Electrochemical Promotion of Catalysis by Lithium-Ion

Abstract

Electrochemical promotion of catalysis (EPOC) or non-Faradaic electrochemical modification of catalytic activity (NEMCA) is a general phenomenon in heterogeneous catalysis that in situ controls reaction rates of thermal catalysts via the application of electrical potential and enables supply/removal of ionic species (promoters) from the electrolyte. In this work, we investigated electrochemical promotion by Li-ion for carbon monoxide oxidation and reverse water gas shift (RWGS) reactions. Nanostructured Pt films (50 and 100 nm thickness) and highly dispersed FeO_x nanowires (d = 10 nm) were deposited on the lithium lanthanum titanate (Li_0.29La_0.57TiO₃, LLTO) solid electrolyte. By applying constant electrical potential/current, the catalytic reaction rates for both CO oxidation and RWGS were modified in a non-Faradaic way due to Li-ion migration to/from Pt and FeO_x catalysts, as evidenced by STEM, XRD, and XPS. For CO oxidation, the reaction rate over FeO_x decreased permanently under positive polarization, returning to the initial state only under negative polarization. Pt films showed similar rate decreases upon positive polarization but experienced an immediate increase after returning to the open circuit. For RWGS, positive polarization over FeO_x led to permanent electrochemical promotion with the rate increasing in the H₂-rich environment and decreasing under CO₂-rich conditions. Pt catalysts showed rate increases under all conditions. These differences suggested that FeO_x reacted with Li-ion in the presence of electrons due to its redox activity, while Pt remained chemically stable and did not exhibit similar interactions. Cyclic voltammetry (CV) provided insights into the interaction of Li⁺ with the catalyst and its influence on electrochemical reactions.