Germany

In this study Distribution of Relaxation Times (DRT) was successfully demonstrated in the analysis of the impedance spectra of High-Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFC) doped with phosphoric acid. Electrochemical impedance spectroscopy (EIS) was performed and the quality of the recorded spectra was verified by Kramers-Kronig relations. DRT was then applied to the measured spectra and polarization losses were separated on the basis of their typical time constants. The main features of the distribution function were assigned to the cell’s polarization processes by selecting appropriate experimental conditions. DRT can be used to identify individual internal HT-PEMFC fuel cell phenomena without any a-priori knowledge about the physics of the system. This method has the potential to further improve EIS spectra interpretation with either equivalent circuits or physical models.

This research aims to determine the position and the breakthrough trajectory of sustainable energy technologies. Fine-grained insights into these breakthrough positions and trajectories are limited. This research seeks to fill this gap by analyzing sustainable energy technologies’ breakthrough positions and trajectories in terms of development application and upscaling. To this end the breakthrough positions and trajectories of seven sustainable energy technologies i.e. hydrogen from seawater electrolysis hydrogen airplanes inland floating photovoltaics redox flow batteries hydrogen energy for grid balancing hydrogen fuel cell electric vehicles and smart sustainable energy houses are analyzed. This is guided by an extensively researched and literature-based model that visualizes and describes these technologies’ experimentation and demonstration stages. This research identifies where these technologies are located in their breakthrough trajectory in terms of the development phase (prototyping production process and organization and niche market creation and sales) experiment and demonstration stage (technical organizational and market) the form of collaboration (public–private private–public and private) physical location (university and company laboratories production sites and marketplaces) and scale-up type (demonstrative and first-order and second-order transformative). For scientists this research offers the opportunity to further refine the features of sustainable energy technologies’ developmental positions and trajectories at a detailed level. For practitioners it provides insights that help to determine investments in various sustainable energy technologies.

This study offers a comprehensive analysis of the feasibility of green hydrogen economies in Western and Southern African regions focusing on the ECOWAS and SADC countries. Utilizing a novel approach based on composite indicators the research evaluates the potential readiness and overall feasibility of green hydrogen production and export across these regions. The study incorporates various factors including the technical potential of renewable energy sources water resource availability energy security and existing infrastructure for transport and export. Country-specific analyses reveal unique insights into the diverse potential of nations like South Africa Lesotho Ghana Nigeria Angola and Namibia each with its unique strengths and challenges in the context of green hydrogen. The research findings underscore the complexity of developing green hydrogen economies highlighting the need for nuanced region-specific approaches that consider technical socioeconomic geopolitical and environmental factors. The paper concludes that cooperation and integration between countries in the regions may be crucial for the success of a future green hydrogen economy

Climate change is projected to have substantial economic social and environmental impacts worldwide. Currently the leading solutions for hydrogen storage are in salt caverns and depleted natural gas reservoirs. However the required geological formations are limited to certain regions. To increase alternatives for hydrogen storage this paper proposes storing hydrogen in pipes filled with gravel in lakes hydropower and pumped hydro storage reservoirs. Hydrogen is insoluble in water non-toxic and does not threaten aquatic life. Results show the levelized cost of hydrogen storage to be 0.17 USD kg−1 at 200 m depth which is competitive with other large scale hydrogen storage options. Storing hydrogen in lakes hydropower and pumped hydro storage reservoirs increases the alternatives for storing hydrogen and might support the development of a hydrogen economy in the future. The global potential for hydrogen storage in reservoirs and lakes is 3 and 12 PWh respectively. Hydrogen storage in lakes and reservoirs can support the development of a hydrogen economy in the future by providing abundant and cheap hydrogen storage.

By passing the delegated acts supplementing the revised Renewable Energy Directive the European Commission has recently set a regulatory benchmark for the classifcation of green hydrogen in the European Union. Controversial reactions to the restricted power purchase for electrolyser operation refect the need for more clarity about the efects of the delegated acts on the cost and the renewable characteristics of green hydrogen. To resolve this controversy we compare diferent power purchase scenarios considering major uncertainty factors such as electricity prices and the availability of renewables in various European locations. We show that the permission for unrestricted electricity mix usage does not necessarily lead to an emission intensity increase partially debilitating concerns by the European Commission and could notably decrease green hydrogen production cost. Furthermore our results indicate that the transitional regulations adopted to support a green hydrogen production ramp-up can result in similar cost reductions and ensure high renewable electricity usage.

