Transmission, Distribution & Storage

Hydrogen and its interaction with metal oxide surfaces is of major importance for a wide range of research and applied fields spanning from catalysis energy storage microelectronics to metallurgy. This paper reviews state of the art of first principles calculations on the well-known ruthenium oxide (RuO₂) surface in its (110) orientation and its interaction with hydrogen. In addition to it the paper also fills gaps in knowledge with new calculations and results on the (001) surface. Bulk and surface interactions are thoroughly reviewed. This includes systematic analysis of adsorption sites local agglomeration propensity of hydrogen and migration pathways in which literature data and their potential deviations are explained. We notably discuss novel results on propensity for agglomeration of hydrogen within bulk channels [001] oriented in which the proton-like behavior of adsorbed hydrogen hinders further agglomeration in adjacent channels. The paper brings new insights into the migration pathways on the surface and in bulk both exhibiting preferential diffusion paths along the [001] direction. The paper finally investigates the subsurface region. We show that while the subsurface has more stable sites for adsorption compared to bulk its accessibility from the surface shows prohibitive activation barriers inhibiting penetration into subsurface and bulk. We further calculate and discuss adsorption and penetration processes on the alternative RuO₂ (001) surface.

In this paper we report the effect of adding Zr + V or Zr + V + Mn to TiFe alloy on microstructure and hydrogen storage properties. The addition of only V was not enough to produce a minimum amount of secondary phase and therefore the first hydrogenation at room temperature under a hydrogen pressure of 20 bars was impossible. When 2 wt.% Zr + 2 wt.% V or 2 wt.% Zr + 2 wt.% V + 2 wt.% Mn is added to TiFe the alloy shows a finely distributed Ti₂Fe-like secondary phase. These alloys presented a fast first hydrogenation and a high capacity. The rate-limiting step was found to be 3D growth diffusion controlled with decreasing interface velocity. This is consistent with the hypothesis that the fast reaction is likely to be the presence of Ti₂Fe-like secondary phases that act as a gateway for hydrogen.

This paper aims at addressing the exploitation of solid-state carriers for hydrogen storage with attention paid both to the technical aspects through a wide review of the available integrated systems and to the social aspects through a preliminary overview of the connected impacts from a gender perspective. As for the technical perspective carriers to be used for solid-state hydrogen storage for various applications can be classified into two classes: metal and complex hydrides. Related crystal structures and corresponding hydrogen sorption properties are reviewed and discussed. Fundamentals of thermodynamics of hydrogen sorption evidence the key role of the enthalpy of reaction which determines the operating conditions (i.e. temperatures and pressures). In addition it rules the heat to be removed from the tank during hydrogen absorption and to be delivered to the tank during hydrogen desorption. Suitable values for the enthalpy of hydrogen sorption reaction for operating conditions close to ambient (i.e. room temperature and 1–10 bar of hydrogen) are close to 30 kJ·molH2 −1 . The kinetics of the hydrogen sorption reaction is strongly related to the microstructure and to the morphology (i.e. loose powder or pellets) of the carriers. Usually the kinetics of the hydrogen sorption reaction is rather fast and the thermal management of the tank is the rate-determining step of the processes. As for the social perspective the paper arguments that as it occurs with the exploitation of other renewable innovative technologies a wide consideration of the social factors connected to these processes is needed to reach a twofold objective: To assess the extent to which a specific innovation might produce positive or negative impacts in the recipient socioeconomic system and from a sociotechnical perspective to explore the potential role of the social components and dynamics in fostering the diffusion of the innovation itself. Within the social domain attention has been paid to address the underexplored relationship between the gender perspective and the enhancement of hydrogen-related energy storage systems. This relationship is taken into account both in terms of the role of women in triggering the exploitation of hydrogen-based storage playing as experimenter and promoter and in terms of the intertwined impact of this innovation in their current conditions at work and in daily life.

