Hydrogen Leakage Research Articles

On the chemistry of the global warming potential of hydrogen

Hydrogen (H2) is considered a promising fuel to contribute to net-zero carbon emission goals. While hydrogen itself is not a greenhouse gas, leakage of hydrogen fuels causes indirect warming due to hydrogen’s influence on methane, tropospheric ozone, and stratospheric water vapor, with the methane term dominating the impact. Some studies consider a simple four-equation box model to explore the climate consequences of leakage from hydrogen fuel use relative to methane, while others have employed much more detailed global photochemical models. Here we use a comprehensive photochemical box model including 66 reactions to show and quantify how the analogous four-equation system is missing a critical OH feedback, leading it to overestimate the time-integrated methane response to a pulse of hydrogen by over 100%. We estimate a hydrogen global warming potential (GWP) relative to carbon dioxide of 28−11+18 on the 20-year time horizon and 10−4+7 on the 100-year time horizon based on the 66-reaction model and information from the literature. GWPs provide a measure of the relative global warming impact of emission of one gas compared to a selected reference gas per unit mass emitted. While CO2 is generally chosen for the reference, any gas can be used. We present the GWP of H2 using CH4 as the reference, as this choice cancels out some uncertainties that are common to both H2 and CH4. The GWP for H2 relative to CH4 from fossil fuel sources is 0.35−0.06+0.13 on time horizons beyond 15 years; put differently, we find that relative to an equivalent mass of emission of fossil CH4, hydrogen emission has a climate impact about three times smaller. These global warming potentials underscore that hydrogen leakage does contribute to climate change, emphasizing the importance of limiting both hydrogen and methane leakage if global net-zero greenhouse gas emissions are to be achieved by 2050.

Microscale chemiresistive hydrogen sensors: Current status and recent developments

Hydrogen is known for its efficient combustion, abundant natural availability, and environmentally friendly characteristics. It is recognized as a promising energy source for the future and is already utilized in various industries, including petrochemicals, electronics, food processing, aerospace, and new energy vehicles. However, challenges arise in the storage and use of hydrogen owing to its tendency to leak, its potential for explosion within a specific concentration range of 4%–75%, and itslow ignition energy requirements. Consequently, there is a demand for hydrogen sensors capable of quickly and accurately detecting low levels of hydrogen leaks. Microelectromechanical systems-based chemiresistive hydrogen sensors offer advantages such as low cost, compact size, low energy consumption, and superior sensing performance, making them a major focus of recent research. This article provides a comprehensive overview and comparison of the sensing principles of various hydrogen sensors, including chemiresistive sensors, electrochemical sensors, thermocatalytic sensors, acoustic sensors, and mechanical sensors. Micro-chemiresistive hydrogen sensors exhibit high sensitivity, low cost, and ease of integration, making them highly promising for practical applications. In response to the challenges encountered in practical applications of chemiresistive hydrogen sensors, such as high operating temperatures and high power consumption, this review explores emerging trends in chemiresistive hydrogen sensor technology from the perspectives of novel materials and activation methods. Finally, it discusses the applications and potential further developments of chemiresistive hydrogen sensors.

Miniaturized Electrochemical Gas Sensor with a Functional Nanocomposite and Thin Ionic Liquid Interface for Highly Sensitive and Rapid Detection of Hydrogen.

