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Background: Human and earth system modeling, traditionally centered on the interplay between the energy system and the atmosphere, are facing a paradigm shift. The Intergovernmental Panel on Climate Change's mandate for comprehensive, cross-sectoral climate action emphasizes avoiding the vulnerabilities of narrow sectoral approaches. Our study explores the circular bioeconomy, highlighting the intricate interconnections among agriculture, forestry, aquaculture, technological advancements, and ecological recycling. Collectively, these sectors play a pivotal role in supplying essential resources to meet the food, material, and energy needs of a growing global population. We pose the pertinent question of what it takes to integrate these multifaceted sectors into a new era of holistic systems thinking and planning. Results: The foundation for discussion is provided by a novel graphical representation encompassing statistical data on food, materials, energy flows, and circularity. This representation aids in constructing an inventory of technological advancements and climate actions that have the potential to significantly reshape the structure and scale of the economic metabolism in the coming decades. In this context, the three dominant mega-trends—population dynamics, economic developments, and the climate crisis—compel us to address the potential consequences of the identified actions, all of which fall under the four categories of substitution, efficiency, sufficiency, and reliability measures. Substitution and efficiency measures currently dominate systems modeling. Including novel bio-based processes and circularity aspects might require only expanded system boundaries. Conversely, paradigm shifts in systems engineering are expected to center on sufficiency and reliability actions. Effectively assessing the impact of sufficiency measures will necessitate substantial progress in inter- and transdisciplinary collaboration, primarily due to their non-technological nature. In addition, placing emphasis on modeling the reliability and resilience of transformation pathways represents a distinct and emerging frontier that highlights the significance of an integrated network of networks. Conclusions: Existing and emerging circular bioeconomy practices can serve as prime examples of system integration. These practices facilitate the interconnection of complex biomass supply chain networks with other networks encompassing feedstock-independent renewable power, hydrogen, CO2, water, and other biotic, abiotic, and intangible resources. Elevating the prominence of these connectors will empower policymakers to steer the amplification of synergies and mitigation of tradeoffs among systems, sectors, and goals. [ABSTRACT FROM AUTHOR]

Climate change mitigation generally require rapid decarbonization in the power sector, including phase-out of fossil fuel-fired generators. Given recent technological developments, co-firing of hydrogen or ammonia, could help decarbonize fossil-based generators, but little is known about how its effects would play out globally. Here, we explore this topic using an energy system model. The results indicate that hydrogen co-firing occurs solely in stringent mitigation like 1.5 °C scenarios, where around half of existing coal and gas power capacity can be retrofitted for hydrogen co-firing, reducing stranded capacity, mainly in the Organization for Economic Co-operation and Development (OECD) countries and Asia. However, electricity supply from co-firing generators is limited to about 1% of total electricity generation, because hydrogen co-firing is mainly used as a backup option to balance the variable renewable energies. The incremental fuel cost of hydrogen results in lower capacity factor of hydrogen co-fired generators, whereas low-carbon hydrogen contributes to reducing emission cost associated with carbon pricing. While hydrogen co-firing may play a role in balancing intermittency of variable renewable energies, it will not seriously delay the phase-out of fossil-based generators. Effects of hydrogen and ammonia co-firing with fossil power generation on decarbonization scenario are assessed. Co-fired generation is limited to <1% because of higher cost of hydrogen. It will not delay the phase-out of fossil-based generators. [ABSTRACT FROM AUTHOR]

Supporters of hydrogen energy urge scaling up technology and reducing costs for competitiveness. This paper explores how hydrogen energy technologies (HET) are perceived by Australia's general population and considers the way members of the public imagine their role in the implementation of hydrogen energy now and into the future. The study combines a nationally representative survey (n = 403) and semi-structured interviews (n = 30). Results show age and gender relationships with self-reported hydrogen knowledge. Half of the participants obtained hydrogen information from televised media. Strong support was observed for renewable hydrogen, while coal (26%) and natural gas (41%) versions had less backing. Participants sought more safety-related information (41% expressed concern). Most felt uncertain about influencing hydrogen decisions and did not necessarily recognise they had agency beyond their front fence. Exploring the link between political identity and agency in energy decision-making is needed, with energy democracy a potentially productive direction. • Hydrogen's strongest appeal to Australians is its benefit for climate change mitigation. • Although widely accepted, there is limited knowledge about hydrogen in terms of how it is produced or used. • The more people know about hydrogen, the more willing they are to participate in the decision-making process. [ABSTRACT FROM AUTHOR]

