MnO₂ enhances electrocatalytic hydrodechlorination by Pd/Ni foam electrodes and reduces Pd needs

A Pd/MnO₂/Ni foam electrode with hierarchical structure was synthesized via electrodeposition for efficient electrocatalytic hydrodechlorination. Compared with the ordinary Pd/Ni foam electrode, the introduction of MnO₂ greatly enhanced the catalytic reactivity and reduced the dose of precious metal Pd. Only a quarter of Pd was required for the Pd/MnO₂/Ni foam compared to the Pd/Ni electrode to achieve complete dechlorination of 2,4-dichlorobenzoic acid (2,4-DCBA) within 120 min. Various characterizations suggested that MnO₂ covered the surface of the Ni foam and increased the specific surface area of the electrode, while Pd nanoparticles were subsequently deposited on MnO₂. The atomic H^∗-based indirect dechlorination was the dominant pathway while only approximately 13% of 2,4-DCBA was removed by direct electron transfer. Atomic H^∗ adsorbed on Pd acted as the key active species for the dechlorination of 2,4-DCBA by the Pd/MnO₂/Ni foam electrode in this study. The introduction of MnO₂ would promote the water dissociation and the hydrogen evolution reaction, and provide Pd with more atomic H^∗. Pd/MnO₂/Ni foam exhibited good stability and reusability according to the XPS spectra and consecutive electrocatalytic experiments, which suggested its long-term potential for efficient removal of chlorinated contaminants. This work demonstrated a new strategy to design efficient electrocatalysts with less precious metal.