Elucidating the Role of Single-Atom Pd for Electrocatalytic Hydrodechlorination

Combining a Pd Cluster and a Built-in Electric Field as a Biomimic for Stable C-Cl Bond Polarization

Adopting the essence of enzyme catalysis, the strong binding of substrates into the active site pocket for their selective activation through multiple noncovalent interactions in the reactive site design can effectively enhance the electrocatalysis process. However, mimicking the enzyme catalytic process, particularly the introduction of reactant activation mechanisms, remains a significant challenge. Herein, we present a Pd cluster inside the Fe2N-Fe3O4-based built-in electric field (BEF), denoted as Pd/Fe2N-Fe3O4, to serve as an enzyme mimic to activate stable C-Cl bonds. Theoretical calculations and in situ Raman indicate that the probe molecule 2,4-dichlorophenol (2,4-DCP) adsorbs onto the Pd site and rotates inside the BEF with the C4-Cl bond being selectively activated and elongated from 1.73 to 1.82 Å. This makes Pd/Fe2N-Fe3O4 an excellent electrocatalytic hydrodechlorination catalyst, with Pd usage down to 2.5 μg cm-2, which is 32.7-360 times less than that of conventional catalysts like Pd/C, and achieving a Faradaic efficiency exceeding 20%. We reveal that besides H*-mediated electrochemical reduction, Pd/Fe2N-Fe3O4 also hydrodechlorinates activated 2,4-DCP via the proton-electron coupled transfer pathway. This understanding of the role of BEF in reactant activation, along with the strategy of integrating BEF and noble metals to mimic enzymes, provides a direction for the design of advanced electrocatalysts.

B-Modified Pd Cathodes for the Efficient Detoxification of Halogenated Antibiotics: Enhancing C-F Bond Breakage beyond Hydrodefluorination

Halogenated antibiotics pose a great threat to aqueous environments because of their persistent biotoxicity from carbon-halogen bonds. Electrochemical reduction (ER) is an efficient technology for dehalogenation, but it still suffers from limited efficiencies in breaking C-F bonds. Herein, we present a strategy to enhance C-F cleavage and promote detoxification by loading benchmark palladium cathodes onto boron-doped carbon. This improves the florfenicol (FLO) degradation rate constant and defluorination efficiency by 1.24 and 1.05 times, respectively, and improves the defluorination of various fluorinated compounds. The cathode with optimal B content shows superior mass activity for FLO degradation (1.11 mmol g-1 Pd min-1), which is 5.9 times that of commercial Pd/C and is among the best-reported cathodes. Notably, the exclusive formation of the direct defluorination product (i.e., FLO-F) on Pd/B-C implies a higher intrinsic C-F cleavage ability endowed by B doping. As revealed by experiments and theoretical calculations, boron modification enhances palladium binding and induces stronger strain effects and higher electron density for surface palladium atoms, which boosts H* generation and reduces the energy barrier for C-F cleavage. This study provides an effective cathode design strategy to enhance C-F activation, which may broadly benefit the destruction and detoxification of fluorinated organics that are limited by sluggish C-F cleavage kinetics.

Efficient Electrocatalytic Hydrodechlorination and Detoxification of Chlorophenols by Palladium-Palladium Oxide Heterostructure

Electrocatalytic hydrodechlorination is a promising approach for simultaneous pollutant purification and valorization. However, the lack of electrocatalysts with high catalytic activity and selectivity limits its application. Here, we propose a palladium-palladium oxide (Pd-PdO) heterostructure for efficient electrocatalytic hydrodechlorination of recalcitrant chlorophenols and selective formation of phenol with superior Pd-mass activity (1.35 min-1 mgPd-1), which is 4.4 times of commercial Pd/C and about 10-100 times of reported Pd-based catalysts. The Pd-PdO heterostructure is stable in real water matrices and achieves selective phenol recovery (>99%) from the chlorophenol mixture and efficient detoxification along chlorophenol removal. Experimental results and computational modeling reveal that the adsorption/desorption behaviors of zerovalent Pd and PdO sites in the Pd-PdO heterostructure are optimized and a synergy is realized to promote atomic hydrogen (H*) generation, transfer, and utilization: H* is efficiently generated at zerovalent Pd sites, transferred to PdO sites, and eventually consumed in the dechlorination reaction at PdO sites. This work provides a promising strategy to realize the synergy of Pd with different valence states in the metal-metal oxide heterostructure for simultaneous decontamination, detoxification, and resource recovery from halogenated organic pollutants.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