Green hydrogen will play a crucial role in the future of emission reduction in air traffic in the long-term as it will completely eliminate CO2 emissions and significantly reduce other pollutants such as contrails and nitrogen oxides. Hydrogen offers a promising alternative to kerosene for short- and medium-haul flights particularly through direct combustion and hydrogen fuel cell technology in new aircraft concepts. Against the background of the immense capital-intensive infrastructure adjustments that are required at airports for this purpose and the simultaneously high future hydrogen demand for the shipping industry this paper analyses the emission savings potential in Europe if airports near seaports would switch to hydrogen-powered flight connections.

The decarbonization of industrial process heat is one of the bigger challenges of the global energy transition. Process heating accounts for about 20% of final energy demand in Germany and the situation is similar in other industrialized nations around the globe. Process heating is indispensable in the manufacturing processes of products and materials encountered every day ranging from food beverages paper and textiles to metals ceramics glass and cement. At the same time process heating is also responsible for significant greenhouse gas emissions as it is heavily dependent on fossil fuels such as natural gas and coal. Thus process heating needs to be decarbonized. This review article explores the challenges of decarbonizing industrial process heat and then discusses two of the most promising options the use of electric heating technologies and the substitution of fossil fuels with low-carbon hydrogen in more detail. Both energy carriers have their specific benefits and drawbacks that have to be considered in the context of industrial decarbonization but also in terms of necessary energy infrastructures. The focus is on high-temperature process heat (>400 ◦C) in energy-intensive basic materials industries with examples from the metal and glass industries. Given the heterogeneity of industrial process heating both electricity and hydrogen will likely be the most prominent energy carriers for decarbonized high-temperature process heat each with their respective advantages and disadvantages.

Underground hydrogen storage in porous rocks is a promising method to stabilize renewable energy fluctuations. However data on the geochemical reactivity of hydrogen with reservoir rocks and its potential effects on reservoir performance are limited. This study investigates the geochemical reactivity of hydrogen with Bunt sandstein reservoir sandstones from northern Germany collected at a depth of about 2.5 km. Experiments were performed at 100 ◦C and 150 bar hydrogen partial pressure for four weeks examining scenarios with dry hydrogen synthetic saline fluid with hydrogen synthetic saline fluid with helium (as a control) and an oxidation environment (air). We measured permeability porosity magnetic susceptibility and fluid element concentration before and after the experiments. Results showed no significant mineral changes attributed to hydrogen. Mag netic susceptibility indicated no formation of magnetic minerals such as magnetite and pyrrhotite. Minor var iations in permeability and porosity were attributed to anhydrite dissolution from fluid chemistry nonequilibrium. Overall our findings suggest hydrogen interactions with Buntsandstein sandstone (no pyrite content) at temperatures up to 100 ◦C do not risk hydrogen loss or reservoir performance degradation.

The defossilization of industry has far-reaching implications regarding the future demand for hydrogen and other forms of energy. This paper presents and applies a fundamental bottom-up model that relies on techno-economic data of industrial production processes. Its aim is to identify across a range of scenarios the most cost-effective low-carbon options considering a variety of production systems. Subsequently it derives the hydrogen and electricity demand that would result from the implementation of these least-cost low-carbon options in process industries in Germany. Aligning with the German government's target year for achieving climate neutrality this study’s reference year is 2045. The primary contribution lies in analyzing which hydrogen-based and direct electrification solutions would be cost-effective for a range of energy price levels under climate-neutral industrial production and what the resulting hydrogen and electricity demand would be. To this end the methodology of this paper comprises the following steps: selection of the relevant industries (I) definition of conventional reference production systems and their low-carbon options (II) investigation and processing of the techno-economic data of the standardized production systems (III) establishment of a scenario framework (IV) determination of the least-cost low-carbon solution of a conventional reference production system under the scenario assumptions made (V) and estimation of the resulting hydrogen and electricity demand (VI). According to the results the expected industrial hydrogen consumption in 2045 ranges from 255 TWh for higher hydrogen prices in or above the range of onshore wind-based green hydrogen supply costs to up to 542 TWh for very low hydrogen prices corresponding to typical blue hydrogen production costs. Meanwhile the direct electricity consumption of the process industries in the results ranges from 122 TWh for these rather low hydrogen prices to 368 TWh for the higher hydrogen prices in the region of or above the hydrogen supply costs from the electrolysis of energy from an onshore wind farm. Most of the break-even hydrogen prices that are relevant to the choice of low-carbon options are in the range of the benchmark purchase costs for blue hydrogen and green hydrogen produced from offshore wind power which span between €40 per MWh and €97 per MWh.

