The contrasting effects of diethylmethylamine during reduction of protons and oxidation of formic acid in diethylmethylammonium-based protic ionic liquids

Goodwin, Sean; Muhammad, Sayyar; Tuan, Li-Ping; Walsh, Darren

Abstract

Ionic liquids are formally defined as liquids that consist entirely of ions, and which are liquid below 100 C. As these liquids are being proposed for use in a range of electrochemical devices and applications, understanding the electrochemical behaviour of these is increasingly important. In this contribution, we describe the effects of parent amine molecules on electrocatalysis in the protic ionic liquids diethylmethylammonium trifluoromethanesulfonate and diethylmethylammonium heptafluorobutanoate. We first show that diethylmethylamine can adsorb onto Pt electrodes during electrocatalytic reduction of trifluoromethanesulfonic acid in diethylmethylammonium trifluoromethanesulfonate. In contrast, diethylmethylamine promotes the oxidation of formic acid in this ionic liquid, by deprotonating the acid to the active formate species. Therefore, the neutral base can either inhibit or enhance electrocatalysis in the liquid, depending on the reaction under consideration. We also show that the mechanism of formic-acid oxidation in diethylmethylammonium heptafluorobutanoate differs significantly from that observed when using diethylmethylammonium trifluoromethanesulfonate. This phenomenon is attributed to adsorption of poisoning spectator species onto the electrode surface, demonstrating that changes to the structure of ionic-liquid anions can have drastic effects on the electrochemistry of these liquids.

Citation

Goodwin, S., Muhammad, S., Tuan, L., & Walsh, D. (2018). The contrasting effects of diethylmethylamine during reduction of protons and oxidation of formic acid in diethylmethylammonium-based protic ionic liquids. Journal of Electroanalytical Chemistry, 819, https://doi.org/10.1016/j.jelechem.2017.10.021

• Journal Article Type: Article
• Acceptance Date: Oct 10, 2017
• Online Publication Date: Oct 13, 2017
• Publication Date: Jun 15, 2018
• Deposit Date: Mar 2, 2018
• Publicly Available Date: Oct 14, 2018
• Journal: Journal of Electroanalytical Chemistry
• Print ISSN: 1572-6657
• Electronic ISSN: 1873-2569
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 819
• DOI: https://doi.org/10.1016/j.jelechem.2017.10.021
• Keywords: Ionic liquid; Ultramicroelectrode; Scanning electrochemical microscopy; Hydrogen evolution reaction; Underpotential-deposited hydrogen; Formic acid
• Public URL: https://nottingham-repository.worktribe.com/output/938509
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S1572665717307221?via%3Dihub