High-temperature Hydrogen Sensor Research Articles

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.

Dense BaCe0.6Zr0.3Y0.1O3-Α Solid-State Electrolyte for Application in Hydrogen Sensors

Fusion energy is a promising solution for the expected energy problems in the mid-term future. This technology is expected to use deuterium and tritium, two hydrogen isotopes, as fuel. Deuterium can be obtained from natural sources, but tritium, which is a non-stable hydrogen isotope, must be in situ generated. To assure the correct monitoring of both isotopes, it will be required the design and qualification of high-temperature sensors. The construction of H2 sensors based on solid-state electrolytes can be the first step towards the development of new analytical tools able to monitor hydrogen isotopes in that aggressive environment.In previous work [1], amperometric sensors based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) solid-state electrolyte have shown good analytical parameters for hydrogen monitoring. However, these materials need high temperatures during sintering to obtain full density due to their refractory nature. This lack of densification can affect their electrochemical response due to their low ionic conductivity. The use of sintering aids, like ZnO, can improve the densification of these ceramics at lower temperatures.In the present work, hydrogen sensors based on BCZY were constructed and evaluated in potentiometric mode. Different sintering conditions for this electrolyte were tested and their potentiometric response was compared. The following disk-shaped electrolytes were prepared for that purpose: 1400 ºC – 30 h, 1650 ºC – 6h. Simultaneously, BCZY was sintered at 1400 ºC -12 h with 5 mol% of ZnO as a sintering aid. Samples were characterized using XRD (to determine the crystallographic phases) and SEM (for microstructural defects and sintering). Then, disks were platinized and sealed with a glass binder to alumina tubes for sensor construction. Measurements were performed at 400 and 500 ºC. The hydrogen concentration in the RE was 1000 ppm H2 in Ar. The response obtained with the three sensors was compared with the theoretical Nernst potential.[1] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

Hydrogen Sensor with 3D Printed BaCe0.6Zr0.3Y0.1O3-α electrolyte for High-Temperature Applications

Fusion energy is considered a promising source of energy for the near future. The most efficient reaction for that purpose is the fusion of deuterium and tritium, two hydrogen isotopes, to release helium, neutrons and energy. To assure the correct operation of this technology, new online devices able to monitor hydrogen isotopes will be required.Electrochemical sensors based on solid-state proton conductor ceramics can be used for that purpose. These materials have attracted significant interest because of their chemical and physical durability, especially at elevated temperatures. These electrolytes are perovskite-type materials with electrical carriers, positive holes, excess electrons and oxide ion vacancies. In previous work [1], amperometric hydrogen sensors based on BaCe0.6Zr0.3Y0.1O3-α (BCZY) electrolyte have been developed and tested in hydrogen atmospheres obtaining good results. These prototypes were constructed using 13 mm BCZY disks obtained by uniaxial pressure.In the present work, hydrogen sensors based on BCZY were constructed and evaluated in amperometric mode. The BCZY powder was disk-shaped using uniaxial pressure and 3D printing. Sensors were constructed as follows: first, sintered disks were platinized using platinum ink. Then, disks were sealed with a glass binder to alumina tubes. This way, the external face of the disk acted as a working electrode (WE) and the inner part of the sensor as a counter electrode (CE). 3D printed disks were fabricated using a Delta WASP 2040 ceramic 3D printer. For that, the ceramic powder was mixed with PEG400 and water until a viscous paste was obtained. Once green bodies were dried, they were heated for debinding and sintering using an optimized thermal program to reduce porosity. XRD (for crystallographic phases) and SEM (for microstructural defects and sintering) were used for the 3D printed and uniaxial pressed sintered disks characterization. The amperometric response of sensors constructed with both electrolytes (the uniaxially pressed and the 3D printed disks) was compared.[1] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

Evaluation of the Response of High-Temperature Hydrogen Sensors for Fusion Applications

The use of hydrogen gas in different chemical processes and industries is common. Hydrogen gas has to be monitored in order to provide control of reactions, detect leakages or avoid accumulations in confined spaces, among many other applications. In this frame, and depending on its final application there is a need to develop hydrogen sensors capable to operate in all kinds of conditions in terms of concentration range and temperature. Moreover, these sensors should provide measurements with high sensitivity, selectivity and fast response time. Furthermore, logistical properties such as low cost, long-term stability and easy operation should also be considered in all applications.In the present work, solid-state electrolyte based amperometric sensors were constructed to measure hydrogen gas under high-temperature conditions. BaCe0.6Zr0.3Y0.1O3-α electrolyte (BCZY) was obtained by the solid-state method and characterized using SEM and XRD. Then, BCZY powder was sintered as a pellet and sealed to an alumina tube to construct the sensors. Finally, operational conditions were optimized and the analytical parameters of these sensors were evaluated at 500 °C and 600 °C. All measurements were performed in an argon atmosphere containing different hydrogen concentrations.

