Germany

This paper investigates environmental impacts of high pressure alkaline water electrolysis systems. An advanced system with membranes on polymer basis is compared to a state-of-the-art system with asbestos membranes using a Life Cycle Assessment (LCA) approach. For the advanced system a new improved membrane technology has been investigated within the EU research project “ELYGRID”. Results indicate that most environmental impacts are caused by the electricity supply necessary for operation. During the construction phase cell stacks are the main contributor to environmental impacts. New improved membranes have relatively small contributions to impacts caused by cell construction within the advanced systems. As main outcome the systems comparison illustrates a better ecological performance of the new developed system

Carbon-free and sustainable energy storage solutions are required to mitigate climate change. One possible solution especially for stationary applications could be the storage of energy in metal fuels. Energy can be stored through reduction of the oxide with green hydrogen and be released by combustion. In this work a feasibility study for iron as possible metal fuel considering the complete energy cycle is conducted. Based on equilibrium calculations it could be shown that the power-to-power efficiency of the iron/iron oxide cycle is 27 %. As technology development requires a more detailed description of both the reduction and the oxidation a first outlook is given on the kinetic analysis of the reduction of iron oxides with hydrogen. Based on thermogravimetric experiments using Fe2O3 Fe3O4 and FeO it could be shown that the reduction is a three-step process. The maximum reduction rate can be achieved with a hydrogen content of 25 %. Based on the experimental results a reaction mechanism and accompanied kinetic data were developed for description of Fe2O3 reduction with H2 under varying experimental conditions.

Transformation concepts towards a low-carbon society often require new technology and infrastructure that evoke protests in the population. Therefore it is crucial to understand positions and conflicts in society to achieve social acceptance. This paper analyses these positions using the example of implementing hydrogen and carbon capture and storage infrastructure to decarbonise the German energy system. The empirical basis of the study are explorative stakeholder interviews which were conducted with experts from politics economics civil society and science and analysed within a discursive and attitudinal framework using qualitative content analysis. These stakeholder positions are assumed to represent dominant social perceptions and reflect chances and risks for acceptance. The results indicate different positions while pursuing the common goal of addressing climate change. The general conflict concerns strategies towards a low-carbon society especially the speed of phasing-out fossil energies. Regarding the combination of hydrogen and carbon capture and storage as instrument in the context of the energy transition the stakeholder interviews indicate controversial as well as consensual perceptions. The assessments range from rejection to deeming it absolutely necessary. Controversial argumentations refer to security of supply competitiveness and environmental protection. In contrast consensus can be reached by balancing ecological and economic arguments e.g. by linking hydrogen technologies with renewable and fossil energy sources or by limiting the use of carbon capture and storage only to certain applications (industry bioenergy). In further decisions this balancing of arguments combined with openness of technology transparency of information and citizen participation need to be considered to achieve broad acceptance.

At the heart of most Power-to-X (PtX) concepts is the utilization of renewable electricity to produce hydrogen through the electrolysis of water. This hydrogen can be used directly as a final energy carrier or it can be converted into for example methane synthesis gas liquid fuels electricity or chemicals. Technical demonstration and systems integration are of major importance for integrating PtX into energy systems. As of June 2020 a total of 220 PtX research and demonstration projects in Europe have either been realized completed or are currently being planned. The central aim of this review is to identify and assess relevant projects in terms of their year of commissioning location electricity and carbon dioxide sources applied technologies for electrolysis capacity type of hydrogen post-processing and the targeted field of application. The latter aspect has changed over the years. At first the targeted field of application was fuel production for example for hydrogen buses combined heat and power generation and subsequent injection into the natural gas grid. Today alongside fuel production industrial applications are also important. Synthetic gaseous fuels are the focus of fuel production while liquid fuel production is severely under-represented. Solid oxide electrolyzer cells (SOECs) represent a very small proportion of projects compared to polymer electrolyte membranes (PEMs) and alkaline electrolyzers. This is also reflected by the difference in installed capacities. While alkaline electrolyzers are installed with capacities between 50 and 5000 kW (2019/20) and PEM electrolyzers between 100 and 6000 kW SOECs have a capacity of 150 kW. France and Germany are undertaking the biggest efforts to develop PtX technologies compared to other European countries. On the whole however activities have progressed at a considerably faster rate than had been predicted just a couple of years ago.

