The Control of Oxygen Activities in Argon-Oxygen Mixtures by Coulometric Titration

High‐temperature electrochemical cells based on stabilized zirconia as a solid electrolyte with porous platinum electrodes may be used either to monitor oxygen activities by open‐circuit measurements or else to pump oxygen into or out of stationary or streaming gas mixtures. In this work, a feed‐back control unit (potentiostat) in combination with a zirconia‐base solid electrolyte tube was used to simultaneously control and measure the oxygen partial pressure in a flowing inert carrier gas (argon). The oxygen activity of "tank" argon was controlled to desired levels between 2 × 10 −2 and 10 −16 atm oxygen. A four‐electrode double cell arrangement is shown to be superior to a three‐electrode arrangement.