Effective electrocatalytic hydrodechlorination of 2,4,6-trichlorophenol by a novel Pd/MnO2/Ni foam cathode

Pd modified electrodes possess problems such as easy agglomeration and low electrolytic ability, and the use of manganese dioxide (MnO2) to facilitate Pd reduction of organic pollutants is just started. However, there is still a limited understanding of how to match the Pd load and MnO2 to realize optimal dechlorination efficiency at minimum cost. Here, a Pd/MnO2/Ni foam cathode was successfully fabricated and applied for the efficient electrochemical dechlorination of 2,4,6-trichlorophenol (2,4,6-TCP). The optimal electrocatalytic hydrodechlorination (ECH) performance with 2,4,6-TCP dechlorination efficiency (92.58% in 180 min) was obtained when the concentration of PdCl2 precipitation was 1 mmol/L, the deposition time of MnO2 was 300 s and cathode potential was −0.8 V. Performance influenced by the exogenous factors (e.g., initial pH and coexisted ions) were further investigated. It was found that the neutral pH was the most favorable for ECH and a reduction in dechlorination efficiency (6%∼47.6%) was observed in presence of 5 mmol/L of NO2−, NO3−, S2− or SO32−. Cyclic voltammetry (CV) and quenching experiments verified the existence of three hydrogen species on Pd surface, including adsorbed atomic hydrogen (H*ads), absorbed atomic hydrogen (H*abs), and molecular hydrogen (H2). And the introduction of MnO2 promoted the generation of atomic H*. Only adsorbed atomic hydrogen (H*ads) was confirmed that it truly facilitated the ECH process. Besides H*ads induced reduction, the direct reduction by cathode electrons also participated in the 2,4,6-TCP dechlorination process. Pd/MnO2/Ni foam cathode shows excellent dechlorination performance, fine stability and recyclable potential, which provides strategies for the effective degradation of persistent halogenated organic pollutants in groundwater.