A Two-Phase Hydrogenation Membrane for Contaminants Reduction at High Hydrogen Reagent Utilization Efficiency

Heterogeneous hydrogenation is surging as a promising strategy for selective removal of water pollutants, yet numerous efforts rely on catalyst design to advance catalytic activity. Herein, we enhanced the mass transfer and the utilization of hydrogen reagent through construction of a two-phase flow-through membrane reaction device (Pd/SiC-MR). Pd/SiC-MR displays high efficiency and selectivity toward removal of multiple pollutants. For instance, rapid (∼0.35 s) and exclusive hydrogenation (>99%) of carbon-chlorine bond in organohalogens were realized at high water flux (220 L/m2/h). More importantly, the two-phase Pd/SiC-MR reaction system achieved 31.4% utilization of hydrogen reagent, 1-3 orders of magnitude higher than those by classical slurry or fixed-bed reactor. The high hydrogenation performance is attributed to the close proximity of the hydrogen source, reactive hydrogen atom, and pollutant under high molecular collision frequency in membrane pores. Our study opens an approach for improved hydrogen reagent utilization while reserving the high pollutant removal efficiency through altering operating conditions, beyond complex material design limitations in hydrogenation water purification.

Synergy of atomic hydrogen reduction and reactive oxygen species oxidation over confined Mn bifunctional site for electrocatalytic deep mineralization

Traditional reduction or oxidation processes generating one-component free radicals face challenges in deep dechlorination and mineralization of chlorophenols from wastewater. Herein, an efficient electrocatalytic process has been developed, which couples atomic H* reduction with reactive oxidation species (•OH and 1O2) oxidation on a bifunctional cathode for 4 -chlorophenol (4 -CP) removal. The N - doped carbon nanotubes encapsulated manganese nanoparticles was fabricated as cathode, which could generate atomic H* , initiating nucleophilic hydrodechlorination in presence of confined MnO sites. Subsequently, electrophilic oxidation by generating mainly 1O2 on confined Mn7C3 sites and •OH on confined MnO sites, facilitating the oxidative processes. Experimental results and theory calculations demonstrated that reductive dechlorination and oxidative mineralization processes could mutually promote each other, resulting in an enhancement factor of 2.90. At pH 7, this process achieved 100 % removal for 4 -CP, 84 % dechlorination, 76 % total organic carbon (TOC) removal and low energy consumption (0.76 kWh g-1TOC) within 120 min. Notably, TOC for chlorophenols containing Cl substituents at different positions and real lake water containing 4 -CP could be almost completely removed. This research establishes confined non-noble bifunctional active sites that synergistically enhance reductive dechlorination and oxidative degradation processes, holding significant treatment potential for application in deep mineralization of organochlorine from water/wastewater.

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.

Synergistic Elimination of Chlorophenols Using a Single-Atom Nickel with Single-Walled Carbon Nanotubes: The Roles of Adsorption, Hydrodechlorination, and the Electro-Fenton Process

Electrocatalytic degradation enables the efficient treatment of chlorinated pollutants (COPs); however, its application has been significantly hindered by the large amounts of unsafe intermediate products. In this study, we present a single-atom nickel with single-walled carbon nanotubes (SWCNTs) as an electrochemical reactor for the complete elimination of chlorophenols. Distinct products and reductive mechanisms were observed for Ni-N-C compared to Cu-N-C. Ni-N-C incorporation has a novel degradation pathway for efficient chlorophenol degradation involving hydrodechlorination and the electro-Fenton process. Most importantly, the weak adsorption between the chlorophenols and the SWCNTs promoted their dechlorination by the attached active atomic hydrogen (H*) formed on the Ni-N-C. Meanwhile, the SWCNTs improved the reduction of O2 to H2O2, which was subsequently decomposed by Ni-N-C to form hydroxyl radicals (·OH) for phenol oxidation. As a result, the degradation rate of 4-chlorophenol was increased by 5 and 10 times compared with those of the Ni-N-C and SWCNTs alone, respectively. The first-order reaction rate constant was 2.7 h-1, and the metal mass kinetics constant was 1956.5 min-1g-1. Aromatic COPs containing benzene rings could be degraded, but chloroacetic acids could not. This study demonstrates a new design for multifunctional electrochemical degradation that functions via dechlorination and the ·OH activation mechanism.