With little time left for humanity to reduce climate change to a tolerable level a highly scalable and rapidly deployable solution is needed that can be implemented by any country. Offshore wind energy in international waters is an underused resource and could even be harnessed by landlocked countries. In this paper the use of sailing wind turbines operating autonomously in high seas to harvest energy is proposed. The electrical energy that is generated by the wind turbine is converted to a renewable fuel and stored onboard. Later the fuel will be transferred to shore or to other destinations of use. The presented idea is explored at the system level where the basic subsystems necessary are identified and defined such as energy conversion and storage as well as propulsion subsystems. Moreover various operating possibilities are investigated including a comparison of different sailing strategies and fuels for storage. Existing ideas are also briefly addressed and an example concept is suggested as well. In this paper the proposed sailing renewable energy conversion system is explored at a higher level of abstraction. Following up on this conceptual study more detailed investigations are necessary to determine whether the development of such a sailing renewable energy conversion system is viable from an engineering economic and environmental point of view.

Achieving net-zero emissions by 2050 will require accelerated efforts that include decarbonizing long-haul truck transportation. In this difficult-to-decarbonize low-margin industry economic transparency on technology options is vital for decision makers seeking to eliminate emissions. Battery electric (BET) and hydrogen fuel cell electric trucks (FCET) can represent emission-free alternatives to diesel-powered trucks (DT). Previous studies focus on cost competitiveness in weight-constrained transportation even though logistics research shows that significant shares of transportation are constrained by volume and analyze cost only for selected technologies hence impeding a differentiated market segmentation of future emission-free trucks. In this study the perspective of a rational investor is taken and it is shown that under current conditions in the U.S. BETs outperform FCETs in various long-haul use cases despite charging times and cargo deficits and will further increase their technological competitiveness to DTs. While future energy and fueling prices are decisive for BET competitiveness the analysis reveals that autonomous driving may change the picture in favor of FCETs.

The rapid conversion of conventional powertrain technologies to climate-neutral new energy vehicles requires the ramping of electrification. The popularity of fuel cell electric vehicles with improved fuel economy has raised great attention for many years. Their use of green hydrogen is proposed to be a promising clean way to fill the energy gap and maintain a zero-emission ecosystem. Their complex architecture is influenced by complex multiphysics interactions driving patterns and environmental conditions that put a multitude of power requirements and boundary conditions around the vehicle subsystems including the fuel cell system the electric motor battery and the vehicle itself. Understanding its optimal fuel economy requires a systematic assessment of these interactions. Artificial intelligence-based machine learning methods have been emerging technologies showing great potential for accelerated data analysis and aid in a thorough understanding of complex systems. The present study investigates the fuel economy peaks during an NEDC in fuel cell electric vehicles. An innovative approach combining traditional multiphysics analyses design of experiments and machine learning is an effective blend for accelerated data supply and analysis that accurately predicts the fuel consumption peaks in fuel cell electric vehicles. The trained and validated models show very accurate results with less than 1% error.

The use of drop-in capable alternative fuels in aircraft can support the European aviation sector to achieve its goals for sustainable development. They can be a transitional solution in the short and medium term as their use does not require any structural changes to the aircraft powertrain. However the production of alternative fuels is often energy-intensive and some feedstocks are associated with harmful effects on the environment. In addition alternative fuels are often more expensive to produce than fossil kerosene which can make their use unattractive. Therefore this paper analyzes the environmental and economic impacts of four types of alternative fuels compared to fossil kerosene in a well-to-wake perspective. The fuels investigated are sustainable aviation fuels produced by power-to-liquid and biomass-to-liquid pathways. Life cycle assessment and life cycle costing are used as environmental and economic assessment methods. The results of this well-towake analysis reveal that the use of sustainable aviation fuels can reduce the environmental impacts of aircraft operations. However an electricity mix based on renewable energies is needed to achieve significant reductions. In addition from an economic perspective the use of fossil kerosene ranks best among the alternatives. A scenario analysis confirms this result and shows that the production of sustainable aviation fuels using an electricity mix based solely on renewable energy can lead to significant reductions in environmental impact but economic competitiveness remains problematic.

