以三氧化鎢薄膜電色製作二氧化碳感測器

Abstract

我們利用 WO3 的電色特性來製作 CO2 的微型感測元 件.由於 WO3 在外加負偏壓時,注入 H+ 離子會使得 WO3 的顏色從淡黃色 變成為深藍色.根據此原理,我們在白金微電極上濺鍍 WO3 薄膜,並在薄膜 上披覆上一層固態電解質(PVA).而此電解質是由透明可透氣的聚乙烯醇和 弱鹼性的碳酸氫鉀所組成.當二氧化碳溶解於 PVA 所含之殘留水份時,會 產生酸化作用,並解離出氫離子使 WO3 薄膜產生電色反應.藉此,可以完成 對二氧化碳的偵測. 而此時電解質的 pH 值與溶解其間之二氧化碳會達成 動態平衡亦和被偵測之二氧化碳濃度達成平衡.在光學實驗中,薄膜對光的 穿透率變化量隨著濺鍍溫度愈高,薄膜厚度愈厚,外加偏壓愈大和二氧化碳 濃度愈高等條件而增加.當外加偏壓為-1.3V 時,可使穿透率改變達 20% .藉由量測光之穿透率改變量,我們可間接偵測出二氧化碳的濃度. A new CO2 sensor has been made by WO3 thin film electrochromism characteristic.The color of WO3 thin film changes form yellowish to dark blue when H+ has been intercalated in the surface of WO3 resulting from the inverse bias on cathod. By the theorem, We have the platinum micro- electrodes sputtered tungsten trioxide and covered the solid electrolyte which is made by bicarbonate contained and gas- permeable transparent poly vinyl alcohel(PVA). The tungsten trioxide will achieve electrochromic reaction when H+ is dissociated from acidification of bicarbonate contained PVA due to the dissolved CO2. Thus CO2 can be sensed by this way. The pH value and quantity of carbon dioxide dissolved in the electrolyte are in equilibrium and the pH value and density of carbon dioxide in measured are in equilibrium. In the optical experiment, the electrochromic of WO3 thin film is highly depended on many conditions: the electrochromic optical transmission will be altered more as the sputtering temperature is higher, the film is thicker,the bias is greater and the concentration of CO2 is larger. 20% change in transmission is measured when the bias is -1.3V. By the change in transmission, we can measure the concentration of CO2.