The pressure on reducing greenhouse gas emissions has increased since the focus on climate change mitigation has grown. As the human development index is directly related to per capita energy consumption, sustainable energy production with reduced carbon footprint is the essential pathway for cleaner environment. Over numerous existing biological processes, hydrogen production via photo fermentation and photolysis of water is considered a more sustainable and economical method of hydrogen production. While both biological modes suffer from certain limitations, such as low yields and low production rates, practical implementation is still a long way off due to these limitations. The unique properties of nanomaterials (NMs) can help increase the efficiency of the biomass to biohydrogen process in significant ways. Applications of organic and inorganic nanoparticles in photocatalytic and photo fermentative hydrogen production is discussed in this paper. This review reports a wide range of applications of nanomaterials including the details of photo fermentative microorganisms and their mechanism of action. The maximum photo fermentative bio-H 2 production was reported in the presence of SiC–Fe 3 O 4 (3.02 mol H 2 /mol acetate), Ni (41 mol H 2 /mol sugar), graphite-C 3 N 4 (64.2 mol H 2 /mol sugar) whereas photocatalytic bio-H 2 yield was highest when Pd–Ni/CdS (54 mmol/g.h), Ni-MO/g-C 3 N 4 (1785 mmol/g.h) and CuO/TiO 2 (20.3 mmol/g.h) nanoparticles were employed. To design photocatalytic systems for practical and scalable use, the future research should be focused on deeper theoretical knowledge of mechanisms of light harvesting, ± charge separation and transport, surface biochemical reactions, semiconductor–liquid interactions, and reactor dynamics. [Display omitted] • Recent developments for improving water photolysis and photo-fermentation are reviewed. • Applications of organic and inorganic nanoparticles in hydrogen production are discussed. • The working principle and mechanism of hydrogen production are discussed. • The influence of key operating factors are presented. • Scope for future research was presented. [ABSTRACT FROM AUTHOR]

The fifth edition of Avogadro Colloquia entitled "From Water to Chemicals: Vision and Opportunities of a Sustainable Hydrogen Society", jointly organized by the Department of Chemical Sciences and Materials Technologies of the National Research Council (DSCTM CNR) and the Italian Chemical Society (SCI), was held at the CNR headquarters in Rome on December 15th–16th, 2022. This relevant periodic conference of SCI also was one of the first event for the celebrations of the Centenary of the Italian CNR. This edition of the Colloquia was focused on the technologies for hydrogen production and use in the so-called green transition towards a society with reduced CO2 emissions. Such technologies well fit the objectives recommended by the United Nations and by Mission EU2030 for the mitigation of the climate change. Greeting addresses to this event were given by the CNR president Maria Chiara Carrozza, the president of SCI Gaetano Guerra, the elected president of the European Chemical Society (EuChemS) Angela Agostiano, the IUPAC president Javier García Martínez and the director of DSCTM CNR Lidia Armelao. All the representatives of the national and international chemical societies underlined the key role of chemical sciences and innovative materials in the green transition. [ABSTRACT FROM AUTHOR]

Climate change mitigation on a global scale will only be possible through the achievement of ambitious decarbonisation goals, requiring an energy transition that involves switching from fossil fuels to clean fuels such as hydrogen. The photocatalytic approach is one of the most studied methods for directly converting sunlight into hydrogen. In this work, we present the synthesis, characterization, and application of the PTZ1‐HA dye, which was obtained by replacing the terminal conventional carboxylic anchoring moieties of a previously studied phenothiazine‐based dye (PTZ1) with hydroxamic acid functionalities. The photoinduced performance of the two dyes as photosensitizers was compared in both dye‐sensitized solar cells and dye‐sensitized photocatalytic systems. PTZ1‐HA‐sensitized photocatalysts showed improved stability in hydrogen generation due to the introduction of the hydroxamic acid as an alternative anchor group, which was shown to slow down hydrolysis in aqueous media. Even though the light harvesting ability of PTZ1‐HA was lower than that of PTZ1, the higher stability of PTZ1‐HA‐sensitized devices allowed for improved photocatalytic generation of H2 over prolonged periods. The superior long‐term efficiency of the hydroxamic acid based dye is important in view of potential practical applications. [ABSTRACT FROM AUTHOR]

