Characterization of the Mixed Oxide Layer Structure of the Ti/SnO₂-Sb₂O₅Anode by Photoelectron Spectroscopy and Impedance Spectroscopy

Abstract

The in-depth chemistry of a Ti/SnO 2 -Sb 2 O 5 anode was investigated by X-ray photoelectron spectroscopy combined with ion etching. The coating was found to be composed of multiple layers of tin and titanium oxides and composition gradients at both the oxide-air and oxide-metal interfaces. The existence of such an extensive titanium oxide layer may be related to the fabrication of the Ti/SnO 2 -Sb 2 O 5 anode and subsequent inter-diffusion of species. Also, the surface tin oxide layer was found to be non-stoichiometric, which, in relation to the extensive titanium oxide structure, could be explained by a migration of oxygen toward the Ti substrate. Electrochemical tests showed that the film was unstable and continued to grow under anodic polarization. Impedance spectroscopy displayed a continuum in the dielectric relaxation time constants with depth. This variation in relaxation time constants was proposed to be caused by the continuous variation of the composition in the film. Anodes made of titanium-supported metal oxides are of industrial importance. Since the inception of the well-known Dimensionally Stable Anode (DSA), 1 many oxides, single or mixed, have been developed. These include RuO 2 , IrO 2 , PbO 2 and SnO 2 that are widely used in areas such as chlorine production, water electrolysis, ozone production, and electro-oxidation of organics in wastewater treatment. [1][2][3][4][5] For wastewater treatment, an electrode material having high efficiency and selectivity toward oxidation of organic compounds is desired.One candidate electrode material is the antimony doped tin oxide on Ti. This electrode is generally written as Ti/SnO 2 -Sb 2 O 5 . The coating material is composed of SnO 2 with a tetragonal structure.6 By doping the SnO 2 with Sb, the conductivity of the SnO 2 film can be greatly enhanced. Compared to other metal oxides, Ti/SnO 2 -Sb 2 O 5 is low in cost, low in toxicity but efficient in the oxidation of organic compounds. Therefore, this electrode material was considered a suitable candidate for wastewater treatment. However, this electrode also suffers the disadvantage of deactivation, and the issue of deactivation has been addressed by several authors.7-9 A primary reason for the deactivation of this anode is the formation of a passive layer underneath the coating. The passive layer was thought to be a TiO 2 layer that was formed from interaction with aqueous electrolytes. The deactivation was found to be particularly severe in the anodes with Ti/SnO 2 -Sb 2 O 5 .9 Since TiO 2 has very high resistivity (10 10 cm), a very high electric field develops under constant current operation. The high electric field then promotes the solid state drift of the ions in the layer. In an anode such as Ti/SnO 2 -Sb 2 O 5 , the oxide anions are driven inwards toward the Ti substrate and titanium ions are driven toward the solution side. Such drift would then result in further growth of the oxide layer.Titanium is known to form a passive layer almost instantly when exposed to air or an aerated electrolyte...

Using Instability of a Non-stoichiometric Mixed Oxide Oxygen Evolution Catalyst As a Tool to Improve Its Electrocatalytic Performance

“…Independent on the electrochemical pretreatment, the Sn 3d peak is centered at ca. 486.9 eV, mainly corresponding to the oxidation state Sn IV [30,31]. However, taking into account the similar binding energies for SnO and SnO 2 , the presence of SnO on the surface of the as-prepared electrode cannot be excluded [30].…”

Fast Semiconductor–Metal Bidirectional Transition by Flame Chemical Vapor Deposition

“…In short, only the equilibrium of the FCVD reaction proceeding for 15 s tended toward full reduction, resulting in the presence of Sn alone (Figures S2a,b and S3a–c). 44,45 Thereafter, the oxidation progresses for process times of 30 and 45 s (Figures S2c,d and S3d–i), and reduction proceeds again at a process time of 60 s, indicating the formation of SnO 2 (Figures S2e and S3j–l).…”

The Galvanic Effect of Titanium and Amalgam in the Oral Environment

“…As the sputtering of the surface continued, the presence of the Ti 2+ peaks became apparent at 455.3 eV (Ti 2+ 2p 3/2 ) and 460.8 (Ti 2+ 2p 1/2 ), as shouldering occurred in the primary metallic peaks [ 44 ]. A third peak was identified at ~461.8 eV, which has been observed in samples with intermixed and poorly defined Ti 2+ and Ti 3+ ; this third peak is likely a non-stoichiometric titanium oxide, and this has been labelled as Ti x+ [ 45 ].…”

“…While the Ti presented a depth-dependent phase evolution, the Sn also presented significant changes with depth ( Figure 6 a). At the surface ( Figure 6 b), the Sn 3d exhibited spin-orbit doublet peaks at 486.1 eV(Sn 4+ 3d 5/2 ) and 494.6 eV (Sn 4+ 3d 3/2 ), with a peak separation of 8.5 eV [ 45 , 46 , 47 ]. As the sputtering progressed, the mixed tin-titanium oxide layer was revealed and the presence of Sn 2+ became strongly apparent ( Figure 6 c), with spin doublet peaks at 492.8 eV (Sn 2+ 3d 3/2 ) and 484.4 eV (Sn 2+ 3d 5/2 ) and a peak separation of 8.4 eV.…”

“…In Figure 8 , the O1s spectra for the sample with amalgam again presented with several unique characteristics as compared to the sample without amalgam. The first characteristic in Figure 8 a is that the surface appears to be heavily terminated with -OH groups, with only a weak presence of lattice site oxygen associated with Sn at 530.1 eV [ 45 , 46 ]. There was no observed peak for the lattice site oxygen associated with Ti.…”