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Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia

Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia
Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia
An oxidation process observed in dilute aqueous solutions of ammonia was investigated under steady-state conditions with gold microelectrodes with radii in the range 2.5-30 mum. Over the ammonia concentration range 0.1-10 mM, a well-defined voltammetric wave was observed at ~1.4 V versus Ag/AgCl. It was attributed to the oxidation of hydroxide ions that arise from the dissociation of the weak base. The steady-state limiting current was found to depend on the concentration of supporting electrolyte, and in solution with low electrolyte, it was enhanced by migration contribution, as expected for a negatively charged species that oxidizes on a positively charged electrode. In addition, the steady-state limiting current was proportional to both the ammonia concentration and the electrode radius. The overall electrode process was analyzed in terms of a CE mechanism (homogeneous chemical reaction preceding the heterogeneous electron transfer) with a fast chemical reaction when measurements were carried out in solutions containing NH3 at less than or equal to5 mM and with electrodes having a radius of greater than or equal to5 mum. This was ascertained by comparing experimental and theoretical data obtained by simulation. The formation of the soluble complex species Au(NH3)(2)+ was also considered as a possible alternative to explain the presence of the oxidation wave. This process however was ruled out, as the experimental data did not fit theoretical predictions in any of the conditions employed in the investigation. Instead, the direct oxidation of NH3, probably to N2O, was invoked ID explain the anomalous currents found when the CE process was strongly kinetically hindered. Throughout this study, a parallel was made between the CE mechanism investigated here and that known to occur during the hydrogen evolution reaction from weak acids.
supporting electrolyte, weak acids, hydrogen evolution, electrochemical oxidation, platinum microelectrodes, mercury microelectrodes, anodiccharacterization, polyprotic acids, reduction, gold
0003-2700
3290-3296
Daniele, Salvatore
cd677266-5cc2-48c2-8145-e95861a0b4d2
Baldo, M. Antonietta
dc81685a-3ceb-4ca5-b767-db7587ec8b5b
Bragato, Carlo
78869737-4e49-4eee-8725-28001ff0e202
Abdelsalam, Mamdouh Elsayed
d1cbddcb-9f5c-46d5-b774-1bbaee26e115
Denuault, Guy
5c76e69f-e04e-4be5-83c5-e729887ffd4e
Daniele, Salvatore
cd677266-5cc2-48c2-8145-e95861a0b4d2
Baldo, M. Antonietta
dc81685a-3ceb-4ca5-b767-db7587ec8b5b
Bragato, Carlo
78869737-4e49-4eee-8725-28001ff0e202
Abdelsalam, Mamdouh Elsayed
d1cbddcb-9f5c-46d5-b774-1bbaee26e115
Denuault, Guy
5c76e69f-e04e-4be5-83c5-e729887ffd4e

Daniele, Salvatore, Baldo, M. Antonietta, Bragato, Carlo, Abdelsalam, Mamdouh Elsayed and Denuault, Guy (2002) Steady-state voltammetry of hydroxide ion oxidation in aqueous solutions containing ammonia. Analytical Chemistry, 74 (14), 3290-3296. (doi:10.1021/ac025530n).

Record type: Article

Abstract

An oxidation process observed in dilute aqueous solutions of ammonia was investigated under steady-state conditions with gold microelectrodes with radii in the range 2.5-30 mum. Over the ammonia concentration range 0.1-10 mM, a well-defined voltammetric wave was observed at ~1.4 V versus Ag/AgCl. It was attributed to the oxidation of hydroxide ions that arise from the dissociation of the weak base. The steady-state limiting current was found to depend on the concentration of supporting electrolyte, and in solution with low electrolyte, it was enhanced by migration contribution, as expected for a negatively charged species that oxidizes on a positively charged electrode. In addition, the steady-state limiting current was proportional to both the ammonia concentration and the electrode radius. The overall electrode process was analyzed in terms of a CE mechanism (homogeneous chemical reaction preceding the heterogeneous electron transfer) with a fast chemical reaction when measurements were carried out in solutions containing NH3 at less than or equal to5 mM and with electrodes having a radius of greater than or equal to5 mum. This was ascertained by comparing experimental and theoretical data obtained by simulation. The formation of the soluble complex species Au(NH3)(2)+ was also considered as a possible alternative to explain the presence of the oxidation wave. This process however was ruled out, as the experimental data did not fit theoretical predictions in any of the conditions employed in the investigation. Instead, the direct oxidation of NH3, probably to N2O, was invoked ID explain the anomalous currents found when the CE process was strongly kinetically hindered. Throughout this study, a parallel was made between the CE mechanism investigated here and that known to occur during the hydrogen evolution reaction from weak acids.

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More information

Published date: 15 July 2002
Keywords: supporting electrolyte, weak acids, hydrogen evolution, electrochemical oxidation, platinum microelectrodes, mercury microelectrodes, anodiccharacterization, polyprotic acids, reduction, gold

Identifiers

Local EPrints ID: 19713
URI: http://eprints.soton.ac.uk/id/eprint/19713
ISSN: 0003-2700
PURE UUID: e3cdcb88-9663-4570-ab90-259cc7b1306e
ORCID for Guy Denuault: ORCID iD orcid.org/0000-0002-8630-9492

Catalogue record

Date deposited: 16 Feb 2006
Last modified: 07 Oct 2020 01:36

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