Electrocatalytic studies on imidazolium based ionic liquids: defining experimental conditions

Abstract

The number of publications devoted to studying electrochemical reactions in room temperature ionic liquids (RTILs) is constantly growing, but very few of them have been devoted to defining proper experimental conditions to obtain reproducible electrochemical results. In this work, we demonstrate that the combination of a proper RTIL purification treatment and a filtered Ar gas stream allow us to obtain featureless voltammograms in [C₄mim][BF₄], [C₄mim][NTf₂], and [C₄m₂im][NTf₂], which otherwise present signals associated with different types of impurities such as water and some minor electroactive impurities acquired during the RTIL synthesis process. Moreover, we demonstrate that bubbling Ar, or another inert gas, through the electrolyte in order to purge O₂ dissolved in RTILs is one of the major sources of water and O₂ impurities incorporated in RTILs within the electrochemical cell. To overcome this source of water uptake, we have incorporated a gas stream purification filter before the gas reaches the RTIL in the electrochemical cell. To illustrate the effect of these impurities in relevant electrocatalytic studies, we study the electrocatalytic reduction of CO₂ on Pt nanoparticles and the key role of an appropiate filter when the CO₂ gas stream is bubbled within imidazolium based RTILs. Our cyclic voltammetric studies point out that CO₂ electroreduction on Pt nanoparticles only presents activity in [C₄mim][NTf₂] and [C₄m₂im][NTf₂], thus suggesting that the C-2 position on the imidazolium ring is not the key position in CO₂ electrochemical reduction. In contrast, the same Pt nanoparticles are inactive towards CO₂ electroreduction in [C₄mim][BF₄], which is a more hydrophilic RTIL.