In Situ Generated Platinum Catalyst for Methanol Oxidation via Electrochemical Oxidation of Bis(trifluoromethylsulfonyl)imide Anion in Ionic Liquids at Anaerobic Condition

Abstract

The bis(trifluoromethylsulfonyl)imide anion is widely used as an ionic liquid anion due to its electrochemical stability and wide electrochemical potential window at aerobic conditions. Here we report an innovative strategy by directly oxidizing bis(trifluoromethylsulfonyl)imide anion to form a radical electrocatalyst on platinum electrode at anaerobic condition. The in situ generated radical catalyst was shown to catalytically and selectively promote the electrooxidation of methanol to form methoxyl radical, in which the formation potential was drastically decreased with the existence of bis(trifluoromethylsulfonyl)imide radical. The electrochemically generated radical catalyst not only facilitates the oxidation of methanol but also provides good selectivity. The unique double layer structure of the 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([Bmpy][NTf2]) likely excludes the diffusion of larger molar mass molecules onto the electrode surface and enables the highly selective methanol oxidation at this IL–electrode interface. Cyclic voltammetry (CV) experiments were used to systematically characterize the details of the electrochemical processes with and without methanol in several other ILs, and a mechanism of the chemical and redox processes was proposed. This study provides a promising new approach for utilizing the unique properties of ionic liquids not only as solvents and electrolytes but also as the medium for in situ generation of electrocatalysts to promote methanol redox reactions for practical applications.

Hydrogen Electrooxidation in Ionic Liquids Catalyzed by the NTf2 Radical

“…This result supports the catalytic activity of the Pt–NTf 2 • radical for the oxidation of hydrogen compare to that of without the presence of this catalyst. Taking together our prior findings of Pt–NTf 2 • radical in methane and methanol oxidation processes, 13 the reaction mechanism for the catalytic hydrogen oxidation in NTf 2 based IL is proposed as shown in eqs 2–5.…”

“…Our earlier work showed that a positive potential larger than 1.4 V is required to oxidize the NTf 2 − anion to NTf 2 • radicals in CV experiments, 13 as shown in eq 2. Thus, the CV at a wider potential (0–1.8 V) window was performed for generating the NTf 2 • radical that mimics a preanodization condition.…”

“…13 The NTf 2 • radicals catalyze oxidation by abstraction of hydrogen atoms from methanol. In addition, the NTf 2 • radicals were further shown to catalyze the electro-oxidation of methane.…”

Electrode Reactions Coupled with Chemical Reactions of Oxygen, Water and Acetaldehyde in an Ionic Liquid: New Approaches for Sensing Volatile Organic Compounds

“…S2 to evaluate the potential window of [Bmpy][NTf 2 ] on platinum electrode. The anodic potential window should be limited to less than 1.5 V since oxidation of the cation to form NTf 2 radicals occurs at Pt electrode[12]. The anodic potential window in the current study was limited to be 1.2 V.…”

“…oxygen [7], methane [8], TDI [9]) in ILs for developing IL-based electrochemical gas sensors. We and others have discovered new electrochemical reactions in the IL that are not feasible in conventional solvents [10–12]. For example, in traditional aqueous based electrochemical systems, oxygen is removed by purging with inert gas such as nitrogen or argon to avoid interference from oxygen reduction reactions (i.e.…”