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-reversib le 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 concentrati on. The potential of the QRHE differed by < 30 mV from the potential o f the reversible hydrogen electrode (RHE). Together with QRHE, platinu m or zirconium electrodes polarized by specially programmed alternatin g current (AC) may be used as sensors for in situ measurements of the concentrations of dissolved oxygen and/or hydrogen peroxide (H2O2). Va lues of the rate constants and activation energy (Q) of H2O2 decomposi tion at temperatures up to 290 degrees C, as obtained using these sens ors, were within the scattering limits of published data.