Palladium/Hydrogen Membrane Electrode for High Temperature/High Pressure Aqueous Solutions

Several reference electrodes have been reported for high temperature/high pressure aqueous solutions, but none of them are fully satisfactory for fast relaxation measurements of electrode kinetics. The charged palladium electrode seems to fulfill all requirements at lower temperatures, but above 200°C the diffusional loss of hydrogen, into a solution not saturated with hydrogen, is very fast and the electrode must be recharged frequently. This problem can be overcome by use of a palladium‐silver alloy membrane as an electrode with suitable hydrogen partial pressure on the dry side. Several electrodes of this type were built and tested over the temperature range from 100° to 300°C at a constant system pressure of 10,000 kPa and a hydrogen pressure range of 300–7000 kPa, in boric acid/lithium hydroxide solutions with a p H range of 5–11. The palladium membrane electrode was found to operate as a classical hydrogen electrode and is usable either as a p H electrode (combined with a p H‐independent reference electrode) or as a reference electrode (in a constant p H solution).