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 wide area monitoring of LH2 releases

The characterization of liquid hydrogen (LH2) releases has been identified as an international research priority to expand the safe use of hydrogen as an energy carrier. The elucidation of LH2 release behavior will require the development of dispersion and other models, guided and validated by empirical field measurements such as those afforded by Hydrogen Wide Area Monitoring (HyWAM). HyWAM can be defined as the quantitative spatial and temporal three-dimensional monitoring of planned or unintentional hydrogen releases. With support provided through the FCH JU Prenormative Research for the Safe Use of Liquid Hydrogen (PRESLHY) program, HSE performed a series of LH2 releases to characterize the dispersion and pooling behavior of cold hydrogen releases. The NREL Sensor Laboratory developed a HyWAM system based upon a distributed array of point sensors that is amenable for profiling cold hydrogen plumes. The NREL Sensor Laboratory and HSE formally committed to collaborate on profiling the LH2 releases. This collaboration included the integration of the NREL HyWAM into the HSE LH2 release hardware. This was achieved through a deployment plan jointly developed by the NREL and HSE personnel. Under this plan, the NREL Sensor Laboratory provided multiple HyWAM modules that accommodated 32 sampling points for near-field hydrogen profiling during the HSE PRESLHY LH2 releases. The NREL HyWAM would be utilized throughout the LH2 release study performed under PRESLHY by HSE, including Work Package 3 (WP3—Release and Mixing--Rainout) and subsequent work packages (WP4—Ignition and WP5—Combustion). Under the auspices of the PRESLHY WP6 (Implementation), data and findings from the HSE LH2 Releases are to be made available to stakeholders in the hydrogen community. Comprehensive data analysis and dissemination is ongoing, but the integration of the NREL HyWAM into the HSE LH2 Release Apparatus and its performance as well as some key outcomes of the LH2 releases in WP3 are presented.     

Adapted tube cleaning practices to reduce particulate contamination at hydrogen fueling stations

The higher rate of component failure and downtime during initial operation in hydrogen stations is not well understood. The National Renewable Energy Laboratory (NREL) has been collecting failed components from retail and research hydrogen fueling stations in California and Colorado and analyzing them using an optical zoom and scanning electron microscope. The results show stainless steel metal particulate contamination. While it is difficult to definitively know the origin of the contaminants, a possible source of the metal particulates is improper tube cleaning practices. To understand the impact of different cleaning procedures, NREL performed an experiment to quantify the particulates introduced from newly cut tubes. The process of tube cutting, threading and beveling, which is performed most often during station fabrication, is shown to introduce metal contaminants and thus is an area that could benefit from improved cleaning practices. This paper shows how these particulates can be reduced, which could prevent station downtime and costly repair. These results are from the initial phase of a project in which NREL intends to further investigate the sources of particulate contamination in hydrogen stations.     

Designing a miniaturized photoacoustic sensor for detecting hydrogen gas

In this paper, photoacoustic spectroscopy method is used for hydrogen gas detection. In order to improve the performance of the sensor, we have used a miniaturized dumbbell-shaped cell containing two buffer volumes and a resonator. The coupled photoacoustic equations have been solved in gaseous environment using finite-element-method and by corresponding validation. The impacts of various effective parameters such as frequency response, quality factor, acoustic pressure and heat have been analyzed. Frequency analysis in the hydrogen gas medium leads to the first natural frequency of the sensor at 88.563 kHz which has 65 kHz difference with the second natural frequency. By studying the behavior of the resonance frequencies of the proposed system, the optimum location for the sensor positioning of the designed system has been investigated for different gases and the results show that the designed photoacoustic sensor has the fingerprint feature for detecting hydrogen gas. Moreover, the results of the cell filled by hydrogen gas have been compared to those obtained from other gases such as propane, nitrogen and carbon dioxide. The performance of the system is also evaluated for volatile organic compounds (VOCs) and nitrogen dioxide (NO₂). The analysis of the proposed miniature system shows a significant improvement in the quality factor as well as the reduction in system losses.     

