Electrochemical characterization of SnO2 electrodes doped with Ru and Pt

Antimony-platinum doped tin dioxide electrodes supported on titanium have been prepared by thermal decomposition. The effect of the progressive replacement of Sb with Ru (x = 0.00; 3.25; 6.50; 13.00 at.%) on their electrochemical response in acid medium has been analysed by cyclic voltammetry. The morphology of the coatings was observed by scanning electron microscopy. Ti/SnO₂-Sb-Pt electrodes without Ru presented a cracked-mud structure, typical of oxide electrodes prepared by thermal decomposition. The introduction of Ru in the oxide layer modified the coating morphology. The roughness increased and passed through a maximum with the increase of Ru content. A relation between the surface morphology, the roughness factor, voltammetric charge and the electrochemical activity has been established. The mechanism and electrocatalytic activity towards the oxygen evolution reaction has been studied from Tafel measurements. The progressive introduction of Ru in the electrodes increased their electrocatalytic activity for the oxygen evolution reaction with a change on the mechanism from non-active to active electrodes. The electrocatalytic activity mainly depends on electronic factors.     

Oxygen gas evolution at,and deterioration of,RuO2/ZrO2-coated titanium anodes at elevated temperature in strong base

It was demonstrated that the addition of a second, more inert oxide (ZrO₂) to the active RuO₂ layer on a titanium substrate substantially increased the service life of DSA-type anodes with respect to oxygen gas evolution (i = 0.75 A cm^?2) in 6.0 mol dm^?3 NaOH at 80°C. The electrocatalytic activity of the mixed oxide layer for this reaction remained virtually constant on altering the composition over the range 60–100 mol% RuO₂. The optimum service life (ca. 200 h) was observed with an 80/20 (RuO₂/ZrO₂) mol% oxide mixture. Electron microscope studies showed that such a layer was highly cracked. The increased stability of the mixed oxide-coated system is attributed to better protection of the base metal attack on the latter, leading to shedding to the active layer, being a major route for deterioration of this type of anode.     

On the RuO2TiO2 interlayer of PbO2 electrodeposited Ti anode

The degradation mechanism of electrodeposited β-PbO₂ on the RuO₂TiO₂ loaded Ti substrate was studied. The electric resistance of the PbO₂ anode was increased the Ti/Ru ratio of the interlayer and the current density of electrodeposition, probably due to oxidation of the interlayer at the initial stage of electrodeposition, so that the electric contact between PbO₂ and the interlayer might fail. The β-PbO₂ deposited anodes prepared carefully to avoid destructive oxidation of the interlayer were examined as the oxygen evolution electrode in 1 M H₂SO₄. The Ti substrate became passive, caused by permeation of oxygen through PbO₂ and the interlayer, when electrolysis was conducted for many hours. The service life time depended on the Ti/Ru ratio of the interlayer and the operating current density.     

Electrocatalytic activity of IrO2-RuO2 supported on Sb-doped SnO2 nanoparticles

Electrocatalytic IrO₂-RuO₂ supported on Sb-doped SnO₂ (ATO) nanoparticles is very active towards the oxygen evolution reaction. The IrO₂-RuO₂ material is XRD amorphous and exists as clusters on the surface of the ATO. Systematic changes to the surface chemical composition of the ATO as a function of the IrO₂:RuO₂ ratio suggests an interaction between the IrO₂-RuO₂ and ATO. Cyclic voltammetry indicates that the electrochemically active surface area of IrO₂-RuO₂ clusters is maximised when the composition is 75 mol% IrO₂-25 mol% RuO₂. Decreasing the loading of IrO₂-RuO₂ on ATO reduces the electrochemically active surface area, although there is evidence to support a decrease in the clusters size with decreased loading. Tafel slope analysis shows that if the clusters are too small, the kinetics of the oxygen evolution reaction are reduced. Overall, clusters of IrO₂-RuO₂ on ATO have similar or better performance for the oxygen evolution reaction than many previously reported materials, despite the low quantity of noble metals used in the electrocatalysts. This suggests that these oxides may be of economic advantage if used as PEM water electrolysis anodes.     