Hydrogen has been widely used in industrial and commercial applications as a carbon-free, efficient energy source. Due to the high flammability and explosion risk of hydrogen-air mixtures, it is vital to develop sensors featuring fast-responding and high sensitivity for hydrogen leakage detection. This paper presents a miniaturized electrochemical gas sensor by elaborately establishing a nanocomposite and thin ionic liquid interface for highly sensitive and rapid electrochemical detection of hydrogen, in which a remarkable response time and recovery time of approximately 6 s was achieved at room temperature. A screen-printed carbon electrode was modified with a reduced graphene oxide-carbon nanotube (rGO-CNT) hybrid and platinum-palladium (Pt-Pd) bimetallic nanoparticles to realize high sensitivity. To achieve miniaturization and high stability of the sensor, a thin-film room-temperature ionic liquid (RTIL) was employed as the electrolyte with a significantly decreased response time. The fast-responding hydrogen sensor demonstrates excellent performance with high sensitivity, linearity, and repeatability at concentrations below the lower explosive limit of 4 vol %. The engineered high-performance interface and gas sensor provide a promising and effective strategy for gas sensor design and rapid hazardous gas monitoring.

Ultrafast and Reproducible Fiber-Optic Hydrogen Sensor via a Tilted Fiber Grating With Pd/WO3 Nanocoating

Hydrogen, a high-density and clean energy, has been widely used in various critical applications. However, the safety risk caused by hydrogen leakage during storage and transportation is still a non-negligible issue. Therefore, it is necessary to offer hydrogen sensors with fast response and high repeatability, and it will be perfect for achieving in situ monitoring over the lifecycle of hydrogen production and utilization. Here, we propose a compact optical fiber sensor with a short section of the tilted Bragg fiber grating (TFBG) inscribed in the fiber core and a palladium and tungsten trioxide (Pd/WO3) combined film of 40 nm thickness over the fiber surface. The TFBG excites tens of narrow cladding resonances, part of which possess refractive indexes matching that of the Pd/WO3 coating and providing the high sensitivity to the surrounding hydrogen concentration change. The sensor offers improved sensing characteristics, including the fast response time (less than 10 s), high repeatability (over tens of measurement), and excellent linear response (higher than 99.6%) over the 0% to 3% concentration range.

Risk assessment of hydrogen leakage and explosion in a liquid hydrogen facility using computational analysis

In this study, the dispersion and explosion of liquid hydrogen (LH2) in leakage accidents are investigated using the Flame Accelerator Simulator (FLACS) code. The study focus was a liquid hydrogen research facility in Gimhae, South Korea. Simulations were conducted under various conditions by varying the mass flow rates (0.61 and 0.3 kg/s), directions (lateral in areas with minimal structures, lateral towards a tube trailer truck, and downward), and durations (90 and 180 s) of leakage. The results indicated that higher leakage mass flow rates produce a larger flammable cloud volume (FCV), resulting in higher maximum overpressures than that caused by lower flow rates. Downward leakage generally resulted in a larger FCV and higher overpressure than lateral leakage. The explosion characteristics were also influenced by geometry of LH2 facility, including the presence of structures in the leakage path. Contrastingly, leakage duration had a minimal effect on the maximum overpressure because an increased duration causes a greater dilution of hydrogen, only slightly expanding the FCV. According to the overpressure–impulse diagram, higher leakage flow rates cause severe health risks, approaching thresholds for lung rupture and 100% fatality. Contrary to the minor damages caused by lower leakage flow rates. High flow rates, particularly with downward leaks, can cause significant structural damage in brick buildings, potentially leading to partial demolition.

The impact of fuel cell vehicle exhaust grille shape under natural ventilation on hydrogen leakage and diffusion

The rapid progression of hydrogen fuel cell vehicles has brought forth various challenges, primarily the frequent occurrence of hazardous incidents stemming from hydrogen leakage and diffusion. Consequently, there is a growing emphasis on hydrogen safety, leading to the development of stricter standards and regulations to mitigate the associated safety risks. Research on the design of exhaust port structures to facilitate the safe diffusion of hydrogen after leakage in diverse scenarios has become increasingly significant. This study examines the impact of exhaust grille shapes on hydrogen leakage and diffusion phenomena within the hydrogen storage compartment of fuel cell vehicles under natural ventilation conditions. Five distinct porous grille shapes were examined: rectangular, circular, square, rhombic, and hexagonal grilles. Numerical simulations of hydrogen leakage and diffusion within the compartment were conducted using Cradle scFLOW software. The effectiveness of the different grille shapes was assessed using several criteria, including average hydrogen molar fraction, pressure drop (indicative of negative pressure regions), density, and Richardson number. Overall, the rectangular grille exhibited superior performance in facilitating hydrogen venting.

