Preparation of composite interlayer PbO2 anode
Why develop the composite interlayer PbO2 coated titanium anode ?
From the perspective of delaying the passivation degree of coated titanium anode matrix and improving the overpotential of anode oxygen evolution, a titanium based lead dioxide(PbO2) electrode with a composite interlayer containing Ta2O5-TiO2 and SnO2-Sb2O5 was prepared by thermal decomposition method. The morphology, phase structure, element composition and chemical properties of the lead dioxide anode of the composite interlayer and the lead dioxide anode of sno2-sb2o5 interlayer were analyzed by means of scanning electron microscope, X-ray diffraction and energy spectrum. The results show that the service life of the composite interlayer anode is significantly longer than that of sno2-sb2o5 interlayer anode, and it has higher oxygen evolution overpotential and corrosion resistance. The titanium based lead dioxide(PbO2) electrode with the composite interlayer of Ta2O5-TiO2 and SnO2-Sb2O5 is a very promising oxygen evolution anode in acidic environment.
PbO2 coated Titanium anode has good electrocatalytic activity and high oxygen evolution overpotential. It is currently recognized as the most cost-effective special anode for oxygen evolution in the environment of pH ≤ 8. It has broad application prospects in hydrometallurgy, organic sewage treatment, industrial electroplating and other industries.
Although Ti based PbO2 coating anode has good stability in the environment of pH ≤ 8, there are still problems such as coating falling off and anode passivation. In view of the above reasons and the deactivation mechanism of PbO2 coated titanium anode, it is envisaged to add a transition layer Ta2O5-TiO2 between the titanium substrate and the coating PbO2, which can prevent oxygen from penetrating into the titanium substrate, indicating that TiO2 cannot be formed and has good conductivity, which improves the anode life. The research shows that in addition to platinum, platinum titanium and other precious metals, the oxygen resistant interlayer also has Ta2O5-TiO2 and SnO2-Sb2O5. This oxide has a high cost performance ratio and the activity is equivalent to that of platinum group metals. Therefore, from the perspective of delaying the passivation of titanium matrix and improving the overpotential and life of anode oxygen evolution, it is a new idea to prepare the composite interlayer PbO2 electrode of Ta2O5-TiO2 and SnO2-Sb2O5 by thermal decomposition method.
Preparation of lead dioxide electrode in the middle layer of composite layer
Mix the tantalum salt solution and tetrabutyl titanate in a certain proportion, dilute it with n-butanol to a certain concentration, and shake it well more than 1h. Evenly coat the pretreated titanium mesh with a brush, dry it in a 100 ℃ drying oven for 10min, and then put it into a 500-600 ℃ muffle furnace for high temperature oxidation for 10min. Repeat this for 5 times (the last oxidation for 30min) to completely oxidize the coating. Then mix the salt solution of tin and the salt solution of antimony in a certain proportion, dilute it with n-butanol and isopropanol to a certain concentration, shake it well and place it for more than 1h. Evenly coat the pretreated titanium mesh with a brush, dry it in a 100 ℃ drying oven for 10-15min, and then put it into a 500-600 ℃ muffle furnace for high temperature oxidation for 10-15min. Repeat this for 3 times (the last oxidation for 30min) to completely oxidize the coating. That is, the composite intermediate layer is prepared.
Prepare a certain concentration of lead nitrate solution with deionized water, heat the lead nitrate solution to about 60 ℃, add a certain amount of sodium hydroxide solution, fully stir, and electroplate with a certain current to prepare α-PbO2.
Prepare a certain concentration of lead nitrate solution with deionized water, add a certain amount of additives and nitric acid, adjust the pH of the solution, heat it to a certain temperature, stir it fully, and conduct electroplating with a certain current to prepare β-PbO2.
Enhanced lifetime testing and conclusions
Using sk-520 adjustable voltage stabilized power supply, the prepared electrode is used as the anode, the pure titanium plate is used as the cathode, and the electrode spacing is kept at 20mm. tested under conditions.
Figure 1, relation curve between cell voltage and electrolysis time when different
intermediate layers are electrolyzed in the same medium
It can be seen from Figure 1 that under the same electrolysis conditions, the cell voltage of the two electrodes began to decline, but after electrolysis for a period of time, the cell voltage was in a stabilized state, and finally the cell voltage rose sharply until the electrode became inactive. Figure 1 clearly shows that the service life of the titanium based lead dioxide electrode of the composite intermediate layer of Ta2O5-TiO2 and SnO2-Sb2O5 is twice that of the SnO2-Sb2O5 intermediate layer electrode. It shows that the introduction of composite interlayer has significantly improved the electrode life. The reason is: in the electrolysis process, due to the penetration of acid electrolyte into the matrix, and part of the oxygen generated in the electrolysis process is adsorbed on the electrode surface and continuously diffused or migrated to the titanium matrix, it is adsorbed on the surface of titanium substrate through the cracks of the active coating, which reacts with the titanium matrix to generate non-conductive TiO2, making the conductivity of the electrode worse, leading to the passivation of the anode coating and the failure of the anode. However, with the addition of Ta2O5-TiO2 and SnO2-Sb2O5 , the composite intermediate layer is relatively dense and has good diffusivity. It is evenly covered on the surface of titanium substrate, making it difficult for electrolyte to penetrate into the surface of titanium substrate. The diffusion of reactive oxygen species precipitated during electrolysis to titanium substrate is blocked, thereby improving the corrosion resistance of the coating to solution and preventing the formation of TiO2 oxide film. Thus, the service life of the anode is prolonged.
