A Review of Current and past Reference Electrode Technology for Use in High Subcritical and Supercritical Aqueous Systems

Abstract The design and performance of reference electrodes for use in high subcritical and supercritical aqueous systems are reviewed. Particular attention is paid to the stability of the electrochemically active elements, to the contribution of the two irreversible thermodynamic potentials (the isothermal liquid junction potential and the thermal liquid junction potential) to the measured potential, to calibration of the reference electrode on to the standard hydrogen scale, and to the application of the electrodes in pH measurements and in potentiometry. Methods for estimating and suppressing the thermal diffusion potential and the isothermal liquid junction potential are also discussed. While significant progress has been made over the past several decades in developing viable reference electrodes for use in high temperature aqueous systems, particularly for potential monitoring in subcritical systems, no universally accepted reference electrode has emerged for potential monitoring in supercritical aqueous systems.