Structure and properties of PbO2-CeO2 anodes on stainless steel

The lack of ideal anodes with excellent activity and stability is one of the critical problems in electrochemical oxidation for organic wastewater treatment. It is reported in this paper that the PbO₂-CeO₂ films electrodeposited on stainless steel were used as catalytic electrodes for treating antibiotic wastewater. The PbO₂-CeO₂ films on stainless steel were proved to be high stability, good activity and relatively low cost. Because of these properties, the films are more attractive than any other electrocatalytic materials among conventional dimensionally stable anodes (DSA). Experimental results showed that the PbO₂-CeO₂ electrode has a service life of 1100 h in 3 M H₂SO₄ solution under a current density of 1 A cm⁻² at 35 °C, compared with 300 h for PbO₂ under the same conditions. The X-ray diffraction (XRD) patterns and SEM images indicated that the PbO₂-CeO₂ films on stainless steel have a dense structure and the preferred crystalline orientation on the substrate surface was changed. Color and chemical oxygen demand (COD) of antibiotics wastewater were studied by electrolysis by using these electrodes as anode and stainless steel as cathode. The results indicated that the anodes have excellent activity in antibiotic wastewater treatment. The PbO₂-CeO₂ electrodes have high chemical stability which contributed by the superstable nature of the electrode, dense microstructure, good conductivity and the improvement of bonding with the stainless steel during electrodeposition.     

Effect of CeO2 and graphite powder on the electrochemical performance of Ti/PbO2 anode for zinc electrowinning

In the zinc hydrometallurgy process, the key to reduce the voltage of the corrosion is to reduce the oxygen evolution potential of the anode. In this experiment, the effects of doped CeO₂ and graphite powder (GP) on the electrochemical properties of Ti/PbO₂ were investigated. Ti/PbO₂, Ti/PbO₂-CeO₂, Ti/PbO₂-GP and Ti/PbO₂-CeO₂-GP anode were prepared by direct current (DC) plating. The surface morphology and composition of these different Ti/PbO₂ electrodes before and after polarisation were analysed by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion mechanism was analysed by linear sweep voltammetry (LSV), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The cell voltage, current efficiency, service life and failure mechanism of Ti/PbO₂ anodes were observed and analysed by simulating electrowinning experiments. The results show that Ti/PbO₂-CeO₂-GP anodes is denser than other electrodes. Ti/PbO₂-CeO₂ (12?g/L)-GP (8?g/L) with the lowest anode potential is 1.5390?V. The potential of the lowest oxygen evolution peak of the Ti/PbO₂-CeO₂ (12?g/L)-GP (8?g/L) electrode is 0.824?V. The Ti/PbO₂-CeO₂-GP anode had a minimum cell voltage of 2.85?V and a current efficiency of 95.8%. The Ti/PbO₂-CeO₂-GP has a minimum corrosion rate of ??0.0320?g·A^?1·h^?1 and a longest anode lifetime of up to 127?h. The best electrode for the surface coating is Ti/PbO₂-CeO₂ (12?g/L)-GP (8?g/L).     

Effects of ultrasound on electrochemical oxidation mechanisms of p-substituted phenols at BDD and PbO2 anodes

