Development of a hydrogen dual sensor for fuel cell applications

The development and application of a hydrogen dual sensor (HDS) for the application in the fuel cell (FC) field, is reported. The dual sensing device is based on a ceramic platform head with a semiconducting metal oxide layer (MOx) printed on Pt interdigitated contacts on one side and a Pt serpentine resistance on the back side. MOx layer acts as a conductometric (resistive) gas sensor, allowing to detect low H₂ concentrations in air with high sensitivity and fast response, making it suitable as a leak hydrogen sensor. The proposed Co-doped SnO₂ layer shows high sensitivity to hydrogen (R₀/R = 90, for 2000 ppm of H₂) at 250 °C in air, and with fast response (<3 s). Pt resistance serves as a thermal conductivity sensor, and can used to monitor the whole range of hydrogen concentration (0–100%) in the fuel cell feed line with short response-recovery times, lower than 13 s and 14 s, respectively. The effect of the main functional parameters on the sensor response have been evaluated by bench tests. The results demonstrate that the dual sensor, in spite of its simplicity and cheapness, is promising for application in safety and efficiency control systems for FC power source.     

Characterization of microstructure and surface oxide of Ti1.2Fe hydrogen storage alloy

In this study, we investigated the microstructures, hydrogen absorption kinetics, and oxide layers of TiFe and Ti_1.2Fe hydrogen storage alloys. Whereas the TiFe alloy has a single phase, the Ti_1.2Fe alloy is composed of three phases: TiFe, Ti₂Fe, and Ti₄Fe. Under no thermal activation process, the TiFe alloy does not absorb hydrogen, though the Ti_1.2Fe alloy starts to absorb hydrogen after 4 min of incubation time. From the XPS results, it is revealed that the Ti concentration in the oxide layer on the Ti₄Fe phase is higher than that on the TiFe phase, indicating that the Ti concentration in the oxide layer would be important in improving hydrogen absorption kinetics. Based on these results, the hydrogen absorption kinetics could be improved by adjusting composition, enabling the formation of a Ti-rich oxide layer.     

Microstructure,corrosion behavior and hydrogen evolution of USSP processed AZ31 magnesium alloy with a surface layer containing amorphous Fe-rich composite

The influence of ultrasonic shot peening (USSP) treatment on the microstructure, corrosion behavior and hydrogen evolution of AZ31 magnesium alloy is investigated. An Fe-rich composite in amorphous state is introduced on the surface layer. Microstructure results indicate that nanoscale grains are formed on the surface layer after USSP treatment. Comparing to the untreated AZ31, the charge transfer resistance of the USSP-treated sample decreases by ~410 times and the hydrogen evolution rate increases by ~64 times. The acceleration of corrosion rate is attributed to the micro-galvanic interaction between the nanocrystalline Mg matrix and amorphous Fe-rich composite.     

A study on preparation of sulfur-iron compounds and their electrochemical and hydrogen barrier properties

Corrosion and hydrogen damage cause problems to oil and gas industry equipment. FeS (sulfur-iron) compounds generated by H₂S causes surface corrosion and covers the surfaces of the equipment where the extent of corrosion and hydrogen damage are influenced by these compounds. Different types of FeS compounds have different crystal structures, and there by influence their corrosion and hydrogen resistance. In this paper, single-structure pyrrhotite and pyrite were synthesized by hydrothermal method, which was controlled by controlling the temperature and Fe, S ratio. Their structures are hexagonal sheet and polyhedron respectively. The interfacial properties and hydrogen barrier properties of FeS were tested and the results show that pyrrhotite possesses anion selectivity. The electrochemistry shows low impedance modulus and high corrosion current density, which indicates low corrosion resistance. Pyrrhotite has the lowest hydrogen permeation current density and has good inhibition of hydrogen permeation ability. For the high impedance modulus and low corrosion current density pyrite possesses cation selective, which shows strong resistance to corrosion. However, its hydrogen permeation current density is high and hydrogen blocking effect is weak.     

