Adsorbed HNO 2/NO redox couple at Pt(111) single-crystal electrode

Abstract

Nitrogen oxide (NOx), produced mainly in the exhaust gases of automobile engines and factory turbines, is known as an injurious substance to the human respiratory organs and nervous system. It is also an important source of acid rain. Nitric oxide has been the subject of intense attention in the last 5 years because of its important biological role in the body which had not been recognized previously [1]. The adsorption and decomposition mechanisms of NO x on a well-defined single-crystal catalyst surface have been studied extensively in the gas phase using a variety of methods, such as low energy electron diffraction (LEED), Auger electron spectroscopy, IR absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) etc., and these results have been well reviewed [2-4]. Electrochemical investigations of NOx have been carried out by many groups, mainly on polycrystalline Pt electrodes. The electrochemical behaviour appears to be more complicated than that observed in gas + solid catalysis. Schmid and Neumann [5] investigated the equilibrium potential of the HNO2/NO redox system in solution and obtained E ° = 0.983 V. Many groups have concluded from the kinetic analysis of cyclic voltammograms obtained in acid solution that the formation of NO is the first reduction step of HNO2 [6-9]. Clavilier and Chauvineau [10] have reported that a (poly)platinum surface was covered by NO during cleaning with an argon glow discharge. The NO was removed irreversibly at 0.45V/SCE in a positive potential scan. Gadde and Bruckenstein [11] carried out bulk electrolysis of nitrite in 0.1 M HCIO4 at a Pt electrode. Their product analysis showed only NO above 0.5V/RHE. Nishimura et al. [12] examined the electroreduction product of nitrite and nitrate ions at a porous Pt electrode in H2SO 4 using the differential electrochemical mass spectroscopy (DEMS) method. NO has been detected in the potential region 0.6-1.0 V/RHE.