Fuel cell vehicles using green hydrogen as fuel can contribute to the mitigation of climate change. The increasing utilization of those vehicles creates the need for cost efficient hydrogen refueling stations. This study investigates how to build the most cost efficient refueling stations to fuel small fleet sizes of 2, 4, 8, 16 and 32 fuel cell busses. A detailed physical model of a hydrogen refueling station was built to determine the necessary hydrogen storage size as well as energy demand for compression and precooling of hydrogen. These results are used to determine the refueling costs for different station configurations that vary the number of storage banks, their volume and compressor capacity. It was found that increasing the number of storage banks will decrease the necessary total station storage volume as well as energy demand for compression and precooling. However, the benefit of adding storage banks decreases with each additional bank. Hence the cost for piping and instrumentation to add banks starts to outweigh the benefits when too many banks are used. Investigating the influence of the compressor mass flow found that when fueling fleets of 2 or 4 busses the lowest cost can be reached by using a compressor with the minimal mass flow necessary to refill all storage banks within 24 h. For fleets of 8, 16 and 32 busses, using the compressor with the maximum investigated mass flow of 54 kg/h leads to the lowest costs. • Designing the most cost efficient refueling stations to fuel small bus fleets. • New approach to minimize hydrogen fueling costs using a thermodynamic refueling model. • It is cost efficient to use a minimum of 4 cascade storage banks when fueling busses. • A high mass flow compressor is cost efficient for fleet sizes above 4 busses. • Energy demand for compression makes up a significant share of refueling costs. [ABSTRACT FROM AUTHOR]

Australia has clear aspirations to become a major global exporter of hydrogen as a replacement for fossil fuels and as part of the drive to reduce CO2 emissions, as set out in the National Hydrogen Strategy released in 2019 jointly by the federal and state governments. In 2021, the Australian Energy Market Operator specified a grid forecast scenario for the first time entitled "hydrogen superpower". Not only does Australia hope to capitalise on the emerging demand for zero-carbon hydrogen in places like Japan and South Korea by establishing a new export industry, but it also needs to mitigate the built-in carbon risk of its export revenue from coal and LNG as major customers, such as Japan and South Korea, move to decarbonise their energy systems. This places hydrogen at the nexus of energy, climate change mitigation and economic growth, with implications for energy security. Much of the published literature on this topic concentrates on the details of what being a major hydrogen exporter will look like and what steps will need to be taken to achieve it. However, there appears to be a gap in the study of the implications for Australia's domestic energy system in terms of energy security and export economic vulnerability. The objective of this paper is to develop a conceptual framework for the implications of becoming a major hydrogen exporter on Australia's energy system. Various green hydrogen export scenarios for Australia were compared, and the most recent and comprehensive was selected as the basis for further examination for domestic energy system impacts. In this scenario, 248.5 GW of new renewable electricity generation capacity was estimated to be required by 2050 to produce the additional 867 TWh required for an electrolyser output of 2088 PJ of green hydrogen for export, which will comprise 55.9% of Australia's total electricity demand at that time. The characteristics of comparative export-oriented resources and their interactions with the domestic economy and energy system are then examined through the lens of the resource curse hypothesis, and the LNG and aluminium industries. These existing resource export frameworks are reviewed for applicability of specific factors to export-oriented green hydrogen production, with applicable factors then compiled into a novel conceptual framework for exporter domestic implications from large-scale exports of green hydrogen. The green hydrogen export superpower (2050) scenario is then quantitatively assessed using the established indicators for energy exporter vulnerability and domestic energy security, comparing it to Australia's 2019 energy exports profile. This assessment finds that in almost all factors, exporter vulnerability is reduced, and domestic energy security is enhanced by the transition from fossil fuel exports to green hydrogen, with the exception of an increase in exposure of the domestic energy system to international market forces. [ABSTRACT FROM AUTHOR]

The war in Ukraine caused Europe to more than double its imports of liquefied natural gas (LNG) in only one year. In addition, imported LNG remains a crucial source of energy for resource-poor countries, such as Japan, where LNG imports satisfy about a quarter of the country’s primary energy demand. However, an increasing number of countries are formulating stringent decarbonization plans. Liquefied hydrogen and liquefied ammonia coupled with carbon capture and storage (LH _2 -CCS, LNH _3 -CCS) are emerging as the front runners in the search for low-carbon alternatives to LNG. Yet, little is currently known about the full environmental profile of LH _2 -CCS and LNH _3 -CCS because several characteristics of the two alternatives have only been analyzed in isolation in previous work. Here we show that the potential of these fuels to reduce greenhouse gas (GHG) emissions throughout the supply chain is highly uncertain. Our best estimate is that LH _2 -CCS and LNH _3 -CCS can reduce GHG emissions by 25%–61% relative to LNG assuming a 100 year global warming potential. However, directly coupling LNG with CCS would lead to substantial GHG reductions on the order of 74%. Further, under certain conditions, emissions from LH _2 -CCS and LNH _3 -CCS could exceed those of LNG, by up to 44%. These results question the suitability of LH _2 -CCS and LNH _3 -CCS for stringent decarbonization purposes.

