Electrocatalytic hydrodechlorination of 2,4-dichlorophenol over palladium nanoparticles: The critical role of hydroxyl group deprotonation

Chlorinated phenol tends to deprotonate at its hydroxyl group in water, and the ionized CPs dominate the species of reactants in electrocatalytic hydrodechlorination reaction (EHDC). Here we determined the high tendency of the hydroxyl group deprotonation on 2,4-dichlorophenol (2,4-DCP) was highly detrimental to the EHDC reaction on Pd catalysts. This adverse effect arised from the repulsive force generated between the cathode and the ionized 2,4-DCP, which repelled them away from the cathode surface. Notably, the hydroxyl group deprotonation replaced the side hydrogen evolution as primary cause of the poor EHDC performance at low potentials (< -0.85 V). The hydroxyl group deprotonation also favored a cleavage superiority of 4-C-Cl to 2-C-Cl, even though 2-C-Cl was more active. Such a reversal resulted from the direction of the repulsive force to the de-protonated hydroxyl site, making the adjacent 2-C-Cl lie farther from cathode, and become more difficult to react with the atomic hydrogen (H*).