Experimental study on dynamic response performance of hydrogen sensor in confined space under ceiling

With the advancement of Fuel Cell Vehicles (FCVs), detecting hydrogen leaks is critically important in facilities such as hydrogen refilling stations. Despite its significance, the dynamic response performance of hydrogen sensors in confined spaces, particularly under ceilings, has not been comprehensively assessed. This study utilizes a catalytic combustion hydrogen sensor to monitor hydrogen leaks in a confined area. It examines the effects of leak size and placement height on the distribution of hydrogen concentrations beneath the ceiling. Results indicate that hydrogen concentration rapidly decreases within a 0.5–1.0 m range below the ceiling and declines more gradually from 1.0 to 2.0 m. The study further explores the attenuation pattern of hydrogen concentration radially from the hydrogen jet under the ceiling. By normalizing the radius and concentration, it was determined that the distribution conforms to a Gaussian model, akin to that observed in open space jet flows. Utilizing this Gaussian assumption, the model is refined by incorporating an impact reflux term, thereby enhancing the accuracy of the predictive formula.

Incident investigation of hydrogen explosion and fire in a residue desulfurization process

A large hydrogen explosion and fire occurred on October 27, 2022 in a residue desulfurization (RDS) process in a refinery in Kaohsiung, Taiwan. RDS is an important process that use hydrogen to convert the sulfur in the fuel into hydrogen sulfide for producing low sulfur fuel. The incident occurred during pressurization of the RDS reactors and downstream coolers by hydrogen. The incident led to significant damages to the downstream coolers and some part of the RDS reactors. Detailed incident investigation was carried out. A reactor effluent air cooler (REAC) in the downstream of RDS reactors was found to be ruptured in the rectangular header box. With security videos, process DCS data, leak and dispersion modelling, and actual damage on the process, it is possible to reproduce the leak rate, size of the initial fireball and damages done to the process. It is also found that the hydrogen leak was accompanied by prompt ignition which is commonly encountered in high-pressure hydrogen services. Recommendations are made to prevent and mitigate any future incident from the RDS process.

Quantitative analysis of hydrogen leakage flow measurement and calculation in the on-board hydrogen system pipelines

The mass flow rate of hydrogen leakage directly affects hydrogen diffusion and concentration distribution. In this paper, a test platform was constructed to measure mass flow rates during hydrogen leakage in the supply pipelines of the on-board hydrogen system. Hydrogen leakage tests were conducted under two different conditions. Mass flow rates were measured for tube fittings with various loosening angles and hydrogen supply pressures. The data were then fitted to extrapolate mass flow rates of hydrogen leakage beyond the tested conditions. Additionally, mass flow rates were measured for hydrogen supply pipelines with small holes of different shapes and sizes. The effects of pipeline size, hydrogen supply pressure, hole shape, and size on the hydrogen leakage mass flow rate were analyzed. Hydrogen leakage flow coefficients were corrected, and the accuracy of three calculation methods for hydrogen leakage flow was compared and analyzed based on the test results. The results provide a foundation for future numerical simulation models of hydrogen leakage diffusion.

Investigation into the Suppression Effect of Water Mist on the Self-ignition and Flame Propagation of High-pressure Hydrogen Release

Abstract The self-ignition accident of pressurized hydrogen leakage is regarded as one of the big potential risks in its wide utilization. In this work, a detailed investigation into the suppression effect of water mist on the hydrogen self-ignition and flame propagation is performed. A parametric study of the effect of water concentration and droplet size on flame dynamic is conducted. The results show that the fine water mist effectively reduces the shock-heating temperature, significantly prolonging the ignition time and distance. The water droplets have a direct contact with the fast growing flame, which leads to more intense two-phase interaction that results in the decoupling of shock wave from the leading flame and a more pronounced bimodal flame structures. The droplet size is found to have small effect when the water concentration is low, and the mist with a medium size of 50 μm shows a better inhibitory performance.