Given the urgency to decarbonize global energy systems, governments and industry are moving ahead with efforts to increase deployment of hydrogen technologies, infrastructure, and applications at an unprecedented pace, including USD billions in national incentives and direct investments. While zero- and low-carbon hydrogen hold great promise to help solve some of the world's most pressing energy challenges, hydrogen is also an indirect greenhouse gas whose warming impact is both widely overlooked and underestimated. This is largely because hydrogen's atmospheric warming effects are short-lived – lasting only a couple decades – but standard methods for characterizing climate impacts of gases consider only the long-term effect from a one-time pulse of emissions. For gases whose impacts are short-lived, like hydrogen, this long-term framing masks a much stronger warming potency in the near to medium term. This is of concern because hydrogen is a small molecule known to easily leak into the atmosphere, and the total amount of emissions (e.g., leakage, venting, and purging) from existing hydrogen systems is unknown. Therefore, the effectiveness of hydrogen as a decarbonization strategy, especially over timescales of several decades, remains unclear. This paper evaluates the climate consequences of hydrogen emissions over all timescales by employing already published data to assess its potency as a climate forcer, evaluate the net warming impacts from replacing fossil fuel technologies with their clean hydrogen alternatives, and estimate temperature responses to projected levels of hydrogen demand. We use the standard global warming potential metric, given its acceptance to stakeholders, and incorporate newly published equations that more fully capture hydrogen's several indirect effects, but we consider the effects of constant rather than pulse emissions over multiple time horizons. We account for a plausible range of hydrogen emission rates and include methane emissions when hydrogen is produced via natural gas with carbon capture, usage, and storage (CCUS) ("blue" hydrogen) as opposed to renewables and water ("green" hydrogen). For the first time, we show the strong timescale dependence when evaluating the climate change mitigation potential of clean hydrogen alternatives, with the emission rate determining the scale of climate benefits or disbenefits. For example, green hydrogen applications with higher-end emission rates (10 %) may only cut climate impacts from fossil fuel technologies in half over the first 2 decades, which is far from the common perception that green hydrogen energy systems are climate neutral. However, over a 100-year period, climate impacts could be reduced by around 80 %. On the other hand, lower-end emissions (1 %) could yield limited impacts on the climate over all timescales. For blue hydrogen, associated methane emissions can make hydrogen applications worse for the climate than fossil fuel technologies for several decades if emissions are high for both gases; however, blue hydrogen yields climate benefits over a 100-year period. While more work is needed to evaluate the warming impact of hydrogen emissions for specific end-use cases and value-chain pathways, it is clear that hydrogen emissions matter for the climate and warrant further attention from scientists, industry, and governments. This is critical to informing where and how to deploy hydrogen effectively in the emerging decarbonized global economy. [ABSTRACT FROM AUTHOR]

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In order to achieve greenhouse gas neutrality, hydrogen generated from renewable sources will play an important role. Additionally, as underlined in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), new technologies to remove greenhouse gases from the atmosphere are required on a large scale. A novel concept for hydrogen production with net negative emissions referred to as HyBECCS (Hydrogen Bioenergy with Carbon Capture and Storage) combines these two purposes in one technological approach. The HyBECCS concept combines biohydrogen production from biomass with the capture and storage of biogenic carbon dioxide. Various technology combinations of HyBECCS processes are possible, whose ecological effects and economic viability need to be analyzed in order to provide a basis for comparison and decision‐making. This paper presents fundamentals for the techno‐economic and environmental evaluation of HyBECCS approaches. Transferable frameworks on system boundaries as well as emission, cost, and revenue streams are defined and specifics for the application of existing assessment methods are elaborated. In addition, peculiarities concerning the HyBECCS approach with respect to political regulatory measures and interrelationships between economics and ecology are outlined. Based on these considerations, two key performance indicators (KPIs) are established, referred to as levelized cost of carbon‐negative hydrogen (LCCNH) and of negative emissions (LCNE). Both KPIs allow deciding whether a specific HyBECCS project is economically viable and allows its comparison with different hydrogen, energy provision, or negative emission technologies (NETs). Carbon‐negative hydrogen production referred to as HyBECCS (Hydrogen Bioenergy with Carbon Capture and Storage) combines hydrogen production from biomass with the capture and storage of biogenic carbon dioxide. Various technology combinations of HyBECCS processes are possible, whose ecological effects and economic viability need to be analysed. This paper presents fundamentals for the techno‐economic and environmental evaluation of HyBECCS approaches. Transferable frameworks on system boundaries as well as emission, cost and revenue streams are defined and specifics for the application of existing assessment methods are elaborated. [ABSTRACT FROM AUTHOR]

