(145f) Insights into the Electrocatalytic Conversion of CO2 into CO, Ethylene, and Ethanol in Alkaline Media

Using CO₂ as a feedstock for the production of intermediates for chemical or fuel production such as formic acid, CO, ethylene, ethanol, and methanol is one of several approaches being explored to help reduce anthropogenic CO₂ emissions, while also reducing society’s dependence on diminishing fossil fuel reserves. A range of active electrocatalysts for the selective reduction of CO₂ have been reported. We have explored both Ag-based and Au-based catalyst as well as micro-structured CuAg alloy films, respectively for the selective and energy efficient reduction of CO₂ to CO [1,2] and to ethylene and ethanol [3]. Partial current densities for CO production exceeding 150 mA/cm² at cell overpotentials less than 1V now can be achieved routinely at CO energetic efficiencies in the range of 50-60%. Similarly, high surface area CuAg alloy films exhibit Faradaic efficiency for C₂H₄ and C₂H₅OH production of 60% and 25%, respectively, at a cathode potential of just −0.7 V vs RHE and a total current density of ∼300 mA/cm², the highest levels of selectivity at high activity and low applied potential reported to date.

This talk will focus on various mechanistic insights of the CO₂ electroreduction process on these different catalysts, especially in the presence of alkaline electrolyte. For example, the onset cathode potentials, the kinetic isotope effect, and Tafel slopes indicate that the production of CO at low overpotentials in alkaline media is the result of a pH-independent rate-determining step (i.e., electron transfer) in contrast to a pH-dependent overall process. Furthermore, in situ Raman and electroanalysis studies suggest the origin of the high selectivity toward C2 products observed with CuAg alloy films to be a combined effect of the enhanced stabilization of the Cu₂O overlayer and the optimal availability of the CO intermediate due to the Ag incorporated in the alloy.

1. Gold Nanoparticles on Polymer-Wrapped Carbon Nanotubes: An Efficient and Selective Catalyst for the Electroreduction of CO₂, H.R.M. Jhong, C.E. Tornow, C. Kim, S. Verma, J. L. Oberst, P.S. Anderson, A.A. Gewirth, T. Fujigaya, N. Nakashima, P.J.A. Kenis, ChemPhysChem, 2017, 18 (22), 3274-3279.
2. Insights into the Low Overpotential Electroreduction of CO₂ to CO on a Supported Gold Catalyst in an Alkaline Flow Electrolyzer, S. Verma, Y. Hamasaki, C. Kim, W. Huang, S. Lu, H.R.M. Jhong, A.A. Gewirth, T. Fujigaya, N. Nakashima, P.J.A. Kenis, ACS Energy Lett., 2018, 3, 193-198.
3. Nanoporous Copper−Silver Alloys by Additive-Controlled Electrodeposition for the Selective Electroreduction of CO₂ to Ethylene and Ethanol, T.T.H. Hoang, S. Verma, S. Ma, T.T. Fister, J. Timoshenko, A.I. Frenkel, P.J.A. Kenis, and A.A. Gewirth, J. Am. Chem. Soc., 2018, accepted.