Study On The Electrochemical Extraction Of Oxygen Using Air Electrode

In this thesis, the electrochemical extraction of oxygen using air electrode was studied. The effect of the membrane on the purity of oxygen in the electrochemical extraction system and the effects of electrolyte carbonating crystallization as well as HO₂^- iron on the electrochemical performance of the system were systematically studied by chemistry titration, purity measurement, polarization, SEM and so on, with an aim of resolving the problems of instability oxygen purity and electrolyte crystallization in the process of electrochemical extraction of oxygen using air electrode. Furthermore, we optimized the design of oxygen extraction system and manufactured a setting with high-quality oxygen purity and long lifetime, which provided a new technical approach for the practical application of electrochemical extraction of oxygen.The experiment results showed that the oxygen in electrobath could contact with the outside air through the air holes in the air electrode and generate many air channels connecting the inside and outside of the electrobath, thus leading to the straight entrance of outside air into the inside of electrobath and the reduction of oxygen purity. The use of proper membrane could hold back the diffusion of tiny air bubbles from anode to cathode and decrease the contact probability of oxygen with outside air, and thus leading to the improvement of oxygen purity in the process of electrochemical extraction of oxygen. The results showed that when big-mesh nylon net, plastic membrane and non-woven fabrics were used as the membrane and the space between air electrode and metal anode was about 1.5mm, the oxygen purity of the system could increase from 98% to above 99.6%.It was found that the addition of MnO2 catalyst led to the progress of electrochemical reaction in the 4e course and decreased the contents of HO₂^- and HO₂^- in the solution, thus leading to the elimination of many adverse effects of HO₂^- on system and the prolonging of lifetime of oxygen extraction system. Our research results indicated that, compared with the air electrode using active carbon as catalyst, the use of the air electrode using 30% MnO2 as catalyst in the system led to the reduction of HO₂^- concentration in the solution from 2.6 to 0g/L and the obvious reduction of discharged gas brought by decomposition of HO₂^-.Through optimum design, the oxygen system is assembled as follows: the air electrode with an area of 50mm² as cathode, a metal nickel net as anode, 30% K2CO3 solution as electrolyte and 20+400-mesh nylon net as membrane. When the interval between anode and cathode is 1.5mm and the current density is 80mA/cm², the purity of oxygen thus produced kept around 99.6%, the electrolysis voltage is between 1.5V and 1.65V and oxygen volume is 20-25mL/min. And the crystallization of KHCO3 did not occur in the system after running for 1000h.