Test methodologies for hydrogen sensor performance assessment: Chamber vs. flow-through test apparatus

Certification of hydrogen sensors to meet standards often prescribes using large-volume test chambers [1,2]. However, feedback from stakeholders such as sensor manufacturers and end-users indicates that chamber test methods are often viewed as too slow and expensive for routine assessment. Flow-through test methods are potentially an efficient and cost-effective alternative for sensor performance assessment. A large number of sensors can be simultaneously tested, in series or in parallel, with an appropriate flow-through test fixture. The recent development of sensors with response times of less than 1s mandates improvements in equipment and methodology to properly capture the performance of this new generation of fast sensors; flow methods are a viable approach for accurate response and recovery time determinations, but there are potential drawbacks. According to ISO 26142 [1], flow-through test methods may not properly simulate ambient applications. In chamber test methods, gas transport to the sensor is dominated by diffusion which is viewed by some users as mimicking deployment in rooms and other confined spaces. Conversely, in flow-through methods, forced flow transports the gas to the sensing element. The advective flow dynamics may induce changes in the sensor behaviour relative to the quasi-quiescent condition that may prevail in chamber test methods. The aim of the current activity in the JRC and NREL sensor laboratories [3,4] is to develop a validated flow-through apparatus and methods for hydrogen sensor performance testing. In addition to minimizing the impact on sensor behaviour induced by differences in flow dynamics, challenges associated with flow-through methods include the ability to control environmental parameters (humidity, pressure and temperature) during the test and changes in the test gas composition induced by chemical reactions with upstream sensors. Guidelines on flow-through test apparatus design and protocols for the evaluation of hydrogen sensor performance have been developed. Various commercial sensor platforms (e.g., thermal conductivity, catalytic and metal semiconductor) were used to demonstrate the advantages and issues with the flow-through methodology.     

Developments in gas sensor technology for hydrogen safety

Gas sensors are applied for facilitating the safe use of hydrogen in, for example, fuel cell and hydrogen fuelled vehicles. New sensor developments, aimed at meeting the increasingly stringent performance requirements in emerging applications, are reviewed. The strategy of combining different detection principles, i.e. sensors based on electrochemical cells, semiconductors or field effects in combination with thermal conductivity sensing or catalytic combustion elements, in one new measuring system is reported. This extends the dynamic measuring range of the sensor while improving sensor reliability to achieve higher safety integrity through diverse redundancy. The application of new nanoscaled materials, nanowires, carbon tubes and graphene as well as the improvements in electronic components and optical elements are evaluated in view of key operating parameters such as measuring range, sensor response time and low working temperature.     

Room temperature hydrogen gas sensing properties of mono dispersed platinum nanoparticles on graphene-like carbon-wrapped carbon nanotubes

We present platinum nanoparticles dispersed wrinkled graphene-like carbon-wrapped carbon nanotubes (Pt/GCNTs) as a room temperature chemiresistive hydrogen gas sensor. Pt nanoparticles are decorated over GCNTs surface using poly (sodium 4-styrene sulfonate) (PSS) functionalization, followed by ethylene glycol reduction method. The highly defective wrinkled graphene-like surface of GCNTs provides large surface area and PSS functionalization provides stable immobilization of mono dispersed Pt nanoparticles on the carbon surface. A simple and inexpensive drop cast technique is used to fabricate the thick film sensor of the material. Hydrogen resistive gas sensing properties of Pt/GCNTs are studied at different gas concentrations, temperatures and Pt wt. % loadings. Pt/GCNTs sensor shows optimal sensitivity at room temperature with stable and reproducible response towards hydrogen. The sensor with 2 wt. % of Pt showed maximum sensitivity that is three fold higher than Pt decorated carbon nanotubes (Pt/CNTs) with the same Pt wt. % loading. The present study shows potential to explore novel H2 sensors^.     

