Patent ID: 7235171

Claim:
A method of detecting a hydrogen concentration comprising: placing a hydrogen sensor in an atmosphere for detecting the hydrogen concentration, the hydrogen sensor having a solid electrolyte and a first and a second electrode provided on a surface of the solid electrolyte; controlling a temperature of the hydrogen sensor; applying a voltage between the first and the second electrodes; and measuring a current flowing between the first electrode and the second electrode to detect a hydrogen concentration, wherein the solid electrolyte includes an ion conductor that conducts protons and oxide ions, the ion conductor is made of a barium-cerium oxide expressed by a general formula BaCe 1−X−y L X M Y O 3−α , where L is a tetravalent element, M is a trivalent element. 0<x<1,0<Y<1, and α represents a deficiency of oxygen, T·C 0 /(C 0 +C H )≦2.7×10 −3 (S/cm) is satisfied at a temperature in the range from 200 to 450° C., where C 0 is a conductance of the oxide ions and C H is a conductance of the protons, and T (S/cm) is a conductivity of the ion conductor, a temperature of the sensor is controlled to be in the range from 200 to 450° C., and the voltage applied between the first and the second electrodes is controlled so that an electrolytic field intensity formed in the solid electrolyte is controlled to be 1.11 V/mm or less.