Surface Ligand Environment Boosts the Electrocatalytic Hydrodechlorination Reaction on Palladium Nanoparticles

Interfacial water activation by Pd promotes SO2 electroreduction to H2S on CuPd bimetallic catalysts

The electrocatalytic reduction of sulfur dioxide (SO2) to hydrogen sulfide (H2S) is a promising strategy for efficient sulfur resource utilization. Copper (Cu) catalysts show high selectivity for SO2 reduction, but their limited hydrogenation capacity restricts H2S production. Palladium (Pd), known for its hydrogenation efficiency, was incorporated to overcome this limitation. We synthesized CuPd bimetallic catalysts to enhance hydrogenation efficiency in SO2 electroreduction. Among these, Cu67Pd33 exhibited superior catalytic performance, achieving a H2S partial current density of 201.56 mA·cm-2 (1.08 mmol·cm-2·h-1), a 120 % increase over Cu and 154 % over Pd. In-situ Fourier-transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations revealed that Cu primarily catalyzes the reduction of *SOH to *S, while Pd facilitates the activation and dissociation of interfacial water to provide hydrogen and reduces the energy barrier for the conversion of *S to *H2S. The synergistic catalysis between Cu and Pd ensures efficient transformation of intermediates and facilitates the conversion of SO2 to H2S. This study highlights a novel strategy for enhancing hydrogenation in SO2 electroreduction and provides insights into the synergistic mechanisms of CuPd bimetallic catalysts, emphasizing the critical role of interfacial interactions in catalytic performance.

Electrochemical reduction for chlorinated hydrocarbons contaminated groundwater remediation: Mechanisms, challenges, and perspectives

Electrochemical reduction technology is a promising method for addressing the persistent contamination of groundwater by chlorinated hydrocarbons. Current research shows that electrochemical reductive dechlorination primarily relies on direct electron transfer (DET) and active hydrogen (H⁎) mediated indirect electron transfer processes, thereby achieving efficient dechlorination and detoxification. This paper explores the influence of the molecular charge structure of chlorinated hydrocarbons, including chlorolefin, chloroalkanes, chlorinated aromatic hydrocarbons, and chloro-carboxylic acid, on reductive dechlorination from the perspective of molecular electrostatic potential and local electron affinity. It reveals the affinity characteristics of chlorinated hydrocarbon pollutants, the active dechlorination sites, and the roles of substituent groups. It also comprehensively discusses the current progress on electrochemical reductive dechlorination using metal, carbon-based, and 3D electrode catalysts, with an emphasis on the design and optimization of electrode materials and the impact of catalyst microstructure regulation on dechlorination performance. It delves into the current application status of coupling electrochemical reduction technology with biodegradation and electrochemical circulating well technology for the remediation of groundwater contaminated by chlorinated hydrocarbons. The paper discusses practical application challenges such as electron transfer, electrode corrosion, water chemistry environment, and aquifer heterogeneity. Finally, considerations are presented from the perspectives of environmental impact and sustainable application, along with a summary and analysis of potential future research directions and technological prospects.

Support electron inductive effect of Pd-Mn/Ni foam catalyst for robust electrocatalytic hydrodechlorination

Structural regulation of Pd-based electrocatalytic hydrodechlorination (EHDC) catalyst for constructing high-efficient cathode materials with low noble metal content and high atom utilization is crucial but still challenging. Herein, a support electron inductive effect of Pd-Mn/Ni foam catalyst was proposed via in-situ Mn doping to optimize the electronic structure of the Ni foam (NF), which can inductive regulation of Pd for improving the EHDC performance. The mass activity and current efficiency of Pd-Mn/NF catalyst are 2.91 and 1.34 times superior to that of Pd/NF with 2,4-dichlorophenol as model compound, respectively. The Mn-doped interlayer optimized the electronic structure of Pd by bringing the d-state closer to the Fermi level than Pd on the NF surface, which optimizied the binding of EHDC intermediates. Additionally, the Mn-doped interlayer acted as a promoter for generating H* and accelerating the EHDC reaction. This work presents a simple and effective regulation strategy for constructing high-efficient cathode catalyst for the EHDC of chlorinated organic compounds.

