Preparation of Antimony Oxide in Different Media and Its Effect on the pH Measurement

A thin film of antimony-oxide on an antimony electrode (Sb-Sb-oxide) is a simple, robust, and low-cost electrode for pH measurement. This study reports on the effect of different electrolytic media on forming a thin-film of Sb-oxide by electrochemical methods and its stability for pH measurements. An antimony electrode was obtained by the melting and solidification of antimony powder. Sb-oxide, thus obtained by electrochemical methods, was characterized by X-ray Photoelectron Spectroscopy (XPS). The cyclic voltammetry (CV) study revealed a complex oxide formation mechanism. This mechanism could be interpreted as a stepwise formation of different Sb species, such as Sb2O3 and Sb2O5, in a low field near an open circuit potential (OCP). XPS results showed that the Sb2O3 and Sb2O5 ratio was almost similar in acidic medium, whereas Sb2O5 was dominant in phosphate solution. All the prepared Sb- Sb-oxide electrodes showed a linear electromotive force (e.m.f.) in pH 2-10, giving a slope of 0.049- 0.052 V/pH at room temperature (RT). The electrodes gave an excellent pH response, and hence they can be used in standard laboratory experiments where the accuracy of ±0.02 pH is required. However, Sb-oxide obtained in phosphate buffer solution of pH 7 showed a lower electrode sensitivity and lower stability due to dominant Sb2O5 formation.