The green-hydrogen sector has created considerable expectations in the Global South about export-oriented development and industrial path creation. However whether and how these expectations are really materializing requires further scrutiny. This article develops a conceptual approach that we call governance of futuremaking. Thereby we want to understand how actors try to coordinate their expectations about future economic development in different contexts and across scales over time. We conceptualize the emergence of new regional development trajectories as resulting from the use of governance instruments with an increasing bindingness which reflect the interplay between governance of and by expectations. Based on this approach we analyze and compare green-hydrogen activities in Namibia and South Africa. We find that future-making is becoming more binding in both countries but has not resulted in path creation yet.

Hydrogen blending offers significant potential for decarbonizing natural gas-based thermal processes particularly in the steel and cement sectors. Due to its distinct combustion properties compared to natural gas – such as lower minimum air requirements and altered flame speeds – the hydrogen fraction of the fuel must be monitored for combustion control. In this study we present an ultrasonic time-of-flight measurement system for hydrogen concentrations of 0–40% in natural gas. The system is verified with test gas mixtures at laboratory scale and validated in a technical-scale setup using a real blower burner (< 60 kW). We evaluate uncertainty of the hydrogen fraction measurement and analyze the influence of varying natural gas compositions. We show that standard uncertainties below 4% can be achieved without knowledge of the specific natural gas composition. Our results provide insights for measurement system design and support the safe application of hydrogen in thermal systems for industrial processes.

Importing renewable energy to Europe may offer many potential benefits including reduced energy costs lower pressure on infrastructure development and less land use within Europe. However open questions remain: on the achievable cost reductions how much should be imported whether the energy vector should be electricity hydrogen or derivatives like ammonia or steel and their impact on Europe’s infrastructure needs. This study integrates a global energy supply chain model with a European energy system model to explore net-zero emission scenarios with varying import volumes costs and vectors. We find system cost reductions of 1-10% within import cost variations of ± 20% with diminishing returns for larger import volumes and a preference for methanol steel and hydrogen imports. Keeping some domestic power-to-X production is beneficial for integrating variable renewables leveraging local carbon sources and power-to-X waste heat. Our findings highlight the need for coordinating import strategies with infrastructure policy and reveal maneuvering space for incorporating non-cost decision factors.

South Africa has excellent conditions for renewable energy generation making it well placed to produce green hydrogen for both domestic use and export. In building a green hydrogen economy around export markets it will face competition from countries with equivalent or better resources and/or that are located closer to export markets (e.g. in North Africa and the Middle East) or have lower capital costs (developed markets like Australia and Canada). South Africa however has an extensive energy system with unserved electricity demand. The ability to trade electricity with the national grid (feeding into the grid during times of peak dedicated renewable energy supply and extracting from the grid during times of low dedicated renewable energy availability) could reduce the cost of producing green hydrogen by as much as 10–25 %. This paper explores the opportunity for South African green hydrogen producers presented by the electricity supply crisis that has been ongoing since 2007. It highlights the potential for a mutually reinforcing growth cycle between renewable energy and green hydrogen to be established which will contribute not only to the mitigation of greenhouse gas emissions but to the local economy and broader society.

The use of hydrogen as a fuel for piston engines enables environmentally friendly and efficient operation. However several challenges arise in the combustion process limiting the development of hydrogen engines. These challenges include abnormal combustion the high burning velocity of hydrogen-enriched mixtures increased nitrogen oxide emissions and others. A rational organization of hydrogen combustion can partially or fully mitigate these issues through the use of advanced methods such as late direct injection charge stratification dual injection jet-guided operation and others. However mathematical models describing hydrogen combustion for these methods are still under development complicating the optimization and refinement of hydrogen engines. Previously we proposed a mathematical model based on Wiebe functions to describe premixed and diffusion combustion as well as relatively slow combustion in lean-mixture zones behind the flame front and near-wall regions. This study further develops the model by accounting for the combined influence of the mixture composition and engine speed mixture stratification and the effects of injection and ignition parameters on premixed and diffusion combustion. Special attention is given to combustion modeling in an engine with single injection and jet-guided operation.

