A gas sensor having a reliable measurement accuracy for specific gases even if a pump electrode is heated and a method for manufacturing the same are provided. The gas sensor is provided with a measurement target gas chamber, a reference gas chamber, a solid electrolyte, a pump electrode, a sensor electrode, a reference electrode and a heater. The pump electrode includes Pt, Au and an aggregate. After the gas sensor has been manufactured, in a state that the pump electrode has not been heated to an activation temperature of the solid electrolyte yet, in the pump electrode, a pore is 5.2 vol % or less, a surface roughness Ra is 0.5 μm to 9.1 μm, and a content ratio of the aggregate 31 is 4.9 vol % or more.

A NO.sub.2 gas sensing element includes an electrolyte, a reference electrode in contact with the electrolyte, and a sensing electrode selective to NO.sub.2 in contact with the electrolyte spaced apart from the reference electrode. The NO.sub.2 selective sensing electrode includes an oxide material comprising: (1) a mixed oxide according to the formula (Mn.sub.2-u-v-wCo.sub.vMg.sub.wSiO.sub.4-u)+ξ(Mn.sub.3Al.sub.2Si.sub.3O.sub.12)+δ(SiO.sub.2), wherein 0≦(u+v+w)≦2.0, 0≦ξ≦0.5, and 0≦δ≦0.1; (2) a mixed oxide according to the formula (Mn.sub.2-x-y-zCo.sub.yMg.sub.zSiO.sub.4-x)+ξ(ZnO)+δ(SiO.sub.2), wherein 0≦(u+v+w)≦2.0, 0≦ξ≦0.5, and 0≦δ≦0.1; or combinations of mixed oxides (1) and (2).

A control device of an exhaust sensor comprises a cell temperature detecting part detecting a temperature of the electrochemical cell, a heater control part controlling the heater so that a temperature of the electrochemical cell becomes the target temperature, and a judging part judging whether a water repellency of the protective layer is falling. The judging part judges that the water repellency of the protective layer is falling if a condition for judging abnormality is satisfied. The condition for judging abnormality includes a temperature of the electrochemical cell detected by the cell temperature detecting part falling from the target temperature and a speed of fall of the temperature being faster than a speed of fall of the temperature of the electrochemical cell when the heater is turned off.

A gas concentration detection device for detecting a gas concentration using a limiting current type gas concentration sensor. In an application voltage line set to pass through a plurality of limiting current regions for different values of gas concentration, the voltage set by the application voltage line is an identical first voltage value used when an air/fuel ratio corresponding to the gas concentration is in a predetermined first range, is an identical second voltage value different from the first voltage value used when the air/fuel ratio is in a second range adjacent to the first range, and the first voltage value and the second voltage value are switched between the first range and the second range.

A sensor element according to the present invention includes an element body having a measurement-object gas flow section into which an exhaust gas is introduced, an adjustment pump cell including a measurement-object-gas-side electrode disposed in a portion exposed to the exhaust gas on an outer side of the element body, the adjustment pump cell being configured to adjust an oxygen concentration in an oxygen concentration adjustment chamber included in the measurement-object gas flow section, a measurement electrode disposed in a measurement chamber located downstream of the oxygen concentration adjustment chamber, and a reference electrode into which a reference gas is introduced. The measurement-object-gas-side electrode has an Au/(Pt+Au) ratio (=an area of a portion where Au is exposed/an area of a portion where Au and Pt are exposed) 0.2-0.7, the Au/(Pt+Au) ratio being measured by using XPS.

A control device of a nitrogen oxide sensor comprises a voltage control part configured to control voltage applied to the pump cell, and a temperature estimation part configured to estimate a temperature of the pump cell. The voltage control part is configured to make the voltage applied to the pump cell a voltage of a starting voltage of decomposition of water or more when the estimated temperature of the pump cell estimated by the temperature estimation part is within a predetermined temperature region of less than an activation temperature of the pump cell as control suppressing evaporation.

An insulating separator of a gas sensor is formed to be dividable into a forward separator having a terminal disposition hole, and a rear separator having four terminal disposition holes. The insulating separator has a ventilation path formed between the forward separator and the rear separator. As a result, moisture and the like which enter the insulating separator from a forward side of the forward separator through the terminal disposition hole can be discharged outward of the insulating separator through the ventilation path. As a result, corrosion of metal terminals caused by entry of moisture can be reduced, whereby transmission of a sensor signal and application of current or voltage through the metal terminals can be appropriately implemented.

A membrane electrode assembly of an electrochemical device includes a proton conductive solid electrolyte membrane and an electrode including Ni and an electrolyte material which contains as a primary component, at least one of a first compound having a composition represented by BaZr.sub.1-x1M.sup.1.sub.x1O.sub.3 (M.sup.1 represents at least one element selected from trivalent elements each having an ion radius of more than 0.720 A° to less than 0.880 A°, and 0<x.sub.1<1 holds) and a second compound having a composition represented by BaZr.sub.1-x2Tm.sub.x2O.sub.3 (0<x.sub.2<0.3 holds).

Provided are: an electrode for a gas sensor formed as a porous electrode so as to stably allow reduction in electrode resistance for excellent low-temperature activity; and a gas sensor. The electrode (108, 110) for the gas sensor is adapted for use on a surface of a solid electrolyte body (109), which is predominantly formed of zirconia, and contains particles (2) of a noble metal or an alloy thereof, first ceramic particles (4) of stabilized zirconia or partially stabilized zirconia and second ceramic particles (6) of one or more selected from the group consisting of Al.sub.2O.sub.3, MgO, La.sub.2O.sub.3, spinel, zircon, mullite and cordierite, wherein the second ceramic particles are contained in an amount smaller than that of the first ceramic particles.

A control system of an exhaust sensor controlling an exhaust sensor comprises a heater control part controlling a heater and a temperature estimating part estimating a temperature of an exhaust pipe around the exhaust sensor. The heater control part sets the target temperature to a first target temperature after startup of the internal combustion engine and until the estimated temperature of the exhaust pipe reaches a first exhaust pipe temperature, sets the target temperature to a second target temperature from when the estimated temperature of the exhaust pipe reaches the first exhaust pipe temperature to when it reaches a second exhaust pipe temperature, and sets the target temperature to an operating temperature of the electrochemical cell when the estimated temperature of the exhaust pipe reaches the second exhaust pipe temperature.