Oxidation of Hydroxylamine on the Rotating Solid Electrodes

Abstract

Hydroxylamine oxidation in acidic media at the rotating platinum, gold, and glassy carbon electrodes was investigated. It was found that the reaction occurred only at the platinum electrode. A single oxidation peak ͑instead of a wave͒ was observed at the rotating platinum electrode. Evidence for a kinetic hindrance of the reaction caused by the platinum oxide layer present at the electrode surface was shown. The reaction proceeds via NHOH, NOH, nitrous acid, and the final products are nitrate ions. The process involves hydroxylamine adsorption, which is the reason for the absence of the electrochemical signal in the case of gold and carbon, materials of lower catalytic activity. Hydroxylamine oxidation was accompanied by various homogeneous chemical reactions. The reaction of hydroxylamine with nitrous acid ͑intermediate product of hydroxylamine oxidation͒, yielding N 2 O, had a rate constant, estimated on the basis of the ring-disk experiments, equal to (6.4 Ϯ 0.4) 10 4 mol Ϫ1 cm 3 s Ϫ1 .Hydroxylamine can exist in water solutions in two forms: above pH 5.9 as simple NH 2 OH and, below this pH, in protonated form,Those two forms have different electrochemical behavior and NH 3 OH ϩ is assumed to be less active. 2,3 Moeller and Heckner, 2 who investigated the electrode reactions of hydroxylamine at the rotating platinum electrode, observed a single oxidation peak in acidic solutions. According to the authors the reaction consists of several steps and the final products are nitrites. In strongly acidic solutions (pH Ӎ 0), the oxidation reaction stops at the electroinactive NHOH ϩ .Karabinas et al. 3 studied NH 2 OH oxidation in 0.5 M H 2 SO 4 solution at the rotating platinum electrode with differential electrochemical mass spectroscopy ͑DEMS͒, a method which enables one to measure the rate of formation of a volatile product as a function of potential. They found that in 0.5 M H 2 SO 4 solution hydroxylamine is less active than in buffered neutral solution. The reaction proceeds at the potential of the platinum oxide layer formation and probably Pt-OH is involved in the process. A single oxidation peak was observed. The following DEMS signals were found 1. N 2 O signal was formed at the potential corresponding to the rising part of the hydroxylamine oxidation peak, indicating that the reaction proceeds via HNO 2 . According to the authors the formation of N 2 O is due to the following chemical reaction2. NO formation was suppressed within the anodic scan, which showed NOH formed to a small extent. The NO signal was strong in the cathodic scan on a freshly reduced ͑more active͒ Pt surface. The authors considered the existence of NO as a proof of NOH formation3. Small amounts of NO 2 were formed at peak potentials ͑i.e., in the range of HNO 3 formation͒. The authors concluded that in acidic solutions at least part of the reaction proceeds via NO 2 , which quickly disproportionatesThe main aim of this work was to study the electrochemical behavior of protonated hydroxylamine at the rotating platinum, gold and glassy c...

Rational Design of Electrocatalytic Interfaces: The Multielectron Reduction of Nitrate in Aqueous Electrolytes

“…The data in panel B was acquired in the same solution with the RDE rotating at a rate of ω = 2500 rpm. In stark contrast with reports published in the literature, 6 Au is active for the oxidation of hydroxylamine, a reaction for which the onset potential is found at about 0.45 V versus SCE. This value is more negative than that associated with the oxidation of nitrite in the same media (see panel A, blue curve).…”

The Influence of Solution-Phase HNO2 Decomposition on the Electrocatalytic Nitrite Reduction at a Hemin−Pyrolitic Graphite Electrode

“…On the other hand, for a pH 1.7 buffer, the production of NH 2 OH initially increases but then levels off for E below −0.32 V. These results are consistent with the more pronounced second wave in a pH 3 buffer as compared to a pH 1.7 solution, such that the higher NH 2 OH production parallels the higher current density during nitrite reduction in a pH 3 solution. The larger NH 2 OH oxidation current observed at pH 3 (see Figure ) is likely due to the higher reactivity of a Pt electrode toward NH 2 OH oxidation in milder acidic media . An increased production of NH 2 OH at pH 3, evidenced by the larger reduction current measured at that pH (see Figure ), could also partly account for this observation.…”

Amperometric Sensor for Hydroxylamine Based on Hybrid Nickel‐Cobalt Hexacyanoferrate Modified Electrode

“…During electrolysis the reference and the auxiliary electrodes were as described above. Spectrophotometric measurement was made with a Cary-500 UV-Vis-NIR spectrophotometer (VARIAN, USA) for the determination of reagent concentration during the bulk electrolysis [41].…”