高温加压变换炉氢腐蚀检验及安全评估

高温加压变换炉由于内保温层局部区域发生了破损和超温，产生了氢腐蚀。本文介绍高温加压变换炉氢腐蚀的产生原因、检测方法以及安全评估。     

Simulation of dynamic response of mixed-potential hydrogen sensors

Knowledge about factors affecting the dynamic response process is crucial for development of mixed-potential gas sensor for various applications such as hydrogen detection. Based on a double layer capacitor model and the Butler-Volmer equation, the present work studied the dynamic hydrogen sensing process by numerical simulation in combination with experimental assessment. Simulation shows that both response and recovery times are jointly determined by the decrease rate of the net reaction current and the magnitude of response. Increase of standard reaction rate constants, transfer coefficients, standard equilibrium potential, or gas concentrations accelerates both the response and recovery processes, while double layer capacitance has a reverse effect. A power-law concentration dependence of the response/recovery time is obtained under Tafel kinetics. The simulated response curves and behavior agree quite well with the experimental results. These findings shed lights on the sensing kinetics of the mixed-potential hydrogen sensor, and may help guide the sensor design.     

Cobalt–iron–boron catalyst-induced aluminum–water reaction

Hydrogen generation based on the corrosion of aluminum has been evaluated with regard to its possible application in on-board mobile and portable power sources. In this study, the aluminum–water reaction induced by Co–Fe–B has been examined. SEM results have shown that the chain-like Co–Fe–B catalyst forms a network structure under the influence of an external magnetic field. Co–Fe–B is actually a mixture of cubic Fe and amorphous Co–Fe–B. The Fe content in Co–Fe–B increases with increasing mass of FeCl₃ used in its synthesis. An increase in the Fe content in Co–Fe–B shortens the induction time and improves the amount of hydrogen generated owing to the formation of Fe/Al, Co–Fe–B/Al, and Co–Fe–B/Fe micro galvanic cells. However, an increase in the Co–Fe–B content slightly decreases the amount of hydrogen generated owing to its agglomeration and oxidation. With increasing temperature, both the reaction rate and the amount of hydrogen generated are improved. The activation energy of this reaction, calculated from the maximum reaction rates at different temperatures, is 40 kJ mol⁻¹. Hydrogen is rapidly generated, without an induction time, upon the addition of consecutive batches of Al, because the occurrence of the high concentration of OH⁻ ions effectively accelerates the corrosion of Al.     

Investigation on high temperature corrosion of water-cooled wall tubes at a 300 MW boiler

Because of the updated requirement on ultra-low NOx emission (<50 mg/Nm³), most of Chinese coal-fired boilers have to be operated at a low NOx combustion mode. However, for high-sulfur coal, water-cooled wall tubes probably suffer severe corrosion in such a strong reduction atmosphere. This work aims to investigate the high temperature corrosion behavior of water-cooled wall tubes inside a 300 MW boiler unit. A short length of corroded water-cooled wall tube was cut down and was analyzed by various characterization methods to further figure out the detailed corrosion mechanism. The typical corrosion products can be distinguished by blue, black and pale-green. Results showed that blue and black color products were mainly consisted of iron sulfides and iron oxides while the pale-green ones were identified as zinc sulfide. Along the radial direction, a layered structure of corrosion products can be observed. The formation of inner layer resulted from the reaction between iron oxide and hydrogen sulfide. The sulfur element displays a gradual increase trend while the Fe element gives out an opposite trend along the radially outward direction. The intermediate layer comes from the fly ash deposition and the outer layer is formed via condensation and deposition of ferrous sulfide gas on the water-cooled wall. The corrosion in this power plant is typical sulfide type for large amounts of Fe and S element were found in the corrosion products.     

Effects of poisoning gases on and restoration of PdCuSi metallic glass in a capacitive MEMS hydrogen sensor

We investigated the effects of poisoning and restoration of PdCuSi-metallic glass (MG), which is a sensing material that offers low power consumption and fast response times when used in capacitive MEMS hydrogen sensors. Four poisoning gases were used: hexamethyldisilazane (HMDS), H₂S, SO₂, and NO₂. Exposure to H₂S resulted in metal sulfide forming at the surface of the PdCuSi-MG, although the sulfur did not diffuse into the PdCuSi-MG. Exposure to NO₂ only resulted in the nitrogen being adsorbed without bonding to metals. The poisoning elements were desorbed by heating. Exposure to H₂S and SO₂ degraded the hydrogen sensitivity in terms of resistance of the PdCuSi-MG, although exposure to HMDS and NO₂ only slowed down the response time. These degradations were recovered by heating. We next examined forming a refresher layer under PdCuSi-MG in a hydrogen sensor. The hydrogen sensitivity of the H₂S-exposed hydrogen sensor was restored by performing a refresh operation for a few minutes.     

