Electrocatalytic hydrodechlorination (EHDC) is a promising environmental technology that can produce highly active atomic hydrogen (H*ad) to detoxify chlorinated hydrocarbon pollutants in water via the hydrogenolysis of C-Cl bonds. However, its efficiency is hampered by hydrogen evolution reaction (HER) in aqueous media which competes with EHDC by consuming H*ad. Here we report that, by controlling the solution pH, we can facilely tune the relative kinetics of EHDC of 2,4-dicholophenol (2,4-DCP) and HER over palladium nanoparticles (Pd NPs) for an optimized EHDC reaction. The batch EHDC experiments with different starting pHs find that both the EHDC efficiency (conversion rate of 2,4-DCP to phenol) and H* utilization efficiency (HUE%, the molar percentage of H*ad used by EHDC) present a volcano-shaped relationship vs. starting solution pH, with the peak EHDC efficiency of 66.4% and HUE% of 35 - 40% achieved at pHs of 2.12 and 3.49, respectively. This volcano relationship originates from the dual effect of pH on both the H*ad production rate and the adsorption behavior of 2,4-DCP over Pd NPs. The overfast generation of H*ad at very low pHs and the poor adsorption of 2,4-DCP on electrode under alkaline conditions will both favor the HER over EHDC. A solution condition of weak acid is desired to optimize the EHDC efficiency and HUE%. This work presents an efficient method to improve the energy selectivity towards EHDC reaction by tuning the competition between EHDC and HER, which should advance EHDC towards environmental remediation applications.

Electrocatalytic hydrodechlorination reaction on Pd-based materials and the related environmental applications

256th National Meeting (2018)

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