The effects of low-frequency (40 kHz) ultrasound are investigated with regard to the effectiveness and mechanisms of electrochemical oxidation of p-substituted phenols (p-nitrophenol, p-hydroxybenzaldehyde, phenol, p-cresol, and p-methoxyphenol) at BDD (boron-doped diamond) and PbO₂ anodes. Although ultrasound improved the disappearance rates of p-substituted phenols at both the BDD and PbO₂ anodes, the degree of enhancement varied according to the type of p-substituted phenol and type of anode under consideration. At the BDD anode, the %Increase values were in the range 73-83% for p-substituted phenol disappearance and in the range 60-70% for COD removal. However, at the PbO₂ anode, the corresponding %Increase values were in the range 50-70% for disappearance of p-substituted phenols and only 5-25% for COD removal, much lower values than obtained at the BDD anode. Further investigations on the influence of ultrasound on the electrochemical oxidation mechanisms at BDD and PbO₂ anodes revealed that the different increase extent were due to the specialized electrochemical oxidation mechanisms at these two anodes. The hydroxyl radicals were mainly free at the BDD electrodes with a larger reaction zone, but adsorbed at the PbO₂ electrodes with a smaller reaction zone. Therefore, the enhancement due to ultrasound was greater at the BDD anode than at the PbO₂ anode.     

Electrochemical promotion of CO conversion to CO2 in PEM fuel cell PROX reactor

The possibility of electrochemically promoting the water–gas-shift reaction and the CO oxidation reaction in a PEM fuel cell reactor supplied with a methanol reformate mixture was investigated in PEM fuel cells with Pt or Au state-of-the-art E-TEK anodes, in order to explore the use of PEMFC units as preferential oxidation of CO (PROX) reactors. The electropromotion of CO removal was investigated both with air or H₂ fed to the cathode side and also by O₂ bleeding to the anode during normal PEMFC operation. It was found that the catalytic activity of the anode for CO conversion to CO₂ can be modified significantly by varying the catalyst potential. The magnitude of the electrochemical promotion depends strongly on the anodic electrocatalyst (Pt or Au), on the CO concentration of the fuel mixture, on the operating temperature and on the presence of oxygen. The electropromotion effect and the Faradaic efficiency were found to be much higher in CO-rich anode environments.     

Comparative studies on the electrocatalytic properties of modified PbO2 anodes

A set of modified PbO₂ anodes doped with the oxides of bismuth and cobalt were prepared by means of electrodeposition in nitrate solutions. Of them, Ti/Bi-PbO₂ anode displayed excellent electrocatalytic performance. Cyclic voltammetric experiments were carried out to get a better understanding of the electrocatalytic properties of these anodes. The Ti/Bi-PbO₂ anode had the highest overpotential of 1.75 V (vs. SCE) for oxygen evolution. Both XRD patterns and scanning electronic microscopy (SEM) images demonstrated that the incorporation of Bi could diminish the size of the crystal particles. Oxidants such as hydroxyl radical, hydrogen peroxide were determined, and their amount was proportional to the electrocatalyitc activities of modified PbO₂ anodes. Electrocatalytic oxidation of o-nitrophenol was conducted by using these anodes as anode and stainless steel sheet as cathode. Ti/Bi-PbO₂ anode displayed not only excellent electrocatalytic performance but also low energy consumption. The Ti/Bi-PbO₂ anode is a promising anode for the treatment of organic pollutants.     

A comparative study on IrO2-Ta2O5 coated titanium electrodes prepared with different methods

The electrodes of IrO₂-Ta₂O₅ coated titanium were prepared using conventionally thermal decomposition procedure and polymer sol-gel (Pechini) method, respectively. The microstructure and electrochemical properties of the electrodes were studied with scanning electron microscope (SEM), energy dispersive X-ray (EDX), atomic force microscope (AFM), potentiodynamic polarization, cyclic voltammetry, electrochemical impedance spectroscopy and accelerated life test. As compared with the electrode formed using the traditional method of thermal decomposition, the oxide electrode prepared by Pechini method presents morphology of higher nano-scale roughness and more uniform surface composition with little precipitates. It also has larger electrochemically active surface area, better electrocatalytic activity for oxygen evolution and higher stability.     

