Under classic chemical Birch-type reduction of benzylic alcohols, the deoxygenative transformation is proposed to proceed via a benzylic carbanionic intermediate. To probe this mechanistic hypothesis under our set of conditions, we set out to explore whether such an intermediate could be trapped with electrophiles other than protons. Our choice fell on carbon dioxide (CO2), a well-established coupling partner for carbanions in the formation of carboxylic acids. Gratifyingly, a switch from an N2 atmosphere to CO2 enabled a selection of arylacetic acids to form, to the best of our knowledge, representing the first examples of deoxygenative C-C bond formation from non-derivatized alcohols under electrochemical conditions (Figure ). The ester-and cyano-substituted phenylacetic acids 4w and 4t were isolated in 43% and 31% yield, respectively. In contrast, the tertiary cyano-substituted acid 4u resulted in mere 3% yield, whereas tertiary alcohols failed to form the carboxylated products (see Section 13 in the ESI). Interestingly, the fluorinated analogue of p-cyanophenylacetic acid 4aa was obtained in a low yield (6%), whereas the fluorinated anti-inflammatory NSAID drug flurbiprofen 4ah with an extended π-system was successfully isolated in 38%. In contrast, the primary non-fluorinated alcohol 1a formed the carboxylation product 4a in mere 4% yield while the electron-rich substrate 4a failed to undergo cross-coupling (see Section 13 in the ESI for a list of all substrates assessed). In most cases, starting material remained at the end of the reaction and would not convert to product even upon extended reaction times or with additional borohydride. To gain further insight into the aforementioned selectivities for the deoxygenative carboxylation we turned to density functional theory calculations (DFT) and cyclic voltammetry (CV) (see Sections 12 and 18 in the ESI for details). Notably, carboxylation products were only formed from alcohols with a calculated thermodynamic standard potential, E°, close to that of CO2. In contrast, alcohols that failed to undergo electrocarboxylation displayed E° values significantly more negative compared to the coupling partner (Figure ). Furthermore, alcohols 1t and 1w that furnished arylacetic acids in good yields were found to have onset potentials less negative compared to that of CO2 under the applied conditions (Figure and ESI, Section 18). In contrast, alcohol 1a with an onset potential almost identical to that of CO2, formed carboxylation product in mere 4% yield, whereas alcohol 1n that failed to form arylacetic acid 4n had an onset potential more negative than that of CO2. As such, the combined DFT and voltammetry data demonstrate that C-C bond formation occurs to a significant extent only when the radical/nucleophile precursor undergoes electron transfer prior to, or simultaneously as, the electrophilic cross-coupling partner, in line with what has previously been observed in other systems. In the present case, considerably more negative standard potentials were determined by DFT for the reduction of the alcohols compared to their corresponding benzylic radical intermediates to carbanions (Figure ). This finding suggests that the radical-polar crossover is favored at the electrode surface once the open-shell intermediate forms. Hence, arylacetic acids are likely to form via carbanionic attack onto neutral CO2 (see Section 12 in the ESI). Due to the continuously decreasing potential under the applied galvanostatic electrolysis conditions, such neutral CO2 is expected to remain in solution in significant concentrations only in the presence of alcohols with a reduction potential less negative or similar to CO2 itself. On the other hand, the small difference in reduction potential between the product-forming alcohols and CO2 indicates that these species may be simultaneously reduced under the applied conditions and compete as electron acceptors (Figure and Section 18, ESI). This notion is supported by the observed increase in reaction time required to afford full conversion of the alcohols in the presence of CO2 (ESI, Section 8.2). As such, it cannot be ruled out that the C-C bond formation may also proceed via radical-radical coupling of benzylic open shell intermediates and CO2 radical anions (ESI, Section 12) and that the contribution of different pathways is substrate dependent. Likewise, it cannot be ruled out that CO2 radical anions can act as reductive electron transfer mediators for certain substrates as reported for electroreduction of benzoate esters and thioethers. It can be noted that alkyl carbonates were not observed in the reaction mixture by NMR, suggesting a distinctly different mechanism for the deoxygenative carboxylation compared to that reported by Senboku and co-workers. It is well established in fuel cell applications that borohydride compounds can undergo electrooxidation to generate H2, and bubble formation at the anode suggested that this is a likely path in the present system. Thus, hydride oxidation was hypothesized to act as the counter reaction to the electroreductive hydrodeoxygenation of study, thereby preventing oxidative formation of, e.g., side-product 3a (Figure ). Effectively, the hydride oxidation can be viewed as the inverse of cathodic proton reduction, a well-established counter reaction to electrooxidative transformations.