Hierarchical Pd/MnO2 nanosheet array supported on Ni foam: An advanced electrode for electrocatalytic hydrodechlorination reaction

Abstract Electrocatalytic hydrodechlorination (EHDC) is deemed as one promising approach for efficient and safe detoxification of the trace halogenated organic pollutants in water. Here we prepared one advanced Pd/MnO2-Ni foam electrode via the construction of oxygen-deficient MnO2 nanosheet arrays on Ni foam skeleton, which then served as the support and electron donator to capture and reduce Pd precursor to nanoparticles. With the three-dimensional porous structure, hierarchical skeleton surfaces and improved Pd dispersion, the Pd/MnO2-Ni foam electrode delivered an unprecedented large mass activity (kobs) of 0.883 min−1 mmolPd−1 for EHDC of 2,4-dichlorophenol (2,4-DCP), in comparison to 0.081 min−1 mmolPd−1 of the Pd/Ni foam electrode and those reported in literatures. The Pd/MnO2-Ni foam electrode also displayed high durability during the repeated batch EHDC experiments without the efficiency decay and the leaching of Mn/Ni/Pd, unless some reduced sulfur compounds and nitrite were included. The mechanism study revealed the MnO2 in electrode served as a mediator to transfer H* from Pd to 2,4-DCP, which extended the reactive area beyond Pd and hindered the molecular hydrogen evolution, leading to the enhanced reactions between H* and 2,4-DCP. The Pd/MnO2-Ni foam electrode was also tested in a continuous-flow EHDC system, and displayed the potential and retention time-dependent performances.