Changement climatique - Recherche française (avec laboratoires CNRS) - 2010-2015

Catalytic reduction of CO2 (saturated in organic polar solvents, e.g. N,N-dimethylfomamide, containing Me4NX or NaBF4) was achieved at smooth gold electrodes and at glassy carbon electrodes galvanostatically capped with a thin layer of gold. Under these quite explicit conditions, very sharp reduction steps were observed near -1.5 V vs. Ag/AgCl. With small cations listed above, an unexpected behavior was observed, a progressive electrode inhibition occurring upon several scans or after a fixed-potential electrolysis at E < -1.7 V. This phenomenon could be attributed to the insertion of CO2 into gold, leading to the formation of a thick iono-metallic multi-strata layer (less conducting than pure metal) that grows with the electrode charge. The formation of this new interface is due to the concur of three elements: transient CO2 anion radical, the metal, and rather small-sized cations (M+ = Na+ or TMA(+)), the three possibly associated in a form {Au-CO2-,M+} apparently very reactive with oxygen, moisture, and with some organic it-acceptors. Upon multi-scans up to -2.2 V, the thickness of formed layer progressively increases reaching more than 10(-7) to 10(-6) mol cm(-2). Such multi-layers undergo decomposition in the anodic domain at about + 1.7 V liberating CO2 beforehand trapped in Au. Coulometric analyses demonstrated that insertion (cathodic) and release (anodic) steps are quite equivalent, which permits to consider this process as chemically reversible sequestration of carbon dioxide. (C) 2015 Elsevier B.V. All rights reserved.