Electrochemical behavior of platinum and gold electrodes in the aprotic ionic liquid N,N-Trimethylbutylammonium Bis(trifluoromethanesulfonyl)imide

Abstract

The behavior of platinum and gold electrodes in the hydrophobic room-temperature ionic liquid (RTIL) N,N-Trimethylbutylammonium Bis(trifluoromethanesulfonyl)imide ([N4111][NTf2]) was investigated using transient electrochemistry e.g. voltammetry and chronoamperometry. As previously observed and contrary to what is often stated, these electrodes are not inert in the electroactivity domain of the solvent, between −3.0 and 2.7 V vs Fc/Fc+ for this RTIL. Indeed, a two-step oxidation of the platinum surface is observed at potentials higher than 1.0 V vs Fc/Fc+. The platinum oxide formed is reduced on reverse scan. Moreover, water being ubiquitous in ionic liquids, we can observe the oxidation of residual water and formation of O2. These processes both generate protons and lead to an activated state of the platinum surface. As a consequence, various signals around 0 V vs Fc/Fc+ can be attributed to the adsorption/desorption of protons and subsequent reduction to H2. In presence of water or HNTf2, this signal is enhanced. The behavior is very similar on a gold electrode but shows some specificity, particularly when it comes to the hydrogen evolution reaction.