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

Abstract

Electrocatalytic hydrodechlorination on Pd, utilizing the H + of H 2 O 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 H 2 O 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/ Ni x Al 100−x -LDH-OH v ) can significantly improve its performance, benefiting from the enhanced H 2 O disassociation at OH v and the facilitated C−Cl cleavage on the supported Pd nanoparticles. Al 3+ is also indispensable because it promotes the formation and regeneration of OH v , but an overload will reduce the number of accessible OH v and weaken its function. Pd/Ni 67 Al 33 -LDH-OH v 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 −1 Pd 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/Ni 67 Al 33 -LDH-OH v 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 g 2,4-DCP g catalyst −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.

Electronic Structure Optimization and Proton-Transfer Enhancement on Titanium Oxide-Supported Copper Nanoparticles for Enhanced Nitrogen Recycling from Nitrate-Contaminated Water

“…With more negative potential, NO 2 – -N becomes less and even vanishes at −0.55 and −0.60 V. Correspondingly, a high NH 3 -N selectivity of 96.9% could be obtained at −0.60 V. These suggest that, under the investigated reaction conditions, the NO 3 – -NO 2 – conversion is faster than the subsequent NO 2 – -N reduction at the active Cu spots, and a more negative potential accelerates the NO 2 – -N reduction. Figure S6a also shows that the FE% for NH 3 -N production exhibited a volcano-like variation with increasing potential, with a peak of 59.6% achieved at −0.40 V. The low FE% at potentials more negative than −0.40 V can be ascribed to the enhanced side hydrogen evolution reaction . Given these results, the working potential should be carefully chosen to balance the NO3RR efficiency and energy consumption.…”

“…Figure S6a also shows that the FE% for NH 3 -N production exhibited a volcano-like variation with increasing potential, with a peak of 59.6% achieved at −0.40 V. The low FE% at potentials more negative than −0.40 V can be ascribed to the enhanced side hydrogen evolution reaction. 47 Given these results, the working potential should be carefully chosen to balance the NO3RR efficiency and energy consumption.…”

Efficient Palladium Catalysts: Application and Challenges of Electrocatalytic Hydrodechlorination Technology in Wastewater Treatment

“…Lv et al loaded Pd on OH À vacancies (OH v ) bearing NiAl-layered double hydroxide nanosheets (Pd/Ni x Al 100x À LDHÀ OH v ) for the removal of 2,4-DCP by ECH reaction. [45] The prepared Pd/Ni x Al 100-x À OH v composite catalyst has higher mass activity and dechlorination efficiency compared to the conventional single Pd catalyst. The introduction of electrondeficient Pd as well as OH v increased the water cleavage, thus greatly increasing the efficiency of the catalyst for ECH.…”

“…containing OH À vacancies, which greatly improved the dechlorination performance of Pd catalysts. [45] The prepared composite Pd catalysts simultaneously formed more electron-deficient palladium favorable for CÀ Cl bond breaking, which improved the dechlorination efficiency for COPs (Figure 5B). Electron-rich as well as electron-deficient Pd played different roles in the ECH reaction, and some scholars had worked on controlling the ratio of the two to obtain the optimal dechlorination efficiency.…”

“…Reprinted with permission from reference. [45] Copyright 2022, American Chemical Society. C) Pd 3d XPS spectra for TiO 2 /Pd, TiO 2 /PdÀ B, TiO 2 @PDA/Pd and TiO 2 @PDA/PdÀ B.…”