Hydrogen, Volume 3, Issue 4 (December 2022) – 13 articles

The geological storage of hydrogen is a seasonal energy storage solution, and the storage capacity of saline aquifers is most appropriately defined by quantifying the amount of hydrogen that can be injected and reproduced over a relevant time period. Cushion gas, stored in the reservoir to support the production of the working gas, is a CAPEX, which should be reduced to decrease implementation cost for gas storage. The cushion gas to working gas ratio provides a sufficiently accurate reflection of the storage efficiency, with higher ratios equating to larger initial investments. This paper investigates how technical measures, such as well configurations and adjustments to the operational size and schedule, can reduce this ratio, and the outcomes can inform optimisation strategies for hydrogen storage operations. Using a simplified open saline aquifer reservoir model, hydrogen storage is simulated with a single injection and production well. The results show that the injection process is more sensitive to technical measures than the production process; a shorter perforation and a smaller well diameter increases the required cushion gas for the injection process but has little impact on the production. If the storage operation capacity is expanded, and the working gas volume increased, the required cushion gas to working gas ratio increases for injection, reducing the efficiency of the injection process. When the reservoir pressure has more time to equilibrate, less cushion gas is required. It is shown that cushion gas plays an important role in storage operations and that the tested optimisation strategies impart only minor effects on the production process, however, there is significant need for careful optimisation of the injection process. It is suggested that the recoverable part of the cushion gas could be seen as a strategic gas reserve, which can be produced during an energy crisis. In this scenario, the recoverable cushion gas could be owned by the state, and the upfront costs for gas storage to the operator would be reduced, making the implementation of more gas storage and the onset of hydrogen storage more attractive to investors. Full article

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development. Full article

This study presents a methodology of a quantitative risk assessment for the scenario of an onboard hydrogen storage tank rupture and tunnel fire incident. The application of the methodology is demonstrated on a road tunnel. The consequence analysis is carried out for the rupture of a 70 MPa, 62.4-litre hydrogen storage tank in a fire, that has a thermally activated pressure relief device (TPRD) failed or blocked during an incident. Scenarios with two states of charge (SoC) of the tank, i.e., SoC = 99% and SoC = 59%, are investigated. The risks in terms of fatalities per vehicle per year and the cost per incident are assessed. It is found that for the reduction in the risk with the hydrogen-powered vehicle in a road tunnel fire incident to the acceptable level of 10⁻⁵ fatality/vehicle/year, the fire-resistance rating (FRR) of the hydrogen storage tank should exceed 84 min. The FRR increase to this level reduces the societal risk to an acceptable level. The increase in the FRR to 91 min reduces the risk in terms of the cost of the incident to GBP 300, following the threshold cost of minor injury published by the UK Health and Safety Executive. The Frequency–Number (F–N) of the fatalities curve is developed to demonstrate the effect of mitigation measures on the risk reduction to socially acceptable levels. The performed sensitivity study confirms that with the broad range of input parameters, including the fire brigade response time, the risk of rupture of standard hydrogen tank-TPRD systems inside the road tunnel is unacceptable. One of the solutions enabling an inherently safer use of hydrogen-powered vehicles in tunnels is the implementation of breakthrough safety technology—the explosion free in a fire self-venting (TPRD-less) tanks. Full article

Hydrogen (H₂) is regarded as a promising and renewable energy carrier to achieve a sustainable future. Among the various H₂ production routes, photocatalytic water splitting has received particular interest; it strongly relies on the optical and structural properties of photocatalysts such as their sunlight absorption capabilities, carrier transport properties, and amount of oxygen vacancy. Perovskite oxides have been widely investigated as photocatalysts for photocatalytic water splitting to produce H₂ because of their distinct optical properties, tunable band gaps and excellent compositional/structural flexibility. Herein, an aluminum cation (Al³⁺) doping strategy is developed to enhance the photocatalytic performance of Ruddlesden-Popper (RP) Sr₂TiO₄ perovskite oxides for photocatalytic H₂ production. After optimizing the Al³⁺ substitution concentration, Sr₂Ti_0.9Al_0.1O₄ exhibits a superior H₂ evolution rate of 331 μmol h⁻¹ g⁻¹, which is ~3 times better than that of Sr₂TiO₄ under full-range light illumination, due to its enhanced light harvesting capabilities, facilitated charge transfer, and tailored band structure. This work presents a simple and useful Al³⁺ cation doping strategy to boost the photocatalytic performance of RP-phase perovskites for solar water splitting. Full article

