Optical Sensor for Unambiguous Trace Hydrogen Detection in the Presence of Oxygen

Next generation crewed spacecraft are expected to produce oxygen, using on-board oxygen generation systems (water electrolysis for example). H2 and O2 being products of electrolysis, a safety sensor for trace hydrogen gas detection is required in a moist O2 gas stream. Currently H2 is vented out of the spacecraft, whereas O2 is bled into the ventilation loop of the spacecraft. Early detection of trace H2 levels and warning of H2 buildup would be critical for ensuring mission and crew safety. To meet this need, InnoSense LLC investigated sensors that can detect the presence of hydrogen in 100% oxygen background unambiguously. The hydrogen sensor design utilizes colorimetric indicators immobilized in an organically modified silicate (ORMOSIL) matrix deposited onto glass substrates. The temperature sensor uses a luminophore immobilized in an ORMOSIL matrix which is further encapsulated by an oxygen barrier layer. The hydrogen and temperature indicating materials are sensitive, selective, and respond to the presence of analytes through absorbanceor luminescence-based pathways. Changes in the luminescence/absorbance properties of the coated substrates are directly related to changes in the analytes of interest. We successfully screened hydrogen-sensing formulations with a working model of a multianalyte optical sensor that detects 25 ppm of H2 in N2 background, 100 ppm H2 in dry 90% O2 and 1000 ppm in moist 90% O2 background. We also demonstrated temperature-sensing capabilities with the optical temperature sensor in the range of 23–100 °C. The optoelectronic design includes feedback loop circuitry for self-referencing and drift-free sensor performance. Electronic temperature and humidity sensors are included for temperatureand humidity-compensated calibration capability. The multi-analyte optical sensor array (MOSA) platform enables the expansion of detected species to include a trace O2 sensor in hydrogen background or other relevant gas phase species. The development of this sensor has broad implications for use in monitoring the air quality of enclosed environments such as aircraft, buildings, submarines and automobiles.