In this work experiments on horizontal hydrogen jet releases from a 2.815 dm³ volume tank to the ambience are described. For the main experimental series tank valve and release line were cooled down to a temperature of approx. 80 K in a bath of liquid nitrogen. As a reference similar experiments were also performed with the uncooled tank at ambient temperature. The releases were carried out through four nozzles with different circular orifice diameters from 0.5 to 4 mm and started from initial tank pressures from 0.5 to 20 MPa (rel.). During the releases pressures and temperatures inside the vessel as well as inside the release line were measured. Outside the nozzle further temperature and hydrogen concentration measurements were performed along and besides the jet axis. The electrostatic field builtup in the jet was monitored using two field meters in different distances from the release nozzle and optical observation via photo and video-cameras was performed for the visualization of the H2-jet via the BOS-method. The experiments were performed in the frame of the EU-funded project PRESHLY in which several tests of this program were selected for a comparative computational study the results of which will also be presented at this conference. So on the one hand the paper gives a comprehensive description of the facility on the other hands it also describes the experimental procedure and the main findings.

Niger offers the possibility of producing green hydrogen due to its high solar energy potential. Due to the still growing domestic oil and coal industry the use of green hydrogen in the country currently seems unlikely at the higher costs of hydrogen as an energy vector. However the export of green hydrogen to industrialized countries could be an option. In 2020 a hydrogen partnership has been established between Germany and Niger. The potential import of green hydrogen represents an option for Germany and other European countries to decarbonize domestic energy supply. Currently there are no known projects for the electrolytic production of hydrogen in Niger. In this work potential hydrogen demand across electricity and transport sectors is forecasted until 2040. The electricity demand in 2040 is expected at 2934 GWh and the gasoline and diesel demand at 964 m3 and 2181 m3 respectively. Accordingly the total hydrogen needed to supply electricity and the transport sector (e.g. to replace 1% gasoline and diesel demand in 2040) is calculated at 0.0117 Mt. Only a small fraction of 5% of the land area in Niger would be sufficient to generate the required electricity from solar PV to produce hydrogen.

Hydrogen (H2) produced using renewable energy could be used to reduce greenhouse gas (GHG) emissions in industrial sectors such as steel chemicals transportation and energy storage. Knowing the delivered cost of renewable H2 is essential to decisionmakers looking to utilize it. The cheapest location to source it from as well as the transport method and medium are also crucial information. This study presents a Monte Carlo simulation to determine the delivered cost for renewable H2 for any usage location globally as well as the most cost-effective production location and transport route from nearly 6000 global locations. Several industrially dense locations are selected for case studies the primary two being Cologne Germany and Houston United States. The minimum delivered H2 cost to Cologne is 9.4 €/kg for small scale (no pipelines considered) shipped from northern Egypt as a liquid organic hydrogen carrier (LOHC) and 7.6 €/kg piped directly as H2 gas from southern France for large scale (pipelines considered). For smallscale H2 in Houston the minimum delivered cost is 8.6 €/kg trucked as H2 gas from the western Gulf of Mexico and 7.6 €/kg for large-scale demand piped as H2 gas from southern California. The south-west United States and Mexico northern Chile the Middle East and north Africa south-west Africa and north-west Australia are identified as the regions with the lowest renewable H2 cost potential with production costs ranging from 6.7—7.8 €/kg in these regions. Each is able to supply differing industrially dominant areas. Furthermore the effect of parameters such as year of construction electrolyser and H2 demand is analysed. For the case studies in Houston and Cologne the delivered H2 cost is expected to reduce to about 7.8 €/kg by 2050 in Cologne (no pipelines considered PEM electrolyser) and 6.8 €/kg in Houston.

Green hydrogen via renewable powered electrolysis has a high relevance in decarbonization and supply security. Achieving economically competitive hydrogen production costs is a major challenge in times of an energy price crisis. Our objective is to show the economically optimal installed capacity of electrolysers in relation to wind and solar power so swift and credible statements can be made regarding the system design. The ratio between renewable generation and electrolysis power as well as scaling effects operating behaviour and development of costs are considered. Hydrogen production costs are calculated for four exemplary real PV and wind sites and different ratios of electrolysis to renewable power for the year 2020. The ideal ratio for PV systems is between 14% and 73% and for wind between 3.3% and 143% for low and high full load hours. The lowest hydrogen production costs are identified at 2.53 €/kg for 50 MW wind power and 72 MW electrolysis power. The results provide plant constructors the possibility to create a cost-optimized design via an optimum ratio of electrolysis to renewable capacity. Therefore the procedures for planning and dimensioning of selected systems can be drastically simplified.

