Electrochemical Tuning of CO2 Reactivity in Ionic Liquids Using Different Cathodes: From Oxalate to Carboxylation Products

Abstract

There is currently quite a lot of scientific interest in carbon dioxide (CO2) capture and valorization with ionic liquids (ILs). In this manuscript, we analyze the influence of the potential applied, the nature of the cathode and the electrolyte using different organic mediators, such as nitro or cyano aromatic derivatives, to promote the electrochemical activation of CO2. An electrocatalytic process using a homogeneous catalysis is seen when nitroderivatives are used, yielding to oxalate in organic electrolytes and ILs. Turnover frequency (TOF) values and Farafay efficiencies were slightly higher in N,N’-dimethylformamide (DMF) than in ILs probably due to the viscosity of the electrolyte. The use of cyano derivatives allows to tune the electrochemical reactivity in function of the reduction potential value applied from electrocarboxylated products (via a nucleophile-electrophile reaction) to oxalate. These electrochemical reactions were also performed using three different cathodes, organic electrolytes and ionic liquids. The use of copper, as a cathode, and ionic liquids, as electrolytes, would be a cheaper and greener alternative for activating carbon dioxide.

The Role of Organic Promoters in the Electroreduction of Carbon Dioxide

“…A straightforward strategy to change the mechanism of the CO 2 RR is to employ redox shuttles. Several catalysts based on this principle have been suggested, and the first confirmed redox shuttle catalysts for the CO 2 RR were based on aromatic esters and nitriles (Scheme , shuttles 1 and 2 ). − When these catalysts are employed in combination with inert electrodes (e.g., Hg) in media with a low availability of protons, the distribution of the reduction products switches from a mixture of CO and oxalate (C 2 O 4 2– ) to only oxalate . Initially, the reaction was believed to occur through an outer-sphere single-electron transfer from the reduced form of the catalyst to CO 2 .…”

Electrochemical Incorporation of Carbon Dioxide into Fluorotoluene Derivatives under Mild Conditions

“…A three-electrode electrochemical system in a one-compartment conical cell was used for the set-up of cyclic voltammetry (CV) and controlled potential electrolysis. The electrochemical details of those techniques have been previously described [13,19,[21][22][23][24][25].…”

“…For example, CO 2 is reduced beyond −2.2 V vs. SCE in aprotic solvents [12]. For this reason, different catalytic pathways for reducing CO 2 have been established, concluding that radical anions of aromatic esters and nitriles are very selective catalysts that can produce high yields of oxalate in the electrochemical reduction of CO 2 , lowering the potential in which it occurs [12,13].…”

Electrocarboxylation of Spiropyran Switches through Carbon‐Bromide Bond Cleavage Reaction

“…Actually, the chemical synthesis of carboxylic acids and their derivatives (e. g., esters or amides) imply the use of many reagents, catalysts [33] or organolithium compounds [34] at mild or strong conditions [35,36] . In this context, the electrochemical carboxylation of organic molecules to produce carboxylic acids by fixing carbon dioxide has emerged during the last years as an efficient green route compared to conventional chemical synthetic methods, especially since this process can be performed efficiently under mild conditions at atmospheric pressure and avoiding the use of additional reagents [37–42] . One of the most popular electrocarboxylation strategies of organic compounds is based on the in situ formation of a carbanion via reduction, which in turn undergoes a nucleophilic addition to CO 2 to yield the carboxylate functional group (Figure 2).…”