Redox potential measurements in the H2SO4-FeSO4-Fe2(SO4)3-H2O system at high temperature using an Ir electrode

Abstract

An Ir electrode was evaluated as a suitable alternative to Pt for redox potential measurements at high temperature and high pressure. Measurements were performed using a flow-through electrochemical cell (FTEC) with a Ag/AgCl in 0.1m LiCl flow-through external pressure-balanced reference electrode (FTEPBRE), at a flow rate of 0.5mL/min, 35atm (500psia) and up to 200°C. The potential was measured for the H2SO4-FeSO4-Fe2(SO4)3-H2O system for concentrations of 1M H2SO4, 10−2M Fe(III), and 10−4–10−2M Fe(II) (ratios of [Fe(II)]/[Fe(III)] equal to 0.01, 0.1, and 1 respectively). The potentials measured with the Ir electrode were similar to those obtained using a Pt electrode, with a maximum difference of 8mV over the range of studied solutions and temperatures. The change in potential measured with the Ir electrode behaved according to the Nernst equation upon changes in the test solution, and were consistent with the corresponding estimated potential variation predicted by the Aqueous (OLI-AQ) model from the OLI® aqueous chemistry simulation software (www.olisystems.com).