Humidity sensors are utilized in a variety of commercial, industrial and consumer applications. A humidity sensor converts a change resulting from humidity and moisture to an electric quantity and executes signal processing by use of an electronic circuit. It has been widely employed to satisfy a demand for humidity control in a variety of objects
One area where humidity sensing is particularly important is the area of fuel cells, including hydrogen based fuel cell devices. Fuel cells are increasingly being used as a power source in a wide variety of different applications. Fuel cells have also been proposed for use in electrical vehicular power plants to replace internal combustion engines. A solid-polymer-electrolyte fuel cell includes a membrane that is sandwiched between an anode and a cathode. To produce electricity through an electrochemical reaction, hydrogen (H2) is supplied to the anode and air or oxygen (O2) is supplied to the cathode.
In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons. The membrane is proton conductive and dielectric. As a result, the protons are transported through the membrane while the electrons flow through an electrical load that is connected across the electrodes. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+), and electrons are taken up to form water (H2O).
To operate efficiently and to produce a maximum amount of electricity, the fuel cell must be properly humidified. To achieve the proper humidity range, the hydrogen stream and/or the air stream are typically humidified by one of several methods known in the art. Conventional humidity control methods generally fail to sufficiently control the humidity of the hydrogen and air streams to the fuel cell. Providing too much humidity to the fuel cell blocks the reacting gases from accessing the catalyst thereby impeding the electrochemical reaction between the hydrogen and air and reducing the production of electricity. Providing too little humidity to the fuel cell restricts or limits the proton transportation required for reaction within the fuel cell.
In order to provide a humidity sensor, which can be adapted for use in applications such as, but not limited to, fuel cells, an improved sensor structure and methodology is required. The humidity sensor described herein therefore offers such a device.