Anodization Of Ti And Ti Alloys Under High Temperature And Low Field Conditions And Supercapacitor Performances Of Their Anodic Oxide Films

Titanium dioxide（TiO₂）nanomaterials have a large specific surface area and stable structure.They are an excellent electrode material for supercapacitors.As a convenient method for preparing TiO₂,anodizing has attracted wide attention.At present,the anodic oxidation of titanium is mainly focused on the preparation of nanotubes under the condition of room temperature and high electric field,but there are very few studies on the anodic oxidation of titanium at high temperature.In addition,anodic oxidation of titanium alloys is rarely studied.Therefore,this article mainly explores the high temperature anodic oxidation of titanium and titanium alloys,and studies the structure of the oxide film and the performance of supercapacitors.Firstly,the titanium oxide film is prepared by anodizing in a glycerin electrolyte of dipotassium hydrogen phosphate（K₂HPO₄）at 180℃.The microscopic morphology,crystal structure and electrochemical properties of the oxide film were studied.Among them,anodized at a lower current density of 5 mA cm^-2 for 30 min,a black mesoporous sponge-type titanium oxide film containing oxygen vacancies was obtained.Titanium oxide crystallizes during anodization and is anatase crystal.Although the crystallinity is low,it is different from the conventional anodized titanium oxide,and the supercapacitor electrode is directly obtained without annealing treatment.The areal capacitance of the black titanium oxide film reaches 11.2 mF cm^-2 at a scanning speed of 100 mV s^-1.After 5000 cycles of continuous charging and discharging,the capacitance retention rate still reaches more than 95%.At a higher current density of 10 mA cm^-2,an ultra-thin dense amorphous titanium oxide film with almost no electrochemical activity is prepared.Combined with the experimental results,the formation mechanism of high temperature and low field anodic oxide film is proposed.Then,the current density and temperature range of high-temperature low-field anodization were explored,and the best anodization conditions were determined.Among them,When the anodic oxidation current density is lower than 7 mA cm^-2 and the temperature is higher than160℃,the titanium oxide films prepared are oxygen vacancy defect type.The crystallinity of the oxide film decreases with the increase of current density,and increases with the increase of temperature.The higher crystallinity is not conducive to the formation of oxygen vacancies,and the capacitance performance is poor.The best anodizing current density and temperature are 3 mA cm^-2 and 170℃,respectively.Under these conditions,anodizing for 1 h,the areal capacitance of the prepared TiO₂film reaches 15.1 mF cm^-2 at 100 mV s^-1 scanning speed.Secondly,the structure and electrochemical properties of high temperature and low field anodic oxide films of different metallurgical titanium alloys（αsingle phase:TA5,TA7;α+βtwo phases:TC1 and TC4）are explored.The doping of titanium oxide with other metal elements in the titanium alloy was studied.Studies have shown that other metal elements in the two-phase titanium alloy can be incorporated into the TiO₂ lattice during the anodization process,which greatly improves the electrochemical performance of the oxide film.After anodizing at 170℃and 3 mA cm^-2 for 1 h,the areal capacitance of the TC4 oxide film reaches 22.5 mF cm^-2 at a sweep speed of 100 mV s^-1.However,other metal elements in the single-phase titanium alloy are transformed into corresponding oxides and exist in the oxide film,and are not incorporated into the TiO₂ lattice.Different metallographic titanium alloy oxide films have excellent electrochemical performance in alkali and salt solutions,and the capacitance retention rate can reach more than 84%after 10,000 cycles of continuous circulation.Finally,the influence of strong acid corrosion on the structure and electrochemical performance of titanium alloy oxide film is explored.It is found that the titanium alloy oxide film has low crystallinity and is easily corroded by strong acid solutions.The electrochemical activity of the oxide film decreases as the corrosion time increases.Titanium alloy oxide film is not suitable for acidic electrolyte.