Inter-laboratory assessment of hydrogen safety sensors performance under anaerobic conditions

Sensors are important devices for alerting to the presence of leaked hydrogen in any application involving the production, storage, or use of hydrogen. Key missions for the sensor test laboratories in the U.S. Department of Energy, National Renewable Energy Laboratory and in the European Commission Joint Research Centre, Institute for Energy and Transport are to assure the availability and proper use of hydrogen safety sensors. As an integral element in a safety system, sensor performance should not be compromised by operational parameters. For example, safety sensors may be required to operate at reduced oxygen levels relative to air, such as that which would exist for nitrogen purges. Some sensor platforms are amenable for anaerobic operation, whereas other platforms will be deactivated and possible permanently altered with anaerobic operation. The NREL and JRC sensors laboratories assessed the ability of a number of sensor platforms to detect hydrogen under conditions of varying oxygen concentration. The performance of three common hydrogen sensor platforms, the thermal conductivity sensor, combustible gas sensor, and a palladium thin-film (metallic resistor) sensor, to operate under anaerobic conditions is presented.     

Hydrogen sensing properties of a Pd/oxide/InAlAs metamorphic-based transistor

A Pd/oxide/InAlAs metal–oxide–semiconductor (MOS) type metamorphic high electron mobility transistor (MHEMT)-based hydrogen sensor is fabricated and investigated. In comparison with the conventional HEMT-based sensors, the MOS MHEMT-based sensor exhibits significantly high sensitivity to the hydrogen. The found hydrogen sensing response is as high as 300%. Using the thermodynamic analysis to estimate the enthalpy value of hydrogen adsorption, the value for the proposed sensor is much lower than that for the other reported HEMT-based sensors. The MHEMT-based sensors are demonstrated to have a relatively fast response as comparing to other HEMT-based ones. The response time of the device is approximately 10 s under exposure to a 1% H₂/air gas. Consequently, the performance of the studied sensors shows the promise characteristics for practical applications.     

Multiphase Nb–TiCo alloys: The significant impact of surface corrosion on the structural stability and hydrogen permeation behaviour

Multiphase Nb_xTi_(100-x)/2Co_(100-x)/2 (x = 30–60) alloys are a promising material for hydrogen separating membranes. These alloy membranes exhibit a rapid decline in hydrogen permeation flux within ∼12 h when operated at 773 K. To address this issue, a dense oxide (e.g. Nb₂O₅, TiO₂ and CoO) layer was prepared between a Pd coating layer and an Nb–TiCo substrate by surface corrosion for improving their thermal stability, and the corrosion resistance of Nb–TiCo alloys was investigated. An increase in the Nb content (x) lowers the corrosion resistance of these alloys, but makes it easier to form the above oxide layer. Substantial enhancement of hydrogen permeability and thermal stability at 773 K was observed for the alloys (x = 30 and 40) after corrosion, which can be ascribed to an increase in hydrogen diffusivity. This improved permeability and stability are closely related to the formation of the above surface oxide layer that impeded interdiffusion between the Pd film and Nb–TiCo substrates. This study demonstrates that insertion of a diffusion barrier between the Pd and Nb-based substrates by surface corrosion is a viable approach to enhance the high-temperature stability of Pd-coated Nb–TiCo alloys, an aspect not widely explored in Nb-based hydrogen separation and purification membranes.     

Pd–Pt alloy as a catalyst in gasochromic thin films for hydrogen sensors

We have used Pd–Pt alloy as the catalyst in the hydrogen sensor thin film. Palladium and platinum were co-sputtered on top of a tungsten oxide layer grown by reactive sputtering. Both the sensitivity and the durability were dramatically improved over the case of a palladium single-component catalyst. The fractional change in the optical absorption on exposure to 1% hydrogen gas was increased by a factor larger than 2, and the fractional change decreased only a little after more than 1000 cycles of repeated exposure to 1% hydrogen and air. Moreover, the sensor film exhibited good selectivity to other organic vapors.     