Consideration of the possibility of transporting compressed hydrogen through existing gas pipelines leads to the need to study the regularities of the effect of hydrogen on the mechanical properties of steels in relation to the conditions of their operation in pipelines (operating pressure range stress state of the pipe metal etc.). This article provides an overview of the types of influence of hydrogen on the mechanical properties of steels including those used for the manufacture of pipelines. The effect of elastic and plastic deformations on the intensity of hydrogen saturation of steels and changes in their strength and plastic deformations is analyzed. An assessment of the potential losses of transported hydrogen through the pipeline wall as a result of diffusion has been made. The main issues that need to be solved for the development of a scientifically grounded conclusion on the possibility of using existing gas pipelines for the transportation of compressed hydrogen are outlined.

Noble metals are added to boiling water reactors (BWRs) to mitigate stress corrosion cracking of structural components made from steels and Ni-based alloys and this technology is referred to as Noble Metal Chemical Addition (NMCA) or NobleChemTM. There is a growing concern that NMCA can cause unwanted harmful effects on the corrosion and hydrogen uptake properties of Zircaloy-2 fuel cladding. To investigate this we have subjected Zircaloy-2 fuel claddings to out-of-pile BWR conditions in a custom-built autoclave. These claddings are oxidized in pressurized hot water (280 °C 9 MPa) for 25 60 and 150 days wherein Pt nanoparticles (~10 nm) were simultaneously injected. Cross-sectional focused ion beam cuts made at the oxide-metal interface reveal that the oxide growth is not significantly influenced by the local Pt loadings (≤ 1 µg·cm^-2). Surprisingly an inverse correlation was observed between oxide thicknesses and metal's hydrogen contents. Interestingly Pt catalysts have led to diminished hydrogen absorption in specimens with liner exposed to the hot water. Overall Pt catalysts exhibited no detrimental effects on the corrosion rate and hydrogen absorption in Zircaloy-2.

Renewable electricity can be converted into hydrogen via electrolysis also known as power-to-H2 (P2H) which when injected in the gas network pipelines provides a potential solution for the storage and transport of this green energy. Because of the variable renewable electricity production the electricity end-user’s demand for “power when required” distribution and transmission power grid constrains the availability of renewable energy for P2H can be difficult to predict. The evaluation of any potential P2H investment while taking into account this consideration should also examine the effects of incorporating the produced green hydrogen in the gas network. Parameters including pipeline pressure drop flowrate velocity and most importantly composition and calorific content are crucial for gas network management. A simplified representation of the Irish gas transmission network is created and used as a case study to investigate the impact on gas network operation of hydrogen generated from curtailed wind power. The variability in wind speed and gas network demands that occur over a 24 h period and with network location are all incorporated into a case study to determine how the inclusion of green hydrogen will affect gas network parameters. This work demonstrates that when using only curtailed renewable electricity during a period with excess renewable power generation despite using multiple injection points significant variation in gas quality can occur in the gas network. Hydrogen concentrations of up to 15.8% occur which exceed the recommended permitted limits for the blending of hydrogen in a natural gas network. These results highlight the importance of modelling both the gas and electricity systems when investigating any potential P2H installation. It is concluded that for gas networks that decarbonise through the inclusion of blended hydrogen active management of gas quality is required for all but the smallest of installations.

To understand hydrogen uptake in porous carbon materials we developed machine learning models to predict excess uptake at 77 K based on the textural and chemical properties of carbon using a dataset containing 68 different samples and 1745 data points. Random forest is selected due to its high performance (R² > 0.9) and analysis is performed using Shapley Additive Explanations (SHAP). It is found that pressure and Brunauer-Emmett-Teller (BET) surface area are the two strongest predictors of excess hydrogen uptake. Surprisingly this is followed by a positive correlation with oxygen content contributing up to ∼0.6 wt% additional hydrogen uptake contradicting the conclusions of previous studies. Finally pore volume has the smallest effect. The pore size distribution is also found to be important since ultramicropores (dp < 0.7 nm) are found to be more positively correlated with excess uptake than micropores (d_p < 2 nm). However this effect is quite small compared to the role of BET surface area and total pore volume. The novel approach taken here can provide important insights in the rational design of carbon materials for hydrogen storage applications.

