Reduction of Nitric Acid to Hydroxylamine at Glassy Carbon Surfaces Modified by the Reduction of p-Phenylenediamine and p-Aminophenol in 1.0 M Nitric Acid: A Scanning Electrochemical Microscopy Study

Abstract

The scanning electrochemical microscope (SECM) was used to study the electrochemical reduction of nitric acid to hydroxylamine at modified glassy carbon (GC) electrodes. The GC surface was modified by holding it at a negative potential in solutions of p-aminophenol, or p-phenylenediamine in 1.0 M nitric acid. The generated products were detected in generation/collection experiments with an SECM Pt ultramicroelectrode. The films that form on GC, apparently polymers of a quinone imine intermediate, can also be grown under similar conditions on indium tin oxide (ITO) coated glass electrodes and appeared as dark orange-brown films. Atomic force microscope imaging revealed a highly porous structure. SECM and cyclic voltammetry studies showed that as a result of this surface filming, the GC electrodes exhibited an increase of at least 1 V in the hydrogen overpotential relative to the unmodified surface and the efficiency of the electrochemical reduction of nitric acid to hydroxylamine was dramatically enhanced. Bulk electrolysis of nitric acid at carbon in the presence of p-phenylenediamine resulted in a 75 to 85% current efficiency for hydroxylamine production at current densities of 0.5 to 0.8 A/cm2. This procedure proved to be useful for the large-scale electrochemical production of hydroxylamine from nitric acid at an electrode other than liquid mercury. © 2001 The Electrochemical Society. All rights reserved.