Electrocatalytic degradation of 4-chlorophenol on F-doped PbO2 anodes

PbO₂ and F-doped PbO₂ (F-PbO₂) anodes have been prepared by a standard thermal decomposition-electrodeposition technique. The electrochemical stability of these anodes has been investigated by the accelerated life tests in sulphuric acid solution. The results show that the service life of the F-PbO₂ anodes is almost three times longer than that of the PbO₂ anodes. Furthermore, in the degradation of 4-chlorophenol (4-CP), the F-PbO₂ anodes give a higher degradation rate than that observed for the PbO₂ anodes. The influence of F⁻ anion doping on the stability and activity of PbO₂ anodes has been discussed. With the F-PbO₂ anodes, the degradation of 4-CP is investigated according to the results of high-performance liquid chromatograph (HPLC), ionic chromatograph (IC) and cyclic voltammetry (CV). In addition, the electron spin resonance (ESR) technique using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trap reagent has been applied to detect free radical intermediates generated during in situ the electrocatalytic degradation of aqueous 4-CP on the F-PbO₂ anodes. ESR measurements give the direct evidence that the active species (OH) are responsible for the decomposition of 4-CP over F-PbO₂ under anodic bias potential, strongly suggesting that the electrocatalytic degradation of most organic compounds on F-PbO₂ anodes proceed via surface intermediates of water oxidation, not via direct oxidation at electrode surface. The formation mechanism of surface intermediates is also discussed.