Cryogenic mechanical performance and gas-barrier property of epoxy resins modified with multi-walled carbon nanotubes

Type V linerless hydrogen storage vessels made of all-composite face the challenges of cryogenic mechanical failure and hydrogen leakage of composites. The cryogenic mechanical performance and gas-barrier property of the carbon fiber reinforced polymer for Type V vessels are largely determined by the epoxy matrix. Carbon nanotubes are widely used as polymer reinforcement material to enhance the cryogenic mechanical performance and gas-barrier property of epoxy resins. In this work, multi-walled carbon nanotubes (MWCNTs) were dispersed into epoxy resins to prepare MWCNTs-modified epoxy resins. The cryogenic mechanical performance, gas-barrier and thermal properties of the modified resin were then investigated. The experimental findings revealed a 34.34% reduction in the gas permeability coefficient for the nanocomposites containing 0.9 wt% MWCNTs compared with the epoxy matrix. The tensile strength and failure strain at cryogenic temperature (77 K) experienced enhancements of 26.99% and 41.53%, respectively. In addition, the thermal stability and glass transition temperature of the modified resin were improved. As a result, the MWCNTs-modified epoxy resin exhibits improved gas-barrier property in addition to excellent cryogenic mechanical performance, making it ideal for manufacturing Type V linerless hydrogen storage vessels.

Ultra-Low-Power, Extremely Stable, Highly Linear-Response Thermal Conductivity Sensor Based on a Suspended Device with Single Bare Pt Nanowire.

The continuous and stable monitoring by sensors is crucial for ensuring the safe utilization of hydrogen due to its inherent high explosiveness. Currently, catalyst aging and oxygen dependence often limit the lifetime of most sensors, which stems from the sensing materials and catalytic reaction in comparison to thermal conductivity sensors. Thermal conductivity sensors possess superior sensing characteristics such as lowpower consumption and exceptional stability attributed to their free-catalysts or free-oxygen nature. Herein, we present an ultralow-power hydrogen-thermal conductivity sensor based on suspended bare platinum nanowires. This sensor incorporates two suspended independent working elements (serpentine/bridge), each of which is thermally decoupled from the substrate. Also, the bridge element operates at significantly lower power levels (the lowest ∼3.32 μW) compared to existing direct-current hydrogen-thermal conductivity sensors. Furthermore, it demonstrates a 99.99% linearity between hydrogen concentration and response under various operating powers. Finally, our sensor shows remarkable stability through a repeatability test (>30,000 cycles). This developed platform provides an optimal structure scheme for integrated sensors with ultralow-power, extremely stable, highly linear-response sensing characteristics, which is expected to be widely used for hydrogen detection and leakage warning under various pipeline distribution systems.

Uniform Nanocrystal Spatial Distribution-Enhanced SnO2-based Sensor for High-Sensitivity Hydrogen Detection.

Hydrogen (H2) is colorless, odorless, and has a wide explosive concentration range (4-75 vol %), making rapid and accurate detection of hydrogen leaks essential. This paper demonstrates a method to modify the spatial distribution of nanocrystals (NCs) by adding surfactants to improve the sensing performance. In order to explore its potential for H2 gas-sensing applications, SnO2, containing different mass percentages of PdCu NCs, was dispersed. The results show that the 0.1 wt % PdCu-SnO2 sensor based on surfactant dispersion performs well, with a response to 0.1 vol % H2 that is 18 times higher than that of the undispersed 0.1 wt % PdCu-SnO2 sensor. The enhanced gas-sensing ability after dispersion can be attributed to the fact that the uniform distribution of NCs generates higher quantum efficiency and exposes more active sites on the carrier surface compared to nonuniform distribution. This study provides a simple, novel, and effective method to improve the sensor response.