Aerogel sheet of carbon nanotubes decorated with palladium nanoparticles for hydrogen gas sensing

In the development of hydrogen sensors, it is required to meet the demands of both high sensor performance as well as the ease of fabrication for mass production. For this purpose we proposed a chemiresistive hydrogen sensors based on an aerogel sheet of carbon nanotubes decorated with palladium nanoparticles (CNT/Pd sheet). The fabrication process is straightforward that a dry-spun CNT aerogel sheet is suspended between concentric electrodes followed by depositing Pd nanoparticles on CNT sheets by thermal evaporation. The present CNT/Pd sheet sensors can detect hydrogen at concentrations as low as 2 ppm at room temperature with a detection range from 2 to 1000 ppm. The aerogel nature of CNT/Pd sheet contributes to low detection limit and broad detection range of the CNT/Pd sensor. Relations between hydrogen concentration and sensor response and response time, and the effects of temperature on sensor performance were investigated.     

Pt doped (8,0) single wall carbon nanotube as hydrogen sensor: A density functional theory study

In this study, it has been investigated the use of Pt doped carbon nanotube for the hydrogen gas sensor at room temperature and compared with available experimental literature data. The WB97XD method with 6-31G(d,p) and LanL2DZ basis sets have been utilized. The charge distributions obtained for the structures show that charge transfer is occurred from the adsorbed hydrogen molecule to the Pt atom of carbon nanotube structure as an electron acceptor. The HOMO–LUMO gap of the Pt doped SWCNT decreased with the adsorption of hydrogen molecule. As a conclusion, the electrical conductivity of Pt doped (8,0) SWCNT cluster increased after a hydrogen molecule adsorption. Accordingly, Pt doped (8,0) SWCNT has potential for sensing of hydrogen gas. Theoretical (DFT) results are in well agreement with available experimental literature data that was reported a chip sensor loaded Pt-CNT gave highest response coefficient for H₂ gas sensing.     

Development of risk mitigation guidance for sensor placement inside mechanically ventilated enclosures – Phase 1

Guidance on Sensor Placement was identified as the top research priority for hydrogen sensors at the 2018 HySafe Research Priority Workshop on hydrogen safety in the category Mitigation, Sensors, Hazard Prevention, and Risk Reduction. This paper discusses the initial steps (Phase 1) to develop such guidance for mechanically ventilated enclosures. This work was initiated as an international collaborative effort to respond to emerging market needs related to the design and deployment equipment for hydrogen infrastructure that is often installed in individual equipment cabinets or ventilated enclosures. The ultimate objective of this effort is to develop guidance for an optimal sensor placement such that, when integrated into a facility design and operation, will allow earlier detection at lower levels of incipient leaks, leading to significant hazard reduction. Reliable and consistent early warning of hydrogen leaks will allow for the risk mitigation by reducing or even eliminating the probability of escalation of small leaks into large and uncontrolled events. To address this issue, a study of a real-world mechanically ventilated enclosure containing GH₂ equipment was conducted, where CFD modeling of the hydrogen dispersion (performed by AVT and UQTR, and independently by the JRC) was validated by the NREL Sensor laboratory using a Hydrogen Wide Area Monitor (HyWAM) consisting of a 10-point gas and temperature measurement analyzer. In the release test, helium was used as a hydrogen surrogate. Expansion of indoor releases to other larger facilities (including parking structures, vehicle maintenance facilities and potentially tunnels) and incorporation into QRA tools, such as HyRAM is planned for Phase 2. It is anticipated that results of this work will be used to inform national and international standards such as NFPA 2 Hydrogen Technologies Code, Canadian Hydrogen Installation Code (CHIC) and relevant ISO/TC 197 and CEN documents.     

