Exploring multivalent cations-based electrolytes for CO2 electroreduction

Abstract Electrochemical reduction of CO2 (CO2RR) to value-added chemicals is a promising, potentially carbon-neutral alternative to the existing thermochemical fossil fuels-based, carbon-positive chemical manufacturing processes. The CO2 electrolysis field has devoted significant attention to the effects of electrolyte composition and concentration on the rates and selectivities of the desired products; however, the effects of multivalent cations have not been widely studied. Here, we explore the feasibility of using multivalent cations-based electrolytes to intensify CO2RR electrochemical performance. We provide experimental evidence that electrolytes containing multivalent cations, in contrast to those containing monovalent alkali metal cations, hinder the rates and selectivities for CO production on Ag nanoparticles. To explain these trends, we explore the possible origin of the reduced CO2RR performance in the presence of multivalent cations-based electrolytes. Using a combination of electrochemical (electrochemical impedance spectroscopy) and physicochemical (grazing incidence X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy) characterization methods, we provide evidence that in the presence of multivalent cations metal oxides and/or metal hydrides deposit on the electrode surface, possibly blocking the catalytically active sites, and thus impairing the adsorption of CO2 on the catalyst surface.