Hydrogen leakage and diffusion in the operational cabin of hydrogen tube bundle containers：A CFD study

The operational cabin of hydrogen tube bundle containers (HTBCs) is susceptible to vibration and fatigue loads during transportation, which may result in hydrogen leakage and deflagration accidents. In this paper, a three-dimensional (3D) computational fluid dynamics (CFD) model is developed to simulate the effects of leakage diameter, leakage pressure, leakage direction and position on hydrogen leakage and diffusion in the operational cabin of HTBCs. The results demonstrate that the formation of vortex recirculation zones leads to the accumulation of flammable gas cloud (FGC) in the operational cabin. The medium leakage diameter (1.5 mm) and higher leakage pressure (20 MPa, 35 MPa) cause the operational cabin to be filled with FGC within 5 s, requiring the operational cabin to be designed with no possible ignition source inside. In addition, when hydrogen leaks from the +Z direction, the sensor responds within 0.31 s, which is 1.7 s earlier than the response time in the -Z direction, indicating that the existing sensor layout cannot meet the requirements of fast response. When the leak position (L3) is close to the vent, the FGC volume proportion at 2 s is 19.3 % and 15.88 % lower than that of L1 and L2, respectively, indicating that the leak position close to the vent can effectively slow down the accumulation of FGC. The research results have implications for the safety design of operational cabin of HTBCs, the layout of hydrogen sensors and vents, and the emergency response measures for hydrogen leakage.

Developing an internet of things system for hydrogen leak detection at hydrogen refueling stations integrating LoRa and global positioning system

Developing a hydrogen leak detection system that can quickly detect even the smallest amount of hydrogen is extremely crucial in the hydrogen industry. Currently, hydrogen refueling stations use a fixed hydrogen leak detection system. This study develops a mobile hydrogen gas leak detection system for hydrogen refueling stations using s, global positioning system, and Internet of Things (IoT) equipment, including LoRa and Wi-Fi. A digital twin is implemented by linking hydrogen gas-sensing data at a location that is quickly required or suspected using Google Maps. A time-series database is used to store the hydrogen gas-sensing data, and the transfer delay of hydrogen gas-sensing data between the hydrogen equipment was measured. Therefore, we developed a prototype system that transmits, stores, and analyzes hydrogen gas-sensing data in real time using IoT equipment for hydrogen refueling stations.

Development of the Quantitative Property-Consequence Relationship Model for Prediction of Hydrogen Leakage and Dispersion Using Response Surface Method and Artificial Neural Network Approaches.

Hydrogen, an environmentally friendly and highly regarded future energy source, can form flammable vapor clouds upon leakage, which may transition into explosion. Predicting the dispersion behavior of hydrogen is crucial for preventing such incidents. This study aims to develop a quantitative property-consequence relationship (QPCR) model using the response surface method (RSM) and artificial neural network (ANN) to swiftly and accurately predict dispersion behavior. Initially, 8 variables were defined from source and dispersion models, constructing a data set through 6,561 PHAST simulations. Subsequently, the RSM-BBD (Box-Behnken design) and ANN-BPNN (Backpropagation neural network) models were developed, alongside a hybrid model incorporating BPNN after excluding four low-influence variables based on analysis of variance (ANOVA). All models achieved an R2 value exceeding 0.99. The hybrid model notably reduced computational costs by 97% compared to ANN-BPNN and exhibited lower mean square error (MSE). These results introduce a cost-effective approach for high-accuracy QPCR modeling and highlight the viability of diverse statistical methods.

