THE ANODIC POLARIZATION OF THE SN02/Ti ELECTRODE IN THE KOH SOLUTION N.T C a m H a ,T X u a n S e n , V, N g o c B a n Department of Chemistry, Hanoi National University, 19 Le Thanh Tong, Hanoi, Vietnam ABSTRACT Sn02 Thin films on titanium metal subotrates have been produced by spray pyrolysis method This type film of has good stability for anodic dissolving in medium contained high concentration of CI- ions and good possibility of electron exchange Sn02/Ti electrodes have been used in the electrochemical oxidation of phenol in alkaline medium contained CI- ions with high efficiency Therefore, it has made them the possibility of new application in the wastewater treatment by electrochemical method INTRODUCTION In electrochemical process, two types of anode are used usually: dissolving and inert one We expect to prepare anodes, which are inert, stable and durable in some conditions of process such as the change of temperature, the corrosion of medium Nowadays, there is the trend to make the coating with a thin film of oxide metal on the surface of inert material that becomes more durable and has higher catalyst activation Titanium is a metal, which shows the good anticorrosion and its passive oxide film on the surface has the semiconductive nature and can ionic conductivity So it is possible to cover a thin film of oxide metal on the surface of titanium to increase conduc- 82 tivity and improve the catalyst activation Meanwhile thin film of Sn02 has been known as inert electrode in several mediums [1.4] Moreover, due to its high overpotential in liberation of oxygen and chlorine, Sn02 electrode is used as anode in synthesis of organic substances, in treatment of wastewater In this paper, it is reported the preparation of thin film Sn02 on the surface of titanium and examination its anodic dissolving stability in medium EXPERIMENTAL The experiments were carried out on a potentioganvanostat PGSHH2 with three-electrodes cell: platinium sheet was used as a counter electrode, a saturated calomel electrode (SCE) was used as reference one and the working electrode were Sn02/Ti samples RESULTS AND DISCUSSIONS 3.1 P r o d u c t i o n of S n thin film on the surface of t i t a n i u m The samples were titanium foils of cm^ geometric area These samples were polished by emery papers, cleaned with solution contained oxalic acid, hydrochloric acid and distilled water [2] Titanium electrodes were coated with Sn02 film by spray pyrolysis method Sn02 film obtained by spraying the solution of mixture SnCl4, NH4F and CH3OH on hot titanium substrates in time of minutes 3.2 Influence of NaOH solution on the anodic dissolving stability of Sn02/Ti electrode In order to determine electrochemical characteristics of SnO^/Ti in NaOH medium, it is measured the anodic current-voltage curves of Sn02/Ti electrode in alkaline medium in potential range of (-1) IV/SCE with sweep rate 0.05 V/s Results showed that Sn02 films were stable in alkaline medium The increase of concentration of NaOH changes lightly the passive region in potential range of (-0.5) 0.5 V/SCE and passive current density The higher increase of the con83 c e n t r a t i o n of N a O H , t h e earlier t h e liberation of oxygen w a s (see Table a n d Fig 1) Table D e p e n d e n c e of p o t e n t i a l of O2 l i b e r a t i o n a n d p a s s i v e r e g i o n o n c o n c e n t r a t i o n of N a O H s o l u t i o n 0.01 0.1 0.2 0.698 0.644 0.591 0.532 Passive region (V/SCE) (-0.500) 0.698 (-0.502) 0.604 (-0.482) 0.591 (-0.464) 0.532 Passive c u r r e n t d e n s i t y (mAycm^) 3.48.10-^' 3.89.10"' 4.09 ' 4.39 ' Concentration of N a O H s o l u t i o n (M) P o t e n t i a l of O2 liberation (V/SCE) r ill \ n- -" o - L - I IL / III / • / / r - » ' t - * - A a-«K — ' w - ^ ! 0 J - i It" '/ J O - ',~.r^ f, -4„ ( , , , I ^ r > ^^ 1J fj o *» — o *^ \") K - f-» o s «t y" ,?