Electrochemical Dechlorination Research Articles

Oxygen-Controlled Electrocatalysis for Selective Dechlorination of 2-Chloro-5-Trichloromethyl Pyridine on Activated Ag Electrode

Electrochemical selective dechlorination can be regarded as one of the most promising strategies for generating high-valued chemicals. In the electrochemical dechlorination process of 2-chloro-5-trichloromethylpyridine (TCMP), except the anticipated dechlorination products involving 2-chloro-5-dichloromethylpyridine (DCMP), 2-chloro-5-chloromethylpyridine (CCMP), and 2-chloro-5-methylpyridine (CMP), some unexpected oxygen-incorporated products (6-chloronicotinic acid (CNA) and 6-chloronicotinoyl methyl ester (MCN)) can be obtained. Consequently, understanding the electrochemical dechlorination behavior of TCMP is crucial. Our research revealed that the activated Ag electrodes in halide ion solution exhibit enhanced electrochemical activities for electrochemical dechlorination of TCMP, compared with the pure Ag owing to the increased active specific surface areas and charge transfer. Second, oxygen participation in the reaction is a necessary condition for the formation of oxygen-incorporated products. A 100% selectivity of oxygen-incorporated products can be obtained at the potential of −0.6 V vs Ag/AgCl. Conversely, insufficient oxygen may lead to the potential becoming the determining condition that affects the reaction pathways. A more negative potential (−1.2 V vs Ag/AgCl) is conducive to the formation of dechlorination products with 94.2% conversion and 100% selectivity. This study, for the first time, elucidates the electrocatalyst, atmosphere, and potential-dependent activity and selectivity for the two dechlorination pathways of TCMP.

Neighboring Catalytic Sites Are Essential for Electrochemical Dechlorination of 2-Chlorophenol.

The electrocatalytic reduction process is a promising technology for decomposing chlorinated organic pollutants in water but is limited by the lack of low-cost catalysts that can achieve high activity and selectivity. In studying electrochemical dechlorination of 2-chlorophenol (2-CP) in aqueous media, we find that cobalt phthalocyanine molecules supported on carbon nanotubes (CoPc/CNT), which is a highly effective electrocatalyst for breaking the aliphatic C-Cl bonds in 1,2-dichloroethane (DCA) and trichloroethylene (TCE), are completely inactive for reducing the aromatic C-Cl bond in 2-CP. Detailed mechanistic investigation, including volcano plot correlation between dechlorination rate and atomic hydrogen adsorption energy on various transition metal surfaces, kinetic measurements, in situ Raman spectroscopy, and density functional theory calculations, reveals that the reduction of the aromatic C-Cl bond in 2-CP goes through a hydrodechlorination mechanism featuring a bimolecular reaction between adsorbed atomic hydrogen and 2-CP on the catalyst surface, which requires neighboring catalytic sites, whereas the aliphatic C-Cl bonds in DCA and TCE are cleaved by direct electron transfer from the catalyst, which can occur on isolated single sites. This investigation leads to the discovery of metallic Co as a highly selective and active electrocatalyst for 2-CP dechlorination. This work provides new insights into the fundamental chemistry and catalyst design of electrochemical dechlorination reactions for wastewater treatment.

Controlled electrocatalysis of the dechlorination and detoxification of chlorinated ethylenes to avoid production of highly toxic intermediates

In this study, electrochemical dechlorination and detoxification of a mixture of chlorinated ethylenes was investigated under various conditions using a double monoatomic synergistic metal catalytic cathode. Electrocatalytic degradation of mixed chlorinated with stepwise voltage and alternating current exhibited excellent dechlorination efficiency. The removal ratios of 1,2-dichloroethylene (1,2-DCE), trichloroethylene (TCE), and tetrachloroethylene (PCE) reached 78.79 %, 79.27 %, and 93.44 % in 10 min, and 98.14 %, 97.56 %, and 98.70 % in 30 min, respectively. The toxicity was evaluated using a quantitative structure–activity relationship model. The cumulative toxicity was reduced to 8.00 % of the initial cumulative toxicity in 30 min. An electrochemical dechlorination strategy for selective degradation and detoxification of mixtures of chlorinated pollutants is proposed. Controlled dechlorination and detoxification under low-voltage control avoided the accumulation of toxic intermediates. Cumulative toxicity was reduced by strategies of selective dechlorination, and segmented and alternating current decreased the energy consumption. The strategy provides a basis for alternating current electrocatalytic dechlorination associated with mixed chlorinated pollutants treatment.