Co(PO3)2@CoP Heterojunction in CoPO/GC/NF Nanoarrays Modulate Proton Hydrogen-Promoted Electrocatalytic Hydrodechlorination

Cobalt phosphide has received much attention as an efficient catalyst for electrocatalytic hydrodechlorination (EHDC). However, the active species proton hydrogen (H*) is consumed by the hydrogen evolution reaction (HER). Herein, we report a crystal regulation strategy for cobalt phosphate/graphitic nanocarbon/nickel foam (CoPO/GC/NF) catalysts applied for the EHDC of 2,4-dichlorophenoxyacetic acid (2,4-D). Characterization revealed that during the high-temperature phosphatization process, CoPO/GC/NF catalysts developed Co(PO3)2@CoP heterojunctions, enhancing charge transfer at the electrolyte-catalyst interface and water dissociation. The interaction between Co(PO3)2 and CoP induced the reconstitution of CoP into the Co-OH species, which facilitated the production of H* by accelerating the Volmer step, enhancing EHDC activity. Furthermore, Co(PO3)2 species improve the catalyst tolerance, with CoPO/GC/NF(450) maintaining over 71% yield of phenoxyacetic acid (PA) in continuous testing for up to 80 h under high-salt conditions. This work clarifies the surface transformation process of CoP/GC/NF during hydrodechlorination and demonstrates great potential for chlorophenol wastewater remediation.

Utilizing an Integrated Flow Cathode-Membrane Filtration System for Effective and Continuous Electrochemical Hydrodechlorination

Pd-based electrodes are recognized to facilitate effective electrochemical hydrodechlorination (EHDC) as a result of their superior capacity for atomic hydrogen (H*) generation. However, challenges such as electrode stability, feasibility of treating complex matrices, and high cost associated with electrode synthesis hinder the application of Pd-based electrodes for EHDC. In this work, we investigated the feasibility of degrading 2,4-dichlorophenol (2,4-DCP) by EHDC employing Pd-loaded activated carbon particles, prepared via a simple wet-impregnation method, as a flow cathode (FC) suspension. Compared to other Pd-based EHDC studies, a much lower Pd loading (0.02-0.08 mg cm-2) was used. Because of the excellent mass transfer in the FC system, almost 100% 2,4-DCP was hydrodechlorinated to phenol within 1 h. The FC system also showed excellent performance in treating complex water matrices (including hardness ion-containing wastewater and various other chlorinated organics such as 2,4-dichlorobenzoic acid and trichloroacetic acid) with a relatively low energy consumption (0.26-1.56 kW h m-3 mg-1 of 2,4-DCP compared to 0.32-7.61 kW h m-3 mg-1 of 2,4-DCP reported by other studies). The FC synthesized here was stable over 36 h of continuous operation, indicating its potential suitability for real-world applications. Employing experimental investigations and mathematical modeling, we further show that hydrodechlorination of 2,4-DCP occurs via interaction with H*, with no role of direct electron transfer and/or HO•-mediated processes in the removal of 2,4-DCP.

