Catalysts for electrocatalytic dechlorination of chlorinated aromatic hydrocarbons: synthetic strategies, applications, and challenges

Abstract

Electrocatalytic hydrodechlorination (EHDC) is a promising technology for degrading chlorinated aromatic hydrocarbons (CAHs), offering high efficiency, minimal secondary pollution, and mild operating conditions. Its effectiveness relies on three critical steps: atomic hydrogen (H∗) generation, C-Cl bond cleavage, and adsorption/desorption of CAHs/products. Developing high-performance electrocatalysts is essential to optimize energy efficiency and cost-effectiveness. It is urgent to summarize research progress on design strategies for catalysts and establish fundamental principles. In this review, we first summarize commonly deployed measurement methods and metrics for assessing catalyst activity and stability in EHDC. Then, a series of strategies for enhancing the production of H∗, facilitating the cleavage of C-Cl bonds, and optimizing the adsorption and desorption kinetics of CAHs and their intermediates/products on the catalyst surface are summarized. These strategies include the loading of catalysts on carbon-based/transition-based support to enhance the dispersion of Pd; constructing heterostructures or forming alloys to modulate the electronic structure of active metal nanocatalysts and optimize its binding affinities with reactants and intermediates; and modulating the microenvironment to modify the interface hydrophilicity/hydrophobicity of catalyst to increase reaction rates or improve stability of catalysts. Additionally, the applications of electrocatalysts for EHDC in recent years, such as Pd-based supported electrocatalysts, Pd-based heterostructure electrocatalysts, Pd-based alloy electrocatalysts, and noble-metal-free electrocatalysts are discussed, as well as the influence of catalyst composition on performance. It is noted that the EHDC efficiency of CAHs is influenced not only by the catalyst but also significantly correlated with the structure of CAHs. Thus, the effects of CAHs structures on EHDC performance are also discussed. Studies demonstrate that weak adsorption between the electrode and CAHs is more conducive to EHDC reactions. The number and position of chlorine functional groups, steric hindrance, and the properties of other functional groups in the substrate molecule can also influence EHDC performance. Finally, the challenges and future prospects of EHDC are highlighted, including improving the catalytic performance of non-noble catalysts, employing advanced in situ and operando characterization techniques, and optimizing DFT calculations to more closely align with real catalytic conditions, all aiming to inspire new investigations and advancements in the field of EHDC of CAHs.