Interlayer Structure Manipulation of FeOCl/MXene with Soft/Hard Interface Design for Safe Water Production Using Dechlorination Battery Deionization

AbstractSuffering from the susceptibility to decomposition, the potential electrochemical application of FeOCl has greatly been hindered. The rational design of the soft‐hard material interface can effectively address the challenge of stress concentration and thus decomposition that may occur in the electrodes during charging and discharging. Herein, interlayer structure manipulation of FeOCl/MXene using soft‐hard interface design method were conducted for electrochemical dechlorination. FeOCl was encapsulated in Ti3C2Tx MXene nanosheets by electrostatic self‐assembly layer by layer to form a soft‐hard mechanical hierarchical structure, in which Ti3C2Tx was used as flexible buffer layers to relieve the huge volume change of FeOCl during Cl− intercalation/deintercalation and constructed a conductive network for fast charge transfer. The CDI dechlorination system of FeOCl/Ti3C2Tx delivered outstanding Cl− adsorption capacity (158.47 ± 6.98 mg g−1), rate (6.07 ± 0.35 mg g−1 min−1), and stability (over 94.49 % in 30 cycles), and achieved considerable energy recovery (21.14 ± 0.25 %). The superior dechlorination performance was proved to originate from the Fe2+/Fe3+ topochemical transformation and the deformation constraint effect of Ti3C2Tx on FeOCl. Our interfacial design strategy enables a hard‐to‐soft integration capacity, which can serve as a universal technology for solving the traditional problem of electrode volume expansion.

Interlayer Structure Manipulation of FeOCl/MXene with Soft/Hard Interface Design for Safe Water Production Using Dechlorination Battery Deionization.

Suffering from the susceptibility to decomposition, the potential electrochemical application of FeOCl has greatly been hindered. The rational design of the soft-hard material interface can effectively address the challenge of stress concentration and thus decomposition that may occur in the electrodes during charging and discharging. Herein, interlayer structure manipulation of FeOCl/MXene using soft-hard interface design method were conducted for electrochemical dechlorination. FeOCl was encapsulated in Ti3C2Tx MXene nanosheets by electrostatic self-assembly layer by layer to form a soft-hard mechanical hierarchical structure, in which Ti3C2Tx was used as flexible buffer layers to relieve the huge volume change of FeOCl during Cl- intercalation/deintercalation and constructed a conductive network for fast charge transfer. The CDI dechlorination system of FeOCl/Ti3C2Tx delivered outstanding Cl- adsorption capacity (158.47 ± 6.98 mg g-1), rate (6.07 ± 0.35 mg g-1 min-1), and stability (over 94.49% in 30 cycles), and achieved considerable energy recovery (21.14 ± 0.25%). The superior dechlorination performance was proved to originate from the Fe2+/Fe3+ topochemical transformation and the deformation constraint effect of Ti3C2Tx on FeOCl. Our interfacial design strategy enables a hard-to-soft integration capacity, which can serve as a universal technology for solving the translational problem of electrode volume expansion.

Reactive P and S co-doped porous hollow nanotube arrays for high performance chloride ion storage

Developing stable, high-performance chloride-ion storage electrodes is essential for energy storage and water purification application. Herein, a P, S co-doped porous hollow nanotube array, with a free ion diffusion pathway and highly active adsorption sites, on carbon felt electrodes (CoNiPS@CF) is reported. Due to the porous hollow nanotube structure and synergistic effect of P, S co-doped, the CoNiPS@CF based capacitive deionization (CDI) system exhibits high desalination capacity (76.1 mgCl– g–1), fast desalination rate (6.33 mgCl– g–1 min–1) and good cycling stability (capacity retention rate of > 90%), which compares favorably to the state-of-the-art electrodes. The porous hollow nanotube structure enables fast ion diffusion kinetics due to the swift ion transport inside the electrode and the presence of a large number of reactive sites. The introduction of S element also reduces the passivation layer on the surface of CoNiP and lowers the adsorption energy for Cl– capture, thereby improving the electrode conductivity and surface electrochemical activity, and further accelerating the adsorption kinetics. Our results offer a powerful strategy to improve the reactivity and stability of transition metal phosphides for chloride capture, and to improve the efficiency of electrochemical dechlorination technologies.

