There is provided a carbon dioxide gas sensor that includes a flow path including an inlet into which a detected target gas is introduced; and a first element and at least one second element arranged in the flow path. The first element includes a first solid electrolyte layer, a first cathode, and a first anode, the first solid electrolyte layer being interposed between the first cathode and the first anode. The at least one second element includes a second solid electrolyte layer, a second cathode, and a second anode, the second solid electrolyte layer being interposed between the second cathode and the second anode. The first solid electrolyte layer and the second solid electrolyte layer are formed of an oxygen ion conductor. The first cathode is inside the flow path. The second cathode and the second anode are inside the flow path and outside the flow path, respectively.

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).

A sensor board includes an insulating substrate having an upper surface and a lower surface, first detection electrodes located on the upper surface of the insulating substrate, second detection electrodes located on the lower surface of the insulating substrate, and a heat generator located between the first detection electrodes and the second detection electrodes inside the insulating substrate and including at least one conductor layer. A portion of the insulating substrate between the heat generator and the first detection electrodes has the same thickness as a portion of the insulating substrate between the heat generator and the second detection electrodes.

A laminated gas sensor element is provided by laminating a plurality of ceramic layers. The gas sensor element includes: a solid electrolyte body having oxygen ion conductivity; a measurement electrode provided on a first principal surface of the solid electrolyte body; a reference electrode provided on a second principal surface of the solid electrolyte body; a chamber facing the measurement electrode and into which a measured gas is introduced; and a heater heating the solid electrolyte body. The chamber comprises at least one projecting corner portion, the at least one projecting corner portion projecting, on a cross section perpendicular to a longitudinal direction of the gas sensor element, in a width direction perpendicular to both of the longitudinal direction and a laminating direction. A tip of the projecting corner portion is disposed on a side closer to the heater than a center of the chamber in the laminating direction is.

A gas sensor has a sensor element, first element pads, second element pads, first contact-point members, and second contact-point members. The sensor element has first and second surfaces that are positioned on opposite sides in a first direction. The first element pads are disposed on the first surface. The second element pads are disposed on the second surface in a quantity greater than that of the first element pads. The first and second contact-point members are connected to the first and second element pads, respectively. The width (Wt) of at least one of the second contact-point members is less than the widths (Wa-Wd) of the rest of the first and second contact-point members.

A gas sensor has a sensor element, first element pads, second element pads, first contact-point members, and second contact-point members. The sensor element has first and second surfaces that are positioned on opposite sides in a first direction. The first element pads are disposed on the first surface. The second element pads are disposed on the second surface in a quantity greater than that of the first element pads. The first and second contact-point members are connected to the first and second element pads, respectively. The width (Wt) of at least one of the second contact-point members is less than the widths (Wa-Wd) of the rest of the first and second contact-point members.

There is provided a method of manufacturing a gas sensor that includes: forming an insulating layer on a main surface of a substrate; forming a porous oxide layer on the insulating layer; and forming a porous metal layer on the porous oxide layer, wherein the forming the porous metal layer is performed by depositing a constituent material of the porous metal layer in an inclined direction with respect to a normal line of a main surface.

A solid electrolyte includes partially stabilized zirconia in which a stabilizer forms a solid solution in zirconia. The partially stabilized zirconia includes at least monoclinic phase particles and cubic phase particles as crystal particles that configure the partially stabilized zirconia, and an abundance ratio of the monoclinic phase particle is 5 to 25% by volume. The partially stabilized zirconia includes stabilizer low-concentration phase particles of which concentration of the stabilizer at a particle center is equal to or less than 1 mol %, as the crystal particles. The stabilizer low-concentration phase particles have a particle-size distribution of number frequency thereof having a peak at which an average particle size is 0.6 to 1.0 μm, and a particle size at 10% of a cumulative number is 0.5 μm or greater, and of the overall low-concentration phase particles, 50% by volume or greater belong to the peak.

A sensor element for a gas sensor includes: an element base being a ceramic structure including a sensing part to sense a gas component to be measured; and a leading-end protective layer being a porous layer to surround a predetermined range from a leading end portion on a side of the sensing part of the element base. The leading-end protective layer protrudes at a first end portion thereof opposite to a portion surrounding the element base in a longitudinal direction of the element base. A/B≥1.1 where A is maximum thickness of the leading-end protective layer, and B is thickness of the leading-end protective layer in a base portion that does not protrude.

In a sensor element for a limiting-current type gas sensor measuring concentration of NOx in a measurement gas, an inner pump electrode located to face a first internal space communicating, under predetermined diffusion resistance, with a gas inlet through which a measurement gas is introduced from an external space is made of a cermet of a Pt—Au alloy and zirconia, and includes a first portion located on a surface farther from a heater part and a second portion located on a surface closer to the heater part from among surfaces opposing each other in the first internal space, an Au content with respect to the Pt—Au alloy as a whole of the second portion is 0.3 wt % or more smaller than that of the first portion, and a total area of the first portion and the second portion is 10 mm.sup.2 to 25 mm.sup.2.