Patent ID: 7276141

Claim:
A hydrogen gas sensor comprising: a proton-conductive layer formed of a polymer electrolyte; first and second electrodes provided in contact with the proton-conductive layer; a diffusion-rate limiting portion disposed between the first electrode and an atmosphere of a gas under measurement containing hydrogen; and a circuit for applying a voltage between the first and second electrodes such that hydrogen introduced from the atmosphere via the diffusion-rate limiting portion undergoes dissociation, decomposition, or reaction to produce protons on the first electrode, and for determining the hydrogen concentration of the gas under measurement based on a saturation current which flows as a result of conduction of protons from the first electrode to the second electrode via the proton-conductive layer; said sensor having a proton-conducting rate from the first electrode to the second electrode that is greater than a rate at which protons derived from hydrogen are introduced onto the first electrode via the diffusion-rate limiting portion, and wherein the gas-diffusion resistance of the diffusion-rate limiting portion is set such that current (a)>current (b): current (a) is a current flowing between the first and second electrodes upon application of a voltage of 50 mV or higher between the first and second electrodes in a state in which the gas-diffusion resistance of the diffusion-rate limiting portion is 0.9 mA/mm 2 or more with current conversion at H 2 =40% and the measurement gas has a H 2 O concentration of 10% or less at 80° C. or a CO concentration of 1,000 ppm or greater; and current (b) is a saturation current flowing between the first and second electrodes in a state in which the gas-diffusion resistance of the diffusion-rate limiting portion is less than 0.9 mA/mm 2 with current conversion at H 2 =40% and the measurement gas has a H 2 O concentration of 15% or greater at 80° C. or a CO concentration of 800 ppm or less.