Sustainable Development Goal 7 highlights the importance of affordable, reliable, and sustainable energy. Transition to clean energy is vital for achieving climate action goals. Hydrogen can serve as a clean energy carrier, with the potential to decarbonize industry, transportation, and other sectors. As of 2021, hydrogen was mainly produced using fossil fuels (grey hydrogen), and only about 1 % of global hydrogen output was produced with renewable energy (green hydrogen). The transition to green hydrogen requires new hydrogen production, storage, and distribution facilities which is challenging to implement due to a lack of associated infrastructure and high upfront costs. This study highlighted barriers and opportunities for hydrogen technologies by reviewing evidence and establishing links with the Sustainable Development Goals (SDGs). The review identified fifty-two opportunities and forty-six challenges linked to SDGs1, 2, 4.6, 7, 9, 11, 12 and 13. Out of all the hydrogen production technologies green hydrogen was the most common choice noted in the. Technical opportunities for green hydrogen production were found to have the potential to positively impact society and environment, but high costs were noted to be a barrier. To reduce economic barriers, recommendations include analysing the impact of subsidies and working further on the development of policies and regulations to support the scaling-up of green hydrogen systems. [Display omitted] • Hydrogen supports SDG 7 ambitions, but high costs and a lack of existing infrastructure noted as barriers. • Review identifies fifty-two opportunities and forty-six challenges connecting hydrogen with SDGs. • Hydrogen presents sustainability synergies (environmental and social) and trade-offs (economic). • Green hydrogen is the most common solution identified in literature with the potential to support SDGs. • Need for subsidies to support scale up of green hydrogen. [ABSTRACT FROM AUTHOR]

Summary: Nuclear power plants provide clean, carbon free, stable, reliable electricity and can offer nonelectric products and services via cogeneration operations to multiple sectors. This contributes to decarbonization of the current energy and industrial systems, supports climate change mitigation and adaptation efforts and ensures sustainable development over the long term, according to the United Nations Sustainable Development Goals (UN SDGs) framework and the provisions of the Conference of Parties 21 (COP21) Paris Agreement, 2015. This work surveys the potential role of nuclear cogeneration projects in meeting these objectives based on the current technological landscape. It focuses on nuclear assisted desalination for freshwater production and electrolytic hydrogen production as the use cases and suggests an assessment framework for their holistic evaluation. New integrated metrics and multi‐criteria performance indicators beyond the levelized cost of production are developed to quantify the likely multi‐dimensional impacts of such projects. The use of these for screening alternatives illustrates the fact that depending on weightage given to different criteria, different technologies may appear to be better suited to deployment under given set of conditions. These metrics are expected to be useful for creation of a decision support system for deployment of nuclear cogeneration projects. [ABSTRACT FROM AUTHOR]

As a secondary energy source, hydrogen produced by water electrolysis is a promising way to sustainably use electricity generated from primary renewable resources. Thereby, hydrogen is not only a highly relevant feedstock for producing chemical products, such as fertilizers and platform chemicals, but also a valuable energy carrier that can be readily transported and stored. This study explores how transporting renewable hydrogen via pipeline from regions with high renewable energy potential to large consumer centers can help overcome current challenges in ensuring a climate-friendly renewable energy supply. To this end, this work assesses the environmental impacts of cross-border hydrogen supply chains relative to the attained operating hours of local hydrogen production and the required hydrogen transport distance via pipeline. Environmental hotspots along the hydrogen supply chain and the main parameters affecting the overall environmental impact were identified. Remarkably, an environmental trade-off emerges: the most suitable local conditions for producing renewable hydrogen need to be balanced against the distance of hydrogen transport to consumers. Nonetheless, the relevance of the transport distance decreases with an increasing share of renewable energies in the electricity mix for operating the compressor stations of the pipeline network. Considering the ongoing transition towards renewable power generation technologies, our results indicate that long-distance hydrogen transport via pipeline is environmentally justified provided that the share of renewable energies used to operate the compressor stations increases. • Renewable hydrogen supply chains are associated with environmental impacts. • Critical parameters focus on hotspots along the hydrogen supply chain. • Regions with high renewable energy potential are ideal for hydrogen production. • Benefits increase as the difference in renewable energy potential increases. • Distance becomes less relevant as energy transition progresses. [ABSTRACT FROM AUTHOR]

Rapidly increasing catastrophic environmental incidents and changes in global climate have compelled researchers to take proactive measures for climate change mitigation. Consequently, reducing greenhouse gas emissions has become one of the most significant global targets. The transportation sector has a massive carbon footprint accounting for 22% of the total carbon dioxide emissions. In this regard, road transport contributes the largest fraction of the total emissions within the transportation sector. Conversely, the railway which is the cleanest form of transportation contributes slightly more than 1% of the total emissions. Moreover, since most of the rail systems are operated by government or private companies, it is relatively convenient to implement policies and replace conventional technology with environmentally friendly ones. This could be achieved by taking certain measures from technical and operational viewpoints for conserving energy to lower the carbon intensity of all transport modalities. Hence, this review paper focuses on investigating the railway sector to encourage a modal shift to the least carbon-intensive option. This study provides a critical review of the past and present rail technologies in terms of the environmental, economic, social, and technical perspectives. Moreover, a comparative assessment of the various locomotive types has been performed. The results reveal that battery-hydrogen hybrid locomotives are the best choice to be considered as a future locomotive technology. Hydrogen locomotives have the potential to be a promising alternative to diesel railway locomotives. However, certain technical barriers need to be overcome to enhance the overall system's performance and reliability to further improve the viability of its deployment in the railway sector. [Display omitted] • A critical review of the various rail technologies is provided through different viewpoints. • The assessment constitutes environmental, economic, social, and technical perspectives. • A decision-support tool for comparison of four rail technologies is also developed. • Battery-hydrogen hybrid locomotive results in the highest score of 1.47. • Standalone hydrogen locomotive results in the second highest score of 1.38. [ABSTRACT FROM AUTHOR]

