Defect Sites in Ultrathin Pd Nanowires Facilitate the Highly Efficient Electrochemical Hydrodechlorination of Pollutants by H*_ads

Abstract

Adsorbed atomic H (H*) facilitates indirect pathways playing a major role in the electrochemical removal of various priority pollutants. It is crucial to identify the atomic sites responsible for the provision of H*. Herein, through a systematic study of the distribution of H* on Pd nanocatalysts with different sizes and, more importantly, deliberately controlled relative abundance of surface defects, we uncovered the central role of defects in the provision of H*. Specifically, the H* generated on Pd in an electrochemical process increased markedly upon introducing defect sites by changing the morphology to ultrathin polycrystalline Pd nanowires (NWs), while dramatically reducing upon decreasing the number of surface defects through an annealing treatment. Benefiting from a proportion of H* up to 40% of the total H* species, the Pd NWs showed an electrochemical active surface area normalized rate constant of 13.8 ± 0.8 h m, which is 8-9 times higher than its Pd/C counterparts. The pivotal role of defect sites for the generation of H* was further verified by blocking such sites with Rh and Pt atoms, while theoretical calculation also confirms that the adsorption energy of H* on these sites is much higher than that on the Pd{111} facet.

Recent advances in electrocatalysts for halogenated organic pollutant degradation

“…In this regard, Pd distinguishes itself not only for its high efficiency in taking up protons to generate H* but also due to its property to retain the H* by adsorption onto the Pd surface (H* ads ) and absorption to the Pd atoms via the formation of Pd hydride (H* abs ). 220 Therefore, Pd can maintain a high surface hydrogen concentration for the ECH process. In most of the cases, it is difficult for other materials (e.g., Pt, Rh) to retain the generated H* ads , since the H* ads are easily transform to molecular hydrogen through the Heyrovsky step or the Tafel step.…”

“…Recently, several effective methods have been applied to further enhance the selectivity of Pd. 190,220 For example, Liu and co-workers 220 found that the defective sits in Pd nanowires could enhance the stability of the generated H* ads and suppress the HER process. Due to the magnificent H* ads generation/provision capacity, the defect-rich Pd nanowires exhibited a higher 2,4dichlorophenol removal efficiency with a six-times-lower Pd loading than the unmodified Pd materials.…”

“…Additionally, the theoretical study based on density functional theory can provide critical information to understand the interaction between catalysts/radicals and pollutants, thus leading to a better understanding of the degradation/mineralization process. 220,256,257 Taking advantages of other useful processes for HOPs degradation, coupling electrocatalysis with those sophisticated methods will significantly upgrade the degradation performance. On one side, to achieve better degradation efficiencies, integrating those verified effective techniques such as membrane techniques, biological methods, Fenton processes, and photocatalysis with electrocatalysis is a promising solution.…”

Elucidating the dechlorination mechanism of hexachloroethane by Pd-doped zerovalent iron microparticles in dissolved lactic acid polymers using chromatography and indirect monitoring of iron corrosion

“…The formation of atomic hydrogen H * on Pd is of crucial importance as adsorbed H * (H * ads ) is the only active hydrogen species in catalytic hydrodechlorination reactions (Jiang et al 2017;He et al 2018;Liu et al 2018).…”

In Situ Chemical Reduction of Chlorinated Organic Compounds

“…Among the different hydrogen species, i.e. H * abs , H * ads and H 2 bubbles, H * ads is the only active hydrogen species in the catalytic hydrodechlorination process (Jiang et al 2017;He et al 2018b), and the presence of defects on Pd surface facilitates the efficient hydrodechlorination by H * ads (Liu et al 2018). Another beneficial effect of this metal is the production of a smaller number of reaction intermediates, especially low chlorinated compounds such as DCE isomers and vinyl chloride (Zhang et al 1998;Lowry and Reinhard 1999).…”