Addressing the pressing challenge of global warming reducing greenhouse gas emissions in the transportation sector is a critical imperative. Battery and fuel cell electric vehicles have emerged as promising solutions for curbing emissions in this sector. In this study we conducted a comprehensive life cycle assessment (LCA) for typical passenger vehicles heavy-duty trucks and city buses using either proton-exchange membrane fuel cells or Li-ion batteries with different cell chemistries. To ensure accuracy we supplemented existing studies with data from the literature particularly for the recycling phase as database limitations were encountered. Our results highlight that fuel cell and battery systems exhibit large emissions in the production phase. Recycling can significantly offset some of these emissions but a comparison of the technologies examined revealed considerable differences. Overall battery electric vehicles consistently outperform fuel cell electric vehicles regarding absolute greenhouse gas emissions. Hence we recommend prioritizing battery electric over fuel cell vehicles. However deploying fuel cell electric vehicles could become attractive in a hydrogen economy scenario where other factors e. g. the conversion and storage of surplus renewable electricity via electrolysis become important.

The importing of renewable energy will be one part of the process of defossilizing the energy systems of countries and regions which are currently heavily dependent on the import of fossil-based energy carriers. This study investigates the possibility of importing renewable methanol comprised of hydrogen and carbon dioxide. Based on a methanol synthesis simulation model the net production costs of methanol are derived as a function of hydrogen and carbon dioxide expenses. These findings enable a comparison of the import costs of methanol and hydrogen. For this the hydrogen production and distribution costs for 2030 as reported in a recent study for four different origin/destination country combinations are considered. With the predicted hydrogen production costs of 1.35–2 €/kg and additional shipping costs methanol can be imported for 370–600 €/t if renewable or process-related carbon dioxide is available at costs of 100 €/t or below in the hydrogen-producing country. Compared to the current fossil market price of approximately 400 €/t renewable methanol could therefore become cost-competitive. Within the range of carbon dioxide prices of 30–100 €/t both hydrogen and methanol exhibit comparable energy-specific import costs of 18–30 €/GJ. Hence the additional costs for upgrading hydrogen to methanol are balanced out by the lower shipping costs of methanol compared to hydrogen. Lastly a comparison for producing methanol in the hydrogen’s origin or destination country indicates that carbon dioxide in the destination country must be 181–228 €/t less expensive than that in the origin country to balance out the more expensive shipping costs for hydrogen.

Non-energy use of natural gas is gaining importance. Gas used for 183 million tons annual ammonia production represents 4% of total global gas supply. 1.5-degree pathways estimate an ammonia demand growth of 3–4-fold until 2050 as new markets in hydrogen transport shipping and power generation emerge. Ammonia production from hydrogen produced via water electrolysis with renewable power (green ammonia) and from natural gas with CO2 storage (blue ammonia) is gaining attention due to the potential role of ammonia in decarbonizing energy value chains and aiding nations in achieving their net-zero targets. This study assesses the technical and economic viability of different routes of ammonia production with an emphasis on a systems level perspective and related process integration. Additional cost reductions may be driven by optimum sizing of renewable power capacity reducing losses in the value chain technology learning and scale-up reducing risk and a lower cost of capital. Developing certification and standards will be necessary to ascertain the extent of greenhouse gas emissions throughout the supply chain as well as improving the enabling conditions including innovative finance and de-risking for facilitating international trade market creation and large-scale project development.

As the share of distributed renewable power generation increases high electricity prices and low feed-in tariff rates encourage the generation of electricity for personal use. In the building sector this has led to growing interest in energy self-sufficient buildings that feature battery and hydrogen storage capacities. In this study we compare potential technology pathways for residential energy storage in terms of their economic performance by means of a temporal optimization model of the fully self-sufficient energy system of a single-family building taking into account its residential occupancy patterns and thermal equipment. We show for the first time how heat integration with reversible solid oxide cells (rSOCs) and liquid organic hydrogen carriers (LOHCs) in high-efficiency single-family buildings could by 2030 enable the self-sufficient supply of electricity and heat at a yearly premium of 52% against electricity supplied by the grid. Compared to lithium-ion battery systems the total annualized cost of a self-sufficient energy supply can be reduced by 80% through the thermal integration of LOHC reactors and rSOC systems.

