A mixed-potential type gas sensor capable of preferably determining the concentration of THC including a kind of gas having a large C number is provided. A sensor element composed of an oxygen-ion conductive solid electrolyte is provided with, on its surface, a sensing electrode formed of a cermet of Pt, Au, and an oxygen-ion conductive solid electrolyte, and includes a reference electrode and a porous surface protective layer that covers at least said sensing electrode. An Au abundance ratio on a surface of noble metal particles forming the sensing electrode is 0.3 or more. The surface protective layer has a porosity of 28% to 40%, a thickness of 10 to 50 μm, and an area ratio of a coarse pore having a pore size of 1 μm or larger of 50% or more; or has a porosity of 28% to 40% and a thickness of 10 to 35 μm.

A sensor element includes an element body including an oxygen-ion-conductive solid electrolyte layer, the element body having a longitudinal direction, a measurement electrode disposed in the element body, a reference electrode disposed in the element body so as to come into contact with a reference gas, and a heater configured to heat the solid electrolyte layer. A center of gravity of the reference electrode overlaps the measurement electrode as viewed in a thickness direction of the solid electrolyte layer. A length of each of the reference electrode and the measurement electrode in a front-rear direction is less than or equal to 1.1 mm, the front-rear direction being a direction along the longitudinal direction of the element body. An area of the reference electrode as viewed in the thickness direction is greater than or equal to 1.0 mm.sup.2.

A gas sensor includes a sensor element, a detection device, a reference gas regulating device. The sensor element includes an element body having disposed therein a measurement-object gas flow section, a measurement-object-gas-side electrode disposed in or out of the element body, a reference electrode disposed within the element body, and a reference gas introducing section that allows a reference gas to be introduced thereinto and to flow therethrough to the reference electrode. The reference gas regulating device allows an oxygen pump-in current to flow between the reference electrode and the measurement-object-gas-side electrode to pump oxygen into around the reference electrode from around the measurement-object-gas-side electrode. A ratio R1/R2 of a reaction resistance R1 of the reference electrode to a diffusion resistance R2 of the reference gas introducing section is greater than or equal to 0.1 and less than or equal to 2.0.

Electrochemical sensors can include at least two electrodes, over which an electrolyte is formed. The electrodes can be isolated from one another in order for reduction/oxidation reactions to occur at the electrodes and for an electric current to flow therebetween. The present disclosure describes the use of a barrier in the electrochemical sensor that is configured to isolate electrodes from one another for the purpose of preventing electrode shorting. Additionally, the physical structure of the barrier can also act as a stencil for shaping the electrodes.

Electrochemical sensors (100) include at least two electrodes (110A, HOB), over which an electrolyte (114) is formed. The electrodes are isolated from one another in order for reduction/oxidation reactions to occur at the electrodes and for an electric current to flow therebetween. The present disclosure describes the use of a barrier (121) in the electrochemical sensor that is configured to isolate electrodes from one another for the purpose of preventing electrode shorting. Additionally, the physical structure of the barrier can also act as a stencil for shaping the electrodes.

A sensor element for detecting a target gas to be measured in a measurement-object gas includes: an element body including an oxygen-ion-conductive solid electrolyte layer; and a protective layer covering at least a part of a surface of the element body. The protective layer includes a porous material that has a pore inside; and, in the pore in the protective layer, a ratio (Lt/Lf) of a pore length (Lt) in a thickness direction perpendicular to the surface of the element body to a pore length (Lf) in a surface direction perpendicular to the thickness direction is 0.6 to 0.9.

A gas sensor includes a gas sensor element for detecting a specific gas concentration in measured gas. The gas sensor element includes a solid electrolyte, a measured gas side electrode into which measured gas is introduced through a porous diffusion resistance layer, a reference gas side electrode facing a reference gas chamber, and a diffusion space portion between the porous diffusion resistance layer and the measured gas side electrode. The porous diffusion resistance layer has a measured gas inlet opened to an element outer surface and a measured gas outlet opened to the diffusion space portion. A relationship between a distance between the inlet and the outlet and a distance between the outlet and the measured gas side electrode is expressed by 0<L1/(L1+L2)<0.4.

The present invention provides methods and devices for detecting and distinguishing various types of gas molecules or volatile organic compounds (VOCs), the methods and devices have enhanced sensing ability; namely response magnitude, sensitivity, detection limit and selectivity (i.e., classification capability). In one embodiment, the present invention provides methods and devices for diagnosing a disease in a subject or a health status of a subject through the detection of VOCs indicative of the disease or health status in question from breath of the subject. In one embodiment, the present invention provides methods and devices for detecting the existence of lung cancer or the stage of lung cancer in a subject through the detection of VOCs indicative of the existence of lung cancer from breath of the subject.

A NOx sensor is provided which decreases a change rate of an oxygen ion current in a sensor electrode and shortens an activation time of the sensor electrode. The NOx sensor is equipped with a solid electrolyte body, a pump electrode working to regulate an oxygen concentration in measurement gas G, and a sensor electrode working to measure the concentration of NOx in the measurement gas G. A metallic component of the sensor electrode is a Pt—Rh alloy. The mass ratio of Pt to Rh in the whole of the sensor electrode is Pt:Rh=70:30 to 35:65. The percentage of Rh in the Pt—Rh alloy in a surface layer of the sensor electrode is higher than that in the whole of the sensor electrode by an atomic composition percentage of 4 to 10 atom %.

A solid electrolyte CO.sub.2 sensor may include a solid electrolyte bonded to a substrate to join and seal the substrate, a sensing electrode formed at a first side of the solid electrolyte, and a reference electrode formed between a second side of the solid electrolyte and one surface of the substrate, and sealed by the solid electrolyte and the substrate.