Alkalinity Initiated Decomposition of Mediating Imidazolium Ions in High Current Density CO2 Electrolysis. Issue 1 (20th October 2016)

• Record Type: Journal Article
• Authors: Neubauer, Sebastian S.; Schmid, Bernhard; Reller, Christian; Guldi, Dirk M.; Schmid, Günter
• Is Part Of: ChemElectroChem. Volume 4:Issue 1(2017)
• Page Start: 160
• Page End: 167
• Publication Date: 2016-10-20
• Subjects: carbon dioxide -- electrochemistry -- energy conversion -- ionic liquids -- NMR spectroscopy; Electrochemistry -- Periodicals; 541.37
• DOI: 10.1002/celc.201600461
• Languages: English
• ISSNs: 2196-0216

Abstract

Abstract: Aqueous ionic liquid electrolytes featuring the promising 1, 3‐dialkyl‐ and 1, 2, 3‐trialkyl‐imidazolium cations are reported in CO2 electrolysis up to 200 mA cm −2 . A close‐to‐application flow cell setup equipped with silver gas diffusion electrode to overcome CO2 mass transport limitations was used. Faraday efficiencies for CO as high as 68 % were achieved, while inhibiting the hydrogen evolution reaction. Particular attention is paid to the stability of the ionic liquids, which is determined by 1 H NMR spectroscopic measurements. The root cause of decomposition is the formation of hydroxide ions through reduction reactions. A high local pH arises that depends on the current density. The water content is also found to play a key role. An overall mechanism is proposed from analysis of the decomposition products including methylamine, ethylamine, formate, acetate and N 1 ‐ethyl‐ N 2 ‐methylethane‐1, 2‐diamine. Methylation of the susceptible C2 position of the imidazolium ring fails to stabilize the system under high conversion rate electrolysis conditions. Abstract : A stable medium? The stability of mediating imidazolium ions in CO2 electrolysis is followed by 1 H NMR analyses. The extent of decomposition is found to depend on pH, water content, and current density. Consequently, a decomposition mechanism is proposed and conditions for a stable process are discussed.