Hydrogen Sensor Research Articles

Hydrogen sensors operated in oxygen-free environments

Hydrogen (H2) is considered a next-generation clean energy source for replacing fossil fuels, and detecting H2 leaks is crucial from a safety standpoint. As the application of H2 energy becomes increasingly diverse and complex, there is a growing need to detect H2 leaks in oxygen-free environments. However, conventional oxygen-dependent H2 sensors lose their ability to detect gas in such environments. This work briefly outlines the research progress toward developing H2 sensors that can operate in oxygen-free environments, including the sensing materials, sensor device structures, gas sensing properties and mechanisms. Finally, we present some perspectives for the future development of H2 sensors for use in oxygen-free environments.

Enhanced Catalytic Palladium Embedded Inside Porous Silicon for Improved Hydrogen Gas Sensing

In this work, we reported on room temperature porous silicon (PS) and embedding PS using simple and economical techniques of electrochemical etching and thermal evaporation. The PS substrate was prepared using the technique of electrochemically etching the n-type Si (100) wafer at a constant current density of 10 mA/cm2 for 10 min under the illumination of incandescent white light. After PS formation, Ge pieces were thermally evaporated onto the two PS substrates in a vacuum condition. This was then followed by the deposition of the ZnO layer onto the Ge/PS substrate by the same method using commercial 99.9% pure ZnO powders. The three samples were identified as PS, Ge/PS and ZnO/Ge/PS samples, respectively. Pd finger contacts were deposited on the PS and embedding PS (Ge/PS and ZnO/Ge/PS) to form Pd on PS hydrogen sensors using RF magnetron sputtering. SEM and EDX suggested the presence of substantial Ge and ZnO inside the uniform circular pores for Ge/PS and ZnO/Ge/PS samples, respectively. Raman spectra showed that good crystalline Ge and ZnO nanostructures embedded inside the pores were obtained. For hydrogen sensing, Pd on ZnO/Ge/PS Schottky diode exhibited a dramatic change of current after exposure to H2 as compared to PS and Ge/PS devices. It is observed that the sensitivity increased exponentially with the hydrogen flow rate for all the sensors. The ZnO/Ge/PS showed more sensitivity towards H2 than that of PS and Ge/PS especially at high flow rate of H2 with higher current gain (69.11) and shorter response (180 s) and recovery times (30 s).

Metal–Organic Framework-Derived Co-Doped ZnO Nanostructures Anchored on N-Doped Carbon as a Room-Temperature Chemiresistive Hydrogen Sensor

The impending need to utilize H2 for multiple applications has surged the need to develop H2 sensors. Development of selective and rapid room-temperature H2 sensors is an uphill task without the doping of precious metals (Pd, Pt, and Au) in semiconductor metal oxide (SMO) sensors. Nanostructure of the SMOs could play a decisive role in gas sensing properties of the material. In this study, metal–organic framework (MOF)-derived Co–ZnO anchored on nitrogen-doped carbon (Co–ZnO–N/C) nanomaterial has been demonstrated as an effective rapid room-temperature H2 sensor. The pyrolysis of monometallic ZIF-8 (Zn) gave rise to amorphous ZnO stabilized on nitrogen-doped carbon (ZnO–N/C) and was found to be innocent for H2 sensing, whereas the pyrolysis of bimetallic ZIF(Co–Zn) resulted in the formation of Co–ZnO–N/C nanostructure with a high dispersion of Co on amorphous ZnO. Co–ZnO–N/C inherited the nanostructure of the parent precursor with rhombododecahedron particles of 200–300 nm and possessed subnanometer pores. Co inclusion into ZnO has converted the innocent amorphous ZnO–N/C into a rapid room-temperature H2 sensor (by measuring the dynamic change in the resistance with respect to time). Co–ZnO–N/C displayed a 3.7% response % with 17–26 s of recovery–response times for 1% concentration of H2 under room-temperature conditions. The unique nanostructure of Co–ZnO–N/C enhanced the signal transduction (via N-doped carbon support) and promoted H2 diffusion (through subnanometer pores). Higher-temperature H2 sensing studies were also conducted at 200 °C, wherein Co–ZnO–N/C displayed an increase in response to 5.7% with 8–16 s of response–recovery times. Co–ZnO–N/C chemiresistor is a rare example that does not contain precious metals yet exhibits room-temperature hydrogen sensing.

