Tuning Selectivity of Acidic Carbon Dioxide Electrolysis via Surface Modification

Promoting Selective CO2 Electroreduction to Formic Acid in Acidic Medium with Low Potassium Concentrations under High CO2 Pressure

“…It is indeed well established that these cations are needed to limit HER and the best results in terms of selectivity were generally achieved with the highest concentration of K + , specifically 3.0 M KCl. [17,23,24,38] Because of the K + solubility limit (3.5 M) some authors have further improved the performances of the system (activity and selectivity) by manipulating the structure of the catalyst in order to generate a high-intensity local electric field and accumulate K + on the surface of the catalyst above the concentration limit. [49] During the course of this work, another study of CO 2 reduction to FA in acidic electrolytes using a Bi-based catalyst has been reported, also showing very high FE HCOOH in the presence of 3.0 M KCl, [24] in full agreement with our results.…”

“…[14][15][16] This problem has been very recently addressed by using acidic electrolyte solutions with a pH below the pKa (3.5) of carbonic acid. [6,[17][18][19][20][21] In such systems, while CO 2 is still converted into (bi)carbonate because of the alkaline local pH at the cathode arising from hydroxide ions stoichiometrically generated during CO 2 reduction, CO 2 is subsequently regenerated, due to the low bulk pH and the presence of an excess of protons, and can be recovered and recycled. [18,22] On the other hand, acidic conditions are detrimental to the selectivity of the reaction, as they obviously favor HER.…”

“…These cations can also accumulate within the cation-exchange membranes, thus adding extra ohmic losses and accelerating their degradation. [17,27] As far as formate/formic acid production is concerned, acidic conditions provide additional advantages: (i) since its dissociation constant is pKa = 3.75, FA is formed directly and can be easily separated by distillation, thus eliminating the costly formate separation steps associated with neutral/alkaline electrolysis; [28,29] (ii) formate can cross over through anionexchange membranes, thus leading to accumulation in the anodic compartment and carbon loss via formate oxidation and adding extra cost associated with recovery of formate from the anolyte. We have thus initiated a project aiming at studying acidic CO 2 electroreduction reaction (CO 2 RR) to FA using a Bismuth (Bi)-based catalyst since Bi, a cheap metal with low toxicity, is well known as a catalyst for CO 2 RR to FA.…”

Role of Ionic Solvents in the Electrocatalytic CO2 Conversion and H2 Evolution Suppression: From Ionic Liquids to Deep Eutectic Solvents

“…This is a relevant factor for potential application of ILs in acidic CO 2 electrolysis. [60,99,100] Regarding the different mechanisms for the HER suppression mediated by ILs, there are two main hypotheses reported in the literature: (i) the modification of the electrode surface by ILs, which increases its hydrophobicity, and (ii) the electrostatic interactions provoked by the presence of IL ions within the EDL. (i) Wang et al performed the reduction of an imidazoliumbased IL on Cu electrode, reporting the formation of an [EMIm] + layer, which played the role of an active catalytic site for CO 2 RR on the electrode surface.…”

Constructing Ionic Interfaces for Stable Electrochemical CO2 Reduction

“…(f) Electrodeposition of an imidazolium-based layer on the nano-Cu particles. Reproduced from ref . Copyright 2023 with permission from American Chemical Society.…”