Overpotentials and Faraday Efficiencies in CO₂ Electrocatalysis–the Impact of 1‐Ethyl‐3‐Methylimidazolium Trifluoromethanesulfonate

Abstract

The mixtures of room temperature ionic liquid 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate ([EMIM]TFO) and water as electrolytes for reduction of CO2 to CO are reported. Linear sweep voltammetry shows overpotentials for CO2 reduction and the competing hydrogen evolution reaction (HER), both of which vary as a function of [EMIM]TFO concentration in the range from 4 × 10−3m (0.006 mol%) to 4869 × 10−3m (50 mol%). A steady lowering of overpotentials up to an optimum for 334 × 10−3m is identified. At 20 mol% and more of [EMIM]TFO, a significant CO2 reduction plateau and inhibition of HER, which is limited by H2O diffusion, is noted. Such a plateau in CO2 reduction correlates to high CO Faraday efficiencies. In case of 50 mol% [EMIM]TFO, a broad plateau spanning over a potential range of 0.58 V evolves. At the same time, the overpotential for HER is increased by 1.20 V when compared to 334 × 10−3m and, in turn, HER is largely inhibited. The Faraday efficiencies for CO and H2 formation feature 95.6% ± 6.8% and 0.5% ± 0.3%, respectively, over a period of 3 h in a separator divided cell. Cathodic as well as anodic electrochemical stability of the electrolyte throughout this time period is corroborated in 1H NMR spectroscopic measurements.

Reactivity of Copper Electrodes towards Functional Groups and Small Molecules in the Context of CO2 Electro-Reductions

“…This result, together with the results from formate (4) and oxalate (5), suggests that carboxylates in general are inert to electro-reduction by the in situ-grown copper catalyst. Acetamide (36), which in contrast to acetate is not negatively charged, also underwent no transformation. Also carboxylate groups, which are part of an α,β-unsaturated π-system as in fumarate (31), remain untouched.…”

“…Copper-catalyzed CO 2 reduction to hydrocarbons was first reported by Hori in 1985 [10]. In the following decades, publications using copper electrodes [11][12][13][14][15][16][17], copper oxide electrodes [18][19][20][21], copper-containing perovskites [22], oxide-supported copper catalysts [23], halide-derived copper catalysts [24][25][26][27], copper-based alloys [28], copper-based metal-organic frameworks [29], molecular copper complexes [30], as well as alternative systems [5,[31][32][33][34][35][36] vastly increased. Also pyridine-based co-catalysis known from Pd electrodes [37] could recently be transferred to copper-based systems [38].…”

Selective Electroreduction of CO2 toward Ethylene on Nano Dendritic Copper Catalysts at High Current Density

“…In order to lower the associated release of the greenhouse gas CO 2 , technologies are generally of interest, which can use CO 2 as an inexpensive raw material for the production of fuels or chemicals. [18] In addition to the mechanistic understanding, a deeper knowledge of electrode material and its behavior according to corrosion processes and its deactivation is required. [1] These processes show several decisive disadvantages in terms of costs versus economic value and energy efficiency.…”

Alkalinity Initiated Decomposition of Mediating Imidazolium Ions in High Current Density CO2 Electrolysis

“…The use of ionic liquid (IL) based electrolytes for the reduction of CO 2 provides numerous advantages. Among these advantages are the impact on the overpotential, the competing hydrogen evolution reaction (HER), the product selectivity, and the product scope . Especially, ILs featuring imidazolium cations have emerged as versatile co‐catalysts.…”