Introduction: The implementation of national hydrogen strategies targeting zero-emission goals has sparked public discussions regarding energy and environmental communication. However gaining societal acceptance for hydrogen technology poses a significant challenge in numerous countries. Hence this research investigates the framing of hydrogen technology through a comparative analysis of opinion-leading newspapers in Germany Saudi Arabia the United Arab Emirates and Egypt. Methods: Utilizing a quantitative framing analysis based on Entman’s framing approach this research systematically identifies media frames and comprehend their development through specific frame characteristics. A factor analysis identified six distinct frames: Hydrogen as a Sustainable Energy Solution Benefits of Economic and Political Collaboration Technological and Scientific Challenges Governance Issues and Energy Security Industrial and Climate Solutions and Economic Risk. Results: The findings reveal that newspapers frames vary significantly due to contextual factors such as national hydrogen strategies media systems political ideologies article types and focusing events. Specifically German newspapers display diverse and balanced framing in line with its pluralistic media environment and national emphasis on green hydrogen and energy security while newspapers from MENA countries primarily highlight economic and geopolitical benefits aligned with their national strategies and state-controlled media environments. Additionally the political orientation of newspapers affects the diversity of frames particularly in Germany. Moreover non-opinion articles in Germany exhibit greater framing diversity compared to opinion pieces while in the MENA region the framing remains uniform regardless of article type due to centralized media governance. A notable shift in media framing in Germany was found after a significant geopolitical event which changed the frame from climate mitigation to energy security. Discussion: This study underscores the necessity for theoretical and methodological thoroughness in identifying frames as well as the considerable impact of contextual factors on the media representation of emerging sustainable technologies.

Given the economic industrial and environmental value of green dihydrogen (H2) optimization of water electrolysis as a means of producing H2 is essential. Binders are a crucial component of electrocatalysts yet they remain largely underdeveloped with a significant lack of standardization in the field. Therefore targeted research into the development of alternative binder systems is essential for advancing performance and consistency. Binders essentially act as the key to regulating the electrode (support)–catalyst–electrolyte interfacial junctions and contribute to the overall reactivity of the electrocatalyst assembly. Therefore alternative binders were explored with a focus on cost efficiency and environmental compatibility striving to achieve desirable activity and stability. Herein the alkaline hydrogen evolution reaction (HER) was investigated and the sluggish water dissociation step was targeted. Controlled hydrophilic poly(vinyl alcohol)-based hydrogel binders were designed for this application. Three hydrogel binders were evaluated without incorporated electrocatalysts namely PVA145 PVA145-blend-bPEI1.8 and PVA145-blend-PPy. Interestingly the study revealed that the hydrophilicity of the binders exhibited an enhancing effect on the observed activity resulting in improved performance compared to the commercial binder Nafion™. Notably the PVA145 system stands out with an overpotential of 224 mV at−10 mA·cm−2 (geometric) in 1.0 M KOH compared to the 238 mV exhibited by Nafion™. Inclusion of Pt as active material in PVA145 as binder exhibited a synergistic increase in performance achieving a mass activity of 1.174 A.cm−2.mg−1 Pt in comparison to Nafion™’s 0.344 A.cm−2.mg−1 Pt measured at−150 mV vs RHE. Our research aimed to contribute to the development of cost-effective and efficient binder systems stressing the necessity to challenge the dominance of the commercially available binders.

Fuel cell vehicles (FCVs) represent an intriguing alternative to battery electric vehicles (BEVs). While the acceptance of BEVs has been widely discussed acceptance-based recommendations for promoting adoption of FCVs remain ambiguous. This paper aims to improve our understanding by reporting results from a pioneer study based on the standardized Unified Theory of Acceptance and Use of Technology 2 (UTAUT2). The sample consists of n1 = 258 registered customers of H2mobility in Germany. For effect control another n2 = 294 participant sample was drawn from the baseline population. Data were analyzed using SmartPLS 4 and importance-performance mapping (IPMA). Results demonstrate that FCV acceptance primarily relies on Perceived Usefulness Perceived Conditions and Normative Influence while surprisingly hypotheses involving Perceived Risk and Green Attitude are rejected. Finally a discussion reveals ways to increase the level of public acceptance. Three practical strategies emerge. For future acceptance analyses the authors suggest incorporating the young concept of ‘societal readiness’.

