Use of Phosphoric and Sulphuric Acids in Hydrocarbon Electrode Investigations

Abstract

DURING an examination of hydrocarbon electrodes, evidence was obtained which confirms that analytical reagent grade phosphoric and sulphuric acids contain an oxidizable impurity. The cell and procedures used will be described elsewhere¹. In Fig. 1 is shown a plot of potential versus log apparent current density for platinized platinum immersed in nitrogen-stirred unpre-electrolysed 5MH₃PO₄ at 80° C (inverted triangles). Prior to these measurements the system had not been in contact with a hydrocarbon or any other oxidizable material. The slope of the linear part of the curve is 143 mV. After an anodic pre-electrolysis (60 h at an anodic current density of 62 m.amp/cm²), the Tafel behaviour was no longer observed with nitrogen stirring, and a limiting current was reached (triangles, Fig. 1). When the purified acid was stirred with ebhylene at 80° C, the polarization curve obtained (circles, Fig. 1) was identical with that obtained with nitrogen stirring of the unpre-electrolysed acid. Similar data obtained with 3N H₂SO₄ are shown in Fig. 2. The slope of the linear parts of the curves in this case is 183 mV.