Electrochemical oxidation of hydroquinone using Eu-doped PbO2 electrodes: Electrode characterization, influencing factors and degradation pathways

The Eu-doped PbO2 electrodes were prepared using co-electrodeposition technique for electrochemical oxidation of hydroquinone. The results of electrochemical measurements, accelerated service lifetime and bulk electrolysis experiments confirmed that Eu-doped PbO2 electrodes possessed higher oxygen evolution overpotential, stability and acetamiprid removal ratio than pure PbO2 electrodes and Eu-PbO2-3 electrode was considered as the ideal anode. The promoted electrocatalytic activity of Eu-PbO2-3 electrode was ascribed to its stronger hydroxyl radical generation ability, more active sites and lower electron transfer resistance. Additionally, the effect of operating parameters, including current density, initial hydroquinone concentration, and pH value, on the electrochemical oxidation of hydroquinone were subjected to systematical investigation. More significantly, the intermediates generated in the degradation process were identified by HPLC-MS and a possible hydroquinone degradation mechanism was proposed accordingly. The degradation pathway can be divided into three stages with the hydroquinone initially attacked by hydroxyl radicals. Finally, all the intermediates were converted to CO2 and H2O. The present work confirmed that Eu-doped electrodes could be potentially applied in removal of refractory organic contaminants from wastewater.