Morphological and Electrochemical Characterization of Ti / MxTiySnzO 2 ( M = Ir or Ru ) Electrodes Prepared by the Polymeric Precursor Method

This paper describes the effect of the composition of the oxide films on the properties of electrodes Ti/MxTiySnzO2 (M = Ir or Ru) prepared by the polymeric precursor method. XRD studies showed that the anodes are formed by solid solutions. The electrodes containing IrO2 exhibit lower activity for the oxygen evolution reaction. The doping of the electrode surface with SnO2 improves the catalytic properties of the anodes. However, it should be held in appropriate compositions, because the change in the atomic ratio of this element shows a marked effect on the stability of the oxides. Electrode Ti/Ir0.2Ti0.3Sn0.5O2 has lower lifetime, i.e. 6 hours. The 20% decrease in the stoichiometric amount of SnO2 increases the time to a value above 70 hours, as observed for Ti/Ir0.3Ti0.4Sn0.3O2. Electrode Ti/Ru0.3Ti0.4Sn0.3O2 shows lifetime of 11 hours; therefore IrO2 is more stable than RuO2 under the conditions investigated. These results suggest that electrode Ti/Ir0.3Ti0.4Sn0.3O2 is promising for different applications, such as water electrolysis, capacitors and organic electrosynthesis.

These electrodes constitute a mixture of oxides frequently prepared by standard thermal decomposition (SD) of metallic precursor salts in aqueous or alcohol solution, supported by metallic titanium [2].
The electro-catalytic properties of metal oxides are associated with electronic and geometric factors [3].The electronic factor is related to the chemical composition of the film, hence the physico-chemical properties of the constituent oxides, affecting the adhesion strength surface/intermediate.The geometric factor is directly related to the morphology of the film.
Research has been conducted to find new materials and procedures to improve the performance of DSA, for example, thermal decompositon of iridium and/or ruthenium precursor salts [4] [5], thermal decomposition of hydroxo-aceto-chloro-based precursors [6], Ti/TiO 2 nanotubes prepared by anodization method [7] spin coating deposition technique [8].The total or partial deactivation of thin films prepared by SD can be observed when they operate under drastic conditions and in a short period of time [4] [9] [10].Electrodes as Ti/RuO 2 and Ti/IrO 2 , prepared by the decomposition of polymeric precursors (Pechini method) [11], have shown better electrochemical activity, i.e. longer life and higher active area than those prepared by the method of chlorides [12]- [14].Moreover, the chemical or mechanical stability of oxide electrodes can be enhanced by incorporating/doping other metal ions into the films [3].
The polymeric precursor method consists in the formation of chelates between metal cations and carboxylic acid and subsequent polymerization by a polyesterification reaction with polyalcohol [15].The central idea is to distribute the cations throughout the polymeric structure.Heat treatment causes the release of organic matter and the formation of crystallites duly ordained [16].This result is particularly interesting when the aims are to obtain materials with high crystallinity and controlled distribution of the constituents in the crystalline lattice.
This study investigates the morphological and electrochemical properties of oxide electrodes Ti/Ir 0.3 Ti 0.4 Sn 0.3 O 2 ; Ti/Ir 0.2 Ti 0.3 Sn 0.5 O 2 and Ti/Ru 0.3 Ti 0.4 Sn 0.3 O 2 prepared by the thermal decomposition of polymeric precursors.[17]), was added to the CA/EG solution.The temperature was then raised up to 85˚C -90˚C and the solution under was kept under rigorous stirring (300 rpm) for 1 -2 hours for esterification and total isopropanol evaporation.

Preparation of Electrodes
The precursor solutions were deposited on both sides of the pretreated metallic titanium (2.5 × 2.5 cm) by brushing, as described in the literature [12].After the application of the coating, the electrodes were dried at 130˚C for 5 minutes and then calcined at 450˚C for 5 minutes.This procedure was repeated until the desired mass (125 mg•cm −2 ) had been achieved.The layers were finally annealed at 450˚C for 1 hour under air flow.

Morphological and Electrochemical Characterizations
This measurement and others are deliberate, using specifications that anticipate your paper as one part of the entire journals, and not as an independent document.Please do not revise any of the current designations.The crystalline structures were physically characterized by X-ray diffraction (XRD) using an XRD-6000 diffractometer (Shimadzu) with a CuKα radiation source (λ = 1.5406Å) operating in the continuous scan mode (4˚ min −1 ) from 10˚ to 90˚.
The surface morphology and microstructure of the deposited oxide films were analyzed through optical microscopy and scanning electron microscopy (SEM).Photomicrographs were obtained by a Zeiss LEO model 440 SEM coupled to an OXFORD operating with electron beam of 15 kV.The average composition was analyzed by PGT PRISM energy dispersive X-ray spectrometer (EDX) coupled to the SEM instrument.

Electrochemical Measurements
Electrochemical experiments were conducted with AUTOLAB model PGSTAT30 instrumentation.Voltammetric curves were recorded at scan rate of 50 mV•s −1 using 0.5 mol•dm −3 of H 2 SO 4 as the supporting electrolyte.A platinum foil served as the auxiliary electrode and the KCl saturated calomel electrode (SCE) was used as the reference.The cell was thermostated at 25˚C.
Impedance spectra were recorded at constant potential between 0.3 and 1.4 V vs Ag/ AgCl.Electrochemical impedance spectroscopy (EIS) measurements were obtained in the 5 mHz -10 kHz frequency interval using the "single sine" method and a sine wave amplitude of 5 mV (p/p).An AUTOLAB software program (FRA analyzer) was used for the analysis of the impedance data.
The stability of the electrodes was assessed based on their lifetime (LT) under galvanostatic conditions at a high current density (400 mA•cm −2 ) in 0.5 mol•dm −3 of H 2 SO 4 .
The electrode lifetime was considered the time necessary for the electrode potential to achieve a value of 8.0 V.

