Sweden

Biomimetic sulfur-deficient indium sulfide (In_2.77S₄) was synthesized by a template-assisted hydrothermal method using leaves of Mimosa pudica as a template for the first time. The effect of this template in modifying the morphology of the semiconductor particles was determined by physicochemical characterization revealing an increase in surface area decrease in microsphere size and pore size and an increase in pore volume density in samples synthesized with the template. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of organic sulfur (Ssingle bondO/Ssingle bondC/Ssingle bondH) and sulfur oxide species (single bondSO₂ SO₃²− SO₄²−) at the surface of the indium sulfide in samples synthesized with the template. Biomimetic indium sulfide also showed significant amounts of Fe introduced as a contaminant present on the Mimosa pudica leaves. The presence of these sulfur and iron species favors the photocatalytic activity for hydrogen production by their acting as a sacrificial reagent and promoting water oxidation on the surface of the templated particles respectively. The photocatalytic hydrogen production rates over optimally-prepared biomimetic indium sulfide and indium sulfide synthesized without the organic template were 73 and 22 μmol g⁻¹ respectively indicating an improvement by a factor of three in the templated sample.

The Swedish steel industry stands before a potential transition to drastically lower its CO₂ emissions using direct hydrogen reduction instead of continuing with coke-based blast furnaces. Previous studies have identified hydrogen direct reduction as a promising option. We build upon earlier efforts by performing a technological innovation system study to systematically examine the barriers to a transition to hydrogen direct reduction and by providing deepened quantitative empirics to support the analysis. We also add extended paper and patent analysis methodology which is particularly useful for identifying actors and their interactions in a technological system. We conclude that while the innovation system is currently focused on such a transition notable barriers remain particularly in coordination of the surrounding technical infrastructure and the issue of maintaining legitimacy for such a transition in the likely event that policies to address cost pressures will be required to support this development.

Hydrogen produced from renewable electricity will play an important role in deep decarbonisation of industry. However adding large electrolyser capacities to a low-carbon electricity system also increases the need for additional electricity generation from variable renewable energies. This will require hydrogen production to be variable unless other sources provide sufficient flexibility. Existing sources of flexibility in hydro-thermal systems are hydropower and thermal generation which are both associated with sustainability concerns. In this work we use a dispatch model for the case of Sweden to assess the power system operation with large-scale electrolysers assuming that additional wind power generation matches the electricity demand of hydrogen production on average. We evaluate different scenarios for restricting the flexibility of hydropower and thermal generation and include 29 different weather years to test the impact of variable weather regimes. We show that (a) in all scenarios electrolyser utilisation is above 60% on average (b) the inter-annual variability of hydrogen production is substantial if thermal power is not dispatched for electrolysis and (c) this problem is aggravated if hydropower flexibility is also restricted. Therefore either long-term storage of hydrogen or backup hydrogen sources may be necessary to guarantee continuous hydrogen flows. Large-scale dispatch of electrolysis capacity supported by wind power makes the system more stable if electrolysers ramp down in rare hours of extreme events with low renewable generation. The need for additional backup capacities in a fully renewable electricity system will thus be reduced if wind power and electrolyser operation are combined in the system.

Condensation of hydrogen Rydberg atoms (highly electronically excited) into the lowest energy state of condensed hydrogen i.e. the ultra-dense hydrogen phase H(0) has gained increased attention not only from the fundamental aspects but also from the applied point of view. The physical properties of ultra-dense hydrogen H(0) were recently reviewed summarizing the results reported in 50 publications during the last ten years. The main application of H(0) so far is as the fuel and working medium in nuclear particle generators and nuclear fusion reactors which are under commercial development. The first fusion process showing sustained operation above break-even was published in 2015 (AIP Advances) and used ultra-dense deuterium D(0) as fuel. The first generator giving a high-intensity muon flux intended for muon-catalyzed fusion reactors was patented in 2017 using H(0) as the working medium. Here we first focus on the different nuclear processes using hydrogen isotopes for energy generation and then on the detailed processes of formation of H(0). The production of H(0) employs heterogeneous catalysts which are active in hydrogen transfer reactions. Iron oxide-based alkali promoted catalysts function well but also platinum group metals and carbon surfaces are active in this process. The clusters of highly excited Rydberg hydrogen atoms H(l) are formed upon interaction with alkali Rydberg matter. The final conversion step from ordinary hydrogen Rydberg matter H(l) to H(0) is spontaneous and does not require a solid surface. It is concluded that the exact choice of catalyst is not very important. It is also concluded that the crucial feature of the catalyst is to provide excited alkali atoms at a sufficiently high surface density and in this way enabling formation and desorption of H(0) clusters. Finally the relation to industrial catalytic processes which use H(0) formation catalysts is described and some important consequences like the muon and neutron radiation from H(0) are discussed.