Hydrogen Sensors Based on In2O3 Thin Films with Bimetallic Pt/Pd Catalysts on the Surface and Tin and Dysprosium Impurities in the Bulk

This paper presents the results of studying the characteristics of hydrogen sensors based on thin In2O3 films modified with tin and dysprosium with dispersed double Pt/Pd catalysts deposited on the surface. To control the content of Sn and Dy in the films, an original technology was developed, and ceramic targets were fabricated from powders of the In–Dy–O, Dy–Sn–O, and In–Dy–Sn–O systems synthesized by the sol–gel method. Films of complex composition were obtained by RF magnetron sputtering of the corresponding targets. Structural features of the obtained thin films were studied by Raman spectroscopy. It is shown that various combinations of tin and dysprosium concentrations, as well as the presence of Pt/Pd catalysts on the surface, have a significant effect on the defectiveness of the films and the density of oxygen adsorption centers. As a result, the resistance of sensors in pure air (R0), the activation energies of the temperature dependences of R0, the bending of the energy bands at the grain boundaries of the semiconductor, and the responses to the action of hydrogen in the concentration range of 20–25,000 ppm change. A unique feature of Pt/Pd/ In2O3: Sn (0.5 at%), Dy (4.95 at%) films is their high sensitivity at 20–100 ppm and the absence of signal saturation in the region of high hydrogen concentrations of 5000–25,000 ppm, allowing them to be used to detect H2 in a wide range of concentrations.

Supercritical processing of thermally stable multiwalled carbon nanotube/boron nitride nanohybrids with synergistically improved electrical conductivity

A novel method of processing of thermally stable nanohybrids (NHs) with synergistically improved electrical conductivity (σDC) has been developed in supercritical carbon dioxide (SCC). Processing of NHs was executed through dispersion of selected weight fractions (wt%) of hexagonal boron nitride (h-BN) into carboxylate functional multiwalled carbon nanotube (c-MWCNT) at 1200 psi, 90 ± 1°C over 5 hr in SCC. Formation of NHs was ascertained through diverse analytical methods. Scanning electron microscopy coupled with energy dispersive spectra, elemental mapping and X-ray diffraction analysis reveals deposition of h-BN over the surface of c-MWCNT. NHs derived at 5 wt% of h-BN has shown reduced optical band gap (Eg, 3.34 eV) with 41 % increase in crystallite size. Working electrodes (WEs) derived from NHs has rendered increasing trend of DC conductivity (mS/cm) with concentration of h-BN up to 5 wt% at 100 V. WEs involving h-BN (5 wt%) has shown enhanced DC conductivity (0.93) followed by c-MWCNT (0.63) and h-BN (0.41) at 100 V. Present investigation delivers a clean, dry and environmentally benign method of processing of NHs suitable for development of inexpensive WEs for potential applications in hydrogen storage, electrocatalysis and sensors.

Catalytic combustion type optical fiber Bragg grating hydrogen gas sensor using platinum-loaded fumed silica powder

In order to ensure the safety of hydrogen energy system, a robust and reliable hydrogen sensor device with an optical fiber Bragg grating (FBG) has been developed. The sensing mechanism is based on temperature changes in the device induced by the heat of the catalytic reaction of hydrogen on platinum-loaded fumed silica catalyst powder. Through optimization of the preparation conditions for the catalyst, which is a hydrogen-sensitive substance, a large degree of heat generation in the presence of hydrogen could be obtained, and good stability was also achieved. A sensor device in which a column filled with the obtained catalyst powder was attached to a commercially available robust FBG for temperature measurement, and integrated with another FBG as a temperature reference via a heat shielding plate, was fabricated and evaluated. A stable baseline was demonstrated even in an environment where the ambient temperature severely fluctuated, and a sensor output proportional to the hydrogen concentration could be obtained. The detection limit was about 0.2 vol%, and the long-term stability of the device was good.

