一氧化碳為無色、無味、無臭的有毒氣體，近年來發生一氧化碳中毒的事件頻傳，尤其以家庭中電器使用不當所引起居多，因此發展能在常溫下偵測一氧化碳的感測器是必須的。本研究中採用平板式一氧化碳感測器，為三極式的感測系統，將白金與黃金電極利用濺鍍法製備在同一側，再以錫修飾感測電極，用以防止一氧化碳毒化，並採用再披覆成膜的Nafion®(recast Nafion®)為固態電解質，因為可隨著電極任意改變成膜形狀，使具有微小化的潛力。再以疏水性材料聚苯乙烯披覆在Nafion®膜上，使減緩Nafion®膜內水分的損耗，進而提高感測器的穩定性。

　　研究結果顯示，經過聚苯乙烯披覆的電極，因為擴散層增厚，導致在氣體流速90 ml/min，800 ppm CO，濕度為100 %R.H.時的感測電流僅為0.827 μA，靈敏度為0.75 nA / ppm，皆小於未披覆聚苯乙烯的電極，而應答與回復時間則隨著擴散層變厚也隨之增長，雖然在靈敏度、應答時間等皆劣於未披覆聚苯乙烯的電極。然而，在100 %R.H.的環境下，連續感測800 ppm的一氧化碳，聚苯乙烯的披覆使電極的衰退率比未披覆的電極在連續感測7次後降低了約20 %，除此之外，經過長時間2週左右的穩定性測試顯示，聚苯乙烯披覆的電極之衰退率更是比未披覆電極降低了約40 %。顯然，聚苯乙烯的披覆確實有減緩Nafion®膜內水分的損耗，使感測電流穩定性提高。即使使用完全不增濕的乾燥氣體進行感測時，雖然感測電流衰退程度比使用增濕氣體時明顯，但是，經過披覆聚苯乙烯的電極仍然具有較低的電流衰退率。

　　在模擬空氣的環境下進行感測，雖然在氣體流速90 ml/min，800 ppm CO，濕度100 %R.H.時，會因為氧氣存在導致感測電流與靈敏度降低，然而，披覆聚苯乙烯的電極感測特性卻受到氧氣的影響甚小，更適用於真實環境中使用，這可能是因為擴散層變厚，不僅能減緩Nafion®膜內水分的損耗，亦能降低氧氣的穿透。此外，空氣中的氧氣會與氫離子反應產生水，藉此補充陽極反應時消耗的水分。若經過聚苯乙烯的披覆，使生成的水分不易揮發，幾乎保存在Nafion®膜內，因此進行連續7次感測穩定性測試時，衰退率僅為2.1 %，即使未經披覆的電極亦能使衰退率有明顯的提升。由此得知，本感測系統在真實環境中具有較佳的穩定性，經過聚苯乙烯披覆之後，可使其感測電流穩定性更佳，使用壽命更長。

　Carbon monoxide is a toxic compound, featuring colorless, tasteless, odorless gas. CO intoxication repeatedly occurs over the years, especially due to the improper use of household electric appliances. Hence, to develop a sensor capable of CO detection at room temperature is an essential issue nowadays. This study focused on planar CO sensor composed of three electrodes, two of which were sputtered Pt and sputtered Au on the same side. The sensing electrode was further modified by Sn in order to prevent itself from the poisoning of CO. The solid electrolyte in this system was recast Nafion® film, for it could be reshaped to fit in with electrode profile, even when miniaturized. The coating of hydrophobic polymer, polystyrene, over Nafion® was an important final step, which actually enhanced the stability of the sensor by detaining water within Nafion® film.

　In this study, the sensing current of 800 ppm CO on PS-coated electrode was 0.827A at gas flow rate of 90ml/min in 100 %R.H., resulting in a sensitivity of 0.75nA / ppm. The sensitivity of PS-coated electrode was lower than that of the uncoated one because the diffusion layer was consequently thickened by PS coating. Response time and recovery time were extended for the same reason as well. When continuously sensing 800 ppm CO at 100%R.H., the current decay percentage of PS-coated electrode reduced by 20% compared to that of uncoated electrode after seven cycles. Moreover, the long-term stability test showed that the current decay percentage of PS-coated electrode reduced by 40% than that of uncoated electrode around two weeks or so. The idea of PS coating turned out to be effective on the detainment of water evaporation within Nafion® so as to enhance the stability of sensing current. Current decayed in both cases when the sensing was accomplished in dry gas. PS-coated electrode was still promising since it showed less current decay.

　In simulated real air, both sensing current and sensitivity of 800 ppm CO at 90 ml/min gas flow rate and 100 %R.H. were lower then in O2-free environment. PS coating was believed to restrain not only water loss but the penetration of oxygen as well on account of the expanding diffusion layer. The effect of oxygen on sensing was less significant in the case of PS-coated electrode, which made it a better sensor candidate in real life. Besides, oxygen in simulated air reacted with hydrogen ions to formed water. It complemented the water consumption at anode. With PS coating, water was effectively kept inside Nafion® film. The conserved water accounted for small current decay percentage for both cases. The least current decay reached 2.1 % when continuously sensing CO at PS-coated electrode after seven cycles. The conclusion goes that the coating of PS improves sensing current, stability, and life expectancy.

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