氧化銥電位式固態微型二氧化碳感測元件

Abstract

一種以氧化銥薄膜作為動作電極,含碳酸根離子的聚乙烯醇為固態電解質 之電位式微型二氧化碳氣體感測元件。其主要反應機制為:氧化銥電極的 電位,會因氧化銥挾入電解質中氫離子或氫氧根離子的多寡而改變;氧化銥 電位會隨電解質的pH值改變。而電解質的pH值則與溶於其間的二氧化碳( pCO2)達成平衡;亦即與被測氣體中的二氧化碳濃度達成平衡。有關氧化銥 的基本電性,我們作了氧化銥在液態(0.1M LiClO4 in 0.06mM PVA)電解質 中的循環伏安實驗,以及在固態電解質(0.5M H3PO4 in 0.06mM PVA)中的 雙定電位掃描實驗。在一感測器的實例中, 氧化銥以RF濺鍍的方法,分別 鍍於二個相近的白金微電極上,以含水及碳酸根離子的聚乙烯醇連接並覆 蓋二電極, 再以環氧樹酯覆蓋其中之一電極。當元件暴露於含二氧化碳的 混合氣體中時,兩個電極間電位差即指示了混合氣體中二氧化碳之含量。 本感測器,在 1 atm, 298K 下工作,對 CO2 含量介於 1-56% 之間時,具有 線性且可逆之反應。可測得最低濃度為 200 p.p.m.。對感測部位注射 0.1 ml的 CO2,其反應時間為0.8秒。而植物行光合/呼吸作用時,吸吐二氧 化碳的情形也以本感測器測得。 A new iridium oxide thin film based microsensor,covered with a bicarbonate doped poly ( vinyl alcohol ) solid electrolyte , sensitive to carbon dioxide has been fabricated. The mechanism is that the potential of iridium oxide can be varied with pH value of the electrolyte. Another,the pH value and quantity of carbon dioxide dissolved in the electrolyte are in equili- brium;i.e. the pH value and density of carbon dioxide in measurand are in equilibrium. To achieve the basic electrical properties of iridium oxide, cyclic votammogram of iridium oxide in liquid phase electro- lyte (0.1M LiClO4 in 0.06mM PVA) and electrical characteristic in solid electrolyte(0.5M H3PO4 in 0.06mM PVA)are measured. In a practical sensor example, iridium oxide is sputtered on each of the two close platinum micro-electrodes. The two elec- trodes are connected and covered by water contained , bicarbo- nate doped poly(vinyl alcohol).One of the them is shielded with an epoxy layer . When the device is exposed to gaseous mixture of carbon dioxide,the potential difference between the two electrodes indicated the containment of carbon dioxide in the measurand.The response to CO2 concentrations is linear and reversible between 1-56% at 1 atm and 298K.The lowest concen- tration,200 p.p.m.,of CO2 has been detected.The rising time is only 0.8 seconds when 0.2ml CO2 is injected on the sensing re- gion.And,the variations in concentrations during photosynthe- sis and respiration of spinach are recorded through our sensor.