Development of Oxygen Sensors Utilizing SPE Composite Electrodes

利用SPE复合电极研制了一种新型的氧传感器。作为SPE材料，全氟离子交换膜，全氟磺酸，选择，因为它的化学和热稳定性。在Nafion上，通过使用肼或四氢硼酸钠作为还原剂的无电镀方法沉积薄的多孔铂以用于检测器电极。将10 μ m的聚乙烯膜热压在铂电极上作为氧的渗透限制膜。通过改变聚乙烯膜的数量来控制层的厚度。该传感器显示其还原电流对高达50%的氧含量的比例响应。传感器的稳定性至少达到2,000小时。为了制备小型化的氧传感器，还使用了直径约为1 mm的Nafion颗粒作为SPE材料。以与上述相同的方式沉积铂。由于任何常规方法都无法均匀地覆盖在如此小的铂层上，因此选择了等离子体聚合技术。选择六氟丙烯作为等离子体聚合物层的起始材料。在所选条件下，即使厚度小于1 μ m，也能均匀地涂覆非常稳定的全氟化聚合物薄层。利用该技术制作了1.2mm的微型传感器。该传感器对气态氧和溶解氧均表现出线性响应。传感器的响应时间比氧渗透限制膜的厚度所期望的值长。为了制备更小和更稳定的传感器，通过等离子体聚合技术制备了新的超薄离子交换膜。为了制作更稳定的传感器，对Nafion进行了处理以提高其选择透过性。

A new type of oxygens sensor was developed by utilizing SPE composite electrodes. As an SPE material, perfluorinated ion-exchange membrane, Nafion, was selected because of its chemical and thermal stability. On the Nafion, thin, porous platinum was deposited for the use of a detector electrode by an electroless plating method using hydrazine or sodium tetrahydroborate as reductant. Polyehtylen film of 10 mum was hot-pressed on the platinum electrode as a permeation limiting membrane for oxygen. The thickness of the layer was controlled by changing the number of polyethylene films. This sensor showed the proportional response in its reduction current to the oxygen content up to 50%. The sensor was stable at least until 2,000 hours.Nafion particles of about 1mm in diameter was also used as an SPE material in order to prepare miniaturized oxygen sensors. Platinum was deposited in the same manner as above. Since any conventional method was not available to cover on such a small platinum layer uniformly, plasma polymerization technique was selected. Hexafluoropropylene was selected as a starting material for plasma polyner layer. Under the selected conditions, very stable thin layers of perfluorinated pofymer was coated uniformly even in the thickness less than 1/mum. Using this technology, miniaturized sensor of 1.2mm was fabricated. This sensor showed linear response to both gaseous oxygen and dissolved oxygen. The response time of the sensor was longer than the value expected from the thickness of the oxygen perm-limiting membrane.In order to fabricated the smaller and more stable sensors, new ultra-thin ion-exchange membranes was prepared by a Plasma Polymerization technology. Nafion was treated to enhance the perm-selectivity for the sake of fabrication of more stable sensors.