N, N'-bidentate ligand anchored palladium catalysts on MOFs for efficient Heck reaction

Metal-organic frameworks (MOFs), recognized as advanced catalyst carriers due to their adjustable porous, diverse structure and highly exposed active sites, have earned increasing attention for their potential to address the longevity of catalytic centers. In this manuscript, we have devised and synthesized a multifunctional amino-pyridine benzoic acid (APBA) ligand to replace the modulator ligand of the MOF-808 and disperse the palladium catalytic centers atomically on the MOF-APBA. The resulting single-site catalytic system, Pd@MOF-APBA, demonstrates preeminent efficiency and stability, as evidenced by a high average turnover number (95000) and a low metal residue (4.8 ppm) in the Heck reaction. This catalyst has exhibited recyclability for multiple runs without significant loss of reactivity for gram-scale reactions. The catalyst's high activity and efficiency can be attributed to the suitable electrical properties and structures of the N, N'-bidentate ligand for the catalytic palladium ions, postponing their deactivations, including leaching and agglomeration.

Electrocatalytic hydro-dehalogenation of halogenated organic pollutants from wastewater: A critical review

Halogenated organic pollutants are often found in wastewater effluent although it has been usually treated by advanced oxidation processes. Atomic hydrogen (H*)-mediated electrocatalytic dehalogenation, with an outperformed performance for breaking the strong carbon-halogen bonds, is of increasing significance for the efficient removal of halogenated organic compounds from water and wastewater. This review consolidates the recent advances in the electrocatalytic hydro-dehalogenation of toxic halogenated organic pollutants from contaminated water. The effect of the molecular structure (e.g., the number and type of halogens, electron-donating or electron-withdrawing groups) on dehalogenation reactivity is firstly predicted, revealing the nucleophilic properties of the existing halogenated organic pollutants. The specific contribution of the direct electron transfer and atomic hydrogen (H*)-mediated indirect electron transfer to dehalogenation efficiency has been established, aiming to better understand the dehalogenation mechanisms. The analyses of entropy and enthalpy illustrate that low pH has a lower energy barrier than that of high pH, facilitating the transformation from proton to H*. Furthermore, the quantitative relationship between dehalogenation efficiency and energy consumption shows an exponential increase of energy consumption for dehalogenation efficiency increasing from 90% to 100%. Lastly, challenges and perspectives are discussed for efficient dehalogenation and practical applications.

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.

Electrocatalytic hydrodechlorination system with antiscaling and anti-chlorine poisoning features for salt-laden wastewater treatment

The high salinity and coexistence of scaling ions (Ca²⁺, Mg²⁺, HCO₃^-) in wastewater challenge the efficacy and durability of palladium (Pd)-mediated electrocatalytic hydrodechlorination (EHDC) reaction for chlorinated organic pollutant detoxification, due to the accompanying Cl^- poisoning at Pd sites and scaling on electrode. In a concentrated NaCl solution (5.8 g L ^- 1) with Ca²⁺ (80.0 mg L ^- 1), Mg²⁺ (30.0 mg L ^- 1) and HCO₃^- (180.0 mg L ^- 1), the EHDC efficiency of Pd towards 2,4-dichlorophenol decreases significantly from 67.8% to 33.1% in 72.0 h of reaction, and the electrode is covered with layers of fluffy aragonite precipitate. Herein we demonstrate the inclusion of a commercial antiscalant 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) can prevent both scale formation and Cl^- poisoning, leading to an efficient and steady EHDC process. A mechanistic study reveals that the unique dual function of PBTC primarily originates from the bearing phosphonate and carboxyl groups. With the large affinity of these groups (especially the phosphonate group) for scaling cations and Pd, the PBTC can chelate and stabilize the scaling cations in water and replace Cl^- at Pd surface. It can also release protons, and trigger the formation of more electron-deficient Pd^δ+ species via PBTC-Pd binding, leading to an enhanced EHDC. This work provides effective solutions to the scaling/poisoning issues that commonly encountered in real wastewater and paves a solid road for EHDC application in pollution abatement.

In situ formed N-containing copper nanoparticles: a high-performance catalyst toward carbon monoxide electroreduction to multicarbon products with high faradaic efficiency and current density

Developing efficient catalysts for electrochemical carbon monoxide reduction (ECOR) with high faradaic efficiency (FE) and current density is highly desirable. In this work, we demonstrate that the N-containing Cu nanoparticles formed in situ by the reconstruction of cuprous 7,7,8,8-tetracyanoquinodimethane possess high-performance ECOR ability. Impressively, the N-containing Cu nanoparticle catalyst presented the highest FE of 81.31% towards multicarbon products with a high commercial-grade partial current density of 162.62 mA cm^-2, which is among the best of the reported Cu-based ECOR catalysts at -0.69 V versus the reversible hydrogen electrode. The retained ligand on the formed catalyst via the convenient in situ formation is crucial for the selectivity of multicarbon products. This work will arouse enthusiasm for the utilization of reconstruction features for designing ligand-containing catalysts with enhanced artificial carbon fixation ability.