Germany

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.

Hydrogen fuel cell systems are a viable option for electrified aero engines due to their efficiency and environmental benefits. However integrating these systems presents challenges notably in terms of overall system weight and thermal management. Heat exchangers are crucial for the effective thermal management system of electric propulsion systems in commercial electrified aviation. This paper provides a comprehensive review of various heat exchanger types and evaluates their potential applications within these systems. Selection criteria are established based on the specific requirements for air and hydrogen heat exchangers in electrified aircraft. The study highlights the differences in weighting criteria for these two types of heat exchangers and applies a weighted point rating system to assess their performance. Results indicate that extended surface microchannel and printed circuit heat exchangers exhibit significant promise for aviation applications. The paper also identifies key design challenges and research needs particularly in enhancing net heat dissipation increasing compactness improving reliability and ensuring effective integration with aircraft systems.

Many countries of the Global South struggle to achieve inclusive growth paths despite investment in the exploitation of rich resources. Resource-based industrialization literature stresses the potential for achieving broader development effects via the development of production linkages with local enterprises. The focus lies on market-driven outsourcing dynamics that foster linkage development such as efficiency location-specific knowledge and technology and scale complexity. However little is known about the opportunity space for both policy making and local firms to create these linkages. To address this issue we incorporate the concept of change agency stemming from the path development literature into the discussion on production linkages to show how both (local) firm agency and system-level agency can achieve linkage creation for inclusive path transplantation. We illustrate the framework by scrutinizing the potential inclusion of solar energy companies in Namibia’s emerging green hydrogen economy. The study finds that while the potential for renewable energy companies in Namibia to participate in the value chain is limited an integrated bundle of measures relying on firm- and system-level agency could address peripheral contextual factors overcome entry barriers and leverage further potential for linkage creation in the solar energy sector: mobilizing the local workforce fostering inter-firm cooperation leveraging local advantages creating knowledge institutions enhancing the regulatory framework upgrading infrastructure and enforcing local content regulations.

Green hydrogen is viewed as a promising pathway to future decarbonized energy systems. However hydrogen production depends on a few critical minerals particularly platinum and iridium. Here we examine how the supply of these minerals is subject to vulnerabilities hidden in interdependent global networks of trade and investment. We develop an index to quantify these vulnerabilities for a combination of a target country an investing country an intermediary country and a commodity. Focusing on the US as the target country for the import of platinum and iridium we show how vulnerability-inducing investing countries changed between 2010 and 2019. We find that the UK is consistently among investing countries that can potentially induce US vulnerabilities via intermediary exporters of platinum and iridium with South Africa being the primary intermediary country. Future research includes incorporating geopolitical factors and technological innovations to move the index closer from potential to real-world vulnerabilities.

The spark-ignited (SI) hydrogen combustion engine has the potential to noticeably reduce greenhouse gas emissions from passenger cars. To prevent nitrogen oxide emissions and to increase fuel efficiency and power output complex air paths and operating strategies are utilized. This makes the engine control problem more complex challenging the conventional engine calibration process. This work combines and extends the state-of-the-art in real-time combustion engine modeling and optimal control presenting a novel control concept for the efficient operation of a hydrogen combustion engine. The extensive experimental validation with a 1.5 l three-cylinder hydrogen SI engine and a dynamically operated engine test bench with emission and in-cylinder pressure measurements provides a comprehensible comparison to conventional engine control. The results demonstrate that the proposed optimal control decreased the load tracking errors by a factor of up to 2.8 and increased the engine efficiency during lean operation by up to 10 percent while decreasing the calibration effort compared to conventional engine control.

