Electrochemical degradation of pentachlorophenol on a palladium modified gas-diffusion electrode.

Pd/C catalyst was prepared by a hydrogen reduction method and used for making a Pd/C gas-diffusion electrode. It was fully characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). In the catalyst, Pd particles with an average size of 4.0 nm were highly dispersed in the activated carbon with an amorphous structure; Pd content on the surface of the Pd/C catalyst reached 1.3 at% (atomic concentration). The Pd/C gas-diffusion electrode was then used as the cathode to investigate the electrochemical degradation of pentachlorophenol (PCP) in a diaphragm electrolysis device, feeding firstly with hydrogen gas then with air, compared with the carbon/polytetrafluoroethylene (C/PTFE) gas-diffusion cathode. The Pd/C gas-diffusion cathode can not only reductively dechlorinate PCP by feeding hydrogen gas, but also accelerate the two-electron reduction of O2 to hydrogen peroxide (H2O2) by feeding air. Therefore, both the removal efficiency and the dechlorination degree of PCP exceeded 80% after 100 min, and the average removal efficiency of PCP in terms of total organic carbon (TOC) was more than 75% after 200 min by using Pd/C gas-diffusion cathode, which was better than that of the C/PTFE gas-diffusion cathode. Phenol was identified as the dechorination product using high-performance liquid chromatography (HPLC).