Effect of annealing treatment on response characteristics of Pd-Ni alloy based hydrogen sensor

The response rate and anti-interference performance are crucial to the detect performance for Pd-based hydrogen sensors. In this study, a resistance- type palladium-nickel (Pd90Ni10) thin film hydrogen sensors were prepared by the ion beam sputtering method. Sensors with an optimized Pd90Ni10 thickness (90 nm) which showed the fastest response for hydrogen were selected to study the effect of annealing treatment to the response rate and anti-interference performance. Four groups of samples were annealed at 250°C, 300°C, 350°C, and 400°C in air atmosphere for 4 hours, respectively. The impact of annealing treatment on base resistance stability and hydrogen response characteristics were studied. SEM, EDS and XRD analysis were carried out to reveal the relationship between response characteristics and microstructures. Results show that annealing treatment was beneficial to the base resistance stability and response rate. Samples annealed at 350°C showed the best base resistance stability and response rate. Furthermore, the difference of response rate ∆ was improved for the annealing treatment, indicating the improvement of the hydrogen sensor regarding the anti-interference effect to other gases. Meanwhile, a new mechanism including mutli-factors of Pd-Ni alloy about the anti-interference of oxygen was proposed based on our study. Besides, the sensors with the optimized fabrication process were tested in mixed standard gas with various hydrogen concentrations. This work provides an outstanding guidance to fabricate of hydrogen sensors of high response rate and anti-interference performance.

Rapid hydrogen detection with low temperature realized by regulating chemisorbed oxygen species of mesoporous indium tin oxide microsphere

With the quick development of hydrogen energy, it is necessary to fabricate hydrogen sensor with high sensitivity, fast response/recovery and low detection limit to monitor the leakage of hydrogen. In this work, a series of indium tin oxide (ITOs) microspheres were successfully synthesized by alkoxide precursors method. Among them, 10.7% In-doped SnO2 (named ITO-II) based sensor exhibits high sensitivity, excellent selectivity, great stability and ultra-fast dynamic process (response time and recovery time<3 s), at a low working temperature of 200 °C. The excellent hydrogen sensing performance of ITO-II should be attributed to the increased chemisorbed oxygen and the high intrinsic reactivity of SnO2 toward hydrogen. This work provides inspiration for the design of novel hydrogen sensing material.

ß-Ga2O3 flake based Schottky diode hydrogen sensor

2D (2-dimensional) (100) plane β phase Ga2O3 (β-Ga2O3) flake based Pt Schottky diode is demonstrated for hydrogen sensing application. The (100) plane β-Ga2O3 flake was formed from the side wall of a mother (2̅01) plane β-Ga2O3 bulk substrate by the cost-effective mechanical exfoliation method. The hydrogen response of the (100) plane Ga2O3 flake based diode with the catalytic Pt Schottky electrode for hydrogen decomposition reaction was measured in the wide concentration range of 50–40,000 ppm hydrogen. The β-Ga2O3 flake based hydrogen sensor showed excellent responsivity of 2.32 × 108% for the 500 ppm hydrogen exposure at 25°C, and exhibited a reliable hydrogen sensing behavior up to 400°C. The decent cross-selectivity of the (100) plane β-Ga2O3 flake based Pt Schottky diode sensor over the other gases including N2, CO, CO2, CH4, NO2, NH3, and O2 was observed. In addition, the effect of the humidity on hydrogen sensing was investigated.

Brief Review on High-Temperature Electrochemical Hydrogen Sensors

Hydrogen sensors, especially those operating at high temperatures, are essential tools for the emerging hydrogen economy. Monitoring hydrogen under process conditions to control the reactions for detecting confined species is crucial to the safe, widespread use and public acceptance of hydrogen as fuel. Hydrogen sensors must have a sensitivity ranging from traces of hydrogen (parts per million (ppm)) up to levels near the lower explosive limit (LEL = 4% H2 in the air) for safety reasons. Furthermore, they need to operate in cryogenic, ambient, and high-temperature environments. Herein, emphasis is given to hydrogen sensors based on solid oxide electrolytes (operating at high temperatures), in particular oxygen ion and proton conductors. The review is devoted to potentiometric, amperometric, and combined amperometric-potentiometric hydrogen sensors. Experimental results already reported in the international literature are presented and analyzed to reveal the configuration, principle of operation, and the applied solid electrolytes and electrodes of the high-temperature hydrogen sensors. Additionally, an amperometric sensor able to detect hydrogen and steam in atmospheric air through a two-stage procedure is presented and thoroughly discussed. The discussion reveals that high-temperature hydrogen sensors face different challenges in terms of the electrodes and solid electrolytes to be used, depending on the operating principle of each sensor type.