Hydrogen sensing ability of Cu particles coated with ferromagnetic Pd–Co layer

A new hydrogen sensor utilizing a ferromagnetic hydrogen absorbing alloy was developed. An optimum sensing element, Cu particles coated with Pd–Co hydrogen absorbing alloy was prepared by the barrel sputtering technique. The surface of prepared Cu particle was covered uniformly by Pd–Co thin layer constituted of aggregated nanoparticles. The sensitivity of the sensing element to H₂ concentrations under flowing dry N₂ and dry air gases was examined. The element has a reasonable sensitivity to the H₂ concentration of the range from 3.8% to 0.2%, and the lower limit of detectable H₂ concentration was estimated to be less than 0.1%. In dry air, the water formation on the Pd–Co surface affected its sensing ability, because the temperature of the sensing element increased by the exothermic reaction. The effect of moisture on the H₂ sensing ability was also investigated. The moisture slightly degraded the output signal under flowing air. It could be ascribed to an additional consumption of hydrogen atoms by water molecules and oxygen atoms on the Pd–Co surface. This sensor takes advantage of magnetic susceptibility measurement, which requires no electrical wire between the sensing element and an electric circuit, leading to a safe evaluation system of H₂ concentration in air.     

Hydrogen entry and absorption in ZrO2 coated iron studied by electrochemical permeation and desorption techniques

One (entry) side of iron membranes was coated with ZrO₂ by sol-gel method. Hydrogen permeation through and hydrogen desorption from the uncoated and ZrO₂ coated iron membranes were studied using the electrochemical detection of hydrogen. The coated and uncoated membranes were charged with hydrogen cathodically generated from 0.1 M NaOH under constant current. During the initial period, the effect of the ZrO₂ coating was insignificant. However, the coating quite efficiently prevented the iron surface become more active to hydrogen entry during a long-lasting charging. After cessation of hydrogen charging, the hydrogen desorption was measured at both sides of the membranes. The analysis of the hydrogen desorption rates enabled the determination of the total amounts of hydrogen and distinction its different forms: the diffusible and reversibly trapped hydrogen.     

Experimental study and numerical simulation on the SSCC in FV520B stainless steel exposed to H2S+Cl− Environment

Constant displacement loading tests using wedge opening loading specimens were carried out in aqueous hydrogen sulfide solution containing sodium chloride to investigate the susceptibility of stress corrosion cracking (SCC) of FV520B precipitation hardening martensitic stainless steel. Results of the SCC tests indicated that the stress corrosion critical stress intensity factor (K_ISCC) dramatically decreased in the corrosion medium investigated and decreased with the increasing of H₂S concentration. Microstructures of fracture surfaces were analyzed using a scanning electron microscope (SEM) with an energy dispersive X-ray spectroscopy (EDS). The fracture surface was typical of sulfide stress corrosion fracture. In addition, large amount of intermittent arc-crack on the side surfaces around the tip of main crack formed even no main crack propagated.A sequentially coupling finite element analysis (FEA) program was utilized to simulate the stress field and calculate the diffused hydrogen concentration distribution of specimen exposed to the corrosion medium investigated. The FEA results indicated that corrosion pit affected the stress and diffusion hydrogen distribution around the corrosion pit where large stress gradients formed. Side surface cracks initiated from those corrosion pits and propagated under the synergy of stress and hydrogen. The effect of the corrosion pit on hydrostatic stress distribution was limited in superficial zone near the side surface, thus side surface cracks propagated along the hoop direction rather than along the direction of specimen thickness. Based on the morphology observation and FEA results, it can be concluded that the SCC mechanism of FV520B steel was hydrogen embrittlement mainly and combination of anodic dissolution. Simultaneously, corrosion pitting was the precondition of side surface crack formation while the stress induced hydrogen diffusion was the dominant factor.     

