| Recently, great interest has been attracted by the R&D of small-size oxygen generators by an awareness of the importance of oxygen therapy and healthcare. By using an oxygen reduction electrode to substitute the hydrogen evolution electrode in a water electrolyzer, an electrochemical oxygen generator without hydrogen evolution can be designed. The advantages of oxygen generator with an oxygen reduction electrode are obvious, while lots of limitations need to be overcome, such as low efficiency, poor stability, etc. In order to solve these problems, we researched systematically into the preparation process and operation factors of carbon based oxygen electrode which is the core part of an electrochemical oxygen generator. Then several electrochemical oxygen generators with single cell and multiple cells were constructed by using carbon based oxygen electrode as cathode, nickel net as anode and KOH aqueous solution as electrolyzer, and the key factors related to the performance of oxygen generator had been investigated in this thesis.Initially, the effects of the preparation conditions, such as the compositions of catalyst layer and hydrophobic layer, and different electric conductors on the performance of oxygen electrode were studied by using linear polariztion technique. The experimental results show that the performance of gas diffusion electrode is greatly depended on its preparation conditions, and the electrode with better performance can be obtained with the following prepartion conditions:mass ratios of acetylene black to activated carbon and PTFE to activated carbon in catalyst layer are3:7and0.15:0.85, respectively; mass ratio of PTFE, acetylene black and Na2SO4in hydrophobic layer is1:1:1;80mesh nickel net is used as electric conductor; each part of the electrode is pressed together at10MPa for1min.The textures and surface chemical properties of activated carbon before and after treatment with nitric acid and air oxidation respectively were examined by N2adsorption and TPD, and their effects on the performance of oxygen electrode were also studied. It is found that the performance of oxygen diffusion electrode declines with the increasing of oxygen functional groups at the carbon surface.A specimen of electrochemical oxygen generator has been constructed by using oxygen electrode with geometric surface area of150cm2as cathode, nickel net as anode,40%KOH aqueous solution as electrolyte. Better results can be obtained with the oxygen generator operated under the optimized conditions listed as following:electrode gap is lcm, current density is83mA/cm, temperature of electrolyte is between25℃and35℃, air flow rate in the gas chamber is120L/h. The oxygen evolution rate and current efficency are ca.5.0L/h and92%, respectively.The abovementioned results show that the electrochemical oxygen generator equipped with a carbon based oxygen electrode as cathode can be considered as a promising competitive technology for small-size oxygen generator. But the practical implementation of this technology still has some technical hurdles to overcome, such as the oxidization of carbon based oxygen electrode by H2O2formed during the reduction of oxygen. Therefore a preliminary study on the electrocatalyst for oxygen reduction reaction (ORR) is conducted at the end of this thesis. It is found that the as-prepared MnOx/MWNTs show high electrocatalytic activity to ORR. And an apparent four-electron transfer at the potential where a two-electron transfer can be obersved when MnOx/MWNTs used as electrocatalysts. This result illustrates the potential application of the as-prepared MnOx/MWNTs in the electrochemical oxygen generator. |
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