Achieving net zero greenhouse gas emissions is very challenging. Given the limitations in the direct use of renewable energy for heat and mobility, electrification of the broad economy seems a must, provided electricity supply is CO2-free. The recent cost reductions of solar and wind technologies, their immense potential, and the improvement in electric technologies for industry and transport, open new avenues for achieving humankind's climate mitigation goals. However, a large fraction of the best solar and wind resources are situated far away from large consumption centres. Moreover, the variability of solar and wind and the shortcomings of electricity storage limit the scope for direct electrification. Indirect electrification through electrolysis of water and the use of hydrogen and hydrogen-rich feedstock and fuels may in all end-use sectors complement electrification where it appears excessively challenging, serve the power sector itself, and also help harness remote resources and ship them to consumers or industries. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Comparing alternative fuels with potential for low-carbon intensities. • Technical process design and economic assessment of hydrogen and CO 2 -based fuels. • Environmental life-cycle assessment considering the full carbon cycle. • Identification of methodological challenges in carbon accounting of CO 2 -fuels. Abstract The deployment of low-emission alternative fuels is crucial to decarbonise the transport sector. A number of alternatives like hydrogen or dimethyl ether/methanol synthesised using CO 2 as feedstock for fuel production (hereafter refer to "CO 2 -based fuels") have been proposed to combat climate change. However, the decarbonisation potential of CO 2 -based fuels is under debate because CO 2 is re-emitted to the atmosphere when the fuel is combusted; and the majority of hydrogen still relies on fossil resources, which makes its prospects of being a low-carbon fuel dependent on its manufacturing process. First, this paper investigates the relative economic and environmental performance of hydrogen (produced from conventional steam methane reforming and produced via electrolysis using renewable energy), and CO 2 -based fuels (dimethyl ether and methanol), considering the full carbon cycle. The results reveal that hydrogen produced from steam methane reforming is the most economical option and that hydrogen produced via electrolysis using renewables has the best environmental profile. Whereas the idea of CO 2 -based fuels has recently gained much interest, it has for the foreseeable future rather limited practical relevance since there is no favourable combination of cost and environmental performance. This will only change in the long run and requires that CO 2 is of non-fossil origin, i.e. from biomass combustion or captured from air. Second, this paper address unresolved methodological issues in the assessment of CO 2 -based fuels, such as the possible allocation of emissions to the different sectors involved. The outcomes indicate that implementing different allocation approaches substantially influences the carbon footprint of CO 2 -based fuels. To avoid allocation issues, expanding the boundaries including the entire system and is therefore recommended. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen as fuel has been a promising technology toward climate change mitigation efforts. To this end, in this paper we analyze the contribution of hydrogen technology to our future environmental goals. It is assumed that hydrogen is being produced in higher efficiency across time and this is simulated on Global Change Assessment Model (GCAM). The environmental restrictions applied are the expected emissions representative concentration pathways (RCP) 2.6, 4.5, and 6.0. Our results have shown increasing hydrogen production as the environmental constraints become stricter and hydrogen more efficient in being produced. This increase has been quantified and provided on open access as Supporting Information to this manuscript. [ABSTRACT FROM AUTHOR]

This paper attempts to evaluate potential reductions in climate damage following the introduction of hydrogen fuel cell vehicles in Malaysia over the period 2015-2030. The simulation produced interesting results. While gross climate damage under the BAU scenario increased to RM7.1 billion in 2030, the commensurate damage under the slow, moderate and high hydrogen adaptation fell to MYR2.0 billion, MYR1.7 billion and MYR1.2 billion, respectively. CO2 emissions will fall from 214MT under the BAU scenario to 203MT, 176MT and 122MT, respectively, under the slow, moderate and high scenarios, respectively. Although real GDP is expected to stagnate over the period 2015-2030 under all three adaptation scenarios, the welfare benefits are expected to expand from the greening environment. While the high adaptation scenarios offer the best quantitative results, the choice of the intensity of adaptation will depend on the regulatory framework and the extent to which consumers can adapt. [ABSTRACT FROM AUTHOR]