Progress in spontaneous ignition of hydrogen during high-pressure leakage with the considerations of pipeline storage and delivery

High-pressure pipeline storage presents a promising method for widespread and efficient hydrogen transfer. However, challenges arise in mitigating pressurized hydrogen leakage due to hydrogen embrittlement issues associated with conventional pipeline materials. Experimental findings indicate that pressurized hydrogen is prone to spontaneous combustion, even at relief pressures as low as approximately 2 MPa - well below the permissible pipeline pressure in most countries. Despite this, there remains a lack of consensus regarding the mechanism of spontaneous ignition from high-pressure hydrogen leakage, and current research in this area is deemed insufficient. This study aims to analyze and discuss the presumed mechanisms of spontaneous ignition comparatively, review the progress in the study of spontaneous ignition of hydrogen in high-pressure leakage based on diffusion ignition theory, and statistically compare and discuss the influences of significant factors existing in pipelines (e.g., macro size factors and internal structure) and/or pipe failures (e.g., rupture factors) on spontaneous ignition. It is hoped that this article will provide scholars involved in the development of hydrogen energy and the theories of spontaneous combustion with a systematic understanding of these phenomena.

High sensitivity potentiometric hydrogen sensor based on ZnFe2O4 electrode

Hydrogen is currently considered to be the best clean energy to replace fossil fuels, so hydrogen leak detection is crucial. The current research field of hydrogen sensors focuses on the discovery and optimization of sensitive materials. ZnFe2O4 powder is prepared by the sol-gel method and sintered at different temperatures. The effects of sintering temperature on electrode morphology and hydrogen sensing performance are investigated. The sensitivity reaches a maximum value of −101.32 mV/decade at the sintering temperature of 1100 °C. The sensor has different sensing performance at different operating temperatures. It has the best response value and sensitivity at 450 °C, and the best response/recovery rate and response curve stability at 550 °C. The sensor responds and recovers in seconds. The material has good H2 selectivity and is suitable for potentiometric hydrogen sensors. CO, NH3, and CH4 have less effect on the response signal and exhibit good long-term stability.

Dispersion characteristics of large-scale liquid hydrogen spills in a real-world liquid hydrogen refueling station with various releasing and environmental conditions

The global expansion of hydrogen refueling stations (HRS) has heightened interest in the development of liquid hydrogen refueling stations (LHRS). This study presents a model for an LHRS, inspired by the Yilan HRS in Shanghai, to simulate large-scale liquid hydrogen (LH2) leakage scenarios. Utilizing the FLACS-CFD software, comprehensive simulations were performed to assess the impact of various environmental conditions and leakage parameters—such as wind speed, wind direction, spill rate, and spill duration—on critical outcomes including the size of the LH2 pool, evaporation rate, flammable volume of the vaporized hydrogen gas cloud, and maximum downwind distance/height. The findings establish a correlation between these factors and the predicted results, providing real-time guidance for managing LH2 leakage incidents at operational LHRS.

An review of research on liquid hydrogen leakage: regarding China’s hydrogen refueling stations

Hydrogen is regarded as the premier energy source for future sustainability and renewability. However, its distinct physicochemical properties render it prone to explosions in the event of a leak. Therefore, there is a need for more comprehensive research dealing with hydrogen leakage, explosion scenarios, and risk assessment. This paper provides an overview of the current hydrogen policies adopted in China. It reviews the processes of hydrogen refueling station construction and the thermophysical mechanisms of liquid hydrogen leakage. In this regard, the effects of various factors, including leakage rate, leakage time, leakage hole size, wind direction and speed, and building location, on the hydrogen leakage rate are analyzed and evaluated. Additionally, the impacts of different factors on hydrogen explosion overpressure are reported, including hydrogen concentration, wind speed, obstacles, and ignition position, in addition to the current applications of quantitative risk assessment methods in hydrogen refueling stations. Finally, the limitations of current research on liquid hydrogen leakage and explosion accidents are highlighted, along with the shortcomings of current risk assessment methods for liquid hydrogen refueling stations.