Current efficiency studies for graphite and SnO2-based anodes for the electro-deoxidation of metal oxides

Studies were performed investigating the electrochemical reduction of chromium oxide (Cr₂O₃) by electro-deoxidation by utilising either a graphite anode or a tin oxide (SnO₂) based anode. Potentiostatic electrolysis was performed at 3.0 V for both a graphite and for a SnO₂-based anode, and also 2.0 V for a graphite anode. The cathode reduction purity, anode mass change, anode potential relative to a glassy carbon pseudo-reference and current efficiency were measured and compared. The key observations are that substituting a SnO₂-based anode for a graphite anode led to greater current efficiencies for electro-deoxidation. This was attributed to the lack of contamination of the melt by carbon and the lower cathode potential due to the higher anodic potential when using tin oxide based anodes for the same applied voltage. The current efficiency was also found to decrease with both anode materials when higher anode surface areas or lower current densities were used. Again this was attributed to a decrease in anodic potentials and a corresponding increase in the cathodic potential resulting in a greater number of parasitic reactions occurring at the cathode.     

The oxygen evolution reaction on platinum,iridium, ruthenium and their alloys at 80°C in acid solutions

Kinetic parametes were determined for the oxygen evolution reaction on 50–50 atom percent alloys of RuIr, RuPt, and IrPt and compared with results obtained using ruthenium, iridium, platinum, and RuO₂/TiO₂ electrodes. The potentiostatic studies were made on oxide covered electrodes at 80°C in both 1.0 M H₂SO₄ and 1.0 M CF₃SO₃H. Cyclic voltammetric studies showed that while these noble metals and alloys are about equally effective as electrocatalysts for the hydrogen evolution reaction, striking differences in activity are found for the oxygen evolution reaction. The order of electrocatalytic activity towards oxygen evolution in H₂SO₄ is Ru > RuIr alloy ～ RuO₂/TiO₂ ～ Ir > IrPt alloy > RuPt alloy > Pt. The type of acid used had very little effect on the kinetic parameters. The lower electrocatalytic activities when platinum is present is probably due to the formation of a platinum oxide film. The dual barrier model is used to interpret the results for the electrodes containing platinum. The best electrocatalysts for oxygen evolution in acid solutions consist of noble metals which form oxide films (RuO₂, IrO₂) possessing metallic characteristics.     

Anodic dissolution of tantalum and niobium in acetone solvent with halogen additives for electrochemical synthesis of Ta2O5 and Nb2O5 thin films

Tantalum(V) and niobium(V) oxide films, which are typically difficult to prepare by electrochemical methods using aqueous solutions, are easily fabricated in an acetone bath using Ta and Nb anodes as the metal sources and a metal-free solvent containing halide ions as the supporting electrolyte. At the initial stage of electrolysis, anodic oxidation of the metal anode proceeds in the presence of water as an impurity in the acetone solvent. Subsequently, pitting corrosion of the oxide film on the metal anode occurs as a result of the action of halide ions. In this stage, anodic corrosion proceeds only in the presence of Br₂, and not in acetone containing I₂. Finally, Ta or Nb species are deposited directly on the cathode surface via the reactions with cathodically generated hydroxide ions, and the films need to be annealed at high temperature to effect crystallization. In these processes, the metal plate acts as a soluble anode with respect to Br⁻ and as a metal source for electrodeposition. The coating on a stainless steel substrate prepared by the present technique acts as an effective barrier against electrolytic corrosion.     

PTFE-F-PbO2 电极在H2SO4溶液中的析氧行为

F-PbO2 electrode and polytetrafluoroethylene （PTFE） doped F-PbO2 electrode （PTFE-F-PbO2） were prepared on a plexiglas sheet substrate by a series of procedure including chemical and electrochemical depositions. The electrochemical activities of these two electrodes for oxygen evolution （OE） reaction were examined by electrochemical tests. In comparison with F-PbO2, PTFE-F-PbO2 electrode exhibited larger active surface area and higher oxygen vacancy deficiency, which resulted in its higher electrocatalytic activity for OE. In addition, both exchange current density and activation energy of the electrodes for OE were calculated in terms of active surface area. The values of exchange current density and activation energy in 0.5 mol·L^-1 H2SO4 aqueous solution were 1.125×10^ -3 mA·cm^-2 and 18.62 kJ·mol^-1 for PTFE-F-PbO2, and 8.384×10^-4 mA·cm^- 2 and 28.98 kJ·mol^-1 for F-PbO2, respectively. Because these values are calculated on the basis of the active surface areas of the electrodes, the enhanced activity of PTFE-F-PbO2 can be attributed to an increase in oxygen vacancy deficiency of PbO2 due to doping by PTFE. The influence of PTFE adulteration on the activity of PbO2 film electrode for OE was investigated in detail in this study.     