From an environmental standpoint carbon-free energy carriers such as ammonia and hydrogen are essential for future energy systems. However their hightemperature chemical behavior remains insufficiently understood posing challenges for the development and optimization of advanced combustion technologies. Ammonia in particular is globally available and cost-effective especially for energy-intensive industries. The addition of ammonia or hydrogen to methane significantly reduces the accuracy of existing predictive models. Therefore validated and detailed data are urgently needed to enable reliable design and performance predictions. This review highlights the compatibility of ammonia with existing combustion infrastructure facilitating a smoother transition to more sustainable heating methods without the need for entirely new systems. Applications in high-temperature heating processes such as metal processing ceramics and glass production and power generation are of particular interest. This review focuses on the systematic assessment of alternative fuel mixtures comprising ammonia and hydrogen as well as natural gas with particular consideration of existing safety-related parameters and combustion characteristics. Fundamental quantities such as the laminar burning velocity are discussed in the context of their relevance for fuel mixtures and their scalability toward turbulent flame propagation which is of critical importance for industrial burner and reactor design. The influence of fuel composition on ignition limits is examined as these are essential parameters for safety margin definitions and operational boundary conditions. Furthermore flame stability in mixed-fuel systems is addressed to evaluate the practical feasibility and robustness of combustion under varying process conditions. A detailed overview of current diagnostic and analysis methods follows encompassing both pollutant measurement techniques and the detection of key radical species. These diagnostics form the experimental basis for reaction kinetics modeling and mechanism validation. Given the importance of emission formation in combustion systems a dedicated subsection summarizes major emission trends even though a comprehensive treatment would exceed the scope of this review. Thermal radiation effects which are highly relevant for heat transfer and system efficiency in large-scale applications are then reviewed. In parallel current developments in numerical simulation approaches for industrial-scale combustion systems are presented including aspects of model accuracy boundary conditions and computational efficiency. The review also incorporates insights from materials engineering particularly regarding high-temperature material performance corrosion resistance and compatibility with combustion products. Based on these interdisciplinary findings operational strategies for high-temperature furnaces are outlined and selected industrial reference systems are briefly presented. This integrated approach aims to support the design optimization and safe operation of next-generation combustion technologies utilizing carbon-free or low-carbon fuels.

The chemical industry faces major challenges worldwide. Since 1950 production has increased 50-fold and is projected to continue growing particularly in Asia. It is one of the most energy- and resource-intensive industries contributing significantly to greenhouse gas emissions and the depletion of finite resources. This development exceeds planetary boundaries and calls for a sustainable transformation of the industry. The key transformation areas are as follows: (1) Non-Fossil Energy Supply: The industry must transition away from fossil fuels. Renewable electricity can replace natural gas while green hydrogen can be used for high-temperature processes. (2) Circularity: Chemical production remains largely linear with most products ending up as waste. Sustainable product design and improved recycling processes are crucial. (3) Non-Fossil Feedstock: To achieve greenhouse gas neutrality oil gas and coal must be replaced by recycling plastics renewable biomaterials or CO2-based processes. (4) Sustainable Chemical Production: Energy and resource savings can be achieved through advancements like catalysis biotechnology microreactors and new separation techniques. (5) Sustainable Chemical Products: Chemicals should be designed to be “Safe and Sustainable by Design” (SSbD) meaning they should not have hazardous properties unless essential to their function. (6) Sufficiency: Beyond efficiency and circularity reducing overall material flows is essential to stay within planetary boundaries. This shift requires political economic and societal efforts. Achieving greenhouse gas neutrality in Europe by 2050 demands swift and decisive action from industry governments and society. The speed of transformation is currently too slow to reach this goal. Science can drive innovation but international agreements are necessary to establish a binding framework for action.

