Effect of Ru Dopant Amount on the Electrocatalytic Capability of Ti/SnO2-Sb-Gd-Ru Electrodes in the Phenol Oxidation

SnO₂ electrodes doped with Sb have been used in the process of anodic oxidation of contaminants organic due to its electrochemical properties, high performance and its low cost [1]. Recent studies have found that by introducing elements of rare earths, especially Gd in Ti/SnO₂-Sb electrodes, favors a be tter performance in the catalytic activity for the electrooxidation of phenol [2], however, the main problem presented by this type of electrode is its short life time which limits its applications to industrial wastewater treatment. Therefore, increase the active life time of these anodes has a significant importance to develop treatment technologies of organic contaminants in wastewater. Different investigations have been directed to extend the useful life of SnO₂-Sb anodes incorporating dopants metallic, as platinum, ruthenium [3] and Iridium  or by the introduction of a interlayer of IrO₂, RuO₂ [4] between the surface of Ti and the SnO₂-Sb film. The results reported indicate that the life time is increased, although decreases the electrocatalytic activity for pollutant elimination due to that reduces the potential of the oxygen evolution reaction (OER). This paper reports the study of influence of the Ru content on the electrocatalytic capability of Ti/SnO₂-Sb(5%)-Gd(1%) electrodes in the electrooxidation of phenol.

The electrodes were synthesized using the Pechini method [5] and calcined at 600° C. The relationship molar acid ethylene glycol/citric/metals was 3/14/1, respectively. The molar relations of Sn/Sb(5%) and Sn/Gd(1%) were constants and Ru amount was variable: Sn/Ru(0, 0.25, 0.5, 0.75%). The obtained electrodes were characterized by X-ray, microscopy electron scanning (SEM), photoelectron spectroscopy (XPS). The electrochemical characterization of electrodes was carried out by cyclic voltammetry, determination of Tafel slope with respect to the oxygen evolution reaction, the roughness factor and accelerated life tests. The electrocatalytic activity of electrodes was evaluated with respect to the electrooxidation of a phenol solution (100 ppm) to constant current (60 mA). The phenol solution was analyzed during the electrolysis by UV-Vis spectroscopy, liquid chromatography high efficiency (HPLC) and total organic carbon (TOC).

The results indicate that the incorporation of Ru in the system Ti/SnO₂-Sb-Gd, induces changes in crystallinity and morphology of the material, also modifies the antimony content and the oxygen content in the SnO₂ network on the surface of the film. The percentages of Sb⁺⁵ were much higher on the surface for Sn/Ru(0.25%) in comparison to others electrode materials. The presence of Ru slightly modifies the potential onset of the oxygen evolution reaction (OER). Therefore, with regard to the system Ti/SnO₂-Sb(5%)-Gd(1%), the addition of small amounts of Ru does not produce a substantial effect on variation in phenol degradation and TOC removal as shown in Fig. 1, in addition, the presence of Ru increases the life time of the electrodes.

 References

1. Yuan Liu, Huiling Liu, Jun Ma and Junjing Li. J. of Hazardous Materials. 213– 214 (2012), 222– 229.
2. Yu-Hong Cui, Yu-Jie Feng, Zheng-Qian Liua, Electrochimica Acta. 54 (2009), 4903-4909.
3. R. Berenguer, C. Quijada, E. Morallon. Electrochimica Acta. 54 (2009), 5230–5238
4. Christos Comninellis and G. Chen (eds.). Electrochemistry for the Environment, chapter 2. 2010, Springer.
5. M.P. Pechini, US Patent 3330697, 1967.