in enediolate intermediates. [1] Recently, a similar mechanism of CO 2 insertion at the unsaturated carbon bond has been adopted in the synthesis of carboxylic acids employing alkynes, [2] α-olefins [3] and internal alkenes as substrates. [4] These methods enabled CO 2 to be harnessed as a renewable one-carbon building block; however, the valorization of CO 2 is still challenging because the gas is thermodynamically and kinetically stable. [5] Consequently, numerous advances in chemical carboxylation using CO 2 have relied on highly reactive organometallic nucleophiles to facilitate the reaction. [5,6] Recent reports have demonstrated that the elaborate design of organometallic nucleophiles is the primary requisite for modulation of site-selectivity and extension of substrates in carboxylation. [6,7] Recently, Martin and co-workers developed an elegant protocol for site-selectivity tunable carboxylation via nickel hydride or nickelalactone formation for the extensive scope of unsaturated hydrocarbons, such as styrenes, alkenes and alkynes. [8] As an alternative approach, heterogeneously catalyzed electrochemical carboxylation has gained increasing attention. This reactions are mainly driven by reductive electrical potential on a cathode electrode. [9] Therefore, the reduction reaction takes place in the absence of a reducing agent and the reducing power can be easily controlled by the applied potentials. Among the unsaturated hydrocarbon feedstocks, this study focused on the electrochemical carboxylation of styrene as a representative model.In the carboxylation of styrene using CO 2 , hydrocarboxylation of the αor β-position and dicarboxylation at both positions are feasible. Vianello and co-workers first pioneered the electrochemical dicarboxylation of styrene to form 2-phenylsuccinic acid (1). [10] Since then, several succeeding works on the electrochemical carboxylation of styrene have reported dicarboxylation as a primary reaction both in the presence [11] and absence [12] of homogeneous catalysts. These studies proposed the electrochemical formation of β-carboxylate radical anions as a key intermediate, followed by additional CO 2 insertion to the benzylic position. [12a,c] It has been hypothesized that the electrochemical carboxylation of styrene is mostly carried out by the dicarboxylation pathway, whereas addition of water as protic agent can change reaction pathway to The carboxylation of hydrocarbons using CO 2 as a one-carbon building block is an attractive route for the synthesis of carboxylic acids and their derivatives. Until now, chemical carboxylation catalyzed by organometallic nucleophiles and reductants has been generally adopted particularly for the precise selectivity control of carboxylation sites. As another approach, electrochemical carboxylation has been attempted but these carboxylation reactions are limited to only a few pathways. In the case of styrene, dicarboxylation at the αand β-positions is mostly observed with electrochemical carboxylation while site-selective hydrocarboxy...