To enable climate-neutral aviation improving the energy efficiency of aircraft is essential. The research project Synergies of Highly Integrated Transport Aircraft investigates cross-disciplinary synergies in aircraft and propulsion technologies to achieve energy savings. This study examines a fuel cell electric powered configuration with distributed electric propulsion. For this a reverse-engineered ATR 72-500 serves as a reference model for calibrating the methods and ensuring accurate performance modeling. A baseline configuration featuring a state-of-the-art turboprop engine with the same entry-into-service is also introduced for a meaningful performance comparison. The analysis uses an enhanced version of the Stanford University Aerospace Vehicle Environment (SUAVE) a Python-based aircraft design environment that allows for novel energy network architectures. This paper details the preliminary aircraft design process including calibration presents the resulting aircraft configurations and examines the integration of a fuel cell-electric energy network. The results provide a foundation for higher fidelity studies and performance comparisons offering insights into the trade-offs associated with hydrogen-based propulsion systems. All fundamental equations and methodologies are explicitly presented ensuring transparency clarity and reproducibility. This comprehensive disclosure allows the broader scientific community to utilize and refine these findings facilitating further progress in hydrogen-powered aviation technologies.

The safe removal transportation and long-term storage of fuel debris in the decommissioning of Fukushima Daiichi is the biggest challenge facing Japan. In the nuclear power field passive autocatalytic recombiners (PARs) have become established as a technology to prevent hydrogen explosions inside the containment vessel. To utilize PAR as a measure to reduce the concentration of hydrogen generated in the fuel debris storage canister which is currently an issue it is required to perform in a sealed environment with high doses of radiation low temperature and high humidity and there are many challenges different from conventional PAR. A honeycombshaped catalyst based on automotive catalyst technology has been newly designed as a PAR and research has been conducted to solve unique problems such as high dose radiation low temperature high humidity coexistence of hydrogen and low oxygen and catalyst poisons. This paper summarizes the challenges of hydrogen generation in a sealed container the results of research and a guide to how to use the PAR for fuel debris storage canisters.

Export-oriented green-hydrogen projects (EOGH2P) are being developed in regions with optimal renewableenergy resources. Their reliance on economies of scale makes them land-intensive and object of spatial planning policies. However the impact of spatial planning on the development of EOGH2P remains underexplored. Drawing on the spatial planning and megaproject literatures the analysis of planning documents and expert interviews this paper analyzes how spatial planning influences the development of EOGH2P in Chile Namibia and South Africa. The three countries have developed different spatial planning approaches for EOGH2Ps and are analyzed by employing a comparative case-study design. Our findings reveal that Namibia pursues a restrictive approach South Africa a facilitative approach whereas Chile is shifting from a market-based to a restrictive approach. The respective approaches reflect different political priorities and stakeholder interests and imply diverse effects on the development of EOGH2Ps in terms of their number size shared infrastructure socioenvironmental impact and acceptance. This study underscores the need for well-designed spatial planning frameworks and provides insights for planners and stakeholders on their potential effects.

According to the international standard ISO 14687:2019 for hydrogen fuel quality the maximum allowable concentration of water in hydrogen for use in refueling stations and storage systems must not exceed 5 µmol/mol. Therefore an adsorption purification process following the electrolyzer is necessary. This study numerically investigates the adsorption of water and the corresponding water loading on zeolite 13X BFK based on the mass flows entering the adsorption column from three 5 MW electrolyzers coupled to a 15 MW offshore wind turbine. As the mass flow is influenced by wind speed a direct comparison between realistic wind speeds and adsorption loading is presented. The presented numerical discretization of the model also accounts for perturbations in wind speed and consequently mass flows. In addition adsorption isobars were measured for water on zeolite 13X BFK within the required pressure and temperature range. The measured data was utilized to fit parameters to the Langmuir–Freundlich isotherm.

Heavy-duty fuel cell trucks are a promising approach to reduce the CO2 emissions of logistic fleets. Due to their higher powertrain energy density in comparison to battery-electric trucks they are especially suited for long-haul applications while transporting high payloads. Despite these great advantages the fleet integration of such vehicles is made difficult due to high costs and limited performance in thermally critical environmental conditions. These challenges are addressed in the European Union (EU) funded project ESCALATE which aims to demonstrate high-efficiency zero-emission heavy-duty vehicle (zHDV) powertrains that provide a range of 800 km without refueling or recharging. Powertrain components and their corresponding thermal components account for a large part of the production costs. For vehicle users higher costs are only acceptable if a significantly higher benefit can be achieved. Therefore it is important to size these components for the actual vehicle mission to avoid oversizing. In this paper an optimization method which determines the optimum component sizes for a given mission scenario under consideration of multiple criteria (e.g. costs performance and range) is presented.

