A Novel Bath For Preparation Of Lead Dioxide Electrode And Its Nucleation Mechanism

The application of electrochemical oxidation technology in water treatment and the properties of different electrodes are reviewed. The emphasis of this work is the preparation of high performance PbO2electrode. Owing to the shortages of the traditional bath, a novel bath was proposed, and the nucleation mechanism of PbO2was also investigated.Firstly, two PbO2electrodes (noted as PbO2-Ⅰ and PbO2-Ⅱ) electrodes were prepared in traditional bath (Pb(NO3)2, HNO3, some additives, which was noted as bath-Ⅰ) and novel environment-friendly bath (Pb(CH3COO)2, H2NSO3H, some additives, which was noted as bath-Ⅱ), respectively. The results of X-ray diffraction (XRD) showed that the crystalline phases of the two electrodes were both β-PbO2, but the XRD of PbO2-Ⅱ had bigger main diffraction half peak width. The average grain size of PbO2-Ⅱ was calculated to be6.6nm by Scherrer equation, while the average grain size of PbO2-Ⅰ was50.7nm. Scanning electronic microscopy (SEM) revealed that PbO2-Ⅱ had a more compact and uniform surface compared with PbO2-Ⅰ, which well agreed with XRD results. The degradation of p-chlorophenol indicated that the electrochemical oxidative performance of PbO2-Ⅱ was better than that of PbO2-Ⅰ. Electrochemical impedance spectroscopy (EIS) study showed that PbO2-II had higher double layer capacitance and lower charge transfer resistance for oxygen evolution in0.5mol·L-1sulfuric acid than PbO2-Ⅰ. The lifetime test showed that PbO2-Ⅱ had higher corrosion resistance.Secondly, the nucleation mechanism of PbO2on the pretreated Ti subtract was investigated by cyclic voltammograms (CV) and chronoamperometry (CA) in two different baths. CV test showed PbO2had higher nucleation overpotential in bath-Ⅱ, and the nucleation overpotential gradually decreased with the increasing number of CV scanning, finally tending to be relatively stable. Using Scharifker-Hill’s model to analyze CA test results, which showed the nucleation process of PbO2in bath-Ⅱ was more inclined to the three-dimensional instantaneous nucleation mode according to Scharifker-Hills’model than that in bath-Ⅰ. It is more easily to get finer grain in instantaneous nucleation, which is well confirmed the results obtained by X-ray Diffraction (XRD) and scanning electron microscope (SEM) tests.Finally, the influences of anode potential, main salt concentration and different additives on mechanism of PbO2nucleation were studied. The results showed PbO2nucleation gradually clined to instantaneous nucleation as the increasing concentration of main salt. PbO2nucleation was not affected by the anode potential in lower concentration than0.05mol/L, while the mode of PbO2nucleation gradually clined to instantaneous nucleation as the increasing of anode potential in high concentration. Addition of F-and CeO2nano-particle could improve the PbO2deposition rate and led the nucleation cline to instantaneous nucleation. However, addition of PTFE emulsion almost had no effect on PbO2nucleation mechanism. LAS could increase the PbO2nucleation overpotential obviously, and the nucleation mode clined to instantaneous nucleation. SEM showed PbO2grains became more fine and compact.A comparative study on pretreating efficiency of acid chemical wastewater by electrochemical oxidation and ozonation was carried out. The results showed that the lead dioxide electrode prepared from bath-Ⅱ had better performance than ozonation in the pretreatment of acidic chemical wastewater.