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The inhibition of the proton donor ability of bicarbonate promotes the electrochemical conversion of CO2 in bicarbonate solutions

2021; Elsevier BV; Volume: 48; Linguagem: Inglês

10.1016/j.jcou.2021.101521

2212-9839

Oriol Gutiérrez‐Sánchez, Nick Daems, W. K. Offermans, Yuvraj Y. Birdja, Metin Bulut, Deepak Pant, Tom Breugelmans,

Ionic liquids properties and applications

Gaseous CO 2 solutions are widely used for CO 2 electrochemical conversion to various valuable products.However, capture, liberation and storage of gaseous CO 2 prior to reduction is cumbersome and costly.CO 2 electrocatalytic reduction from captured CO 2 (in the form of concentrated bicarbonate solution) offers an option to optimize CO 2 reduction processes.Using concentrated bicarbonate solutions from captured CO 2 as large carbon feedstock and reducing CO 2 directly from bicarbonate electrolyte remain a challenge.Indeed, current efficiency is too low (i.e.low selectivity and/or activity) as a consequence of the strong competition with the hydrogen evolution reaction, which bicarbonate promotes to a great extent.In this study, up to 2 M bicarbonate solution is used as electrolyte (mimicking a captured CO 2 solution from an alkaline media) for a CO 2 electrochemical reduction system, which potentially pretends to be a 2 M carbon source, compared to 0.033 M present in a saturated gaseous CO 2 solution.In order to improve the Faradaic efficiency of the process and thereby making the CO 2 electrocatalytic reduction from a bicarbonate feedstock an efficient system and attractive alternative for the reduction starting from gaseous CO 2 , a reaction mechanism where bicarbonate acts as a CO 2 donor instead of as a proton donor is proposed.To achieve such property, we inhibit the proton donor ability of bicarbonate and water by covering the surface of the electrode with cationic surfactants, allowing non-polar molecules, like the CO 2 derived from the equilibrium with bicarbonate, to diffuse to the surface of the electrode while avoiding bicarbonate and water to promote the hydrogen evolution reaction.To the best of our knowledge, the Faradaic Efficiency to formate obtained in this study (>70 %) sets a new benchmark in systems involving unsaturated and saturated bicarbonate solutions without previously purging CO 2 .