Electrocatalytic hydrodechlorination of 2,4,5-trichlorobiphenyl on a palladium-modified nickel foam cathode.

Palladium-modified materials have been found to be effective electrodes for the reductive degradation of chlorinated compounds in aqueous solution. This study investigated the electrocatalytic hydrodechlorination (ECH) of polychlorinated biphenyls (PCBs) in solvent/surfactant-aided solutions in a palladium-modified nickel foam electrode using a divided flow-through cell. The reaction pathways of 2,4,5-PCB hydrodechlorination were proposed due to the analysis of intermediates by GC/MS. The mechanism of electrocatalytic reaction on the Pd/Ni foam cathode was examined by studying the effect of surfactant type, sorption behavior of PCBs on the electrode, and current densities on the ECH efficiency of PCBs. The conversion of PCBs was controlled by the micelle structures of the surfactants instead of the charged species. According to the analysis of hydrogen transformation processes on the electrode surface, we propose that the ECH process was initiated by the transfer of highly active hydrogen atoms [H] from the prior polarized Pd particles to the less polarized Pd particles by spillover on the Pd/Ni foam cathode. Therefore, the total available surface was larger than the originally polarized surface, and [H] could smoothly react with PCBs that were adsorbed on the surface. As a result, a high ECH efficiency can be achieved with the Pd/Ni foam electrode.