Defective Layered Double Hydroxide Nanosheet Boosts Electrocatalytic Hydrodechlorination Reaction on Supported Palladium Nanoparticles

ABSTRACT: Electrocatalytic hydrodechlorination on Pd, utilizing the H+ of H2O as hydrogen sources, represents a promising technology to detoxify the chlorinated organic pollutants (COPs) in water bodies. However, Pd alone affords limited activity due to its low efficacy in H2O disassociation and the poor mass diffusion of COPs that are commonly of low concentrations in the environment. Herein, we demonstrate that arming Pd with OH- vacancy-bearing NiAl-layered double hydroxide nanosheets (Pd/ NixAl100-x-LDH-OHv) can significantly improve its performance, benefiting from the enhanced H2O disassociation at OHv and the facilitated C-Cl cleavage on the supported Pd nanoparticles. Al3+ is also indispensable because it promotes the formation and regeneration of OHv,but an overload will reduce the number of accessible OHv and weaken its function. Pd/Ni67Al33-LDH-OHv with the optimal Ni/Al ratio delivers a peak specific activity of 0.53 min-1 m-2 and mass activity of 6.54 min-1 g-1Pd in treating 50.0 mg L-1 2,4-dichlorophenol (2,4-DCP, a probe COP) at -0.25 V versus RHE, outperforming most of the reported catalysts. To address the mass diffusion issue, Pd/Ni67Al33-LDH-OHv is integrated into a customized continuous-flow membrane cell. When fed a dilute wastewater (20.4 mg L-1), the system affords a 2,4-DCP removal rate of 3.75 g2,4-DCP gcatalyst-1 h-1 and faradaic current efficiency of 42.6%, which is 3.2 and 4.0 times that obtained in a traditional batch reaction system, respectively.