Specific Cation Adsorption: Exploring Synergistic Effects on CO₂ Electroreduction in Ionic Liquids

Abstract

Ionic liquids (ILs) have gained attention as promising solvents as reaction media for the electrochemical conversion of CO 2 into valued-added products. ILs can co-catalyze the CO 2 reduction reaction (CO 2 RR), in particular, when Ag is applied as the primary metallic electrocatalyst. To broaden this co-catalysis concept, we conducted a comprehensive study of a range of electrode materials exposed to three ILs, which differed in the chemical nature of their anions and cations. Here, we examine the activity of the electrode/IL combinations toward the CO 2 RR based on cyclic voltammetry data. The voltammetric experi-ments are complemented by gas chromatography analysis of the products, demonstrating that CO is the main product for most of the electrode/IL combinations. Our results demonstrate that the specific adsorption of the IL cation on the electrode plays a crucial role in the co-catalytic effect of the ILs. Based on our analysis, we identify three classes of electrode materials, which differ in their synergistic interaction with the IL cations and their resulting CO 2 RR activity. The key criterion for this classification is the extent to which the CO 2 RR is superimposed on the reductive decomposition of the ILs.[a] Dr.

The Role of Organic Promoters in the Electroreduction of Carbon Dioxide

“…It is important to underline that the electrode is not innocent in this process, as no reaction is detected when a glassy-carbon electrode is employed: 51 i.e., the outcome of the reaction is highly dependent on the electrode material employed. 52 can also switch the selectivity of the CO 2 RR. For example, on a lead electrode oxalate is the main reduction product, whereas in the presence of an Im IL the dominant product is carbon monoxide.…”

“…Moreover, the parasitic HER was suppressed, which resulted in a FE CO value of close to 100%. It is important to underline that the electrode is not innocent in this process, as no reaction is detected when a glassy-carbon electrode is employed: i.e., the outcome of the reaction is highly dependent on the electrode material employed . IL additives can also switch the selectivity of the CO 2 RR.…”

A Tandem (Bi2O3 → Bimet) Catalyst for Highly Efficient ec-CO2 Conversion into Formate: Operando Raman Spectroscopic Evidence for a Reaction Pathway Change

“…• − radical anion, which is considered to be a key intermediate in the reaction pathway of formate production. 23−25 Previous studies have focused on two-dimensional (2D) Bi materials, e.g., foils, 26 nanosheets, 23,24,27 thin layers of Bi, 28 and dendritic Bi catalysts. 29 However, in most of these cases, an excellent formate efficiency was achieved only within a rather narrow potential window (e.g., a faradaic efficiency of ∼86% and PCD formate of approximately −13.33 mA cm −2 at −1.1 V vs RHE) 27 and on a comparably short electrolysis time scale of a few hours.…”

“…Previous studies have focused on two-dimensional (2D) Bi materials, e.g., foils, nanosheets, ,, thin layers of Bi, and dendritic Bi catalysts . However, in most of these cases, an excellent formate efficiency was achieved only within a rather narrow potential window (e.g., a faradaic efficiency of ∼86% and PCD formate of approximately −13.33 mA cm –2 at −1.1 V vs RHE) and on a comparably short electrolysis time scale of a few hours. ,,− The latter suggests substantial catalyst degradation over more extended electrolysis times. ,,,, …”

Interfacial Electrolyte Effects on Electrocatalytic CO2 Reduction

“…The [EMIM]-BF 4 acted as a co-catalyst that could lower the overpotential in the first reaction step to form CO 2 – intermediate via a possible complexing between CO 2 and BF 4 – anions. Since then, numerous cations- and anions-based ionic liquids have been used as solvents or co-catalysts for CO 2 RR, such as 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide ([EMIM]­[Tf 2 N], 2 ), 1-ethyl-3-methylimidazolium chlorides ([EMIM]­Cl, 3 ), 1-butyl-3-methylimidazolium hexafluorophosphates ([BMIM]­[PF 6 ], 4 ), superbasic tetraalkyl phosphonium ionic liquid ([P 66614 ]­[124Triz], 5 ), and so on. ,,− Generally, most of the ILs are supposed to reduce the activation energy of CO 2 reduction via chemical absorption or complexing with CO 2 through their functional groups in triazolide or imidazolium rings. , As shown in Figure c, the C4 and C5 hydrogen of imidazolium cation were proved to be the binding sites to interact with CO 2 anion radicals, resulting in a promoted CO 2 RR on the Ag electrode . The 1,2,4-triazole anion can also chemisorb CO 2 molecule and further reduce it to HCOOH at a low overpotential of 0.17 V on Ag electrode (Figure d) …”