Potential-mediated enol-keto equilibrium in phenol electro-hydrogenation on platinum

The selective formation of cyclohexanone under cathodic potentials during electrocatalytic hydrogenation (ECH) of phenol on transition metal catalysts attracts extensive interest, yet the mechanistic understanding of this potential-dependent product distribution remains limited. By combining ab initio molecular dynamics with explicit solvation and electrode potential control, we demonstrate that cathodic polarization shifts the enol-keto equilibrium toward the keto form through surface-mediated charge transfer, thereby promoting aromatic ring hydrogenation to cyclohexanone. Moreover, the negatively charged surface electrostatically stabilizes cyclohexanone in a metastable "floating" state, which kinetically suppresses its further hydrogenation. This work addresses the question of cyclohexanone selectivity in phenol ECH by identifying potential-controlled tautomerization as the key step affecting selectivity, offering a clear mechanistic basis for the experimentally observed product distribution.