Electrochemical and physical characterisation of lead-based anodes in comparison to Ti–(70%) IrO2/(30%) Ta2O5 dimensionally stable anodes for use in copper electrowinning

The suitability of various dimensionally stable anodes (DSAs^?) was investigated in comparison to the conventional lead alloy anodes in the electrowinning of copper. DSA^? plate and mesh specimens of composition Ti–(70%) IrO₂/(30%) Ta₂O₅ and lead–(6%) antimony were evaluated. The electrochemical behaviour of these anodes was studied by carrying out open circuit potential measurements, galvanostatic chronopotentiometry, cyclic voltammetry and chronoamperometry. Physical characterisation was done using a scanning electron microscope. It was observed that the DSA^? plate anode exhibited the highest corrosion resistance followed by the DSA^? mesh and lead anodes, respectively. The results also showed that during copper electrowinning using lead anodes, dissolution of the anode occurs while for both DSAs^? marginal loss of coating was observed. The lead anode had the highest anode potential followed by the DSA^? plate and mesh anodes, respectively. Overall, it was demonstrated that the DSA^? plate anode is the most suitable anode for copper electrowinning.     

Electrochemical Quartz Microbalance characterization of Ni(OH)2-based thin film electrodes

The use of the Electrochemical Quartz Crystal Microbalance (EQCM) to study the proton intercalation performance of thin film Ni(OH)₂ layers, nowadays widely used as cathode electrode material in rechargeable Ni(OH)₂-based battery systems such as NiMH and NiCd, is reviewed. In addition, the impact of incorporating foreign metals in these layers on the electrochemical performance will be highlighted.Using EQCM much information can be obtained, as both the electrochemical response and accompanying mass changes can be measured simultaneously. EQCM was extensively used to investigate the effect of the conditions on the formation of Ni(OH)₂ thin layers, the α-to-β modification changes and the details of the redox mechanism. The proposed redox mechanisms differ in whether H⁺ or OH⁻ is transferred, the reactants and/or products are hydrated and cations from the solution take part in the reaction.By incorporation of other metals in the structure, the characteristics of thin Ni(OH)₂ layers can be tuned. This affects the oxidation and reduction potential, the reversibility, the stability of the structure and the oxygen evolution side reaction. Co²⁺ and Fe²⁺ were shown to replace Ni-sites in the hydrous oxide lattice, thereby forming very dense structures with higher stability. However, structural changes still occur in most cases. Due to this inhomogeneity, the layers are usually a combination of different structures, depending on the distribution of the incorporated metal(s). Suppression of the oxygen evolution reaction is reported for Co, Pb, Pd, Zn and Mn. The effects of Co and Mn are shown to depend on the incorporated amount. Co shifts the standard redox potential for the oxygen evolution reaction towards more cathodic potentials and decreases the oxygen overpotential significantly. Light-weight rare-earth elements also catalyze the oxygen evolution reaction.     

