| Summary: | 碩士 === 國立成功大學 === 化學工程研究所 === 85 === Pt was loaded on Nafion R for different types sensing cells with impregnation-reduction method. The sensing behaviors on CO with these cells were then studied.
Pt loading depended upon the electrode preparing conditions. The electrode for the maximum Pt loading (1.40 mg/cm2) was obtained with impregnation in 0.02 M Pt(NHs)4Cl2 at 40℃ for 2 hrs, then reduction in 0.2 M NaBH4, pH11 at 40℃ for 30 min. The surface of the deposite was observed in the form of black with SEM.
The applied voltage for limiting current of CO oxidation on the Pt/Nafion R electrode was in the range of 0.6~0.7 V vs. Ag/AgCl. The sensing current of CO on the Pt/Nafion R electrode was proportional to CO concentration at 0.65 V vs. Ag/AgCl. The highest sensitivities of CO for Pt/Nafion R electrodes prepared with reducing solution of pH 10~13 is 0.36 μA/ppm CO at pH 11. The response time these pH was about 30 sec.
The applied voltage for limiting current of CO oxidation on the PtA/Nafion R /Pta cell was in the range of 0.1~0.2 V vs. PtB, with background current smaller than 10 U.A. The sensing current of CO on the PtA/Nafion R /Pta cell was proportional to CO concentration at 0.15 V vs. Pte. The sensitivity and respose time were 0.32πA/ppm CO and about 400 sec.
The applied voltage for limiting current of CO oxidation on the PtA-PtB/Nafion R /Ptc cell was in the range of -0.20~-0.10 V vs. Ptc. PtA and Pts were separated and situated on the same side of Nation R and used as the working and counter electrode respectively. On the other side was the reference electrode. The sensing current of CO on this cell was proportional to CO concentration at 0.15 V vs. Ptc. The preparation condition for PtA-PtB/Nafion R /Ptc cell with the maximum sensitivity of CO (0.33 μA/ppm CO) was impregnation in 0.02 M Pt(NH3)4Cl2 at 40℃ for 2 hrs, and reduction with 0.2 M NaBH4, pH11 at 40℃ for 30 min. The sensitivities of CO of PtA-PtB/Nafion R /Ptc cell without eletrolyte outside of Nation R were 0.33, 0.30, 0.26, 0.20, and 0.17μA/ppm CO for relative humidity 96.4%, 91.4%, 84.0%, 75.2%, and 69.3%, respectively. The response time was about 30 sec. When the applied voltage was more negative than -0.15V vs. Ptc, O2 was reduced easily with 20% 02 in N2. The sensitivities of CO for PtA-PtB/Nafion R /Ptc cell in synthesis air with RH 87.5% is 0.175 μA/ppm CO at -O.1 V vs. Ptc. This sensitivity was smaller than that without O2 influence.
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