Hydrogen sensors are of increasing importance in connection with the development and expanded use of hydrogen gas as an energy carrier and as a chemical reactant. There are an immense number of sensors reported in the literature for hydrogen detection and in this work these sensors are classified into eight different operating principles. Characteristic performance parameters of these sensor types, such as measuring range, sensitivity, selectivity and response time are reviewed and the latest technology developments are reported. Testing and validation of sensor performance are described in relation to standardisation and use in potentially explosive atmospheres so as to identify the requirements on hydrogen sensors for practical applications.

Hydrogen Sensors - A review

We developed a simple and cost-effective fabrication technique to construct a hydrogen nanosensor by decorating single-walled carbon nanotubes with Pd nanoparticles. By varying the sensor's synthesis conditions (e.g., Pd electrodeposition charge, deposition potential, and initial baseline resistance of the SWNT network), the sensing performance was optimized. The optimized sensor showed excellent sensing properties toward hydrogen (ΔR/R of 0.42%/ppm) with a lower detection limit of 100 ppm and a linear response up to 1000 ppm. The response time decreased from tens of minutes to a few minutes with increasing hydrogen concentration at room temperature. The sensor's recovery time improved under humid air conditions compared to dry air conditions.

Palladium Nanoparticles Decorated Single-Walled Carbon Nanotube Hydrogen Sensor

High‐Performance, Flexible Hydrogen Sensors That Use Carbon Nanotubes Decorated with Palladium Nanoparticles

Palladium (Pd) has received attention as an ideal hydrogen sensor material due to its properties such as high sensitivity and selectivity to hydrogen gas, fast response, and operability at room temperature. Interestingly, various Pd nanostructures that have been realized by recent developments in nanotechnologies are known to show better performance than bulk Pd. This review highlights the characteristic properties, issues, and their possible solutions of hydrogen sensors based on the low-dimensional Pd nanostructures with more emphasis on Pd thin films and Pd nanowires. The finite size effects, relative strengths and weaknesses of the respective Pd nanostructures are discussed in terms of performance, manufacturability, and practical applicability.

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Low-Dimensional Palladium Nanostructures for Fast and Reliable Hydrogen Gas Detection

Pd doped WO3 films prepared by sol–gel process for hydrogen sensing

On the basis of a Pt/In052Al048As metal-semiconductor structure, a novel hydrogen sensor is fabricated and demonstrated The studied Pt/In052Al048As Schottky diode-type hydrogen sensor exhibits significant sensing performance including high relative sensitivity ratio of about 2600% (under the 1% H2/air gas and VR=-05 V at 30 degC), large current variation of 310 muA (under the 1% H2/air gas and VR=-5 V at 200 degC), widespread reverse-voltage regime (0~-5 V), stable hydrogen-sensing current-voltage (I-V) curves, and fast transient response time of 15 s The calculated Schottky barrier-height change and series-resistance variation, from the thermionic-emission model and Norde method, are 870 meV and 288 Omega, respectively (under the 1% H2/air gas at 30 degC) The hydrogen concentrations and operating temperatures tested in this letter are in the range of 15 ppm-1% H2/air and 30 degC-250 degC, respectively Based on the excellent integration compatibility with InP-based electronic devices, the studied device provides the potentiality in high-performance sensor-array applications

A Novel $\hbox{Pt/In}_{0.52}\hbox{Al}_{0.48}\hbox{As}$ Schottky Diode-Type Hydrogen Sensor

An ammonia sensor based on a Pt/AlGaN/GaN Schottky diode, fabricated by the electroless plating (EP) technique, has been studied in this work. The studied sensor device shows a significant sensing response under an extremely low ammonia concentration of 10 ppb NH 3 /air at 115 °C. As exposed to a 1000 ppm NH 3 /air gas, a high sensing response of 16.22 with a response (recovery) time of 8.73 (2.04) min is obtained. Even at room temperature (25 °C), the studied sensor exhibits good ammonia sensing performance with a sensing response of 2.68 at 1000 ppm NH 3 /air and a low detection limit of 1 ppm NH 3 /air. Based on the excellent sensing performance and inherent advantages of low-power consumption and low-temperature operation, the studied sensor device provides the promise for high-performance ammonia sensing applications.

Study of an electroless plating (EP)-based Pt/AlGaN/GaN Schottky diode-type ammonia sensor

Comprehensive study on hydrogen sensing properties of a Pd–AlGaN-based Schottky diode

The influences of (NH/sub 4/)/sub 2/S/sub x/ treatment on an AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) are studied and demonstrated. Upon the sulfur passivation, the studied device exhibits better temperature-dependent dc and microwave characteristics. Experimentally, for a 1/spl times/100 /spl mu/m/sup 2/ gate/dimension PHEMT with sulfur passivation, the higher gate/drain breakdown voltage of 36.4 (21.5) V, higher turn-on voltage of 0.994 (0.69) V, lower gate leakage current of 0.6 (571) /spl mu/A/mm at V/sub GD/=-22 V, improved threshold voltage of -1.62 (-1.71) V, higher maximum transconductance of 240 (211) mS/mm with 348 (242) mA/mm broad operating regime (>0.9g/sub m,max/), and lower output conductance of 0.51 (0.53) mS/mm are obtained, respectively, at 300 (510) K. The corresponding unity current gain cutoff frequency f/sub T/ (maximum oscillation frequency f/sub max/) are 22.2 (87.9) and 19.5 (59.3) GHz at 250 and 400 K, respectively, with considerably broad operating regimes (>0.8f/sub T/,f/sub max/) larger than 455 mA/mm. Moreover, the relatively lower variations of device performances over wide temperature range (300/spl sim/510 K) are observed.

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

A hydrogen sensor based on the Pd/GaAs pseudomorphic high electron mobility transistor (PHEMT) is fabricated and investigated under various hydrogen concentrations in air and N2 environments. Experimentally, in nitrogen (air) ambiances, the studied sensor exhibits a hydrogen detection limit of 4.3 ppm H2/N2 (98 ppm H2/air) at 130 °C, a high sensitivity of 1295 μA/mm-ppm H2/N2 (275.8 μA/mm-ppm H2/air) in 14 ppm H2/N2 (H2/air) at 30 °C, a fast transient response time of 2 (3) s in 9970 ppm H2/N2 (H2/air) at 130 °C, and a large initial rate of 774.4 (589.8) μA/s in 9970 ppm H2/N2 (H2/air) at 90 °C. However, the studied sensor shows a longer recovery time in nitrogen than in air due to the lack of additional desorption process. From the experimental results, it is speculated that the oxygen in air occupies the adsorption sites and reduces the adsorbed hydrogen atoms at the Pd/GaAs interface. This interprets that the studied sensor shows a larger hydrogen-induced current variation in nitrogen than in air under the same hydrogen concentration. In addition, there is no overshoot phenomenon in transient response observed in the nitrogen atmosphere due to the absence of oxygen.

Ching-Wen Hung

Papers

A Novel $\hbox{Pt/In}_{0.52}\hbox{Al}_{0.48}\hbox{As}$ Schottky Diode-Type Hydrogen Sensor

Study of an electroless plating (EP)-based Pt/AlGaN/GaN Schottky diode-type ammonia sensor

Comprehensive study on hydrogen sensing properties of a Pd–AlGaN-based Schottky diode

Influences of sulfur passivation on temperature-dependent characteristics of an AlGaAs/InGaAs/GaAs PHEMT

On the hydrogen sensing properties of a Pd/GaAs transistor-type gas sensor in a nitrogen ambiance