Electrochemical carboxylation of titanium to generate versatile new interfaces

Titanium covered with a thin layer of titanium dioxide was reduced in aprotic polar solvents (dimethylformamide or acetonitrile) saturated with carbon dioxide in the presence of tetraalkylammonium salts (TAAX). When using tetramethylammonium salts CO 2 is irreversibly reduced at potentials  KClsat , generating an inactive surface down to −3.2 V. Anodic oxidation of the modified surface in the same solvent led to regeneration of a titanium interface free of oxide. Employing other TAAX salts permits reversible reduction of CO 2 ( E p/2  = −2.21 V in the presence of TBuABF 4 ). Under conditions of total passivation of the Ti surface followed by sonication, stable electrode surfaces inactive in organic polar solvents between −3 V and +2 V were obtained. Within the cathodic range, several organic π-acceptors were reversibly reduced down to −3 V, which shows the potential of such “Ti-CO 2 ” surfaces as new working electrodes.