| Summary: | 碩士 === 國立成功大學 === 化學工程學系 === 88 === The use of alcohol sensor is wildly, for example: wine-making industry, cosmetic industry, prevention of drunk driving, and prevention of liver patient drinking. There are two kinds of commercial alcohol sensor, enzymatic alcohol sensor and semi-conduct sensor. The former has high selectivity but is unstable and hard to store. The later has low selectivity and shot life-time. All of the problem must be improve.
In this study, an amperometric alcohol was developed by using electroless or sputtered nickel as working electrode. And the system was also made by micro fabrication. The system was expected to improve the problem of the commercial alcohol sensor and made the measurement more convenient.
When using electroless nickel as working electrode, the effect of bath temperature, bath composition, and deposition time have to be considered. The results indicated that the sensing of alcohol by electroless nickel as working electrode had the higest sensitivity, 8.75μA/ppm×cm2, when the bath was applying at a composition of 0.076M nickel ion, 0.160M hypophosphate, 0.034Msodium acetate, and 0.074M sodium citrate at 70℃ for 20 min. The average response time is 9sec and the stability is three months.
When using sputtered nickel as working electrode, the effect power and deposition time have to be considered. The sensing of alcohol by sputtered nickel as working electrode had the highest sensitivity, 7.5μA/ppm×cm2, when the bath was applying at 25kW for 15 min. The average response time is 6 secs and the stability is four months.
The relationship of alcohol concentration and response current is linear of the home-made alcohol sensing probe and its linear fit is Y=0.35+15.85X. Comparing with the commercial alcohol sensor, home-made alcohol sensor is more accurate because the varience analysis of the response data shows to be smaller. The measurement value of home-made alcohol sensor is lower bias from the true value at high alcohol concentration. The measurement value of commercial alcohol sensor is unstable and poor reproducible at low alcohol concentration.
X-ray diffraction (XRD) and cyclovoltammetry were applying for exploring the reactivity and reversibility of nickel foil, electrodeposited nickel, electroless nickel and sputtered nickel as working electrode. The results indicate that electroless nickel is amorphous because the phosphate contains. And in the nickel deposited layer, the distribution of active sites is more uniform than others, thus has higher reactivity. The potential of oxidation peak is approaching to reduction peak and the ratio of the peak area is approaching to 1 in the case of sputtered nickel and nickel foil. Thus sputtered nickel and nickel foil have better reversibility。
From the mechanism of ethanol oxidation by NiOOH/Ni(OH)2 and experimental data, the rate constants can be derived as follow:
(5-14)
(5-15)
Then get a relation about I-E-C:
(5-17)
Simulating the I-E curve for 200, 600, 1000ppm ethanol and comparing with the experimental data can obtain they were coincide. Thus the module of anodic oxidation of ethanol is explainable.
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