Enhanced Mineralization of Organic Pollutants through Atomic Hydrogen-Mediated Alternative Transformation Pathways

Electrocatalytic hydrogen atom-hydroxyl radical (H*-·OH) redox system is a promising approach for contaminant removal and mineralization. However, its working mechanism, especially the effect of H*, remains unclear, hindering its practical application. Herein, we constructed an electrochemical reactor equipped with our self-made Pd-loaded Ti/TiO2 nanotube cathode and a commercial boron-doped diamond anode. After fulfilling the electrode characterization and free radical detection, we employed coumarin and 7-azido-4-methylcoumarin as probes to confirm the participation of H* in the transformation of organic compounds. A comprehensive study on the degradation kinetics, reaction, and mineralization mechanisms using benzoic acid (BA) and 4-chlorophenol (4-CP) as model compounds was further conducted. The rate constants and total organic carbon removal of BA and 4-CP in the redox system increased compared with those of the individual oxidation and reduction processes. Theoretical calculations demonstrate that H* opens up alternative pathways for BA and 4-CP ring cleavage, forming quinones as reactive intermediates. Furthermore, H* facilitates the mineralization of the typical intermediates, maleic acid and fumaric acid, through C=C bond addition and H-abstraction from the 1,1-diol structure. The presence of H* provides alternative pathways for pollutant transformation, consequently reducing the treatment duration.

CO2-Promoted Electrocatalytic Reduction of Chlorinated Hydrocarbons

Electrochemical reactions and their catalysis are important for energy and environmental applications, such as carbon neutralization and water purification. However, the synergy in electrocatalysis between CO2 utilization and wastewater treatment has not been explored. In this study, we find that the electrochemical reduction of chlorinated organic compounds such as 1,2-dichloroethane, trichloroethylene, and tetrachloroethylene into ethylene in aqueous media, which is a category of challenging reactions due to the competition of H2 evolution, can be substantially enhanced by simultaneously carrying out the reduction of CO2 on an easily prepared and cost-effective Cu metal catalyst. In the case of 1,2-dichloroethane dechlorination, a 6-fold improvement in Faradaic efficiency and a 19-fold increase in partial current density are demonstrated. Through electrochemical kinetic studies, in situ Raman spectroscopy, and computational simulations, we further find that CO2 reduction reduces hydrogen coverage on the Cu catalyst, which not only exposes more active sites for the dechlorination reaction but also enhances the effective reductive potential on the catalyst surface and reduces the kinetic barrier of the rate-determining step.

Controllable Pyridine N-Oxidation-Nucleophilic Dechlorination Process for Enhanced Dechlorination of Chloropyridines: The Cooperation of HCO4- and HO2. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2024;58:4438-4449. [PMID: 38330552 DOI: 10.1021/acs.est.3c09878] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Dechlorination of chloropyridines can eliminate their detrimental environmental effects. However, traditional dechlorination technology cannot efficiently break the C-Cl bond of chloropyridines, which is restricted by the uncontrollable nonselective species. Hence, we propose the carbonate species-activated hydrogen peroxide (carbonate species/H2O2) process wherein the selective oxidant (peroxymonocarbonate ion, HCO4-) and selective reductant (hydroperoxide anion, HO2-) controllably coexist by manipulation of reaction pH. Taking 2-chloropyridine (Cl-Py) as an example, HCO4- first induces Cl-Py into pyridine N-oxidation intermediates, which then suffer from the nucleophilic dechlorination by HO2-. The obtained dechlorination efficiencies in the carbonate species/H2O2 process (32.5-84.5%) based on the cooperation of HCO4- and HO2- are significantly higher than those in the HO2--mediated sodium hydroxide/hydrogen peroxide process (0-43.8%). Theoretical calculations confirm that pyridine N-oxidation of Cl-Py can effectively lower the energy barrier of the dechlorination process. Moreover, the carbonate species/H2O2 process exhibits superior anti-interference performance and low electric energy consumption. Furthermore, Cl-Py is completely detoxified via the carbonate species/H2O2 process. More importantly, the carbonate species/H2O2 process is applicable for efficient dehalogenation of halogenated pyridines and pyrazines. This work offers a simple and useful strategy to enhance the dehalogenation efficiency of halogenated organics and sheds new insights into the application of the carbonate species/H2O2 process in practical environmental remediation.

