(145d) Electrochemical Promotion of Catalysis: Non-Faradaic Effects of Applied Potential on CO2 Hydrogenation and Ethylene Oxidation Reactions

Sullivan, M. - Presenter, Massachusetts Institute of Technology
Vayenas, C., University of Patras
Roman, Y., MIT
Zagoraios, D., University of Patras
Electrochemical promotion of catalysis is achieved in gas phase reactions over solid catalysts via the coordination of a dual-function working electrode/catalyst and catalytically inert counter and reference electrodes connected via a purely ionically conducting solid electrolyte (H+ or O2- conductor). Catalytic reaction rates of CO2 hydrogenation and C2H4 oxidation can be reversibly modified by nearly two orders of magnitude via the application of a potential between the catalyst and reference electrodes. Faradaic efficiencies, defined by the ratio of the change in catalytic rate (dr) to the galvanostatically-defined rate of ionic species supplied to the catalyst surface (I/nF), are far in excess of unity. These non-Faradic processes result in changing selectivity of CO2 reduction catalysis over Ru at 693 K by increasing CH4 formation rates and concurrently reducing CO formation rates with the application of a positive potential, and positive potential application modifies C2H4 oxidation reaction rates at 693 K over Pt by over an order of magnitude with Faradaic efficiencies in excess of 50. Applied potentials result in the changing reactant equilibrium binding constants as modeled by Langmuir-Hinshelwood-type rate expressions. Potential application results in the back-spillover of ionic species from the solid electrolyte onto the ionic surface to form an electrically neutral effective double layer that can be quantified via analysis of galvanostatic transients in conjunction with C2H4 oxidation kinetic modeling. This work investigates and models the fundamental non-Fardaic effects of applied potential upon a catalytically active surface with regards to gas phase reactions via alteration of site densities and energetics.