Electrochemical reduction of NO2 at a Pt/membrane electrode—Application to amperometric NO2 sensing

A reductive kinetic study of amperometric NO2 gas sensing at the Pt/Nafion® electrode (or cathode) has been investigated in the concentration range of 0–25 ppm. The Pt/Nafion® electrode was prepared using an impregnation–reduction chemical plating method. A Nafion® membrane was used as a supporting material and Pt/Nafion® sensing electrode as a cathode maintained at a fixed potential of preferably 0.72–0.68 V (vs. Ag/AgCl), which corresponded to the diffusive regions or mass transfer-controlled regions. The SEM photographs showed that the electrode surface with a reductive pretreatment at 0.70 V was porous. By cyclic voltammogram with different scan rates, it was found that the rate of NO2 reduction was much slower than that of NO2 oxidation. For NO2 reduction at the Pt/Nafion® cathode fixed in the range of 0.8–0.82 V, transfer coefficient (α), standard apparent rate constant (rk0) and the exchange current density calculated were 0.32, 9.72 × 10−4 m/s and 19.22 μA/cm2, respectively. The sensing performance, including the long-term stability and the interferences of CO and NO, was also examined.