity electrocatalysts almost exclusively produce carbon monoxide and formate, which are not typically regarded as fuels.  Recently, copper nanoparticles supported on glassy carbon were shown to selectively reduce CO2 to methane with Faradaic efficiencies as high as 75% at an applied potential of -1.4V vs RHE.17  Furthermore, cycling the potential of a polycrystalline copper electrode in a halogenated electrolyte prior to conducting CO2R has been shown to result in surface nanostructuring that enhances the selectivity to ethene production.11,18–20  However, there have been no reports in the literature of electrocatalysts that can selectively reduce CO2 to C2+ oxygenates, which are widely regarded as more effective transportation fuels than the hydrocarbon products.  Unfortunately, the lack of understanding of the reaction mechanism that leads to C-C coupling makes it difficult to design such an electrocatalyst.  Interestingly, highly disordered Cu electrodes have been reported to reduce CO to C2+ oxygenates with high selectivity at low overpotential.21  However, the efficacy of this electrocatalyst is extremely limited due to the use of CO as the reacting species, which limits the C2+ oxygenate partial current density to ~0.4 mA/cm2.

Herein we report the rational design of a metallic CO2 electrocatalyst that produces C2+ oxygenates as the primary reaction products.  The novel electrocatalyst concept is supported by DFT calculations which help to explain the origin of this electrocatalysts unique selectivity.   

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