Gas sensor

A mixed-potential gas sensor configured to sense a sensing target gas component contained in measurement gas and identify a concentration of the sensing target gas component, the gas sensor comprising:

• a sensor element made of an oxygen-ion conductive solid electrolyte, the sensor element having a leading end part which contacts the measurement gas and a base end part at an opposite end from the leading end part and does not contact the measurement gas;
• a first sensing electrode as a cermet electrode provided on a surface of said sensor element on one side of the leading end part and containing a Pt—Au alloy;
• a second sensing electrode as a cermet electrode provided on the surface of said sensor element on said one side of the leading end part and containing Pt;
• a reference electrode provided inside said sensor element to be made contact with air;
• an electrode protective layer as a porous layer covering said first and second sensing electrodes;
• a housing inside which said sensor element is fixed;
• a protective cover that is attached to said housing and surrounds said one leading end part of said sensor element and into which measurement gas flows;
• and
• a controller and an electronic control unit (ECU) configured to identify the concentration of said sensing target gas component in said measurement gas, said controller being configured to acquire, while said gas sensor is disposed in said measurement gas, a first sensor output as a potential difference occurring between said first sensing electrode and said reference electrode in accordance with the concentration of said sensing target gas component and a concentration of oxygen, and a second sensor output as a potential difference occurring between said second sensing electrode and said reference electrode in accordance with the concentration of oxygen, and provide the first and second sensor outputs to the ECU, and the ECU being configured to identify the concentration of said sensing target gas component in said measurement gas based on said first and second sensor outputs,
• wherein said first sensing electrode and said second sensing electrode are disposed on the surface of said sensor element on said one side of the leading end part so that said measurement gas flowing into said protective cover reaches said first sensing electrode earlier than said second sensing electrode.