• Discourse analysis on hydrogen of 179 newspaper articles and new multi-sector transition framework. • Most actors generally support hydrogen deployment, but conflicts on use, production method, and imports. • Policymakers highlight economic opportunities and role for climate change mitigation. • Especially NGOs argue that hydrogen is expensive, inefficient, and overestimated in its potential. • Positions range between a restricted use of exclusively green hydrogen, and a wide use including non-green hydrogen. With net-zero emission goals, low-carbon transitions enter a new phase of development, leading to new challenges for policymaking and research. Multiple transitions unfold in parallel across different sectors. This involves a broad range of technologies, while actors engage in increasingly complex discourses. Here, we study the discourses on hydrogen in Germany. Based on the analysis of 179 newspaper articles from 2016 to 2020, we find that a diverse set of actors, including many industry incumbents, speak favorably about hydrogen, emphasizing economic opportunities and its relevance for the energy transition, whereas skeptics highlight its low energy efficiency and expected scarcity. With the help of discourse network analysis, we identify three emerging conflicts around the use, production, and import of hydrogen. We explain these conflicts and the widespread support of incumbents with a conceptual framework that captures the complex interplay of sectoral contexts, specific technologies and actor interests. [ABSTRACT FROM AUTHOR]

[Display omitted] • Climate impacts of e-fuels can vary, depending on the source of electricity, CO 2 and H 2 , and their production technologies. • Today, e-fuels have smaller climate impacts than fossil fuels only if produced with a clean electricity source. • By 2050, stricter climate policies can decarbonize average European electric grid and cut climate impacts of e-fuels by 84%. • Climate change impacts of future e-fuels can be up to 58% lower than those of fossil fuels. • A clean electricity for H 2 production and the use of non-fossil CO 2 are key determinants of the climate benefits of e-fuels. 'E-fuels' or 'synthetic fuels' are hydrocarbon fuels synthesized from hydrogen (H 2) and carbon dioxide (CO 2), where H 2 can be produced via electrolysis of water or steam reforming of natural gas, and CO 2 is captured from the combustion of a fossil or biogenic source or directly from the atmosphere. E-fuels are drop-in substitutes for fossil fuels, but their climate change mitigation benefits are largely unclear. This study evaluates the climate change impacts of e-fuels for aviation by combining different sources of CO 2 and H 2 up to 2050 under two contrasting policy scenarios. The analysis includes different climate metrics and the effects of near-term climate forcers, which are particularly relevant for the aviation sector. Results are produced for European average conditions and for Poland and Norway, two countries with high and low emission intensity from their electricity production mix. E-fuels can either have higher or lower climate change impacts than fossil fuels, depending on multiple factors such as, in order of importance, the electricity mix, the origin of CO 2 , the technology for H 2 production, and the electrolyzer efficiency. The climate benefits are generally higher for e-fuels produced from CO 2 of biogenic origin, while e-fuels produced from CO 2 from direct air capture or fossil fuel combustion require countries with clean electricity to outperform fossil fuels. Synthetic fuels produced from H 2 derived from natural gas have higher impacts than fossil fuels even when coupled with carbon capture and storage, if CO 2 is sourced from fossil fuels or the atmosphere. Climate change impacts of e-fuels improve in the future, and they can all achieve considerable climate change mitigation in 2050 relative to fossil jet fuel, provided that strict climate policy measures are implemented to decarbonize the electricity sector. Under reduced policy efforts, future climate impacts in 2050 of e-fuels from atmospheric or fossil CO 2 are still higher than those of fossil jet fuels with an average European electricity mix. This study shows the conditions to maximize the climate change mitigation benefits of e-fuels, which essentially depend on progressive decarbonization of the electricity sector and on reduced use of CO 2 sourced from fossil fuels. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biofuels are necessary to mitigate the climate impacts in the EU maritime transport. • Impacts of biofuels are heavily dependent on countries' electricity mixes. • Without carbon capture, synthetic natural gas has the highest mitigation potential. • Among carbon-free biofuels, bio-ammonia has the highest mitigation potential. • By 2050, bio-hydrogen can provide the lowest emissions per unit of energy. Alternative fuels are crucial to decarbonize the European maritime transport, but their net climate benefits vary with the type of fuel and production country. In this study, we assess the energy potential and climate change mitigation benefits of using agricultural and forest residues in different European countries for drop-in (Fast Pyrolysis, Hydrothermal Liquefaction, and Gasification to Fischer-Tropsch fuels or Bio-Synthetic Natural Gas) and hydrogen-based biofuels (hydrogen, ammonia, and methanol) with or without carbon capture and storage (CCS). Our results show the combinations of countries and biofuel options that successfully achieve the decarbonization targets set by the FuelEU Maritime initiative for the next years, including a prospective analysis that include technological changes projected for the biofuel supply chains until 2050. With the current technologies, the largest greenhouse gas (GHG) mitigation potential per year at a European scale is obtained with bio-synthetic natural gas and hydrothermal liquefaction. Among carbon-free biofuels, ammonia currently has higher mitigation, but hydrogen can achieve a lower GHG intensity per unit of energy with the projected decarbonization of the electricity mixes until 2050. The full deployment of CCS can further accelerate the decarbonization of the maritime sector. Choosing the most suitable renewable fuels requires a regional perspective and a transition roadmap where countries coordinate actions to meet ambitious climate targets. [ABSTRACT FROM AUTHOR]