Regulating the electronic structure by P-doping cobalt-based catalyst for atomic hydrogen mediated electrocatalytic dechlorination

Electrocatalytic dechlorination by atomic hydrogen (H*) is efficient, but limited by the low efficiency of H* production. Herein, a phosphorus-doped cobalt nitrogen carbon catalyst (Co-NP/C) was prepared, which had high catalytic activity in a wide pH range (3−11). The turnover frequency of Co-NP/C (3.54 min−1) was 1.21–59000 times superior to that of current Pd-based and non-noble metal catalysts (0.00006–2.92 min−1). Co-NP/C significantly enhanced H* generation, which was 1.52, 2.44, and 3.77 times stronger than that of Co-N/C, NP/C, and N/C, respectively, since the introduction of phosphorus was found enhanced the electron density of cobalt and regulated the electron transfer. Co-NP/C showed outstanding catalytic performance after ten cycles and could achieve nearly complete chloramphenicol removal. This regulation method was verified to be effective for other non-noble metal (Fe, Mn, Cu, Ni) phosphorus doped catalysts, proposing a general class for efficient electrochemical dechlorination, which would be of great significance for the elimination of chlorinated organic pollutants.

Cobalt Single-Atom Reverse Hydrogen Spillover for Efficient Electrochemical Water Dissociation and Dechlorination.

Efficient water dissociation to atomic hydrogen (H*) with restrained recombination of H* is crucial for improving the H* utilization for electrochemical dechlorination, but is currently limited by the lack of feasible electrodes. Herein, we developed a monolithic single-atom electrode with Co single atoms anchored on the inherent oxide layer of titanium foam (Co1-TiOx/Ti), which can efficiently dissociate water into H* and simultaneously inhibit the recombination of H*, by taking advantage of the single-atom reverse hydrogen spillover effect. Experimental and theoretical calculations demonstrated that H* could be rapidly generated on the oxide layer of titanium foam, and then overflowed to the adjacent Co single atom for the reductive dechlorination. Using chloramphenicol as a proof-of-concept verification, the resulting Co1-TiOx/Ti monolithic electrode exhibited an unprecedented performance with almost 100 % dechlorination at -1.0 V, far superior to that of traditional indirect reduction-driven commercial Pd/C (52 %) and direct reduction-driven Co1-N-C (44 %). Moreover, its dechlorination rate constant of 1.64 h-1 was 4.3 and 8.6 times more active than those of Pd/C (0.38 h-1) and Co1-N-C (0.19 h-1), respectively. Our research sheds light on the rational design of hydrogen spillover-related electrocatalysts to simultaneously improve the H* generation, transfer, and utilization for environmental and energy applications.

Cobalt Single‐Atom Reverse Hydrogen Spillover for Efficient Electrochemical Water Dissociation and Dechlorination

AbstractEfficient water dissociation to atomic hydrogen (H*) with restrained recombination of H* is crucial for improving the H* utilization for electrochemical dechlorination, but is currently limited by the lack of feasible electrodes. Herein, we developed a monolithic single‐atom electrode with Co single atoms anchored on the inherent oxide layer of titanium foam (Co1−TiOx/Ti), which can efficiently dissociate water into H* and simultaneously inhibit the recombination of H*, by taking advantage of the single‐atom reverse hydrogen spillover effect. Experimental and theoretical calculations demonstrated that H* could be rapidly generated on the oxide layer of titanium foam, and then overflowed to the adjacent Co single atom for the reductive dechlorination. Using chloramphenicol as a proof‐of‐concept verification, the resulting Co1−TiOx/Ti monolithic electrode exhibited an unprecedented performance with almost 100 % dechlorination at −1.0 V, far superior to that of traditional indirect reduction‐driven commercial Pd/C (52 %) and direct reduction‐driven Co1−N−C (44 %). Moreover, its dechlorination rate constant of 1.64 h−1 was 4.3 and 8.6 times more active than those of Pd/C (0.38 h−1) and Co1−N−C (0.19 h−1), respectively. Our research sheds light on the rational design of hydrogen spillover‐related electrocatalysts to simultaneously improve the H* generation, transfer, and utilization for environmental and energy applications.