This work investigates the impacts of variation management on the cost-optimal electricity system compositions in four regions with different pre-requisites for wind and solar generation. Five variation management strategies involving electric boilers batteries hydrogen storage low-cost biomass and demand-side management are integrated into a regional investment model that is designed to account for variability. The variation management strategies are considered one at a time as well as combined in four different system contexts. By investigating how the variation management strategies interact with each other as well as with different electricity generation technologies in a large number of cases this work support policy-makers in identifying variation management portfolios relevant to their context. It is found that electric boilers demand-side management and hydrogen storage increase the cost-optimal variable renewable electricity (VRE) investments if the VRE share is sufficiently large to reduce its marginal system value. However low-cost biomass and hydrogen storage are found to increase cost-optimal investments in wind power in systems with a low initial wind power share. In systems with low solar PV share variation management reduce the cost-optimal solar PV investments. In two of the regions investigated a combination of variation management strategies results in a stronger increase in VRE capacity than the sum of the single variation management efforts.

Renewable power-to-hydrogen (P2H) technology is one of the most promising solutions for fulfilling the increasing global demand for hydrogen and to buffer large-scale fluctuating renewable energies. The high-power high-current ac/dc converter plays a crucial role in P2H facilities transforming medium-voltage (MV) ac power to a large dc current to supply hydrogen electrolyzers. This work introduces the general requirements and overviews several power converter topologies for P2H systems. The performances of different topologies are evaluated and compared from multiple perspectives. Moreover the future trend of eliminating the line frequency transformer (LFT) is discussed. This work can provide guidance for future designing and implementing of power-electronics-based P2H systems.

Dark fermentation is an anaerobic digestion process of biowaste used to produce hydrogen- for generation of energy- that however releases high amounts of polluting volatile fatty acids such as acetic acid in the environment. In order for this biohydrogen production process to become more competitive the volatile fatty acids stream can be utilized through conversion to high added-value metabolites such as omega-3 fatty acids. The docosahexaenoic acid is one of the two most known omega-3 fatty acids and has been found to be necessary for a healthy brain and proper cardiovascular function. The main source is currently fish which obtain the fatty acid from the primary producers microalgae through the food chain. Crypthecodinium cohnii a heterotrophic marine microalga is known for accumulating high amounts of docosahexaenoic acid while offering the advantage of assimilating various carbon sources such as glucose ethanol glycerol and acetic acid. The purpose of this work was to examine the ability of a C. cohnii strain to grow on different volatile fatty acids as well as on a pre-treated dark fermentation effluent and accumulate omega-3. The strain was found to grow well on relatively high concentrations of acetic butyric or propionic acid as main carbon source in a fed-batch pH-auxostat. Most importantly C. cohnii totally depleted the organic acid content of an ultra-filtrated dark fermentation effluent after 60 h of fed-batch cultivation therefore offering a bioprocess not only able to mitigate environmental pollutants but also to provide a solution for a sustainable energy production process. The accumulated docosahexaenoic acid content was as high as 29.8% (w/w) of total fatty acids.

The manuscript presents the conceptual design phase of an unmanned aerial vehicle with the objective of a systems approach towards the integration of a hydrogen fuel-cell system and Li-ion batteries into an aerodynamically efficient platform representative of future aircraft configurations. Using a classical approach to aircraft design and a combination of low- and high-resolution computational simulations a final blended wing body UAV was designed with a maximum take-off weight of 25 kg and 4 m wingspan. Preliminary aerodynamic and propulsion sizing demonstrated that the aircraft is capable of completing a 2 h long mission powered by a 650 W fuel cell hybridized with a 100 Wh battery pack and with a fuel quantity of 80 g of compressed hydrogen.

Water electrolysis is a promising approach for the sustainable production of hydrogen however the unfavorable thermodynamics and sluggish kinetics of oxygen evolution reaction (OER) are associated with high anodic potentials. To lower the required potentials an effective strategy is proposed to substitute OER with partial oxidation of degradation products of carbohydrate origin from the waste stream of a chemical pulping industry. In this work two different catalytic materials e PdNi and NiO are investigated comparatively to understand their catalytic performance for the oxidation of carbohydrate alkaline degradation products (CHADs). PdNi can catalyze CHADs with low potential requirements (0.11 V vs. Hg/HgO at 150 mA cm2 ) but is limited to current densities opportunities to study earth-abundant electrocatalysts to efficiently oxidize biomass-derived substances.

The growing share of intermittent renewable energy sources for power generation indicates an increasing demand for flexibility in the energy system. Energy storage technologies ensure a balance between demand and supply and increase the system flexibility. This study investigates increased application of renewable energy resources at a regional scale. Power-to-gas storage that interacts with a large-scale rooftop photovoltaic system is added to a regional energy system dominated by combined heat and power plants. The study addresses the influence of the storage system on the production planning of the combined heat and power plants and the system flexibility. The system is modeled and the product costs are optimized using the Mixed Integer Linear Programming method as well as considering the effects on CO₂ emissions and power import into the regional system. The optimization model is investigated by developing different scenarios for the capacity and cost of the storage system. The results indicate that the proposed storage system increases the system flexibility and can reduce power imports and the marginal emissions by around 53% compared with the current energy system. There is a potential to convert a large amount of excess power to hydrogen and store it in the system. However because of low efficiency a fuel cell cannot significantly contribute to power regeneration from the stored hydrogen. Therefore for about 70% of the year the power is imported to the optimized system to compensate the power shortfalls rather than to use the fuel cell.