As a continuation of part 1 which examined the development status and system foundations of sustainable energy systems (SES) in the context of German energy transition this paper provides a comprehensive review of the core technologies enabling the development of SES. It covers recent advances in photovoltaic (PV) wind energy geo‑ thermal energy hydrogen and energy storage. Key trends include the evolution of high-efficiency solar and wind technologies intelligent control systems sector coupling through hydrogen integration and the diversification of electrochemical and mechanical storage solutions. Together these innovations are fostering a more flexible resil‑ ient and low-carbon energy infrastructure. The review further highlights the importance of system-level integration by linking generation conversion and storage to address the intermittency of renewable energy and support longterm decarbonization goals.

Since the early days of space exploration the efficient production of oxygen and hydrogen via water electrolysis has been a central task for regenerative life-support systems. Water electrolysers are however challenged by the near-absence of buoyancy in microgravity resulting in hindered gas bubble detachment from electrodes and diminished electrolysis efficiencies. Here we show that a commercial neodymium magnet enhances water electrolysis with current density improvements of up to 240% in microgravity by exploiting the magnetic polarization of the electrolyte and the magnetohydrodynamic force. We demonstrate that these interactions enhance gas bubble detachment and displacement through magnetic convection and achieve passive gas–liquid phase separation. Two model magnetoelectrolytic cells a proton-exchange membrane electrolyser and a magnetohydrodynamic drive were designed to leverage these forces and produce oxygen and hydrogen at near-terrestrial efficiencies in microgravity. Overall this work highlights achievable lightweight low-maintenance and energy-efficient phase separation and electrolyser technologies to support future human spaceflight architectures.

Hydrogen recognized as a critical energy source requires green production methods such as proton exchange membrane water electrolysis (PEMWE) powered by renewable energy. This is a key step toward sustainable development with economic analysis playing an essential role. Life cycle costing (LCC) is commonly used to evaluate economic feasibility but traditional LCC analyses often provide a single cost outcome which limits their applicability across diverse regional contexts. To address these challenges a Python-based tool is developed in this paper integrating a bottom-up approach with net present value (NPV) calculations and Monte Carlo simulations. The tool allows users to manage uncertainty by intervening in the input data producing a range of outcomes rather than a single deterministic result thus offering greater flexibility in decision-making. Applying the tool to a 5 MW PEMWE plant in Germany the total cost of ownership (TCO) is estimated to range between €52 million and €82.5 million with hydrogen production costs between 5.5 and 11.4 €/kg H2. There is a 95% probability that actual costs fall within this range. Sensitivity analysis reveals that energy prices are the key contributors to LCC accounting for 95% of the variance in LCC while iridium membrane materials and power electronics contribute to 75% of the variation in construction-phase costs. These findings underscore the importance of renewable energy integration and circular economy strategies in reducing LCC.

Natural hydrogen is generated via serpentinization radiolysis and organic metagenesis in geological settings. After expulsion from the source and along its upward migration path the free gas may encounter hydratebearing sediments. To simulate this natural scenario CH4 hydrate and CH4 + C3H8 hydrate were synthesized at 5.0 MPa and exposed to a hydrogen-containing gas mixture. In-situ Raman spectroscopic measurements demonstrated the incorporation of H2 molecules into the hydrate phase even at a partial pressure of 0.5 MPa. Exsitu Raman spectroscopic characterization of hydrates formed from a CH4 + H2 gas mixture at 5.0 MPa confirmed the H2 inclusion within the large cavities of structure I. The results show that the interactions between H2 and the natural gas hydrate phase range from the incorporation of H2 molecules into the hydrate phase to the rapid dissociation of the gas hydrate depending on thermodynamic conditions and H2 concentration in the coexisting gas phase.

The carbon emission reduction mission requires a multifaceted approach in which green hydrogen is expected to play a key role. The accelerated adoption of green hydrogen technologies is vital to this journey towards carbon neutrality by 2050. However the energy transition involving green hydrogen requires a data-driven approach to ensure that the benefits are realised. The introduction of testing sites for green hydrogen technologies will be crucial in enabling the performance testing of various components within the green hydrogen value chain. This study involves an areal assessment of a selected test site for the installation of a grid-tied solar PV-green hydrogen-battery storage microgrid system at a factory facility in South Africa. The evaluation includes a site energy audit to determine the consumption profile and an analysis of the location’s weather pattern to assess its impact on the envisaged microgrid. Lastly a design of the microgrid is conceptualised. A 39 kW photovoltaic system powers the microgrid which comprises a 22 kWh battery storage system 10 kW of electrolyser capacity an 8 kW fuel cell and an 800 L hydrogen storage capacity between 30 and 40 bars.