Electrochemical reductive removal of trichloroacetic acids by a three-dimensional binderless carbon nanotubes/ CoP/Co foam electrode: Performance and mechanism

Numerous chlorinated disinfection by-products (DBPs) are produced during the chlorination disinfection of water. Among them, chloroacetic acids (CAAs) are of great concern due to their potential human carcinogenicity. In this study, effective electrocatalytic dechlorination of trichloroacetic acids (TCAA), a typical CAAs, was achieved in the electrochemical system with the three-dimensional (3D) self-supported CoP on cobalt foam modified by carbon nanotubes (CNT/CoP/CF) as the cathode. At a 10 mA cm−2 current density, 74.5% of TCAA (500 μg L−1) was converted into AA within 100 min. In-situ growth of CoP increased the effective electrochemical surface area of the electrode. Electrodeposited CNT promoted electron transfer from the electrode surface to TCAA. Therefore, the production of surface-adsorbed atomic hydrogen (H*) on CNT/CoP/CF was improved, further resulting in excellent electrochemical dechlorination of TCAA. The dechlorination pathway of TCAA proceeded into acetic acids via direct electronic transfer and H*-mediated reduction on CNT/CoP/CF electrode. Additionally, the electroreduction efficiency of CNT/CoP/CF for TCAA exceeded 81.22% even after 20 cycles. The highly efficient TCAA reduction performance (96.57%) in actual water revealed the potential applicability of CNT/CoP/CF in the complex water matrix. This study demonstrated that the CNT/CoP/CF is a promising non-noble metal cathode to remove chlorinated DBPs in practice.

Carbon-based materials for electrochemical dechlorination

Carbon-based materials for electrochemical dechlorination

Pd nanoparticles supported on microflower NiMOF modified roughed nickel foam with the enhanced active site for electrochemical dechlorination of trichloroacetic acid

Electrocatalytic hydrodechlorination (ECH) has been considered as an effective method to convert refractory chlorinated organics into biodegradable chlorine-free organics under mild conditions. In this work, a composite electrode of Pd/NiMOF/roughed nickel foam (Pd/NiMOF/RNF) with excellent dechlorination performance was prepared by electrodeposition of Pd nanoparticles on the flower-shaped NiMOF interlayer grown in-situ. Benefiting from the high specific surface area of NiMOF structure and excellent dispersion of Pd facilitated, the Pd/NiMOF/RNF offered abundant active hydrogen and larger open channels for the easy diffusion of reactants and products in the electrochemical dechlorination process. 97% of 6 μmol/L trichloroacetic acid (TCAA) was dechlorinated at a cathodic potential of −1.2 V within 90 min. The corresponding palladium mass activity was calculated to be 0.39 μg min−1 cm−2 mg−1 Pd, which was approximately 3.5 times greater than other report on ECH cathode. Moreover, the Pd/NiMOF/RNF cathode remained stable even after five consecutive cycle tests. Toxic assessment results indicated that the dechlorination process was beneficial to the detoxification of TCAA at the end of reaction. The hydrodechlorination mechanism of TCAA was proposed by density functional theory (DFT) analysis and electrochemical characterization on the Pd/NiMOF/RNF electrode. The findings of this study have the potential to contribute to the development of electrocatalytic treatment methods for chlorinated organic compounds in drinking water.