The use of chemical hydrogen carriers such as ammonia (NH3) methanol (MeOH) dimethyl ether (DME) and liquid organic hydrogen carriers (LOHC) is considered as a potential option for hydrogen imports. Following import the carriers are either converted centrally into hydrogen or transported further to the point of use. This study evaluates various domestic transport options – truck rail inland waterway and pipeline – as unimodal or intermodal transport for hydrogen and chemical hydrogen carriers. Based on this the potential of transport and decentralized integration of carriers for various locations is assessed. A cost comparison is used to determine the maximum specific costs that a decentralized conversion plant can incur while remaining competitive with a centralized conversion plant in the port. The analysis shows that the specific costs of decentralized conversion plants at numerous locations can be significantly higher than those of centralized plants indicating considerable cost-saving potential.

Hydrogen can play a key role as short- and long-term energy storage solution in an energy grid with fluctuating renewable sources. In technologies using hydrogen there is always the risk of unintended leakages due to the low density of gaseous hydrogen. The risk becomes specifically high in confined areas where leaking hydrogen could easily mix with air and form flammable gas mixtures. In the maritime transportation large and congested geometries can be subject to accumulation of hydrogen. A mitigation measure for areas where venting is insufficient or even impossible is the installation of catalytic recombiners. The operational behavior can be described with numerical models which are required to optimize the location and to assess the efficiency of the mitigation solution. In the present study we established an experimental procedure in the REKO-4 facility a 5.5 m³ vessel to determine the recombination rate obtained from a recombiner. Based on the experimental data an engineering correlation was developed to be used for simulations in safety assessments.

For reaching the European greenhouse gas emission targets the phase-in of alternative technologies and energy carriers is crucial for all sectors. For the transport sector synthetic fuels are–next to electromobility–a promising option especially for long-distance shipping and air transport. Within this context the import of synthetic fuels from the Middle East and Northern Africa (MENA) region seems attractive due to low costs for renewable electricity in this region and low transport costs of synthetic fuels at the same time. Against this background this paper analyzes the role of the MENA region in meeting the future synthetic fuel demand in Europe using a cost-optimizing energy supply model. In this model the production storage and transport of electricity hydrogen and synthetic fuels by various technologies in both European and MENA countries in the period up to 2050 are explicitly modeled. Thereby different scenarios are analyzed to depict regional differences in investment risks: a base scenario that does not take into account regional differences in investments risks and three risk scenarios with different developments of regional investment risks. Sensitivity analyses are also carried out to derive conclusions about the robustness of results. Results show that meeting the future synthetic fuel demand in Europe to a large extent by imports from the MENA region can be an attractive option from an economic point of view. If investment risks are incorporated however lower import quotas of synthetic fuels are economically attractive for Europe: the higher generation costs are outweighed by the lower investments risks in Europe to a certain extent. Thereby investment risks outweigh other factors such as transport distance or renewable electricity generation costs in terms of exporting MENA regions and a synthetic fuel import is especially attractive from MENA countries with low investment risks. Concluding within this paper detailed export relations between MENA and EU considering investment risks were modeled for the first time. These model results should be complemented by a more in-depth analysis of the MENA countries including evaluating opportunities for local value chain development sustainability concerns (including social factors) and optimal site selection.

In order to minimize emissions of the aerospace sector and thus its impact on the climate several novel concepts of propulsion systems for aircraft are being developed. Many of these concepts do not use an energy source based on the combustion of hydrocarbons but other means of energy generation and storage like hydrogen fuel cells and corresponding hydrogen storage systems. The use of hydrogen as a primary energy carrier in aircraft poses novel and different hazards when compared to conventional propulsion and fuel storage systems. The study described in the present paper identifies analyzes and evaluates failure conditions and corresponding hazards that are associated with the electrified propulsion systems. Mitigation strategies to prevent failures to occur or decrease their severity are recommended. The effects of the assessed failures on aircraft crew and occupants are classified as catastrophic hazardous or major as defined in the according Certification Specifications. Failure Conditions occurring at the aircraft system and subsystem levels are considered and their effect on the aircraft and propulsion system is assessed. The hazards identified mostly emerge due to the properties of the gaseous or liquid hydrogen. They include the flammability of gaseous hydrogen and the very low temperatures of cryogenic liquid hydrogen as well as the installation of high voltage power infrastructure and high capacity heat exchangers.