Effect of hydrogen on Fe and Pd alloying and physical properties

Metastable Fe–Pd powder samples were synthesized by mechanically activated solid-state diffusion using high-energy ball milling. The Fe and Pd alloying and the hydrogen effect on this process were followed by preparation of two samples: the A-sample was a mixture of Fe powder and of Pd powder pre-charged with hydrogen (PdH) and milled under Ar atmosphere, the B-sample was a mixture of the Fe and Pd powders milled under hydrogen atmosphere.The fundamental properties, i.e., chemical and phase composition, lattice parameters, microstructure, morphology, grain size, defect structure, and macro- and micro-magnetic properties, were monitored after several steps of the alloying at room and appropriately at elevated temperatures.The alloying of Fe and Pd in both samples begins already after 5 h of milling and two phases are formed, the dominating bcc-Fe(Pd) phase and a minor fraction of the fcc-Pd(Fe) phase. The occurrence of the fcc phase, not observed previously by solid-state diffusion under argon atmosphere, is ascribed to mainly a positive effect of hydrogen reducing the formation energy of lattice defects and facilitating their formation. Consequently, the moving defects during mechanical alloying make the solid-state diffusion of Pd into bcc-Fe lattice and Fe into fcc-Pd lattice easier. On the other hand, hydrogen used as atmosphere in the milling procedure is adsorbed on the particle surfaces and after the vial opening hydrogen atoms form water molecules with oxygen from air. This exothermic reaction causes a removal of hydrogen atoms from the particle surface which thus becomes more sensitive to oxidation. Nothing similar was observed after mechanical alloying under argon atmosphere having positive impact on the particle surface stability.     

Surface coating with a high resistance to hydrogen entry under high-pressure hydrogen-gas environment

Development of a surface coating with high resistance to hydrogen entry under a high-pressure hydrogen-gas environment is presented. Two aluminum-based coatings were developed on the basis of preliminary tests: two-layer (alumina/Fe–Al) and three-layer (alumina/aluminum/Fe–Al) coatings, deposited onto cylindrical and pipe (Type 304 austenitic stainless steel) surfaces by immersion into a specially blended molten aluminum alloy. The coated specimens were exposed to hydrogen gas at 10–100 MPa at 270 °C for 200 h. Specimen hydrogen content was measured by thermal desorption analysis; hydrogen distributions were analyzed by secondary ion mass spectroscopy. Both coatings showed high hydrogen-entry resistance at 10 MPa. However, resistance of the two-layer coating clearly decreased with an increase in pressure. In contrast, the three-layer coating showed excellent hydrogen-entry resistance at a wide pressure range (10–100 MPa), achieved by the combined effect of alumina, aluminum, and Fe–Al layers.     

Stress corrosion cracking behavior of ZK60 magnesium alloy under different conditions

The stress corrosion cracking (SCC) behavior of ZK60 magnesium alloy was investigated under different conditions, i.e. thin electrolyte layer (TEL) and solution, by slow strain rate tensile tests, electrochemical techniques, Auger electron spectroscopy, scanning electron microscopy coupled with electron backscattered diffraction, and time of flight secondary ion mass spectrometry. Results indicated that the ZK60 magnesium alloy in solution exhibits a higher SCC susceptibility with a combined SCC mechanism of weaker anodic dissolution (AD) and stronger hydrogen embrittlement (HE) compared to under TEL. Moreover, the HE mechanism under various conditions was discussed.     

Detecting hydrogen concentrations during admixing hydrogen in natural gas grids

The first applications of hydrogen in a natural gas grid will be the admixing of low concentrations in an existing distribution grid. For easy quality and process control, it is essential to monitor the hydrogen concentration in real time, preferably using cost effective monitoring solutions. In this paper, we introduce the use of a platinum based hydrogen sensor that can accurately (at 0.1 vol%) and reversibly monitor the concentration of hydrogen in a carrier gas. This carrier gas, that can be nitrogen, methane or natural gas, has no influence on the accuracy of the hydrogen detection. The hydrogen sensor consists of an interdigitated electrode on a chip coated with a platinum nanocomposite layer that interacts with the gas. This chip can be easily added to a gas sensor for natural gas and biogas that was already developed in previous research. Just by the addition of an extra chip, we extended the applicability of the natural gas sensor to hydrogen admixing. The feasibility of the sensor was demonstrated in our own (TNO) laboratory, and at a field test location of the HyDeploy program at Keele University in the U.K.