Modulating adsorption of active hydrogen atoms on palladium nanoparticles: Doping ruthenium into metal–organic frameworks for efficient electrocatalytic hydrodechlorination

To simultaneously optimize the dispersion and electrocatalytic activity of palladium (Pd) nanoparticles, we report a novel Pd-NiRu-MOF/NF composite electrode with low noble metal dosage for electrocatalytic hydrodechlorination. The as-prepared electrode exhibits outstanding activity, particularly the complete dechlorination of 2-chlorophenol within 75 min at −0.85 V, outperforming reported state-of-the-art electrode materials. Moreover, the catalytic activity could be well-maintained after continuous five catalytic cycles and even 30-day exposure to air as well as deliver excellent catalytic performance for other priority chlorophenols. CO-stripping experiments demonstrate that the dispersion of Pd nanoparticles increases the electrochemically active surface area of Pd. X-ray photoelectron spectroscopy and density functional theory analysis disclose that the electronic structure of Pd is modulated via introducing Ru atoms into Pd-Ni-MOF/NF, thereby enhancing the adsorption of H*ads on Pd-NiRu-MOF/NF and boosting the electroreductive remediation of chlorophenols. Notably, the electrochemical dechlorination of chlorophenols remains effective in natural water or soil, indicating that Pd-NiRu-MOF/NF composite electrode has a good application potential in removing organic halides in wastewater or soil.

Electrochemical Dechlorination of Trichloroethylene by Manganese Phthalocyanine: Performance and Mechanisms

Trichloroethylene (TCE) is one of the most abundant persistent organic pollutant in subsurface environment. TCE can be reduced electrochemically, but the extremely negative applied potential limits the application of this technology. Manganese phthalocyanine (MnPc) catalyst was used for the electrochemical reductive dechlorination of TCE. The results show that MnPc can be reduced by electrons attachment at −-0.21 V, −-1.22 V and −-1.77 V, respectively. With the decrease of applied potential from −-0.3 V to −-1.8 V, the transformation from TCE to dichloroethylene (DCE) efficiency increased from 19.9% to 41.8% after 5 hours of reaction. Although the electron transfer ability was enhanced with applied potential decreasing, the intensive HER caused the electron selectivity decreased when MnPc attached more electrons. MnPc catalyze the electrochemical reduction of TCE, which has potential application on the remediation of TCE-contaminated groundwater.

Cubic CuFe2O4 Spinel with Octahedral Fe Active Sites for Electrochemical Dechlorination of 1,2-Dichloroethane.

CuFe2O4 spinel has been considered as a promising catalyst for the electrochemical reaction, while the nature of the crystal phase on its intrinsic activity and the kind of active site need to be further explored. Herein, the crystal phase-dependent catalytic behavior and the main active sites of CuFe2O4 spinel for electrochemical dechlorination of 1,2-dichloroethane are carefully studied based on the combination of experiments and theoretical calculations. Cubic and tetragonal CuFe2O4 are successfully prepared by a facile sol-gel method combined with high temperature calcination. Impressively, CuFe2O4 with the cubic phase shows a higher activity and ethylene selectivity compared to CuFe2O4 with the tetragonal phase, suggesting a significant facilitation of electrocatalytic performance by the cubic crystal structure. Moreover, the octahedral Fe atom on the surface of cubic CuFe2O4(311) is the active site responsible to produce ethylene with the energy barrier of 0.40 eV. This work demonstrates the significance of crystal phase engineering for the optimization of electrocatalytic performance and offers an efficient strategy for the development of advanced electrocatalysts.

An Investigation of Electrochemical Dechlorination of Wrought Iron Specimens from the Marine Environment

The research shows the benefits provided by the use of electrochemical treatment, with the application of impressed current combining the use of a porous medium for the dechlorination of large iron structures removed and/or located in the marine environment. Considering the previous work for the dechlorination of the paddle wheel of the shipwreck “Patris”, located in the Aegean Sea, this study aims to determine the optimum parameters of the amount of current density, the time and the use of the porous medium to stimulate the chloride ion diffusion into an alkaline solution. Specimens of wrought iron coming from the shipwreck were electrochemically treated and the efficiency of the method was verified by the determination of the chloride concentration removal using a chloride ion selective electrode. Samples of corrosion products before and after treatment were analyzed for chloride content using SEM-EDX analysis. The results found that changing the porous medium every 24 h with replenished alkaline solution and using a stainless steel mesh is the best approach for the dechlorination of the specimens. This electrochemical method, is economical and fast, and can be applied to the conservation of large iron structures in situ, coming from and/or located near a marine environment with less waste than the traditional dehlorination methods.

