Surface Ligand Environment Boosts the Electrocatalytic Hydrodechlorination Reaction on Palladium Nanoparticles.

We present an enhanced catalytic efficiency of palladium (Pd) nanoparticles (NPs) for the electrocatalytic hydrodechlorination (EHDC) reaction by incorporating the tetraethylammonium chloride (TEAC) ligand into the surface of NPs. Both experimental and theoretical analyses reveal that the surface-adsorbed TEAC is converted to molecular amine (primarily triethylamine) under reductive potentials, forming a strong ligand-Pd interaction that is beneficial to the EHDC kinetics. Using the EHDC of 2,4-dichlorophenol (2,4-DCP), a dominant persistent pollutant identified by the U.S. Environmental Protection Agency, as an example, the Pd/amine composite delivers a mass activity of 2.32 min-1 gPd-1 and a specific activity of 0.16 min-1 cm-2 at -0.75 V versus Ag/AgCl, outperforming Pd and most of the previously reported catalysts. The mechanistic study reveals that the amine ligand offers three functions: the H+-pumping effect, the electronic effect, and the steric effect, providing a favorable environment for the generation of reactive hydrogen radicals (H*) for hydrogenolysis of the C-Cl bond. It also weakens the adsorption strength of EHDC products, alleviating their poisoning on Pd. Investigation into the intermediate products of EHDC on Pd/amine and the biological safety of the 2,4-DCP-contaminated water after EHDC treatment demonstrates that EHDC on Pd/amine is environmentally benign for halogenated organic pollutant abatement. This work suggests that the tuning of NP catalysis using facile ligand post-treatment may lead to new strategies to improve EHDC for environmental remediation applications.