Direct Electroreduction of Carbonate to Formate

Abstract

A cause of losses in energy and carbon conversion efficiencies during the electrochemical CO 2 reduction reaction (eCO 2 RR) can be attributed to the formation of carbonates (CO 3 2− ), which is generally considered to be an electrochemically inert species. Herein, using in situ Raman spectroscopy, liquid chromatography, 1 H nuclear magnetic resonance spectroscopy, 13 C and deuterium isotope labeling, and density functional theory simulations, we show that carbonate intermediates are adsorbed on a copper electrode during eCO 2 RR in KHCO 3 electrolyte from 0.2 to −1.0 V RHE . These intermediates can be reduced to formate at −0.4 V RHE and more negative potentials. This finding is supported by our observation of formate from the reduction of Cu 2 (CO 3 )(OH) 2 . Pulse electrolysis on a copper electrode immersed in a N 2 -purged K 2 CO 3 electrolyte was also performed. We found that the carbonate anions therein could be first adsorbed at −0.05 V RHE and then directly reduced to formate at −0.5 V RHE (overpotential of 0.28 V) with a Faradaic efficiency of 0.61%. The nature of the active sites generating the adsorbed carbonate species and the mechanism for the pulse-enabled reduction of carbonate to formate were elucidated. Our findings reveal how carbonates are directly reduced to a high-value product such as formate and open a potential pathway to mitigate carbonate formation during eCO 2 RR.

A minireview on electrochemical CO2 conversion based on carbonate/bicarbonate media

“…Moreover, the theoretical research on Fe-Porphyrin also indicated that the direct electrochemical conversion of CO 3 2− /HCO 3 − is feasible. Actually, there have been reports indicating that both carbonate 45 and bicarbonate 46 could be directly electrochemically reduced into formate. Compared to CO 3 2− /HCO 3 − electrolyzers that rely on the in situ generation of CO 2 , direct CO 3 2− /HCO 3 − electrolysis technology makes it easier to achieve full utilization of carbon.…”

Revealing the Lattice Carbonate Mediated Mechanism in Cu2(OH)2CO3 for Electrocatalytic Reduction of CO2 to C2H4

“…[14] Further, recently, Ma et al reported a direct carbonate electroreduction to formate. [15] Based on these considerations, Cu 2 (OH) 2 CO 3 , containing carbonate groups and Cu that is widely used in C 2 production, was chosen as the candidate to investigate whether the lattice carbonate could be involved in the CO 2 RR to C 2 products. Combined 13 C stable isotope ratio mass spectrometry (IRMS) tests with experiments, we proved that lattice carbonate could act as a mediator to connect external CO 2 molecules to active Cu atoms on Cu 2 (OH) 2 CO 3 surface, which is named lattice carbonate mediated mechanism (LCMM).…”

Direct Electrochemical Reduction of Ammonium Carbamate on Transition Metal Surfaces: Finding Activity and Stability Descriptors beyond those for CO2 Reduction

“…Some of the first works in the electrochemical upgrading of CO 2 from amine and bicarbonate capture solutions by us and others have shown that it is the small amounts of dissolved and free CO 2 in equilibrium with the capture solutions that are being reduced electrochemically to carbon monoxide on silver electrodes. [7][8][9][10] Higher temperatures increase the partial pressure of dissolved CO 2 in equilibrium with the capture solution and lead to higher partial current densities for CO 2 reduction products at the expense of a higher thermal energy requirement. 7,11 So far, mainly silver catalysts have been studied systematically for the electrochemical upgrading of amine and bicarbonate capture solutions, and only recently copper has been shown to be able to upgrade carbonates with Faradaic efficiencies of 0.61% under pulse electrolysis conditions.…”

“…7,11 So far, mainly silver catalysts have been studied systematically for the electrochemical upgrading of amine and bicarbonate capture solutions, and only recently copper has been shown to be able to upgrade carbonates with Faradaic efficiencies of 0.61% under pulse electrolysis conditions. 9 In the RCC works reported so far, hydrogen evolution reaction (HER) dominates, and it is already evident that interactions of the capture agent with the catalyst increase the complexity of these systems compared to those where only CO 2 and the catalyst are considered.…”