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Electrochemical Generation of Ozone Using Solid Polymer Electrolyte - State of the Art

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Electrochemical Generation of Ozone Using Solid Polymer Electrolyte - State of the Art Indian Journal of Chemistry Vol. 43A, August 2004, pp. 1599-1614 Advances in Contemporary Research Electrochemical generation of ozone using solid polymer electrolyte - State of the art Sang-Do Han*", Jung Duk Kim", K C Singh*b & R S Chaudhar/ "Korea Inst itute of Energy Research, Yuseong-gu, Daejeon 305-343, Korea bDepartment of Chemistry, Maharshi Dayanand University, Rohtak, Haryana, India Received 22 September 2003; revised 1 June 2004 In this review article, up-to-date information about the electrochemical generation of ozone using solid polymer electrolyte, fabrication of the electrochemical cell, deposition and mechanism of the anode and cathode catalysts, preparation of current collectors and optimum conditions for the proton exchange membrane, cell assembly and high ozone cUlTent efficiency have been described. IPC Code: lnt. Cl 7 COIB 13110; C25B 1/13 Dr. K. C. Singh did hi s Ph.D. from M. D. materials. Currently, he is working as Head of Sensors and University Rohtak, Haryana, in 1980. He Materials Research Center of KIER and is the Editor of th e has been working as a lecturer and Reader Journal of Korean Sensors Society. since 1980 in the same University. His areas of research are solutions thermodynamics, anodic oxide films & Prof. Chaudhary did his Ph.D. in 1972 and water electrolysis and hydrogen/oxygen/ then worked as faculty member at Banaras ozone production. He has published nearly Hindu University, Varanasi till 1989. He 90 research papers in the research journals joined Maharshi Dayanand University as of national and international repute. He worked as a visiting Professor in 1989. His research interests are ~c ientist at Korea Institute of Energy Research, Korea for one and in the fields of electrochemistry, cOlTosion half years in 1999, 2001 and 2003. The present work has been control and development of speciality can'ied out in Korea. chemicals for industries. He has developed many products, which have found applications in industries. Prof. Chaudhary has worked as visiting Mr. Jung-Duk Kim received hi s B.E. scientist at reputed laboratories like Max-Planck-Institute fuer degree from the Department of Chemical Eisenforschung, Dusseldorf, Germany, Technische Hogeschool Engineering, Seoul National University, Delft, University of Twente, Enschede, The Netherlands. He has Seoul, Korea, in 1976. He has been worked on nine sponsored projects -and has won several awards working at Korea Institute of Energy for hi s research work. He has been head of the Chemistry Research (KIER) since 1980. Currently he Department and Dean of the Faculty of Physical Sciences, is working as Senior Researcher at the Maharshi Dayanand University and the university honored him Sensors and Materials Research Center of with Award of Excellence. He has published 68 research papers in KIER. His major interest fields are: (i) hi ghly reputed journals and guided 12 Ph.D. students. water electrolysis and hydrogen/oxygen/ozone production, (i i) inorganic/organic nanophosphor materials and sensor materi als. Ozone, 0 3, is a very powerful oxidant having an Dr. Sang-Do Han did his B.Sc. from oxidation potential of 2.07 volts. This potential makes Kyungpook National University in 1975, it the fourth strongest oxidizing chemical known. M.Sc. course from Chungnam National Ozone is present in large quantity in the upper University, Korea, in 1984, and received his atmosphere of the earth and provides protection from Ph.D. degree in Solid State Chemistry from University of Bordeaux, France in 1994. He harmful ultra violet rays of the sun. Due to its strong has worked at LG Semiconductor Co. Ltd. oxidation potential 0 3 has a very short li fe. Ozone, from 1978-1980, and is cUlTently working dissolved in water may decompose in about 20 at Korea Institute of Energy Research minutes. Ozone decomposes into secondary oxidants (KIER) since 1980. His areas of interest are: (i) electronic and electrolyte materials, (ii) chemical sensors, (i ii ) hydrogen, oxygen such as highly reactive hydroxyl (OHO) and peroxyl and ozone production, and (iv) inorganic/organic phosphor (H02°) radicals. These radicals are among the most 1600 INDIAN J CHEM. SEC A. AUGUST 2004 reactive oxidizing species known. They undergo fast of nitrogen. Further, when the ozone generated by free radical reactions with dissolved compounds. electric discharge is used for water treatment, varioLls Hydroxyl free radicals have an oxidation potential of disadvantages arise. In particular, because of its low 2.8 V which is higher than most oxidizing species concentration, the ozone dissolved in water is including 0 3. Most of the OH" radi cals are produced insufficient to treat the water and results in low in chain reactions where OH" itself or H02", act as operational efficiency. Additionally, dry ozone from 1Il ltlators. Hydroxyl radicals act on organic