Amperometric nitric oxide gas sensor: preparation of Au/SPE and sensing behavior

Anion-type (NEOSEPTA®) and cation-type (Nafion®) solid polymeric electrolytes (SPEs) prepared with Au were used as the working electrodes of the amperometric nitric oxide (NO) gas sensor. The decrease in electrochemical activity of the anodic oxidation of NO on Au/NEOSEPTA® was caused by the irreversible adsorptions on the electrode surface. The maximum electrochemical active areas of Au/Nafion® prepared by using N2H4·2HCl and NaBH4 as reducing agents were 140.5 and 200.0 cm2 when the Au loading were 8.2 and 7.5 mg/cm2, respectively. The sensitivity of NO gas sensor in the absence of diffusion barrier was 1.33 μA/ppm when Au/Nafion® was used as the working electrode and the gas flow rate was 45 ml/min. Using 0.2 μm PTFE film as a diffusion barrier, the effect of gas flow rate was insignificant and the sensitivity was evaluated as 1.53 μA/ppm with the gas flow rate greater than 150 ml/min. The limiting current of 360 ppm NO decreased from 551 to 75 μA upon continuously operating the NO gas sensor for 119 h.