Gas sensor

摘要

A hydrogen gas sensor is configured such that a first electrode (3) is provided on one surface of a proton conduction layer (1); a second electrode (5) and a reference electrode (7) are provided on the other surface of the proton conduction layer (1) in opposition to the first electrode (3); and these components are supported in a support element (10) consisting of a first support element (8) and a second support element (9). The first support element (8) has a diffusion controlling portion (19) for establishing communication between an ambient atmosphere and a first recess (11) (thus the first electrode (3)). The diffusion controlling portion (19) is a small hole adapted to introduce to the side toward the first electrode (3) a fuel gas (thus hydrogen gas contained therein), which is a gas to be measured, and to control diffusion of the gas. The diffusion controlling portion (19) is disposed away from an end portion (T) of the second electrode (5) located on the side toward the reference electrode (7), in the direction away from the reference electrode (7). The ratio (area ratio) S1/S2 between a first area (S1) (the area of the meshed portion in FIG. 2) and a second area (S2) (the area of the hatched portion in FIG. 2) is less than 0.35, where the first area (S1) is the area of a portion of a first electrode (3) on which the projected image of a second electrode (5) is not superimposed when the second electrode (5) is projected onto the first electrode (3), and the second area (S2) is the area of a portion of the second electrode 5 which is superimposed on the first electrode (3) when the second electrode (5) is projected onto the first electrode (3). That is, the arrangement and respective areas of the first electrode (3) and the second electrode (5) are determined such that, when the second electrode (5) is projected onto the first electrode (3), the projected image of the second electrode (5) falls within the first electrode (3), and the area ratio (S1/S2) is less than 0.35.