Effects of Y2O3 doping on the phase composition, chemical diffusion coefficient and electrochemical properties of CaHfO3 proton conductor

In order to further understand the effect of Y2O3 doping on the electrical conductivity of CaHf1−xYxO3−δ, which was prepared by conventional solid-state reaction. The electrical conductivity of CaHf1−xYxO3−δ was measured by two-terminal AC method in an oxygen-rich atmosphere, hydrogen-rich atmosphere and water vapor-rich atmosphere at the temperature between 973 and 1373 K. The test results show that the conductivity of CaHf1−xYxO3−δ first increases and then decreases with x from 0.08 to 0.20, and its total conductivity and conductivity activation energy are 3.88 × 10−7 to 5.34 × 10−5S/m and 0.76–0.92eV respectively. Combined with the test results of the H/D isotope effect, it is found that protons are the main conductive carriers in the three different atmosphere at temperatures range of 973–1173 K. In addition, in the temperatures range of 1273–1373 K, the positive holes are the main conductive carriers in the oxygen rich atmosphere, and the vacancies participates in the conductive process as the main conductive carriers in the water vapor rich atmosphere. The chemical diffusion coefficients of CaHf1−xYxO3−δ is 3.9 × 10−6 to 2.4 × 10−5 cm2/s in the temperature range of 973–1373 K. According to the test results of electromotive force, the theoretical electromotive force is consistent with the measured electromotive force. The proton transfer number of CaHf1−xYxO3−δ exceeded 97% in hydrogen atmosphere at temperatures from 973 to 1173 K. In sum, these findings of CaHf1−xYxO3−δ can be used as alternative materials for hydrogen sensor electrolytes.

Performance of Fiber-Optic Hydrogen Sensor Based on Locally Coated π-Shifted FBG

Pd-based alloy coating on optical fiber is widely employed for hydrogen concentration sensing. However, it is difficult to distinguish the Pd-based alloy expansion from hydrogen adsorption or thermal effect. In this article, a novel fiber-optic hydrogen sensor based on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -shifted fiber Bragg grating (FBG) with locally coated Pd/Ta alloy layer, which enables an in situ temperature compensation, is proposed and experimentally demonstrated. The hydrogen sensitivity difference between the extremely narrow peak of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -shifted FBG and the sidelobe wavelength is employed to realize the hydrogen concentration detection with temperature compensation. Theoretical simulation and experiment show that the hydrogen sensitivity of the structure can be enhanced by optimizing the partially coating length. When the alloy length is 2 mm for a 10-mm grating, the wavelength shifts of central and sidelobe 19.2 pm and 6.0 pm are achieved, respectively, at 1% hydrogen concentration. Maximum hydrogen sensitivity after temperature compensation of 13.2 pm is obtained. The proposed local-compensated method based on partially coating on <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pi $ </tex-math></inline-formula> -shifted FBG is particularly potential for oxygen-free environments with high requirement on hydrogen accuracy.

Hydrogen Sensor Based on NTC Thermistor with Pt-Loaded WO3/SiO2 Coating.

A novel hydrogen sensor based on a negative temperature coefficient (NTC) thermistor with Pt-loaded WO3/SiO2 coating is proposed and demonstrated experimentally. When the Pt-loaded WO3/SiO2 film is exposed to the mixture of air and H2, the exothermic reactions caused by hydrogen and WO3 with the cooperation of the Pt catalyst raise the local temperature of the NTC thermistor and lower its resistance. Hence, hydrogen concentration can be measured by monitoring the voltage across the NTC thermistor in a series circuit. The proposed device has a rapid response time, high sensitivity, and excellent repeatability to hydrogen as well as immunity to humidity, a compact size, a low manufacturing cost, and is easy to use.