Metal–Nitrogen–Carbon Single‐Atom Aerogels as Self‐Supporting Electrodes for Dechlorination of 1,2‐Dichloroethane

AbstractSingle‐atom catalysts (SACs) have received widespread interest for their high atomic efficiency, enriched active sites, excellent catalytic performance, and low cost. However, the agglomeration of single metal atoms and the use of inactive additives for affixing powdery SACs on planar electrodes may reduce the density of active sites, diminish the charge transport to active sites, and thus suppress their performance. Herein, a series of metal–nitrogen–carbon single‐atom aerogels (M‐SAAs, M: Cu, Ni, Au, Ru) are synthesized via a universal strategy, in which the merits of metal organic frameworks and carbon aerogels are perfectly combined to prevent the agglomeration of single metal atoms and overcome the problem of poor electrical conductivity. The as‐prepared M‐SAAs can be directly employed as self‐supporting electrodes for the electrochemical dechlorination of 1,2‐dichloroethane, and outstanding activity and stability are observed. Significantly, the Cu‐SAA with abundant Cu−N4 sites shows an extraordinarily high ethylene production rate of 446 µmol h−1, with a selectivity of 99% and Faradaic efficiency of 64%. Moreover, theoretical calculations are performed to demonstrate the selectivity and activity of different metal active sites. This study provides a new strategy to exploit highly effective SACs and offers an intensive insight into the mechanism of electrochemical dechlorination reactions.

Noble-metal-free 3D hierarchical Ni-WC heterostructure with enhanced interfacial charge transfer for efficient electrocatalytic hydrodechlorination

Electrocatalytic hydrodechlorination (EHDC) provides a promising approach to efficiently remove the halogenated organic pollutants in water. Herein, a kind of noble-metal-free three-dimensional (3-D) hierarchical nickel-tungsten carbide (Ni-WC) heterostructure supported on nickel foam (NF) (Ni-WC/NF) was fabricated via the in-situ hydrothermal growth and annealing treatment of Ni,W-rich polyoxometalate {Ni54W72}. Featuring self-supported 3-D hierarchical skeleton structures and abundant Ni-WC interfaces, Ni-WC/NF exhibited high-efficient EHDC performance towards 4-chlorophenol (4-CP) with 100 % conversion efficiency in 3 h, large reaction rate constant of 2.2 × 10-2 min−1 and high current efficiency of 13.9 %, which is comparable to the-state-of-the-art Pd-based catalysts. The active atomic hydrogen (H*) generation kinetics and the interactions of Ni-WC heterostructure with 4-CP/phenol were evaluated. DFT calculations demonstrated that the coverage of 4-CP determines the EHDC efficiency, the Ni-WC heterostructure optimizes the electronic structure of Ni, enhances the adsorption of 4-CP and facilitates the desorption of phenol, thus promoting EHDC performance. This work provides an efficient noble-metal-free catalyst for enhanced electrochemical dechlorination in organic-pollutant treatment.

Coordinatively Unsaturated Reduced Iron Sites Enable Hemin-Catalyzed Electrochemical Dechlorination of Trichloroethylene

Coordinatively Unsaturated Reduced Iron Sites Enable Hemin-Catalyzed Electrochemical Dechlorination of Trichloroethylene

Self-activated Ni(OH)2 cathode for complete electrochemical reduction of trichloroethylene to ethane in low-conductivity groundwater

This study investigates the electrochemical dechlorination of trichloroethylene (TCE) to non-toxic and value-added ethane by self-activated Ni(OH)2 cathode. The Ni(OH)2 cathode was fabricated by drop-casting the as-synthesized Ni(OH)2 suspensions on a glassy carbon electrode. At −1.0 V applied potential, 94.6% of TCE is reduced after 5 h of electrolysis. TCE is efficiently transformed to ethane at a wide pH range in simulated groundwater environment with low-conductivity. The air-exposed Ni(OH)2 cathode can still dechlorinate 49.8% TCE, showing the antioxidative capacity of Ni(OH)2 cathode is superior than that of pristine Ni electrode. Both the directly transferred electrons and the generated atomic H* at the active Ni(0) sites contributed to the hydrodechlorination of TCE. Our work not only provides an effective way to completely detoxify chlorinated organic contaminants (COCs) under environment-relevant conditions, but also proves a concept that the chemical energy in COCs can be harvested during their electrochemical reduction processes.