(Digital Presentation) Electrochemical Sensors for Hydrogen/Deuterium Speciation

By the end of the century, global energy demand is expected to increase by a factor of three due to population growth. In this context, fossil fuels should not be the main power source due to the elevated environmental cost. Nuclear fusion technology is planned as an alternative to this demand as it is expected to generate large quantities of energy without all the inconveniences of fossil fuels. The most feasible reaction to take place is the fusion between two hydrogen nuclei. Specifically, deuterium and tritium will react releasing helium, neutrons, and large amounts of energy [1]. 2H + 3H → 4He + n + 17.59 MeV (1)In the present work, BaCe0.6Zr0.3Y0.1O3-α electrolyte (BCZY) was used to construct amperometric sensors for hydrogen monitoring. Firstly, BCZY powder was synthesized by the solid-state method and characterized using SEM and XRD. Secondly, it was sintered as a pellet and bound to an alumina tube to construct the electrochemical sensors. Finally, amperometric measurements were performed inside a stainless-steel reactor at 500 °C and applying 0.15 V between electrodes. The response of the sensors was evaluated using hydrogen and deuterium calibration mixtures. The concentration in the WE ranged from 150 to 300 ppm H2 or D2 in Ar. Argon was used in the CE as a cover gas. Finally, measurements with hydrogen and deuterium were compared to determine the isotope effect on the response.[1] J.Kenneth. Shultis, R.E. Faw, Fundamentals of nuclear science and engineering, Marcel Dekker, 2002.[2] E.C.C. de Souza, R. Muccillo, Properties and applications of perovskite proton conductors, Materials Research. 13 (2010) 385–394. https://doi.org/10.1590/S1516-14392010000300018.[3] A. Benes, A. Molinari, R. Witte, R. Kruk, J. Brötz, R. Chellali, H. Hahn, O. Clemens, Proton Conduction in Grain-Boundary-Free Oxygen-Deficient BaFeO2.5+δ Thin Films, Materials. 11 (2017) 52. https://doi.org/10.3390/ma11010052.[4] A. Hinojo, I. Soriano, J. Abellà, S. Colominas, Evaluation of High-Temperature Hydrogen Sensors Based on BaCe0.6Zr0.3Y0.1O3-α and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-α Perovskites for Industrial Applications, Sensors. 20 (2020) 7258. https://doi.org/10.3390/s20247258.

Doping and temperature-dependent UV-Vis optical constants of cubic SrTiO3: a combined spectroscopic ellipsometry and first-principles study

SrTiO3 is the model perovskite compound and has demonstrated technological relevance from being the foundation of oxide electronics to a promising candidate as a high-temperature hydrogen sensor. Here, we fully investigate the temperature-dependent UV-Vis optical constants of pristine and doped SrTiO3 in the spectral range 0.73-5.90 eV using spectroscopic ellipsometry and first-principles. The oscillator model is applied to analyze and quantify the temperature and doping effect. After heating SrTiO3 from 300 to 873 K, the amplitude of the dominant absorption peak at 4.752 eV is reduced by 11% and the shoulder of optical spectrum at 3.708 eV gradually disappears. By doping SrTiO3 with Nb element from 0.05 to 0.7% wt, extra momentum is provided to enable indirect absorption and an unconventional Urbach tail is observed due to the increased crystalline disorder. Moreover, the first-principles calculations considering the many-body excitonic effect and phonon-assisted indirect absorption are performed, which help to determine the physics origin of absorption peaks and explain the temperature influence. This work sheds light on temperature and doping dependence of UV-Vis dielectric functions of cubic SrTiO3, aiming to elucidate the novel fundamental optical phenomena of SrTiO3-based heterostructures or devices.