Morphological and Chemical Characterizations
Figure 1 shows the XRD patterns for different compositions of electrodes prepared at 450˚C.In the electrodes containing iridium, characteristic diffraction peaks were Figure 3 shows some representative SEM images of the oxide films.Films containing   IrO 2 (a, b) show uniform and continuous structures with cracks, i.e., mud-cracked-type morphology which are typical of thermally prepared oxide layers [10] [12].Moreover, one observe that due to the increase in the amount of SnO 2 in the electrode composition, cracks become larger (b), however the surface becomes less rough (see Table 1).
However, the SEM image of the films containing RuO Table 2 shows the EDX analyses of the micrographs Figure 3.The EDX analysis of the electrodes indicated a good correlation between experimental and nominal compositions.The control of the composition of the films can be explained by the method used, since this polymer is formed before the calcination and the metal atoms are trapped in the matrix, which hinders its evaporation and consequent loss.All electrodes exhibited a homogenous distribution of particles on the electrode surface.

Electrochemical Characterizations
Figure 4 shows the j/E curve obtained in the cyclic voltammetric experiments.This profile is typical of thermally prepared oxide layer electrodes [19] [20] and characteristic of DSA® electrodes [21].The figure also shows a blurred peak at around 0.5 V associated with the Ru (III)/Ru(IV) redox transition [22] for the Ti/Ru 0.3 Ti 0.4 Sn 0.3 O 2 electrode.The voltammograms of the electrodes containing IrO 2 showed a peak typical of the Ir(III)/Ir (IV) transition in the region between 0.4 and 0.8 V [6].
The oxygen evolution reaction occurs at a more positive potential for the electrode containing the largest amount of SnO 2 .According to Fukunaga et al. [23], the doping of the electrode surface with SnO 2 is an effective strategy to improve performance even in   3).
The lifetime of oxide electrodes is directly correlated with two factors: passivation and dissolution of the coating [21].The first factor is due to the penetration of the electrolyte through the pores or cracks towards the substrate, resulting in the oxidation of the metallic support and forming a non-conductive layer between the substrate and the oxide coating [28]- [30].The second factor involves the loss of electroactive material (erosion or dissolution), resulting in a gradual reduction of the voltammetric charge.
This may occur due to the pores in the layer and the rapid evolution of gas on the surface, inducing the separation of weakly bound parts of the active layer [28] [31] [32].
Morphological changes of the electrode surface after the lifetime test can be observed   through microstructural analysis (Figure 7), which shows worn structures with erosion of the active layer.The EDX analysis revealed a decrease in the quantity of Ir and Ru, confirming the loss of the electroactive material, well as a decrease of Sn (Table 4).
The curves obtained for the lifetime showed a slow increase in the potential followed by an abrupt increase at the end of the experiment for all compositions investigated.This behavior indicates a rise in the electrode structure resistance.Such an increase may have resulted from the loss of Ir or Ru in the top layers of the electrode and/or the formation and growth of a non-conductive oxide film between the metallic substrate and the conductive oxide [9] [31].
EDX analysis after lifetime revealed a considerable increase in the titanium signal.
These results suggest that besides the process of erosion, there is also a process of anodic passivation of the metallic base due to the formation of an insulating film composed primarily of TiO x .

Conclusion
This study has demonstrated the effect of the composition of oxide films on the properties of DSA prepared by the thermal decomposition of polymeric precursors.IrO 2based electrodes are more stable than RuO 2 -based electrode under the conditions investigated and show lower activity for the oxygen evolution reaction, which makes it attractive in the oxidation of organic substances.The introduction of tin oxide in the composition film enhances the catalytic properties of the anodes.However, it should be held in appropriate compositions, because the change in the atomic ratio of this element produces marked effects on the stability of the oxides.The thin films formed are composed of a solid solution among the various oxides constituents of the film.The procedure employed for the preparation of the anodes is a good alternative to SD, minimizing the volatilization of the metal.
(2016) Morphological and Electrochemical Characterization of Ti/M x Ti y Sn z O 2 (M = Ir or Ru) Electrodes Prepared by the Polymeric Precursor Method.Advances in Chemica Engineering and Science, 6, 364-378.
Thin film electrodes of nominal compositions Ir 0.3 Ti 0.4 Sn 0.3 O 2 , Ir 0.2 Ti 0.3 Sn 0.5 O 2 and Ru 0.3 Ti 0.4 Sn 0.3 O 2 were prepared by the thermal decomposition of a polymeric precursor solution (DPP) [11].This method consists in synthesizing resins of metallic precursors by mixing citric acid (CA) in ethylene glycol (EG).The Ru, Ir, Sn, and Ti resins were prepared separately.First, 8 g of citric acid (Merk) were dissolved in 9 mL ethylene glycol (Merk) at 60˚C -65˚C.After the dissolution of the acid, a solution of the precursor metal in isopropanol with 0.1 mol•L −1 concentration (RuCl 3 •xH 2 O, IrCl 3 •xH 2 O, TiCl 2 •6H 2 O all purchased from Aldrich and C 6 H 5 O 7 Sn 2 synthesized from SnCl 2 (Aldrich), as described in
2 (c) indicate a distinct morphology, and in this case, the morphology change severally where the amount of fissures and cracks increase.The oxide surface morphology shows a clear relationship with the coating compositions investigated.

Table 2 .
Atomic ratios (%) of the oxide films with different nominal compositions.

Table 3 .
Lifetime values obtained for the oxide electrodes under galvanostatic conditions at a high current density (400 mA•cm −2 ) in 0.5 mol•dm −3 of H 2 SO 4 .