Chronopotentiometric Approach of CO₂Reduction in Molten Carbonates

Abstract

Carbon capture and valorization is a new route increasingly discussed to reduce greenhouse gas emissions. One of the paths foreseen for CO 2 valorization is its transformation into fuels by electrochemical reduction of carbon dioxide. In this approach, molten carbonates are of particular interest since they can be used to capture CO 2 molecule because of its high solubility; hence, valorization by electrolysis is possible in molten carbonate media. To better understand CO 2 reduction, chronopotentiometric and chronoamperometric techniques were used at gold and graphite electrodes immersed in four alkali carbonate eutectics, Li-Na, Li-K, Li-Na-K and Na-K. The results complemented a previous work based on cyclic voltammetry and confirmed the existence of a main CO 2 reduction phenomena around −1.2 V vs Ag/Ag + that involves two one-electron steps or a two-electron unique step. Transition time analysis showed that the reduction mechanism is either simultaneous reduction of CO 2 adsorbed and diffusion species or rapid equilibrium between adsorbed and diffusing species. Furthermore, we identified another electrochemical system involving adsorbed CO 2 and CO at higher potentials. In summary, we have succeeded in proving and précising some previous results, as well as identifying reduction mechanisms.

Electrochemical Reduction of CO2 by the SnS| PTFE| Pt Surface in an Aqueous Imidazole Medium: Catalysis and Kinetics

“…In the single-step mode, a broad spectrum of potentials ranging from −0.5 V was sequentially increased to −0.6, −0.7, −0.8, −0.9, −1.0, and −1.1 V during the recording of chronoamperograms. A sudden exponential increase in reduction current was observed at −0.9 V (Figure A), suggesting that electron transfers likely occurred at this potential . To investigate the number of steps involved in the electron transfer process, a second-step chronoamperometry experiment was performed with the first step being held constant at −0.9 V. The results of this experiment are shown in Figure B.…”

“…To investigate the number of steps involved in the electron transfer process, a second-step chronoamperometry experiment was performed with the first step being held constant at −0.9 V. The results of this experiment are shown in Figure B. However, no substantial change in current for the second step was observed, which may account for the involvement of multiple-step electron transfer process in the reduction reaction . In addition, the exponential decay of current density at −0.9 V with time entails that CO 2 reduction on the SnS| PTFE| Pt electrode follows first-order kinetics (Figure B).…”

Molten salt electro‐preparation of graphitic carbons

“…However, the obtained carbon products contain large amounts of amorphous carbon. [27][28][29][30][49][50][51][52][53][54][55][56] An increased temperature can only slightly enhance the graphitization degree of the obtained carbon. [51,53] In order to convert the amorphous carbons into graphitic carbons, small amounts of additives or catalysts are usually needed, depending on the salt system.…”

CO2 Electroreduction in Organic Aprotic Solvents: A Mini Review

“…Among them, the most studied are ionic liquids [19][20][21][22][23][24][25][26], methanol solutions [27][28][29], and organic aprotic solvents [30][31][32][33][34][35][36][37][38][39][40]. In recent years, there has also been engagement in the CO 2 electrochemical reduction process in molten salts [41][42][43][44][45][46]. e following valuable nanomaterials can be obtained in such an environment: carbon nanofibers [43], carbon nanotubes (CNTs), carbon spheres (CSs), and honeycomb carbon [44].…”