The computer-aided engineering approach has made it possible to achieve virtual prototypes and to describe expected performances of new apparatuses. In this study, a direct production of syngas with biogas using the configuration of the cascade conversion cell in the supply feed direction of the system was exhibited. Momentum, heat, mass and charge balances were solved using COMSOL Multiphysics^® commercial software. These simulations allowed calculation of distributions of partial pressures for all gas species within the anode (CH₄, H₂, CO, CO₂, H₂O, N₂), as well as velocity field and temperature. The conversion process included methane reforming (steam and dry) associated with the water–gas shift reaction. The computing results showed that the configuration of three porous oxide solid cells based on a solid oxide fuel cell (SOFC) system conferred a larger active surface area and limited thermal stress in oxide materials. In addition, depending on the production process of the biogas, feeding composition strongly influences the conversion rate of CO₂ and CH₄. We observed that production of syngas was optimal for a CO₂/CH₄ ratio = 1. Full article

Hydrogen embrittlement of a Ni-based superalloy, IN740H, was evaluated after gas-phase hydrogen pre-charging. Specimens with different grain sizes were prepared to induce different precipitation behavior under annealing treatment; the formation of needle-like MC carbide was found only in a specimen with a larger grain size and incoherent twin boundaries after annealing treatment at 1173 K. While other parameters including the grain size and annealing treatment turned out not to undermine the resistance to hydrogen embrittlement, the needle-like MC carbide was found to induce premature failure after hydrogen absorption. Full article

An oxygen pump sensor was constructed using yttria-stabilized zirconia, which is an oxide ion conductor, and oxygen was discharged from steam to generate hydrogen. The oxygen pump sensor consisted of a pump that discharges oxygen and a sensor that controls the oxygen partial pressure by having electrodes in two places. Oxygen was discharged by applying a current to the pump by controlling the potential of the sensor. Hydrogen was then generated from water vapor. Furthermore, an oxygen pump sensor was installed in the second stage, oxygen was supplied by the pump, and the amount of generated hydrogen was measured in situ. This measurement showed that the oxygen partial pressure of the atmosphere decreased as hydrogen was generated. Specifically, the partial pressure of the water vapor generated more hydrogen at 30.8 vol.% than at 12.2 vol.%. Moreover, the amounts of oxygen discharged and hydrogen generated inversely correlated with the potential. Full article

Among all hydrocarbons, the methane molecule contains the highest amount of hydrogen with respect to carbon. Therefore, the catalytic decomposition of methane is considered as an efficient approach to produce hydrogen along with nanostructured carbon product. On the other hand, the presence of hydrogen in the composition of the initial gas mixture is required for the stable operation of the catalyst. In present work, the experiments on the catalytic decomposition of methane–hydrogen mixture were performed in a flow-through quartz reactor equipped with McBain balances under atmospheric pressure. The catalyst NiO-CuO/Al₂O₃ was prepared by the mechanochemical activation technique. The maximum carbon yield of 34.9 g/g_cat was obtained after 2 h of experiment at 610 °C. An excess of hydrogen in the reaction mixture provided the long-term activity of the nickel–copper catalyst. The durability tests ongoing for 6 h within a temperature range of 525–600 °C showed no noticeable deactivation of the catalyst. Two kinetic models, D1a and M1a, were proposed for the studied decomposition of the methane–hydrogen mixture over the nickel–copper catalyst. The kinetic constants for these models were determined by means of mathematical modelling. Full article

An under-expanded hydrogen jet from high-pressure equipment or storage tank is a potential incident scenario. Experiments demonstrated that the delayed ignition of a highly turbulent under-expanded hydrogen jet generates a blast wave able to harm people and damage property. There is a need for engineering tools to predict the pressure effects during such incidents to define hazard distances. The similitude analysis is applied to build a correlation using available experimental data. The dimensionless blast wave overpressure generated by delayed ignition and the follow-up deflagration or detonation of hydrogen jets at an any location from the jet, $∆P_{exp}/P_0$, is correlated to the original dimensionless parameter composed of the product of the dimensionless ratio of storage pressure to atmospheric pressure, $P_s/P_0$, and the ratio of the jet release nozzle diameter to the distance from the centre of location of the fast-burning near-stoichiometric mixture on the jet axis (30% of hydrogen in the air by volume) to the location of a target (personnel or property), $d/R_w$. The correlation is built using the analysis of 78 experiments regarding this phenomenon in the wide range of hydrogen storage pressure of 0.5–65.0 MPa and release diameter of 0.5–52.5 mm. The correlation is applicable to hydrogen free jets at ambient and cryogenic temperatures. It is found that the generated blast wave decays inversely proportional to the square of the distance from the fast-burning portion of the jet. The correlation is used to calculate the hazard distances by harm thresholds for five typical hydrogen applications. It is observed that in the case of a vehicle with onboard storage tank at pressure 70 MPa, the “no-harm” distance for humans reduces from 10.5 m to 2.6 m when a thermally activated pressure relief device (TPRD) diameter decreases from 2 mm to a diameter of 0.5 mm. Full article

