Electrodeposition of PbO2 on Reticulated Vitreous Carbon for Organic Electrooxidation

The problems caused by the growing of the environmental contamination by organics have been calling the attention of researches, authorities, and population in general since their effects have been more present in our lives. Environmental contamination can be avoided by using, in most cases, biological treatments; however, some classes of compounds are refractory to this kind of treatment and require different technologies to oxidize the organic compound.

In this context, the electrochemical technology emerged as an alternative environmentally, technically, and economically viable. Advantages of electrochemical technology are elimination of transport and storage of hazardous chemicals, reduction of the workmanship, and ease to automatization. Despite these advantages, for the effective use of the electrochemical technology for effluent treatment some drawbacks must be overcome, mainly mass transfer limitations resulting of the low concentrations in industrial effluents, which affect the current efficiency and the energy consumption.  As an attempt to improve mass transfer, in this work we address the electrochemical oxidation using three-dimensional electrodes of reticulated vitreous carbon (RVC) covered by PbO₂film as the electroactive material.

The RVC/PbO₂ electrode was prepared in a flow electrochemical reactor. The PbO₂ film was electrodeposited on RVC applying different charges by varying the current density and electrolysis time. The porosities (in pores per inch) of the RVC substrates were 45, 60, and 80 ppi. The electrode was characterized by electrochemical techniques and scanning electronic microscopy. The decolorization reaction of the reactive blue 19 dye was used to evaluate the electrocatalytic power of the RVC/PbO₂and compared to the flat plate electrode.

The results for the 45 ppi RVC showed that the PbO₂electrodeposition was not uniform within RVC due to non-uniform current penetration (Fig. 1 and 2). The best electrodeposit morphology and uniformity was obtained applying low current densities for longer electrolysis time (Fig 1c).  Contrary, fast decolorization rate was obtained using the films deposited applying high current density (Fig. 2).

A comparison between the flat plate and RVC/PbO₂electrodes in Fig. 3 shows that the three-dimensional electrode was very effect to remove color.

In order to increase the electrode specific surface area, PbO₂ films were electrodeposited on RVC with 60 ppi and 80 ppi. After current density optimization, the PbO₂ film was successfully deposited on the 60 ppi RVC.  On the other hand, an optimum current density cannot be found in order to obtain a uniform deposit on the 80 ppi RVC.  Moreover, the low porosity of this electrode and the high hydrophobic nature of RVC led to low surface wettability, thus contributing for the uneven PbO₂ film.