On a heterostructure field-effect transistor (HFET) based hydrogen sensing system

An interesting heterostructure field-effect transistor (HFET) based hydrogen sensing system is developed and demonstrated. Even at a low hydrogen concentration of 15 ppm H₂/air, the studied sensor still exhibits high sensitivity at room temperature. Furthermore, a simple sensing system is also designed and reported. In contrast to conventional hydrogen measurement, the detecting system consists of a hydrogen sensor and some sensing circuits. This proposed hydrogen detection system is based on the micro-controller with advantages of low cost, fast response, portable, and easy operation. From experimental results, the proposed system is shown to be good for use.     

Carbon-doped ZnO nanotube-based highly effective hydrogen gas sensor: A first-principles study

The hydrogen gas sensing properties of carbon-doped ZnO nanotube has been theoretically investigated by employing first-principles density functional theory in combination with non-equilibrium Green's function. The figure of merits is creating the new states in ZnO nanotube structure by adding carbon substitution for an oxygen site. The calculation of adsorption energy indicates strong chemical adsorption of hydrogen on the outside and inside of carbon-doped ZnO nanotube. Moreover, density of state, current-voltage and sensor response have been performed for energetically favorable adsorption geometries of hydrogen. The involvement of carbon valence electrons in the chemical adsorption of hydrogen has been examined by partial density of state diagram. The current-voltage diagram of carbon-doped ZnO nanotube indicates negative-differential resistance trend. This trend has been disappeared after the chemical adsorption of hydrogen. The sensor response calculations reveal the high response of the sensor occurs in 3.5 V on the outside and inside of carbon-doped ZnO nanotube.     

Understanding on the effect of morphology towards the hydrogen and carbon monoxide sensing characteristics of tin oxide sensing elements

Though the gas sensing properties of atmospheric plasma sprayed tungsten oxide, zinc oxide, titanium oxide, tin oxide and copper oxide coatings were well investigated, reports comparing sensing characteristics of plasma sprayed sensor thick film coating with its bulk counterpart are hardly found in the literature. This work attempts to compare hydrogen and carbon monoxide sensing characteristics, namely gas response, response time, recovery time of plasma sprayed tin dioxide thick film with tin dioxide bulk sensor. Gas response in the presence of hydrogen gas (23–81%) was superior to that of carbon monoxide gas (19–79%). An attempt was made to understand plausible reason behind superior hydrogen gas response. Thus, gas response as a function of temperature was simulated using a gas diffusion equation for hydrogen and carbon monoxide gases. Estimated parameters, namely, activation energy of transduction and first order kinetics were correlated with sensor microstructure and experimental gas response values. For hydrogen sensing, shorter response time (30–138 s) and recovery time (118–161 s) of thick film as compared to response time (64–234 s) and recovery time (183–196 s) of bulk sensor was correlated with microstructure of sensory elements. It was observed that tin dioxide thick film, owing to its porous morphology with small-sized particulates exhibited superior hydrogen gas response, short response time and recovery time as compared to its bulk counterpart.     

Critical review and analysis of hydrogen safety data collection tools

The wider adoption of hydrogen in multiple sectors of the economy requires that safety and risk issues be rigorously investigated. Quantitative Risk Assessment (QRA) is an important tool for enabling safe deployment of hydrogen fueling stations and is increasingly embedded in the permitting process. QRA requires reliability data, and currently hydrogen QRA is limited by the lack of hydrogen specific reliability data, thereby hindering the development of necessary safety codes and standards [1]. Four tools have been identified that collect hydrogen system safety data: H2Tools Lessons Learned, Hydrogen Incidents and Accidents Database (HIAD), National Renewable Energy Lab's (NREL) Composite Data Products (CDPs), and the Center for Hydrogen Safety (CHS) Equipment and Component Failure Rate Data Submission Form. This work critically reviews and analyzes these tools for their quality and usability in QRA. It is determined that these tools lay a good foundation, however, the data collected by these tools needs improvement for use in QRA. Areas in which these tools can be improved are highlighted, and can be used to develop a path towards adequate reliability data collection for hydrogen systems.     

