Electrocatalysis enhancement of α, β-PbO2 nanocrystals induced via rare earth Er(III) doping strategy: Principle, degradation application and electrocatalytic mechanism

Novel Ti/Sb2O3-SnO2/Er-PbO2 anodes were fabricated based on doping Er ions into the PbO2 crystal and enhanced electrocatalytic degradation efficiency for organic pollutants was achieved successfully. The doping principle, possible degradation pathway of methylene blue and electrocatalytic mechanism have been discussed in depth. Based on the comprehensive analysis of crystal parameters by X-ray diffraction (XRD) results and typical formulas, the doping principle was confirmed to be the partial substitution of Pb ions by Er ions in PbO2 nanocrystal and might form point defects. Additionally, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) investigation indicated that the Ti/Sb2O3-SnO2/Er-PbO2 anodes possessed higher oxygen overpotential and better conductivity than undoped electrodes. The optimum conditions for the degradation of methylene blue were obtained via studying the effects of different parameters, such as electrolyte concentration (0.01-0.4 M Na2SO4), current density (20-60 mA cm(-2)), initial methylene blue concentration (10-70 mg L-1) and initial pH (3-11). At the optimum conditions, the total organic carbon (TOC), the decolorization rate constant (k(dec)) and the energy consumption (EC) reached up to 65.34%, 0.036 min(-1) and 0.08 (kWh(gTOC))(-1), respectively. Moreover, the electrocatalytic degradation mechanism of the Ti/Sb2O3-SnO2/Er-PbO2 anodes to methylene blue was proposed to be that, the presence of point defects induced an increase of electron transport tunnels, and promoted the production of more hydroxyl radicals (center dot OH) and SO4 center dot-. The possible electrocatalytic mineralization pathway of methylene blue at Ti/Sb2O3-SnO2/Er-PbO2 anodes was also speculated by UV-visible absorption spectroscopy, gas chromatography combined with mass spectrometry (GC-MS) and liquid chromatography combined with mass spectrometer (LC-MS). This work will provide significant references for exploring the mechanism between doped electrodes materials and electrocatalytic degradation performance. (C) 2019 Elsevier Ltd. All rights reserved.