Hydrogen enhanced decohesion is expected to play a major role in ferritic steels especially at grain boundaries. Here we address the effects of some common alloying elements C V Cr and Mn on the H segregation behaviour and the decohesion mechanism at a Σ5(310)[001] 36.9∘ grain boundary in bcc Fe using spin polarized density functional theory calculations. We find that V Cr and Mn enhance grain boundary cohesion. Furthermore all elements have an influence on the segregation energies of the interstitial elements as well as on these elements’ impact on grain boundary cohesion. V slightly promotes segregation of the cohesion enhancing element C. However none of the elements increase the cohesion enhancing effect of C and reduce the detrimental effect of H on interfacial cohesion at the same time. At an interface which is co-segregated with C H and a substitutional element C and H show only weak interaction and the highest work of separation is obtained when the substitute is Mn.

Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large-scale transport and storage of hydrogen with higher densities. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducted pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The central research consisted of a broad experimental program combined with analytical work modelling and simulations belonging to the three key phenomena of the accident chain: release and mixing ignition and combustion. The presented results improve the general understanding of the behavior of LH2 in accidents and provide some design guidelines and engineering tools for safer use of LH2. Recommendations for improvement of current international standards are derived.

Background: The wider background to this article is the shift in the energy paradigm from fossil energy sources to renewable sources which should occur in the twenty-first century. This transformation requires the development of alternative energy technologies that enable the deployment of renewable energy sources in transportation heating and electricity. Among others hydrogen and fuel cell technologies have the potential to fulfill this requirement and to contribute to a sustainable and emission-free transport and energy system. However whether they will ever reach broad societal acceptance will not only depend on technical issues alone. The aim of our study is to reveal the importance of nontechnical issues. Therefore the article at hand presents a case study of hydrogen and fuel cells in Germany and aims at highlighting the cultural context that affects their development.<br/>Methods: Our results were obtained from a rich pool of data generated in various research projects through more than 30 in-depth interviews direct observations and document analyses.<br/>Results: We found that individual and collective actors developed five specific supportive practices which they deploy in five diverse arenas of meaning in order to attach certain values to hydrogen and fuel cell technologies.<br/>Conclusions: Based on the results we drew more general conclusions and deducted an overall model for the analysis of culture in technological innovations that is outlined at the end of the article. It constitutes our contribution to the interdisciplinary collaboration required for tackling the shift in this energy paradigm.

In the near future the challenges to reduce the economic and social dependency on fossil fuels must be faced increasingly. A sustainable and efficient energy supply based on renewable energies enables large-scale applications of electro-fuels for e.g. the transport sector. The high gravimetric energy density makes liquefied hydrogen a reasonable candidate for energy storage in a light-weight application such as aviation. Current aircraft structures are designed to accommodate jet fuel and gas turbines allowing a limited retrofitting only. New designs such as the blended-wing-body enable a more flexible integration of new storage technologies and energy converters e.g. cryogenic hydrogen tanks and fuel cells. Against this background a tank-design model is formulated which considers geometrical mechanical and thermal aspects as well as specific mission profiles while considering a power supply by a fuel cell. This design approach enables the determination of required tank mass and storage density respectively. A new evaluation value is defined including the vented hydrogen mass throughout the flight enabling more transparent insights on mass shares. Subsequently a systematic approach in tank partitioning leads to associated compromises regarding the tank weight. The analysis shows that cryogenic hydrogen tanks are highly competitive with kerosene tanks in terms of overall mass which is further improved by the use of a fuel cell.

Grid integrated water electrolysers have the potential of coupling electric power systems subjected to high shares of renewable energy sources with sectors of hydrogen demand thus contributing to European decarbonization goals in future. We therefore investigate the business potential of future electrolyser applications in cross-commodity arbitrage trading by applying a complex power market simulation method for future scenarios and different European countries. Based on this we evaluate the potential of additional provision of grid services towards grid operators in order to increase the electrolyser utilization ratio. For this we use a method that identifies measures of transmission grid operators in order to ensure secure grid operation. In this context uncertain hydrogen prices and different sectors of hydrogen demand are addressed through sensitivities of different hydrogen sales prices. The analysis shows a high dependency of business model efficiency on the hydrogen price. While cross-commodity arbitrage trading can achieve profitability for the transportation sector applications for the industry sector and natural gas system are less efficient. The results however indicate that for these less efficient applications grid service provision can be an option of increasing the electrolyser utilization ratio thus increasing its profitability.