Morphology control of aluminum nitride (AlN) for a novel high-temperature hydrogen sensor

Hydrogen is a promising renewable energy source for fossil-free transportation and electrical energy generation. However, leaking hydrogen in high-temperature production processes can cause an explosion, which endangers production workers and surrounding areas. To detect leaks early, we used a sensor material based on a wide bandgap aluminum nitride (AlN) that can withstand a high-temperature environment. Three unique AlN morphologies (rod-like, nest-like, and hexagonal plate-like) were synthesized by a direct nitridation method at 1400°C using γ-AlOOH as a precursor. The gas-sensing performance shows that a hexagonal plate-like morphology exhibited p-type sensing behavior and showed good repeatability as well as the highest response (S = 58.7) toward a 750 ppm leak of H2 gas at high temperature (500°C) compared with the rod-like and nest-like morphologies. Furthermore, the hexagonal plate-like morphology showed fast response and recovery times of 40 and 82 s, respectively. The surface facet of the hexagonal morphology of AlN might be energetically favorable for gas adsorption-desorption for enhanced hydrogen detection.

High-Temperature Hydrogen Sensing Performance of Ni-Doped TiO2 Prepared by Co-Precipitation Method.

This work deals with the substantially high-temperature hydrogen sensors required by combustion and processing technologies. It reports the synthesis of undoped and Ni-doped TiO2 (with 0, 0.5, 1 and 2 mol.% of Ni) nanoparticles by a co-precipitation method and the obtained characteristics applicable for this purpose. The effect of nickel doping on the morphological variation, as well as on the phase transition from anatase to rutile, of TiO2 was investigated by scanning electron microscopy, X-ray diffraction and Raman spectroscopy. The resistive sensors prepared with these powders were tested toward H2 at 600 °C. The results indicate that 0.5% Ni-doped TiO2 with almost equal amounts of anatase and rutile shows the best H2 sensor response (ΔR/R0 = 72%), response rate and selectivity. The significant improvement of the sensing performance of 0.5% Ni-doped TiO2 is mainly attributed to the formation of the highest number of n-n junctions present between anatase and rutile, which influence the quantity of adsorbed oxygen (i.e., the active reaction site) on the surface and the conductivity of the material.

A Schottky-junction-based platinum nanoclusters@silicon carbide nanosheet as long-term stable hydrogen sensors

Hydrogen gas sensors which could be applied in harsh environments (high temperature, corrosion atmosphere, etc.) are highly demanded in special fields such as aerospace and chemical industry. Here, we have successfully produced a platinum nanoclusters@silicon carbide nanosheets (Pt NCs@SiC NSs) gas sensor via a simple one-step wet chemical reduction reaction. The Pt NCs@SiC NSs show good response (15.7%) towards 500 ppm hydrogen under 300 °C. Besides, this device possesses a good linear response towards different hydrogen concentration under 500 ppm and keeps a good stability in one month. The gas sensing properties of Pt NCs@SiC NSs are mainly from the Schottky junction-based structure, in which both reception and transduction process play important roles. This work provides a simple way to prepare high-temperature hydrogen sensors without complex equipment, and the large-scale preparation is also available.

Calcination temperature dependence of synthesis process and hydrogen sensing properties of In-doped CaZrO3

The CaZr0.9In0.1O3-δ can be used as solid electrolyte material for high temperature hydrogen sensors. In this paper, thermogravimetric–differential thermal analysis and X-ray diffractometer analysis were employed to investigate the calcination temperature dependence of fabricating this material. The results show that CaZrO3 matrix phase can be synthesized directly by CaO and ZrO2 at 1000 °C or stepwise by intermediate oxide CaZr4O9 at higher temperatures between 1000 °C and 1200 °C during solid-state reaction process. Doping of indium into CaZrO3 occurs in the temperature range of 1200 °C–1400 °C. With calcination temperature exceeding 1400 °C, no obvious improvement of doping occurs. Even a sharp deterioration of doping effect happens with a temperature of 1550 °C. The CaZr0.9In0.1O3-δ electrolyte powders with a main phase purity of 98.75% were synthesized at 1400 °C for 10 h. The electrolyte tubes with a relative density of 96.8% and a homogeneous crystal size between 2 μm and 3 μm are fabricated out. Hydrogen sensor assembled with the electrolyte tube exhibits good hydrogen sensing performance obeying the Nernst law at 700 °C–800 °C.