This study analyzes the factors leading to the deployment of Power-to-Hydrogen (PtH₂) within the optimal design of district-scale Multi-Energy Systems (MES). To this end we utilize an optimization framework based on a mixed integer linear program that selects sizes and operates technologies in the MES to satisfy electric and thermal demands while minimizing annual costs and CO₂ emissions. We conduct a comprehensive uncertainty analysis that encompasses the entire set of technology (e.g. cost efficiency lifetime) and context (e.g. economic policy grid carbon footprint) input parameters as well as various climate-referenced districts (e.g. environmental data and energy demands) at a European-scope.

Minimum-emissions MES with large amounts of renewable energy generation and high ratios of seasonal thermal-to-electrical demand optimally achieve zero operational CO₂ emissions by utilizing PtH₂ seasonally to offset the long-term mismatch between renewable generation and energy demand. PtH₂ is only used to abate the last 5–10% emissions and it is installed along with a large battery capacity to maximize renewable self-consumption and completely electrify thermal demand with heat pumps and fuel cells. However this incurs additional cost. Additionally we show that ‘traditional’ MES comprised of renewables and short-term energy storage are able to decrease emissions by 90% with manageable cost increases.

The impact of uncertainty on the optimal system design reveals that the most influential parameter for PtH2 implementation is (1) heat pump efficiency as it is the main competitor in providing renewable-powered heat in winter. Further battery (2) capital cost and (3) lifetime prove to be significant as the competing electrical energy storage technology. In the face of policy uncertainties a CO₂ tax shows large potential to reduce emissions in district MES without cost implications. The results illustrate the importance of capturing the dynamics and uncertainties of short- and long-term energy storage technologies for assessing cost and CO₂ emissions in optimal MES designs over districts with different geographical scopes.

Bi-directional solid oxide cell systems (Bi-SOC) are being increasingly considered as an electrical energy storage method and consequently as a means to boost the penetration of renewable energy (RE) and to improve the grid flexibility by power-to-gas electrochemical conversion. A major advantage of these systems is that the same SOC stack operates as both energy storage device (SOEC) and energy producing device (SOFC) based on the energy demand and production. SOEC and SOFC systems are now well-optimised as individual systems; this work studies the effect of using the bi-directionality of the SOC at a system level. Since the system performance is highly dependent on the cell-stack operating conditions this study improves the stack parameters for both operation modes. Moreover the year-round cumulative exergy method (CE) is introduced in the solid oxide cell (SOC) context for estimating the system exergy efficiencies. This method is an attempt to obtain more insightful exergy assessments since it takes into account the operational hours of the SOC system in both modes. The CE method therefore helps to predict more accurately the most efficient configuration and operating parameters based on the power production and consumption curves in a year. Variation of operating conditions configurations and SOC parameters show a variation of Bi-SOC system year-round cumulative exergy efficiency from 33% to 73%. The obtained thermodynamic performance shows that the Bi-SOC when feasible can prove to be a highly efficient flexible power plant as well as an energy storage system.

The development of hydrogen energy is hindered by the lack of high-efficiency hydrogen storage materials. To explore new high-capacity hydrogen storage alloys reversible hydrogen storage in AB₂-type alloy is realized by using A or B-side elemental substitution. The substitution of small atomic-radius element Zr and Mg on A-side of YNi₂ and partial substitution of large atomic-radius element V on B-side of YNi₂ alloy was investigated in this study. The obtained ZrMgNi₄ ZrMgNi₃V and ZrMgNi₂V₂ alloys remained single Laves phase structure at as-annealed hydrogenated and dehydrogenated states indicating that the hydrogen-induced amorphization and disproportionation was eliminated. From ZrMgNi₄ to ZrMgNi₂V₂ with the increase of the degree of vanadium substitution the reversible hydrogen storage capacity increased from 0.6 wt% (0.35H/M) to 1.8 wt% (1.0H/M) meanwhile the lattice stability gradually increased. The ZrMgNi₂V₂ alloy could absorb 1.8 wt% hydrogen in about 2 h at 300 K under 4 MPa H₂ pressure and reversibly desorb the absorbed hydrogen in approximately 30 min at 473 K without complicated activation process. The prominent properties of ZrMgNi₂V₂2 elucidate its high potential for hydrogen storage application.