Temperature‐ and Ambient Pressure‐Independent Sensing of Hydrogen in Fluids Using Cascaded Interferometers Incorporated in Optical Fibers

AbstractPractical gas sensors are indispensable for the healthy operation of cutting‐edge hydrogen‐based systems. An optical fiber‐based hydrogen sensor incorporating a robust Fabry–Perot interferometric structure on a fiber tip with high sensitivity, selectivity, and reliability of operation and a micrometer‐scale footprint is demonstrated. The hydrogen‐sensitive volume expansion of palladium provides bi‐metal operation with a silicon nitride mirror to tune the interferometer cavity and therefore the resonance modes by switching the mirror form factor from a flat to convex shape. It does not require any peripherals, including a power supply or data communication modules. In addition to fiber‐inherent advantages, such as remote and multiplexed monitoring without electromagnetic field interference, the sensor guarantees temperature‐ and pressure‐independent operation by adding a simple glass sub‐cavity and microwindows in the mirror layer, respectively. Critically, the sensor highlights reliable operation in a liquid fluid (electrical transformer oil) to monitor hydrogen as its “damage marker” escaping from a mechanical shield or selective gas screen. The detection limit, sensitivity, and response time of the sensor under atmospheric conditions are 15 ppm, 29.6 nm/%, and 12.5 s, respectively. In addition, the unimpaired operation of the sensor in 60 °C transformer oil is verified experimentally.

Enhancing Tungsten Oxide Gasochromism with Noble Metal Nanoparticles: The Importance of the Interface.

Crystalline tungsten trioxide (WO3 ) thin films covered by noble metal (gold and platinum) nanoparticles are synthesized via wet chemistry and used as optical sensors for gaseous hydrogen. Sensing performances are strongly influenced by the catalyst used, with platinum (Pt) resulting as best. Surprisingly, it is found that gold (Au) can provide remarkable sensing activity that tuned out to be strongly dependent on the nanoparticle size: devices sensitized with smaller nanoparticles display better H2 sensing performance. Computational insight based on density functional theory calculations suggested that this can be related to processes occurring specifically at the Au nanoparticle-WO3 interface (whose extent is in fact dependent on the nanoparticle size), where the hydrogen dissociative adsorption turns out to be possible. While both experiments and calculations single out Pt as better than Au for sensing, the present work reveals how an exquisitely nanoscopic effect can yield unexpected sensing performance for Au on WO3 , and how these performances can be tuned by controlling the nanoscale features of the system.

Effect of Annealing on the Microstructure, Opto-Electronic and Hydrogen Sensing Properties of V2O5 Thin Films Deposited by Magnetron Sputtering

This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited films from amorphous to nanocrystalline V2O5 with crystallite sizes in the range of 23 to 27 nm. Simultaneously, annealing resulted in an increase in surface roughness and grain size. Moreover, a decrease in transparency was observed in the visible wavelength range of approximately 50% to 30%, while the resistivity of formed vanadium pentoxide thin films was almost unchanged and was in the order of 102 Ω·cm. Simultaneously, the best optoelectronic performance, testified by evaluated figure of merit parameter, indicated the as-deposited amorphous films. Performed Seebeck coefficient measurements indicated the electron type of electrical conduction of each prepared thin film. Furthermore, gas sensing properties towards diluted hydrogen were investigated for annealed V2O5 thin films, and it was found that the highest senor response was obtained for a thin film annealed at 673 K and measured at operating temperature of 623 K.