Economic analysis of standalone and grid connected hybrid energy systems

A pilot region was selected and cost analysis of using renewable energy sources with a hydrogen system for that region’s energy demand is introduced, in a techno-economic perspective, in this paper. The renewable energy potential for the region was evaluated by implementing energy cost analysis. The study also evaluates the feasibility of utilizing solar and wind energy with hydrogen as a storage unit to meet the electricity requirements of the pilot region as a standalone system and in conjunction with the conventional grid based electricity.In order to simulate the operation of the system and to calculate the technical and economic parameters, micropower optimization program Homer (NREL, US) was used in this study. Homer requires some input values, such as technological options, cost of components, and resource compliance; and then the program ranges the feasible system configurations according to the net present cost (system cost) by using these inputs.The pilot region in this study, where the renewable based energy will be used, is determined to be Electrics & Electronics Faculty, Istanbul Technical University.     

Hydrogen sensor using the Pd film supported on anodic aluminum oxide

Highly sensitive hydrogen gas sensors were fabricated using a microelectromechanical system (MEMS) and anodic aluminum oxides (AAOs) process. MEMS based gas sensor platform was designed with the multi-layer type for Pd film morphology manipulations. The operating temperature of the micro heater was positively correlated with the heater. Hydrogen sensing response of the sensor showed a good positive linearity as the gas sensitivity increased with increasing hydrogen concentration. The hydrogen sensitivity (defined as ratio of sensor resistances in air and after the hydrogen gas injection) was 0.638% at hydrogen concentration of 2000 ppm. The H₂ sensitivity was very dependent on the thickness and morphology of Pd-nanosized film. The gas sensitivity and response properties showed different behaviors when palladium film was deposited on the anodic aluminum oxide (AAO) layer. The hydrogen sensitivity for the Pd on AAO layer was about 0.783% at the hydrogen concentration of 2000 ppm. The sensitivity of the Pd-AAO layer improved with respect to the pure Pd thin film due to nanoporous nature of AAO.     

Development of a polyaniline nanofiber-based carbon monoxide sensor for hydrogen fuel cell application

The sensing of carbon monoxide (CO) impurity contained in hydrogen fuel is a challenging work in the field of low temperature proton exchange membrane fuel cell (PEMFC). In the present work a chemiresistive gas sensor based on polyaniline (PANI) nanofibers was developed to detect CO in hydrogen. The sensor was fabricated by a template-free electrochemical polymerization of aniline on an interdigitated electrode. The most distinctive feature of the fabricated sensor was the formation of a horizontally oriented, monolayered PANI nanofiber network on the insulating gap area. The gas sensing character of the PANI nanosensor was evaluated by measuring the change in electrical resistance when gas atmosphere was changed from pure hydrogen to mixtures of CO in hydrogen. The results demonstrated that the PANI nanosensor had an excellent responding ability on CO in hydrogen with a concentration as low as 1 ppm. The influences of parameters, such as nanostructure, doping level, dopants, and CO concentrations, on the sensing characters of the nanosensor were discussed. The responding mechanism was attributed to the different binding sites of CO and H₂ with PANI: H₂ with the protonated amine nitrogen atoms and CO with the unprotonated amine nitrogen atoms. In view of its novel sensing mechanism and high sensing performance, the fabricated sensor is very promising to be applied as a new type of CO sensor to prevent the catalysis poisoning of PEMFC.     

Proposal for a new system for simultaneous production of hydrogen and hydrogen peroxide by water electrolysis

Authors have proposed a new hydrogen production system that simultaneously produces hydrogen and hydrogen peroxide by water electrolysis. Experimental apparatus of the system is composed of a hydrogen electrode with platinum meshes, a hydrogen peroxide electrode with carbon material and an electrolyte with Nafion^®. In this paper, the superiority of the system is outlined, and the experimental results of the electrolytic synthesis of hydrogen and hydrogen peroxide from water are reported. Hydrogen peroxide is synthesized at the high efficiency when some kinds of carbon material are used as the hydrogen peroxide electrode. Furthermore, the possibility of applying the solar energy to this system is also 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.