Parallel oxygen and chlorine evolution on Ru1−xNixO2−y nanostructured electrodes

Nanocrystalline materials with chemical composition corresponding to formula Ru_1−xNi_xO_2−y (0.02 < x < 0.30) were prepared by sol-gel approach. Substitution of Ru by Ni has a minor effect on the structural characteristics extractable from X-ray diffraction patterns. The electrocatalytic behavior of Ru_1−xNi_xO_2−y with respect to parallel oxygen (oxygen evolution reaction, OER) and chlorine (chlorine evolution reaction, CER) evolution in acidic media was studied by voltammetry combined with differential electrochemical mass spectrometry (DEMS). The DEMS data indicate a significant decrease of the over-voltage for chlorine evolution with respect to that of pure RuO₂. The oxygen evolution is slightly hindered. The increasing Ni content affects the electrode material activity and selectivity. The overall material's activity increases with increasing Ni content. The activity of the Ru-Ni-O oxides towards Cl₂ evolution shows a distinguished maximum for material containing 10% of Ni. Further increase of Ni content results in suppression of Cl₂ evolution in favor of O₂ evolution. A model reflecting the cation-cation interactions resulting from Ni-doping is proposed to explain the observed trends in electrocatalytic behavior.     

The anodic characteristics of modified Mn oxide electrode: Ti/RuOx/MnOx

The Ti-supported Mn oxide electrode was modified by introducing a Ru oxide film as an intermediate layer into the Ti/Mn oxide interface, and its anodic characteristics were examined in aqueous solutions of 0.5 M H₂SO₄, 1 M KOH and 5 M NaCl. The intermediate thin film of the Ru oxide served effectively as a good conductor to improve the electric characteristics of the Ti-supported Mn oxide electrode and hence the modified electrode exhibited the excellent anodic characteristics similar to those of the Pt-based Mn oxide. From the kinetic considerations, it was proved that the anodic evolution of oxygen takes place on the surface of Mn oxide. The Mn oxide was found to be virtually active electrocatalyst for electrolytic chlorine evolution as well as electrolytic oxygen evolution. As a result of the evaluation of the catalytic activity, it was considered that the Mn oxide is one of the most active material of all, except for some DSA-type electrodes such as Ru and Ir oxides, for the anodic evolution of oxygen. In conclusion, the presented results suggest that the modified Mn oxide electrode has a promising character for the practical use in water electrolysis.     

Sn and Sb co-doped RuTi oxides supported on TiO2 nanotubes anode for selectivity toward electrocatalytic chlorine evolution

The (Ru_0.3Ti_0.34Sn_0.3Sb_0.06)O₂–TiO₂ nanotubes (TNTs) anode has been prepared via anodization, deposition, and annealing. X-ray diffraction, field-emission scanning electron microscopy, cyclic voltammetry, and linear scanning voltammetry were used to scrutinize the electrodes and the electrochemical activity. The results indicate that highly ordered TNTs with large specific surface area could be implanted with active metal oxides. The catalyst firmly binds with the TNTs and enhances the electrochemical stability of the electrode. It displays high over-potential for oxygen evolution reaction. Accordingly, the constructed (Ru_0.3Ti_0.34Sn_0.3Sb_0.06)O₂–TNTs anode exhibits a greater potential difference (ΔE) between the evolutions of oxygen and chlorine than that exhibited by the traditional dimensionally stable anode, which is beneficial for improving the selectivity toward chlorine evolution reaction. This superior performance is explained in terms of the surface properties and geometric structure of coated catalyst, as well as the electrochemical selectivity ascribed by the addition of tin and antimony species.     

Monolithic-like TiO2 nanotube supported Ru catalyst for activation of CH4 and CO2 to syngas

Highly-ordered TiO₂ nanotube arrays (TiNTA) were prepared by an electrochemical anodization method and used as the carrier material to load 1 wt.% Ru. The Ru/TiNTA catalyst was then applied to the combination reactions of the partial oxidation of methane reaction (POM) with the carbon dioxide reforming with methane reaction (CRM) for syngas production. In comparison with the commercial TiO₂ powder (P25) supported 1 wt.% Ru catalyst, Ru/TiNTA shows higher activity and much better stability. The superior performance of Ru/TiNTA is attributed to the specific monolithic-like structure and confinement effect of TiNTA.