A Nonequilibrium Approach to Development of Reference Electrodes and Oxygen Sensors for High-Temperature Aqueous Systems

A palladium electrode polarized continuously by cathodic current below the hydrogen exchange current was shown to behave as a quasi-reversible hydrogen electrode (QRHE) that can be used as an internal reference electrode (RE) in any high-temperature aqueous solution containing < 300 ppb dissolved oxygen, regardless of dissolved hydrogen concentration. The potential of the QRHE differed by < 30 mV from the potential of the reversible hydrogen electrode (RHE). Together with QRHE, platinum or zirconium electrodes polarized by specially programmed alternating current (AC) may be used as sensors for in situ measurements of the concentrations of dissolved oxygen and/or hydrogen peroxide (H₂O₂). Values of the rate constants and activation energy (Q) of H₂O₂ decomposition at temperatures up to 290°C, as obtained using these sensors, were within the scattering limits of published data.