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。选择全氟离子交换膜Nafion作为固相萃取材料，是因为它具有良好的化学稳定性和热稳定性。在Nafion上，以肼或四氢硼酸钠为还原剂，通过化学镀的方法沉积了用于探测器电极的薄而多孔的铂。在铂电极上热压10微米的聚对苯二甲酸乙二酯薄膜作为氧气的渗透限制膜。通过改变聚乙烯薄膜的数量来控制薄膜的厚度。该传感器在氧含量高达50%时，其还原电流呈正比响应。该传感器至少稳定到2000小时。为了制备小型化的氧传感器，还使用了直径约1 mm的Nafion颗粒作为固相萃取材料。铂的沉积方式与上述相同。由于任何常规方法都不能在这么小的铂层上均匀覆盖，因此选择了等离子体聚合技术。选用六氟丙烯作为等离子体聚合物层的起始材料。在选定的条件下，即使在厚度小于1/微米的情况下，也可以均匀地涂覆非常稳定的薄层全氟聚合物。利用该工艺制作了1.2 mm的小型化传感器。该传感器对气态氧和溶解氧均表现出良好的线性响应。为了制备更小、更稳定的传感器，采用等离子体聚合技术制备了新型超薄离子交换膜。为了制作更稳定的传感器，对Nafion进行了处理，以提高PERM的选择性。

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.