Critical Review of Pd-Catalyzed Reduction Process for Treatment of Waterborne Pollutants

Catalyzed reduction processes have been recognized as important and supplementary technologies for water treatment, with the specific aims of resource recovery, enhancement of bio/chemical-treatability of persistent organic pollutants, and safe handling of oxygenate ions. Palladium (Pd) has been widely used as a catalyst/electrocatalyst in these reduction processes. However, due to the limited reserves and high cost of Pd, it is essential to gain a better understanding of the Pd-catalyzed decontamination process to design affordable and sustainable Pd catalysts. This review provides a systematic summary of recent advances in understanding Pd-catalyzed reductive decontamination processes and designing Pd-based nanocatalysts for the reductive treatment of water-borne pollutants, with special focus on the interactions and transformation mechanisms of pollutant molecules on Pd catalysts at the atomic scale. The discussion begins by examining the adsorption of pollutants onto Pd sites from a thermodynamic viewpoint. This is followed by an explanation of the molecular-level reaction mechanism, demonstrating how electron-donors participate in the reductive transformation of pollutants. Next, the influence of the Pd reactive site structure on catalytic performance is explored. Additionally, the process of Pd-catalyzed reduction in facilitating the oxidation of pollutants is briefly discussed. The longevity of Pd catalysts, a crucial factor in determining their practicality, is also examined. Finally, we argue for increased attention to mechanism study, as well as precise construction of Pd sites under batch synthesis conditions, and the use of Pd-based catalysts/electrocatalysts in the treatment of concentrated pollutants to facilitate resource recovery.

Water Flow-Driven Coupling Process of Anodic Oxygen Evolution and Cathodic Oxygen Activation for Water Decontamination and Prevention of Chlorinated Byproducts

Electrochemical advanced oxidation process (EAOP) is a promising technology for decentralized water decontamination but is subject to parasitic anodic oxygen evolution and formation of toxic chlorinated byproducts in the presence of Cl-. To address this issue, we developed a novel electrolytic process by water flow-driven coupling of anodic oxygen evolution reaction (OER) and cathodic molecular oxygen activation (MOA). When water flows from anode to cathode, O2 produced from OER is carried by water through convection, followed by being activated by atomic hydrogen (H*) on Pd cathode to produce •OH. The water flow-driven OER/MOA process enables the anode to be polarized at low potential (1.7 V vs SHE) that is lower than that of conventional EAOP whose •OH is produced from direct water oxidation (>2.3 V vs SHE). At a flow rate of 30 mL min-1, the process could achieve 94.8% removal of 2,4-dichlorophenol (2,4-DCP) and 71.5% removal of chemical oxygen demand (COD) within 45 min at an anode potential of 1.7 V vs SHE and cathode potential of -0.5 V vs SHE. To achieve the comparable 2,4-DCP removal performance, 4.3-fold higher energy consumption was needed for the conventional EAOP with titanium suboxide anode (anode potential of 2.9 V vs SHE), but current efficiency declined by 3.5 folds. Unlike conventional EAOP, chlorate and perchlorate were not detected in the OER/MOA process, because low anode potential <2.0 V vs SHE was thermodynamically unfavorable for the formation of chlorinated byproducts by anodic oxidation, indicated by theoretical calculations and experimental data. This study provides a proof-in-concept demonstration of water flow-driven OER/MOA process, representing a paradigm shift of electrochemical technology for water decontamination and prevention of chlorinated byproducts, making electrochemical water decontamination more efficient, more economic, and more sustainable.

Enhanced Hydrosaturation Selectivity and Electron Transfer for Electrocatalytic Chlorophenols Hydrogenation on Ru Sites

Electrocatalytic hydrogenation is acknowledged as a promising strategy for chlorophenol dechlorination. However, the widely used Pd catalysts exhibit drawbacks, such as high costs and low selectivity for phenol hydrosaturation. Herein, we demonstrate the potential and mechanism of Ru in serving as a Pd substitute using 2,4,6-trichlorophenol (TCP) as a model pollutant. Up to 99.8% TCP removal efficiency and 99% selectivity to cyclohexanol, a value-added compound with an extremely low toxicity, were achieved on the Ru electrode. In contrast, only 66% of TCP was removed on the Pd electrode, with almost no hydrosaturation selectivity. The superiority of Ru over Pd was especially noteworthy in alkaline conditions or the presence of interfering species such as S2-. The theoretical simulation demonstrates that Ru possesses a hydrodechlorination energy barrier of 0.72 eV, which is comparable to that on Pd. Meanwhile, hydrosaturation requires an activation energy of 0.69 eV on Ru, which is much lower than that on Pd (0.92 eV). The main reaction mechanism on Ru is direct electron transfer, which is distinct from that on Pd (indirect pathway via atomic hydrogen, H*). This work thereby provides new insights into designing cost-effective electrocatalysts for halogenated phenol detoxification and resource recovery.

