Electrocatalytic Hydrodenation-Reduction Dechlorination Of Palladium-based Nanomaterials And Its Activity Optimization Strategy

In recent years,water pollution by Chlorophenols has attracted much increased attention because of their high toxicity,persistent,and more important,strong resistance to biodegradation.Many countries including China have thus listed the chlorinated phenols as priority pollutants.To alleviate the pollution risk,much efforts have been devoted to developing the chlorophenol-related pollutant treatment technologies,of which the electrocatalytic hydrodechlorination technology?EHDC?is receiving ever-increased attention due to its advantages of high efficiency,no secondary pollution,and mild conditions.The preparation of highly efficient and durable catalyst towards the EHDC reaction is the core part for the development of this technology,and till now,the noble metal palladium is the most favorable one due to its high efficiency in H^*generation and retainment via both H^*adsorption on the Pd surface and H^*absorption into the Pd crystal lattice forming Pd hydride?In this paper,we succesfully synthesized monodisperse Pd nanoparticles?Pd NPs?which are then used as a model catalyst to explore the EHDC mechanism of 2,4-dichlorophenol?2,4-DCP?.Furthermore,a ternary Pd/Co/nickel foam electrode was prepared,which is highly efficient and durable in EHDC of 2,4-DCP.By using X-ray diffraction?XRD?,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,cyclic voltammetry?CV?and linear sweep voltammetry?LSV?techniques,the particle size,surface element distribution and content,and evolution of hydrogen species over the prepared C-Pd NP catalysts were characterized.It was demonstrated that the deposition of palladium nanoparticles on carbon black can prevent the aggregation of Pd NP without changing its phase.The peaks appearing in the potential range of-0.80^-0.60 V,-0.20 and-0.10 V and-0.10 to-0.00 V?vs Ag/AgCl?originate from the oxidation of the molecular hydrogen?H₂?,atomic absorption of hydrogen(H^*_abs)and the atomic adsorption of hydrogen(H^*_ads),respectively.The key active hydrogen species in the EHDC reaction was identified to be the H^*_ads.Through the preparation of C-Pd nanoparticles/carbon paper electrodes,the effects of three H^*on the EHDC activity were explored.Using inductively coupled plasma emission spectroscopy?ICP?analysis,the Pd loading in the electrode was 4.56 mg.Our results show that H^*_ads,H^*_abs,and H₂ all emerge at-0.65 V?vs Ag/AgCl?and have increased amounts at more negative potentials,except for H^*_adsds that exhibits a reversed trend with the potential varying from-0.85 to-0.95 V?vs Ag/AgCl?.By correlating the evolution of each hydrogen species with 2,4-DCP EHDC kinetics and efficiency,we find that H^*_adsds is the active species,H^*_absbs is inert,while H₂ bubbles are detrimental to the EHDC reaction.Accordingly,for an efficient EHDC reaction,a moderate potential is desired to yield sufficient H^*_adsds and limit H₂ negative effect.The main reaction pathway for the removal of 2,4-DCP by EHDC is 2,4-DCP?o-CP?P.To further improve the EHDC efficiency,a ternary Pd/Co/nickel foam electrode were prepared.X-ray photoelectron spectroscopy?XPS?,energy dispersive X-ray spectrometer?EDX?,SEM,and XRD were used to analyze the phase and morphology of the prepared electrode.The specific surface area of the electrode was observed to be large.The ICP analysis showed that the Pd loading was 4.89 mg.After optimized preparation conditions and reaction conditions,the EHDC efficiency of Pd/Co/nickel foam electrode can maintain at a high level above 80%in the electrolysis potential of-0.7 V^-1.0 V?vs Ag/AgCl?,and reach the peak of 95.2%at-0.85 V?vs Ag/AgCl?after300-min reaction.Our work presents a systematic investigation on the reaction mechanism of EHDC on Pd catalysts,which should advance the application of EHDC technology in practical environmental remediation.