Carbon dioxide sensing mechanisms of an electrocatalytic sensor/cell based on a tungsten stabilized bismuth oxide solid electrolyte

This work describes the specific O₂/CO₂ sensing mechanisms of a solid-state, thick-film, electrocatalytic cermet (ceramic/metallic) gas sensor based on a tungsten stabilized bismuth oxide (WBO) solid electrolyte. The sensors embody the same configuration of classical planar oxygen sensors with two catalytic electrodes sandwiching an oxygen ion conducting solid electrolyte and a buried metal oxide reference. The technique of cyclic voltammetry is used where a cyclic voltage is ramped across the electrodes to promote electrochemical reactions on the surface of the sensor. These reactions alter the ionic current flow through the solid electrolyte, generating voltage-current related responses (voltammograms) which are gas specific. The WBO sensors have the identical configuration of previously investigated sensors of this type based on a yttria stabilized zirconia (YSZ) solid electrolyte which show good response to O ₂ but do not respond to CO₂ to any degree. This dissertation examines the specific function of each solid electrolyte layer and relates them to both the WBO sensors ability to respond uniquely to CO₂ and the YSZ sensors incapability to respond to CO₂. The research suggests that the tungsten component of the WBO electrolyte along with the porosity of the WBO layer together are responsible for the unique CO ₂ response of this sensor.