This paper presents results of experimental investigations on unignited horizontal hydrogen jets in air in presence of co- cross- and counter-flow. Hydrogen concentration distributions are obtained as functions of distance to the hydrogen release nozzle. The H2-jet variables are two nozzle diameters 1 mm and 4 mm and two H2-jet mass flow rates 1 g/s up to 5 g/s. A propeller fan is used to provide forced ventilation compared to the case with no ventilation three different airflow velocities up to 5 m/s were studied systematically. It was found that any forced ventilation in co- cross- and counter-flow direction reduces the size of the burnable mixture cloud of the H2-jet compared to a free jet in quiescent air.

The H₂ internal combustion engine (ICE) is a key technology for complete decarbonization of the transport sector. To match or exceed the power density of conventional combustion engines H₂ direct injection (DI) is essential. Therefore new injector concepts that meet the requirements of a H₂ operation have to be developed. The macroscopic free stream behavior of H2 released from an innovative fluidic oscillating nozzle is investigated and compared with that of a conventional multi-hole nozzle. This work consists of H₂ flow measurements and injection tests in a constant volume chamber using the Schlieren method and is accompanied by a LES simulation. The results show that an oscillating H₂ free stream has a higher penetration velocity than the individual jets of a multi-hole nozzle. This behavior can be used to inject H₂ far into the combustion chamber in the vertical direction while the piston is still near bottom dead center. As soon as the oscillation of the H₂ free stream starts the spray angle increases and therefore H2 is also distributed in the horizontal direction. In this phase of the injection process spray angles comparable to those of a multi-hole nozzle are achieved. This behavior has a positive effect on H2 homogenization which is desirable for the combustion process.

To solve the challenge of decarbonizing the transport sector a broad variety of alternative fuels based on different concepts including Power-to-Gas and Power-to-Liquid and propulsion systems have been developed. The current research landscape is investigating either a selection of fuel options or a selection of criteria a comprehensive overview is missing so far. This study aims to close this gap by providing a holistic analysis of existing fuel and drivetrain options spanning production to utilization. For this purpose a case study for Germany is performed considering different vehicle classes in road rail inland waterway and air transport. The evaluated criteria on the production side include technical maturity costs as well as environmental impacts whereas on the utilization side possible blending with existing fossil fuels and the satisfaction of the required mission ranges are evaluated. Overall the fuels and propulsion systems Methanol-to-Gasoline Fischer–Tropsch diesel and kerosene hydrogen battery-electric propulsion HVO DME and natural gas are identified as promising future options. All of these promising fuels could reach near-zero greenhouse gas emissions bounded to some mandatory preconditions. However the current research landscape is characterized by high insecurity with regard to fuel costs depending on the predicted range and length of value chains.

Multiscale characterization of the hydrogenation process of silicon solar cell contacts based on c-Si/SiO_x/nc-SiC_x(p) has been performed by combining dynamic secondary ion mass-spectrometry (D-SIMS) atom probe tomography (APT) and transmission electron microscopy (TEM). These contacts are formed by high-temperature firing which triggers the crystallization of SiCx followed by a hydrogenation process to passivate remaining interfacial defects. Due to the difficulty of characterizing hydrogen at the nm-scale the exact hydrogenation mechanisms have remained elusive. Using a correlative TEM-SIMS-APT analysis we are able to locate hydrogen trap sites and quantify the hydrogen content. Deuterium (D) a heavier isotope of hydrogen is used to distinguish hydrogen introduced during hydrogenation from its background signal. D-SIMS is used due to its high sensitivity to get an accurate deuterium-to-hydrogen ratio which is then used to correct deuterium profiles extracted from APT reconstructions. This new methodology to quantify the concentration of trapped hydrogen in nm-scale structures sheds new insights on hydrogen distribution in technologically important photovoltaic materials.