In the transformation process from fossil-fuel based to carbon-neutral combustion full or partial replacement of natural gas with hydrogen is considered in numerous industrial applications. As hydrogen flames yield significantly higher NOX emissions than natural gas flames understanding what factors influence these emissions in flames of natural gas/hydrogen blends is crucial for the retrofitting process. Our work is concerned with the simplest form of industrial retrofitting where hydrogen is injected into the natural gas line without any modifications to the burner construction while keeping the burner power constant. We provide quantifications of NOX emissions with respect to changes in hydrogen content (pure natural gas to 100% hydrogen) swirl number (S=0.6 to S=1.4) excess air ratio ( = 1 to =4.5) and air preheat (ambient air to 300 ◦C). The changes were determined in small steps and over a large range. The emission data is to be used in industrial CFD for both validation and tuning therefore Laser Doppler Velocimetry was used for precise determination of the burner inlet conditions. Key findings of the investigation include that for hydrogen flames the NOX emission index [mg/kWh] is 1.2 to 3 times larger than for pure natural gas flames at similar firing conditions. The steepest increase in NOX emissions occurs above 75% volume fraction of hydrogen in the fuel. For natural gas flames NOX emissions peak at 1.3 to 1.4 excess air while the maximum for hydrogen and natural gas/hydrogen blends lays at =1.6. NOX emissions decrease slightly as the swirl number increases but this effect is minor in comparison to the effects of hydrogen content excess air ratio and air temperature.

On the path to an emission free energy economy proton exchange membrane water electrolysis (PEMWE) is a promising technology for a sustainable production of green hydrogen at high current densities and thus high production rates. Long lifetime increasing the current density and the reduction of platinum group metal loadings are major challenges for a widespread implementation of PEMWE. In this context this work investigates the aging of a PEMWE stack operating at 4 A cm-2 which is twice the nominal current density of commercial electrolyzers. Specifically an 8-cells PEMWE stack using catalyst coated membranes (CCMs) with different platinum group metal (PGM) loading was operated for 2200 h. To understand degradation phenomena physical ex-situ analyses such as scanning electron microscopy (SEM) atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were carried out. The same aging mechanism were observed in all cells independent on their position in stack or the specific PGM loading of the membrane electrode assembly (CCM): (i) a decrease of ohmic resistance over time related to membrane thinning (ii) a significant loss of ionomer at anodes (iii) loss of noble metal from the electrodes leading to deposition of small Ir and Pt concentrations in the membrane (iv) heterogeneous enrichment of Ti on the cathode side likely originating from the cathode-side of the Ti bipolar plates (BPPs). These results are in good agreement with the electrochemical performance loss. Thus we were able to identify the degradation phenomena that dominate under high-current operation and their impact on performance.

A numerical sensitivity analysis of a hydrogen pore storage system is carried out on a reservoir-scale geological model of the Ketzin site (Germany) to analyze the influence of uncertainty in geological parameters and fluid properties on storage performance. Therefore the following physical geological parameters and fluid properties were investigated: Porosity and permeability of the reservoir rock the brine salinity relative permeability and capillary pressure and mechanical dispersion. The range of the applied parameters is based on experimental and field data of the chosen location obtained during the former CO2 storage projects at the Ketzin site from 2008 to 2013. Using the open-source reservoir software MUFITS for the numerical simulations strong differences between the results can be observed. The results were evaluated based on measures to quantify performance such as the ratio of produced hydrogen mass to produced cushion gas (nitrogen) productivity index and sustainability index. The strongest impact on the performance parameters was observed with variations in the capillary pressure and the relative permeability curves followed by the absolute permeabilities while the least impact was seen with changes in the porosity and salinity of the brine. This work is not only crucial as a pre-feasibility study for the Ketzin storage site for hydrogen storage but also as a basis for decision-making for other potential storage sites in sedimentary basins.