High-temperature hydrogen sensor based on platinum nanoparticle-decorated SiC nanowire device

A single SiC nanowire gas sensor was fabricated, and its fast-response and ultrahigh sensitivity for hydrogen sensing at high temperature was demonstrated. The surface of SiC nanowire was decorated with Pt nanoparticles as a hydrogen catalyst. The decorated SiC nanowire was mounted on Ag electrodes in ohmic contact. Changes in the current were monitored at the low hydrogen concentration with a 1V forward bias. An obvious change in current was observed when the nanowire sensor was exposed to the low hydrogen concentration atmosphere. High sensing performances such as fast response (3s) and recovery (45s), and high sensitivity (S≈20%) toward H2 were demonstrated at 600°C. The hydrogen gas sensing characteristics in air as a background gas were investigated. The possible Pt catalytic hydrogen sensing mechanism of the SiC nanowire sensor was also discussed.

Investigation of doped-gadolinium zirconate nanomaterials for high-temperature hydrogen sensor applications

The incorporation of selective nanomaterials, such as common metal oxide semiconductor compositions, into resistive-type gas sensors has been shown by many researchers to lead to very high sensitivities and response rates, especially for micro-sized chemical sensors for room-temperature applications. The same strategy utilizing sensing nanomaterials has not been demonstrated for high-temperature sensors due to the intrinsic instability of typical metal oxide semiconductor nanomaterials at temperatures >500 °C. Within this work, doped Gd2Zr2O7 (GZO) nanomaterial compositions were investigated for H2 resistive-type sensors for applications between 600 and 1000 °C. This paper investigates the mechanism of H2 sensing for doped GZO nanomaterials and SnO2/GZO nanocomposites at the elevated temperatures. By integrating 10 vol.% nano-SnO2 into yttrium-doped GZO nanomaterials, a sensitivity of 4.15 % was retained for 4000 ppm H2 levels with a low signal drift of 0.42 %/h at 1000 °C in a 20 % O2/N2 gas stream. The signal drift was reduced by more than half of that compared to pure nano-SnO2 at the same conditions. The nano-GZO limited the grain growth of the nano-SnO2 particles and also prevented the nano-SnO2 from fully reducing to Sn at high temperatures in a low oxygen atmosphere. It is among the first resistive-type sensors operating at 1000 °C with sensing times of <5 min. This demonstration provided an example of a strategy of combining traditional metal oxide semiconductor and refractory nanomaterial compositions to form sensing nanocomposites with new sensing mechanisms, as well as, enhanced chemical and microstructural stabilities in high-temperature environments.

A stable BaCe0.7Ta0.1In0.2O3−δ electrolyte membrane for proton-conducting solid oxide fuel cells

Abstract In and Ta co-doping BaCeO 3− δ (BaCe 0.7 Ta 0.1 In 0.2 O 3− δ ) powders were synthesized by an improved route combining solid state reaction and wet chemical method. Green BaCe 0.7 Ta 0.1 In 0.2 O 3− δ (BCTI) |NiO+BaCe 0.7 Zr 0.1 Y 0.2 O 3− δ (BZCY) half cells were successfully fabricated by co-pressing BCTI powders on NiO–BZCY substrate, which were sintered at a relatively low temperature of 1300 °C for 5 h and then produced dense BCTI membrane. The stability testing showed that BCTI membrane is excellently stable against carbon dioxide and boiling water. A single fuel cell with 44 μm-thick BCTI electrolyte was assembled by brushing Sm 0.5 Sr 0.5 CoO 3− δ Ce 0.8 Sm 0.2 O 2− δ (SSC–SDC) composite cathode on dense electrolyte membrane, which generated maximum power densities of 59, 49, 34 mW/cm 2 at 650, 600 and 550 °C, respectively. Meanwhile, the resistances of the cell were measured by electrochemical impedance spectroscopy under open circuit condition. Moreover, the long-term test of the cell showed stable power output and open circuit voltages. The above described performance indicates that BCTI is stable electrolyte material for intermediate-temperature solid oxide fuel cells. Besides, the super stable electrolyte material can be used as online high-temperature hydrogen sensor.

