Abstract
Herein, a simplified fabrication method for the producing of a pH-sensitive iridium electrode is developed. The in situ electrochemical fabrication of an iridium oxide film is optimized and shown to be achievable under neutral conditions rather than the acidic conditions hitherto employed. The formation of a pH sensitive Ir(III/IV) hydrous film is confirmed via XPS. The amperometric pH-sensing properties of this electrochemically generated material were investigated using square wave voltammetry. In the pH range 2–13, the iridium oxide redox signal has a pH dependency of 86.1 ± 1.1 mV per pH unit for midpoint potentials with uncertainties being ± 0.01–0.05 pH. Finally, the newly developed pH sensor was used to measure the pH of a natural water sample with excellent results as compared to a conventional glass pH probe.
Highlights
The determination of pH quantifies how acidic or basic an aqueous solution is
We first explore the oxidative voltammetry of iridium metal under conditions of near neutral pH to show the in situ formation of iridium oxide features which are subsequently used as the basis for amperometric pH sensing
The pH response was further explored using square wave voltammetry (SWV) and an analytical methodology for pH defined in which the surface bound pH sensing redox couple is generated in situ from an iridium wire
Summary
The determination of pH quantifies how acidic or basic an aqueous solution is. It is probably the most commonly made measurement by a chemical sensor. This process has been reported to involve various possible redox reactions between the reduced and oxidised forms of oxyhydroxide where the exact stoichiometric composition of the hydrous film is reported as hard to determine [64, Fig. 1 (a) Cyclic voltammograms in a degassed buffer solution with pH = 7.25 showing the activation of an Ir wire at a scan rate of 0.5 V s−1 for multiple cycles.
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