Palladium Single-Atom (In)Stability Under Aqueous Reductive Conditions

Here, we investigate the stability and performance of single-atom Pd on TiO2 for the selective dechlorination of 4-chlorophenol. A challenge inherent to single atoms is their high surface free energy, which results in a tendency for the surface migration and aggregation of metal atoms. This work evaluates various factors affecting the stability of Pd single-atoms, including atomic dispersion, coordination environment, and substrate properties, under reductive aqueous conditions. The transition from single atoms to clusters vastly enhanced dechlorination kinetics without diminishing carbon-chlorine bond selectivity. X-ray absorption spectroscopy analysis using both in situ and ex situ conditions followed the dynamic transformation of single atoms into amorphous clusters, which consist of a unique unsaturated coordination environment and few nanometer diameter. The intricate relationship between stability and performance underscores the vital role of detailed characterization to properly determine the true active species for dehalogenation reactions.

Pulsed Electrolysis of Boron-Doped Carbon Dramatically Improves Impurity Tolerance and Longevity of H2O2 Production

Electrocatalytic water treatment has emerged in the limelight of scientific interest, yet its long-term viability remains largely in the dark. Herein, we present for the first time a comprehensive framework on how to optimize pulsed electrolysis to bolster catalyst impurity tolerance and overall longevity. By examining real wastewater constituents and assessing different catalyst designs, we deconvolute the complexities associated with key pulsing parameters to formulate optimal sequences that maximize operational lifetime. We showcase our approach for cathodic H2O2 electrosynthesis, selected for its widespread importance to wastewater treatment. Our results unveil superior performance for a boron-doped carbon catalyst over state-of-the-art oxidized carbon, with high selectivity (>75%) and near complete recoveries in overpotentials even in the presence of highly detrimental Ni2+ and Zn2+ impurities. We then adapt these fine-tuned settings, obtained under a three-electrode arrangement, for practical two-electrode operation using a novel strategy that conserves the desired electrochemical potentials at the catalytic interface. Even under various impurity concentrations, our pulses substantially improve long-term H2O2 production to 287 h and 35 times that attainable via conventional electrolysis. Our findings underscore the versatility of pulsed electrolysis necessary for developing more practical water treatment technologies.

Enhancing Electrocatalytic Hydrodechlorination through Interfacial Microenvironment Modulation

Electrochemical reduction (ER) is a promising approach to safely remove pollutants. However, sluggish reaction kinetics and significant side reactions considerably limit the applicability of this green process. Herein, we uncovered the previously ignored role of interfacial hydrophilicity in determining the ER performance through electron microscopy observations, contact angle (CA) analysis, and electrochemical measurements. A Pd/C electrocatalyst forms dense nanopores on the electrode surface, rendering it highly hydrophobic and achieving a CA of up to 145°. This imposes a large mass-transfer barrier for the diffusion of water and pollutants into Pd sites. Moreover, the release of H2 is suppressed, which changes the solid-liquid (Pd-polluted water) interface into a solid-gas (H2)-liquid interface. This further slows down mass transfer and the decontamination process. This dilemma can be easily alleviated by adding hydrophilic polymers like polyethylene glycol to increase hydrophilicity and improve mass transfer. By this way, the activity and Faraday efficiency of Pd/C in the electrochemical hydrodehalogenation of 2,4-dichlorophenol could be increased by 4-5 times. Moreover, this interfacial microenvironment modulation strategy is parallel to other approaches, such as Pd structural engineering, and therefore these strategies can be combined to further increase the electrochemical decontamination performance of electrocatalysts.