High-temperature resistive hydrogen sensor based on thin nanoporous rutile TiO 2 film on anodic aluminum oxide

Thin titanium oxide (TiO 2) films were prepared through electron-beam evaporation of titanium metal on substrates followed by oxidizing and sintering at 600 °C in flowing oxygen. The thicknesses of the as-deposit metal films were 25 nm, 50 nm and 100 nm. The phase of the TiO 2 converted from the thermal oxidation was detected to be rutile. Nanoporous anodized aluminum oxide (AAO) and plain thermal silicon oxide on top of a commercial silicon wafer were used as substrates to support the TiO 2 thin layer. A pair of interdigit platinum electrodes with a spacing of 5 μm was fabricated on the TiO 2 thin films by photolithography. At 500 °C, the samples showed different sensing behaviors to hydrogen concentration levels ranging from 5 ppm to 500 ppm, with nitrogen as the background gas. It was found that the sensitivity was significantly enhanced by the increased specific surface area of the TiO 2 thin film due to the shaping of the porous AAO substrate. The performance of the sensor based on the TiO 2 film converted from 25-nm-thick Ti on the porous AAO substrate, which has the largest specific surface area among all the other samples, was featured by a conductance change of 25–90 times and considerable resolution for 5 ppm to 500 ppm H 2, as well as very fast response and recovery (the time delay to reach or retreat to half of the maximum stable signal, t 50%, was always no more than 10 s). The rutile-phased thin TiO 2 film on AAO is proven to be a promising high-temperature hydrogen sensor with satisfactory performance, excellent durability, and ideal compatibility to micro-miniaturization.

Ruthenium as Schottky metal for SiC-based high temperature hydrogen sensors

ABSTRACTSensor response characteristics of Ru/3C-SiC (epitaxial layer of SiC on Si substrates) Schottky junctions were studied at different temperatures (200 – 400 °C) in presence of varying concentrations of hydrogen from 5000 – 20000 ppm. The output signal of the sensor, the response time and the reversibility were investigated from the transient response characteristics of the sensors. The sensor parameters improved with higher operating temperature, up to 400 °C. The sensitivity of the sensors was found to be a function of applied bias across the Schottky junction. As compared with the Pd/3C-SiC junctions, the Ru/3C-SiC Schottky sensors showed higher resolution and better reversibility in the hydrogen concentration range 10000 to 20000 ppm. The SIMS (Secondary Ion Mass Spectrometry), RBS (Rutherford Backscattering Spectrometry) and GIXRD (Glancing Incidence X-ray Diffraction) studies indicated that up to 400 °C there was no formation of ruthenium silicide at the Ru/3C-SiC interface.

Kev Ion Beam Induced Surface Modification of Sic Hydrogen Sensor

AbstractSilicon carbide, a wide-bandgap semiconductor, is currently used to fabricate an efficient high temperature hydrogen sensor. When a palladium coating is applied on the exposed surface of silicon carbide, the chemical reaction between palladium and hydrogen produces a detectable change in the surface chemical potential. Rather than applying a palladium film, we have implanted palladium ions into the silicon face of 6H, n-type SiC samples. The implantation energies and fluences, as well as the results obtained by monitoring the current through the sample in the presence of hydrogen are included below. The exposure to hydrogen of this kind of sensor while monitoring the current flow with respect to time, has revealed a completely different behavior than the samples that have Pd deposited as a surface layer.

High-temperature hydrogen sensor based on stabilized zirconia and a metal oxide electrode

A zirconia-based electrochemical device attached with an oxide electrode was developed for the detection of H 2 in air at elevated temperature. Among the oxides tested, ZnO was found to be best suited for the sensing electrode. The device attached with ZnO showed fairly good sensing characteristics to 50–500 ppm H 2 in air at 450–600°C. The 90% response and 90% recovery times to 200 ppm H 2 at 600°C for the ZnO-attached device were 5 s and 10 s, respectively. The EMF value of the device was almost linear with the logarithm of H 2 concentration. It was also observed that the device exhibited excellent selectivity to H 2 in the coexistence of NO, NO 2, CH 4, CO 2 and H 2O, as well as a good long-term stability. On the basis of the measurements of anodic and cathodic polarization curves, the sensing mechanism was confirmed to involve a mixed potential at the oxide sensing electrode.