Patent ID: 7513157

Claim:
A Method for determining the redox state of an anode of a high-temperature fuel cell or a reaction surface of a reformer, which anode or reaction surface is in contact with a gas flow containing at least one of H 2 , CO and CH 4 and is coated with or made from a catalyst material, comprising the steps of (a) bringing at least a first resonator of a piezoelectric sensor device into contact with said gas flow of said high-temperature fuel cell or said reformer, a surface of the first resonator having a coating which is oxidized or reduced in said gas flow, (b) measuring at least one change in a resonance property of the first resonator, and (c) inferring the redox state of the anode of said high-temperature fuel cell or the reaction surface of said reformer from a change of the resonance properties of the first resonator.