Sensitive Hydrogen Sensor Research Articles

Optimization of physical filtering for selective high temperature H 2 sensors

This paper investigates the improvement in selectivity by means of applying a physical gas filter. Looking for a selective and highly sensitive hydrogen sensor, various filter systems, single, dual and buried filter systems, were deposited on top of a basic high-temperature semiconducting Ga 2O 3 thin film sensor. Sensor respondence on a big variety of gases present in domestic ambience and especially hydrogen and ethane, which is the hardest test on cross sensitivity, is shown. Using a single filter SiO 2 layer a selective hydrogen sensor is realized, which is able to detect 50 ppm hydrogen at an operation temperature of 700°C in humid air without any interference caused by other gases. Dual SiO 2/metal oxide filter systems and buried metal oxide layer filters show behaviors varying from selective ethane to selective hydrogen detection.

Highly sensitive hydrogen sensors using palladium coated fiber optics with exposed cores and evanescent field interactions

A novel fiber optic hydrogen sensor which is constructed by depositing palladium over an exposed core region of a multimode fiber is reported. The sensing mechanism is based on evanescent field interaction with the palladium coating. Since the length, thickness, and composition of the palladium patch can be controlled independently of each other, it is possible to increase the speed of our sensor at lower temperatures while maintaining its sensitivity. In micromirror sensors such an optimization is not possible due to a restriction imposed on their active area of interaction by the fiber optic cross-section. Micromirror fiber optic sensors, studied in the past, take advantage of the reflection/absorption of a palladium film deposited at the end of a fiber resulting in one sensor per fiber optic strand. On the other hand, many evanescent field-based sensors can be deposited over a single fiber optic strand. Using a 100 Å thick palladium with 1.5 cm interaction length, we could detect hydrogen in the 0.2–0.6% range with corresponding response times of 30–20 s at room temperature. At −10°C, these response times increased by a factor of only 2.

A highly sensitive and selective hydrogen gas sensor from thick oriented films of MoS2

A new process is developed to fabricate a highly sensitive and selective hydrogen sensor by depositing a partially crystalline and highly oriented film of MoS2 from its single layer suspension on an alumina substrate. When these films are promoted with some catalysts selected from Pt-group metals (Pt, Pd, Ru or any combination of these metals) they exhibit a high sensitivity and selectivity to hydrogen gas. Unlike other metal oxide sensors which are sensitive to many reducing and oxidizing gases and operate at a temperature of 350 °C or higher; this sensor is highly selective to hydrogen gas and its operating temperature is from 25 to 150°C. The lower operating temperature enhances safety when dealing with hydrogen gas. The sensor response to hydrogen at 120 °C is linear in concentration from 30 to 104 ppm with a 10 to 30 second response time and a 45 to 90 second recovery time. Above 104 ppm the sensor is still linear but the slope of conductance versus hydrogen concentration changes.

A new technique for the preparation of highly sensitive hydrogen sensors based on SnO 2(Bi 2O 3) thin films

H 2 in air can be detected with sensors based on semiconductor oxides. A new technique for growing a hydrogen sensor based on SnO 2(Bi 2O 3) thin films is presented here. The thin films have a thickness of 200–250 nm and the metals are in the atomic ratio Bi/Sn = (3–5) at.%/(97-95) at.%. The two metals are deposited by means of evaporation in a high vacuum; the metal-semiconductor phase transformation consists of a thermal cycle in air. The initial step involves a fast transition from room temperature up to 350 °C over a few minutes, and causes a local partial melting of the metallic alloy. The surface of these thin films is made up of spongy agglomerates, having a surface area about 1000 times larger than a flat surface and covering about 60–70% of the total area. Sensors grown with this method also seem to be able to detect a few ppm of H 2 in air at 450°C with a response time of about 10–20 s.