Sensing Characteristics and Working Mechanism of Four-Probe Type Solid-State Hydrogen Sensor Using Proton Conductor

A solid-state proton conductor (antimonic acid) sensor capable of detecting dilute hydrogen in air at room temperature has been developed. The sensor element has a four-probe type structure with two inner Ag probes and two outer Pt electrodes. With the outer electrodes short-circuited, the potential difference between the two inner probes was used as a signal output. It was found that the output was not only proportional to hydrogen concentration (up to 1.3%) in air, but also independent of relative humidity (7-90%). The 90% response time was as short as 20s to 0.2% H₂ at 25°C. The signal output had a small positive temperature coefficient (ca. 2 mV/°C) in the range from 10° to 35°C. The sensor was fairly stable during the test period of about one month. A hydrogen sensing mechanism was proposed and discussed with supporting evidence about electric potential profiles inside the proton conductor.