Amperometric NO gas sensor based on Au/C/Nafion: Preparation and Characterization of Au/C/Nafion

摘要

Au/C/Nafion was prepared by hot pressing of the Au/C which was obtained from the chemical plating of AuCLf onto the carbon powder on Nafion? polymeric electrolyte. The effect of the reduction time, the temperature and the reducing agent on the loading of Au/C was insignificant. The diameter of Au on support and the dispersion of Au/C prepared on this work were analyzed by the XRD. Changing the loading of Au on XC-72 (Du Pout) and DARCO (VULCAN) carbon powder the maximum dispersion of Au were obtained to be 4.02% and 5.36%, respectively, when ethyl alcohol was used as reducing agent. Compared with the untreated DARCO? carbon powder the dispersion of Au increased from 5.36% to 7.22% when the carbon powder was pretreated with the aqueous solution containing SnCl2 and HC1. The cyclic voltammograms indicated that NO was oxidized at 1.0 V and the auric oxides were reduced at 1.0 V, respectively. The limitmg current of the anodic oxidation of NO on Au/C (DARCO) found from the polarized curve was located in the potential greater than 1.1 V when the concentration of NO and the gas flow rate were 500 ppm and 100 ml min"1, respectively. Increasing the loading of Au from 0 to 1.358 mg cm"2 the limiting current of the anodic oxidation of NO increased from 0.12 mA to a maximum value of 0.647 mA. Further increase of the loading of Au to 4.910 mg cm'2 the limiting current decreased to 0.228 mA. Using Au/C (DARCO) with loading of 1.358 mg cm'2 as sensing electrode, the response time for 95% limiting current (tgs) and the recover time for 5% limiting current (t_5) were evaluated to be 25 and 30 min, respectively. Au/C (DARCO) prepared with ethyl alcohol as reducing agent exhibited the maximum dispersion of Au on C and sensing current for the anodic oxidation of NO compared with the other reducing agents, such as CH3OH, N2H4 and NaBH4. Using Au/C (DARCO) with the Au loading of 1.358 mg cm"2 as sensing electrode, the sensitivity of NO gas sensor was found to be 2.028 uA ppm"1 for the concentration of NO in the range of 2.5 ~ 500 ppm and the gas flow rate of 300 ml min~-1.