Hydrogen-Sensing Properties of Ultrathin Pt-Co Alloy Films

The present work aims to investigate the feasibility of utilizing Pt and PtCo alloy ultrathin films as hydrogen gas sensors in order to reduce the cost of the hydrogen gas sensors by using low-cost metallic materials. In this study, ultrathin Pt and PtCo alloy thin films are evaluated for hydrogen sensors. The stoichiometry and structural characterization of the thin films are observed from XPS, SEM, and EDX measurements. The 2-nm-thick Pt and PtCo films deposited by sputtering onto Si/SiO2 covers homogeneously the surface in an fcc crystalline plane (111). The hydrogen gas-sensing properties of the films are assessed from the resistance measurement between 25 °C and 150 °C temperature range, under atmospheres with hydrogen concentration ranging from 10 ppm to 5%. The hydrogen-sensing mechanism of ultrathin PtxCo1-x alloy films can be elucidated with the surface scattering phenomenon. PtCo thin alloy films show better response time than pure Pt thin films, but the alloy films show lower sensor response than pure Pt film’s sensor response. Aside from these experimental investigations, first-principles calculations have also been carried out for bare Pt and Co, and also PtCo alloys. Compared to the theoretical calculations, the sensor response to change decreases with increasing Co content, a result that is compatible with the experimental results. In an attempt to explain the decrease in the sensor response of PtCo alloy films compared to bare Pt film, a variety of different phenomena are discussed, including the shrinking lattice of the structure or dendritic surface structure of PtCo alloy films by the increasing cobalt ratio.

Highly integrated hydrogen sensor based on inverse surface plasmon polaritons

We report a novel hydrogen sensor based on inverse surface plasmon polaritons (ISPPs) which may be used in integrated optical circuit. If a light beam hits a prism with Kretschmann configuration at a proper angle, the surface plasmon polaritons (SPPs) will be excited at the surface of the metal film. And the angle depends on the optical properties of the film. We use a palladium (Pd) film which changes its dielectric function in hydrogen gas. Thus, the incident angle can be used to indicate the concentration of hydrogen. Our sensor inverted all the process: SPPs are excited by a grating integrated on the Pd film, and decoupled by the prism, the angle of departure will indicate the hydrogen concentration. According to our simulation, if the concentration of hydrogen increases by 1%, the angle changes by and the intensity decreases by 1.55%. Our proposal can be used to improve the integration of ISPPs sensors.

Pd/In2O3-based bilayer H2 sensor with high resistance to silicone toxicity and ultra-fast response

Hydrogen sensors are easily deactivated by hexamethyldisiloxane (HMDSO) poisoning. Moreover, the existing anti-poisoning strategies can also damage the overall sensing performance of these hydrogen sensors. Therefore, a new bilayer design with a Pd/In2O3 sensitive layer and an In2O3/Al2O3 catalytic filter layer is proposed to avoid the deactivation of hydrogen sensors. The In2O3/Al2O3 layer helps in hindering HMDSO and its decomposition products from reaching the Pd/In2O3 layer. The H2 response of the sensors is enhanced due to the small size of In2O3 and the electronic sensitization of Pd. As a result, the bilayer sensors exhibit high response (Ra/Rg = 53) and ultra-fast response time (1 s) towards 3000 ppm H2 at 365 °C. The resistance and the H2 response of the bilayer sensors are almost unchanged after 40 min of 10 ppm HDMSO poisoning. In this paper, the mechanism of resistance against silicone poisoning and the H2 response of the bilayer sensors are discussed from the separation of sensing and catalytic filtration reactions to the behavior of adsorbed oxygen.

Lateral Offset Single-Mode Fiber-Based Fabry-Perot Interferometers with Vernier Effect for Hydrogen Sensing.

A high-sensitive optical fiber hydrogen (H2) sensor with Vernier effect by cascading three Fabry-Perot interferometers (FPIs) has been proposed. It is prepared by welding three sections of a single-mode fiber with a lateral offset structure and coating polydimethylsiloxane (PDMS) at the offset part to form three cascaded FPIs and generate a Vernier envelope spectrum. To realize H2 sensing, the hydrogen-sensitive material Pd/WO3 is fabricated and coated on the outside of the PDMS. Pd/WO3 will generate local heat when in contact with H2, which will cause the thermal expansion and refractive index change of PDMS and finally lead to the Vernier envelope wavelength shifting with the change of H2 concentration. Due to the Vernier effect, the H2 sensor can achieve a linear measurement sensitivity of 6.214 nm/% in the concentration range of 0-1%, which is 16.11 times that of a single FPI. The proposed H2 sensor possesses advantages of high sensitivity, easy preparation, compact structure, low cost, and easy long-distance transmission.