The successful and fast start-up of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (cold start) is very important for the use of PEMFCs as energy sources for automotive applications. The effective thermal management of PEMFCs is of major importance. When hydrogen is stored in hydride-forming intermetallics, significant amounts of heat are released due to the exothermic nature of the reaction. This excess of heat can potentially be used for PEMFC thermal management and to accelerate the cold start. In the current work, this possibility is extensively studied. Three hydride-forming intermetallics are introduced and their hydrogenation behavior is evaluated. In addition, five thermal management scenarios of the metal hydride beds are studied in order to enhance the kinetics of the hydrogenation. The optimum combination of the intermetallic, hydrogenation behavior, weight and complexity of the thermal management system was chosen for the study of thermal coupling with the PEMFCs. A 1D GT-SUITE model was built to stimulate the thermal coupling of a 100 kW fuel cell stack with the metal hydride. The results show that the use of the heat from the metal hydride system was able to reduce the cold start by up to 8.2%. Full article

With increasing shares of variable and uncertain renewable generation in many power systems, there is an associated increase in the importance of energy storage to help balance supply and demand. Gas networks currently store and transport energy, and they have the potential to play a vital role in longer-term renewable energy storage. Gas and electricity networks are becoming more integrated with quick-responding gas-fired power plants, providing a significant backup source for renewable electricity in many systems. This study investigates Ireland’s gas network and operation when a variable green hydrogen input from excess wind power is blended with natural gas. How blended hydrogen impacts a gas network’s operational variables is also assessed by modelling a quasi-transient gas flow. The modelling approach incorporates gas density and a compressibility factor, in addition to the gas network’s main pressure and flow rate characteristics. With an increasing concentration of green hydrogen, up to 20%, in the gas network, the pipeline flow rate must be increased to compensate for reduced energy quality due to the lower energy density of the blended gas. Pressure drops across the gas pipeline have been investigated using different capacities of P2H from 18 MW to 124 MW. The results show significant potential for the gas network to store and transport renewable energy as hydrogen and improve renewable energy utilisation without upgrading the gas network infrastructure. Full article

Solar thermal technology can provide the United Arab Emirates and the Middle East region with abundant clean electricity to mitigate the rising levels of carbon dioxide and satisfy future demand. Hydrogen can play a key role in the large-scale application of solar thermal technologies, such as concentrated solar plants, in the region by storing the surplus electricity and exporting it to needed countries for profit, placing the Middle East and the United Arab Emirates as major future green hydrogen suppliers. However, a hydrogen supply chain comparison between hydrogen from CSP and other renewable under the UAE’s technical and economic conditions for hydrogen export is yet to be fully considered. Therefore, in this study we provide a techno-economic analysis for well-to-ship solar hydrogen supply chain that compares CSP and PV technologies with a solid oxide water electrolyzer for hydrogen production, assuming four different hydrogen delivery pathways based on the location of electrolyzer and source of electricity, assuming the SOEC can be coupled to the CSP plant when placed at the same site or provided with electric heaters when placed at PV plant site or port sites. The results show that the PV plant achieves a lower levelized cost of electricity than that of the CSP plant with 5.08 ¢/kWh and 8.6 ¢/kWh, respectively. Hydrogen production results show that the scenario where SOEC is coupled to the CSP plant is the most competitive scenario as it achieves the payback period in the shortest period compared to the other scenarios, and also provides higher revenues and a cheaper LCOH of 7.85 $/kg_H2. Full article

In this paper, we report the first hydrogenation (activation) of a 1.2Ti-0.8Fe alloy synthesized by induction melting (9 kg ingot). The alloy presented a three-phase structure composed of a main TiFe phase, a secondary Ti₂Fe phase and a Ti-rich BCC phase. The alloy required cold rolling to achieve activation at room temperature. However, it did so with good kinetics, reaching saturation (2.6 wt.% H) in about 6 h. After activation, the phases identified were TiFe, Ti₂FeH_x and an FCC phase. The Ti₂FeH_x and FCC are the stable hydrides formed by the secondary Ti₂Fe and BCC phases, respectively. The stoichiometry of the Ti₂FeH_x was calculated to be between x = 3.2–4.75. As the microstructure obtained by an industrial-scale synthesis method (induction melting) may be different than the one obtained by laboratory-scale method (arc melting), a small 3 g sample of Ti_1.2Fe_0.8 was synthesized by arc melting. The lab-scale sample activated (2 wt.% H in ~12 h) without the need for cold rolling. The phases identified for the lab-scale sample matched those found for the induction-melted sample. The phase fractions differed between the samples; the lab-scale sample presented a lower abundance and a finer distribution of the secondary phases. This explains the difference in the kinetics and H capacity. Based on these results it can be concluded that the alloy of composition, 1.2Ti-0.8Fe, can absorb hydrogen without the need for a heat treatment, and that finer microstructures have a strong influence on the activation kinetics regardless of the secondary phases’ phase fractions. Full article