Catalysis

Mechanism for acetate formation in electrochemical CO(2) reduction on Cu: Selectivity with potential, pH, and nanostructuring

Authors

  • Hendrik H. Heenen Department of Physics, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark & Fritz-Haber-Institut der Max-Planck-Gesellschaft, D-14195 Berlin, Germany ,
  • Haeun Shin Center for Catalytic Science and Technology, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA ,
  • Georg Kastlunger Department of Physics, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark ,
  • Sean Overa Center for Catalytic Science and Technology, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA ,
  • Joseph A. Gauthier SUNCAT Center for Interface Science and Catalysis, Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States ,
  • Feng Jiao Center for Catalytic Science and Technology, Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, DE, USA ,
  • Karen Chan Department of Physics, Technical University of Denmark, DK-2800, Kgs. Lyngby, Denmark

Abstract

Nanostructured Cu catalysts have increased the selectivities and geometric activities for high value C-C coupled (C2) products (ethylene, acetate, and ethanol) in the electrochemical CO(2) reduction reaction (CO(2)RR). The selectivity among the high-value C2 products is also altered, where for instance the yield of acetate increases with alkalinity and is dependent on the catalyst morphology. The reaction mechanisms behind the selectivity towards acetate vs. other C2 products remain controversial. In this work, we elucidate the reaction mechanism towards acetate by using ab-initio simulations, a coupled kinetic-transport model, and loading experiments. We find that trends in acetate selectivity can be rationalized from variations in electrolyte pH and the local mass transport properties of the catalyst and not from changes of Cu's intrinsic activity. The selectivity mechanism originates in the transport of ketene, a stable (closed shell) intermediate, away from the catalyst surface into solution where it reacts to acetate. While such a mechanism has not yet been discussed in CO(2)RR, variants of it may explain similar selectivity fluctuations observed for other stable intermediates like CO and acetaldehyde. Our proposed mechanism suggests that acetate selectivity increases with increasing pH, decreasing catalyst roughness and significantly varies with applied potential.

Version notes

Few corrections in title and declaration to version change for: "We added a large body of new experiments, which strongly support our theoretical model and the novel mechanism we propose. In particular we provide new experiments which clearly demonstrate effects following catalyst loading and particle size. Furthermore, we significantly simplified the manuscript to reach a larger audience."

Content

Thumbnail image of Acetate_Selectivity_Latex.pdf

Supplementary material

Thumbnail image of Acetate_Selectivity_Supporting_Information_Latex.pdf
Supporting Information: Mechanism for acetate formation in electrochemical CO(2) reduction on Cu: Selectivity with potential, pH, and nanostructuring
Additional data, raw experimental data, further computational details and tests, derivations for analytical models

Supplementary weblinks

Model for Acetate Selectivity & CO(2)RR data sets
Includes the code for the multi-scale simulations and digitized CO(2)RR data sets