the electric discharge method takes a longer time to contaminants either by hydrogen abstraction or by dissolve in the water to be treated than wet ozone hydrogen addition to a double bond, the res ulting from the electrolytic process. Also, the ozone radicals disproportionate or combine with each other produced from the discharge process contain s formin g many types of intermediates which react impurities of the electrode material, which may be a further to produce peroxyls, aldehydes and hydrogen problem if ultra pure water is to be produced. To peroxides. avoid these disadvantages of electri c discharge Due to its strong oxidative property, 0 3, has been generated ozone, the industry is shifti ng attenti on to recognized as a useful chemical in disinfection and the electrolytically generated ozone. sterilization processes. It ki lls micro-organisms, Nevertheless, th is method of ozone production has decomposes organic molecules, removes cyanide, been exploited widely and many equipments have phenols, iron, manganese, detergents and coloration been designed to use ozone for sterili zation, fro m aqueous systems . It is used to disinfect potable purification of water, treatment of sewage water, water, food, surgical equipment and to treat sewage laundry waste, soils, food products etc. It has been water, swimming pool etc.1-I6. Ozone is also used in observed that ozone yield increases when oxygen pressure is increased in the corona discharge industries such as semiconductor production, 17 ~ breweries, pharmaceuticals, bio-technology etc ., chamber . where ul tra pure water is required in the Ozone can also be produced by the electrolytic manufacturing processes. It may also be employed as process where water is used as electrolyte which a raw material in the manufacture of certain organic dissociates into oxygen and hydrogen at anode and compounds such as oleic acid, peroxyacetic acid etc. cathode respectively. Under certain suitable The use of ozone for purification of water is conditions , the oxygen is evolved as 0 3 species. particularly advantageous as it does not leave any harmful residuals in water as in the case of chlorine. However, the cost of ozone production is high due to poor energy efficiency of the manufacturing !J.Ho 298 value in the electrolytic process is almost six processes. Its application and use will certainly times that in corona discharge process. Thus, the expand if its cost of production may be reduced. electrolytic process appears to be at about six-times Further, the transportation of ozone is hazardous due disadvantageous. To compete wi th the electric to its explosive nature when concentrated either as a discharge process for 0 3, the electrolytic process must gas or liquid, or when dissolved into solvents or be at least six times more efficient. adsorbed into cells. Therefore, it is always preferred The evolution of 0 3 by electrolysis of vari oLls to generate ozone on the site where it is to be used. el ectrolytes has been known sin ce a long ti me and Commercially, ozone is produced by corona cunent efficiency as high as 35% of 0 3 by volume has l 8 discharge process, where oxygen or air is passed been reported in the literature . It means that O2 and through an intense high frequency A.c. electric field. 0 3 produced at the anode are comprised 35% 0 3 by The followi ng reaction occurs. volume. However, such high yields of 0 3 could only be achieved utilizing very low temperature of the !J.ff298 = 34.1 kcal electrolyte (-30 to -65°C). Maintaining the necessary low temperature, obviously requires costly equipment Ozone production efficiency in this process is and additional energy cost of the operation. appro~imately 2% (by weight) only, but it is still sufficiently high to furnish usable quantities of ozone Electrochemical cell assembly for the commercial purposes. Another disadvantage of Electrochemical cell for the production of 0 3 is just the corona process is the production of harmful oxides a common type of electrochemical cell consisting of HAN el al.: ELECTROCHEMICAL GENERATION OF OZONE USING SOLID POLYMER ELECTROLYTE 1601 anode, cathode and electrolyte(s). Oxidation occurs at the resistance of the circuit and the electrolyte and the anode and reduction at cathode. The electrons flow in overpotential required in order to make reactions (2) the external circuit from anode to cathode and to and (3) proceed at significant rates at 25°C, the actual complete the circuit of the cell, the charge is cell voltage will be of the order of 3.0 V. transferred by ionic conduction through the To lower this actual cell voltage and, hence, electrolyte in the cell. The electrolyte must be poor minimize the consumption of electrical energy, the electronic conductors to prevent internal short­ electrodes need to be placed as close as possible to circuiting of the cell. each other. It is possible by using an ion exchange A typical electrochemical cell will have a positively membrane such as Nafion of thickness in the range of charged anode and negatively charged cathode and 50-175 ~m.
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