Abstract: Gases like CH4, CO2 and H2 may play a key role in establishing a sustainable energy system: CH4 is the least carbon-intensive fossil energy resource; CO2 capture and storage can significantly reduce the climate footprint of especially fossil-based electricity generation; and the use of H2 as energy carrier could enable carbon-free automotive transportation. Yet the construction of large pipeline infrastructures usually constitutes a major and time-consuming undertaking, because of safety and environmental issues, legal and (geo)political siting arguments, technically un-trivial installation processes, and/or high investment cost requirements. In this article we focus on the latter and present an overview of both the total costs and cost components of the distribution of these three gases via pipelines. Possible intricacies and external factors that strongly influence these costs, like the choice of location and terrain, are also included in our analysis. Our distribution cost breakdown estimates are based on transportation data for CH4, which we adjust for CO2 and H2 in order to account for the specific additional characteristics of these two gases. The overall trend is that pipeline construction is no longer subject to significant cost reductions. For the purpose of designing energy and climate policy we therefore know in principle with reasonable certainty what the minimum distribution cost components of future energy systems are that rely on pipelining these gases. We describe the reasons why we observe limited learning-by-doing and explain why negligible construction cost reductions for future CH4, CO2 and H2 pipeline projects can be expected. Cost data of individual pipeline projects may strongly deviate from the global average because of national or regional effects related to the type of terrain, but also to varying costs of labor and fluctuating market prices of components like steel. [Copyright &y& Elsevier]

Abstract: The aim of this study is to examine how the options for producing electricity, fuels, and heat in a carbon-constrained world affect the cost-effectiveness of a range of fuels and propulsion technologies in the transportation sector. GET 7.0, a global energy system model with five end-use sectors, is used for the analysis. We find that an energy system dominated either by solar or by nuclear tends to make biofuels in plug-in hybrids cost-effective. If coal with carbon capture and storage (CCS) dominates the energy system, hydrogen cars, rather than plug-in hybrids tend to become cost-effective. Performing a Monte Carlo simulation, we then show that the general features of our results hold for a wide range of assumptions for the costs of vehicle propulsion technologies (e.g., batteries and fuel cells). However, sufficiently large changes in say the battery costs may overturn the impact of changes in the energy supply system, so that plug-in hybrid vehicles become cost-effective even if coal with CCS dominate the energy supply. We conclude that analyses of future energy carriers and propulsion technologies need to consider developments in the energy supply system. [Copyright &y& Elsevier]

Members of the Green Hydrogen Catapult (GHC), a coalition of leaders in green hydrogen development convened with the support of the UN High Level Champions for Climate Action and hosted by RMI, have announced a commitment for 45GW of electrolysers to be developed with secured financing by 2026, with targeted commissioning in 2027. The initial target set by the coalition at the time of its launch in December 2020 was 25GW. [ABSTRACT FROM AUTHOR]

Reducing greenhouse gas emissions in the transport sector is known to be an important contribution to climate change mitigation. Some parts of the transport sector are particularly difficult to decarbonize; this includes the heavy-duty vehicle sector, which is considered one of the "hard-to-abate" sectors of the economy. Transitioning from diesel trucks to hydrogen fuel cell trucks has been identified as a potential way to decarbonize the sector. However, the current and future costs and efficiencies of the enabling technologies remain unclear. In light of these uncertainties, this paper investigates the investments required to decarbonize New Zealand's heavy-duty vehicle sector with green hydrogen. By combining system dynamics modelling literature and hydrogen transition modelling literature a customized methodology is developed for modelling hydrogen transitions with system dynamics modelling. Results are presented in terms of the investments required to purchase the hydrogen production capacity and the investments required to supply electricity to the hydrogen production systems. Production capacity investments are found to range between 1.59 and 2.58 billion New Zealand Dollars, and marginal electricity investments are found to range between 4.14 and 7.65 billion New Zealand Dollars. These investments represent scenarios in which 71% to 90% of the heavy-duty vehicle fleet are replaced with fuel cell trucks by 2050. The wide range of these findings reflects the large uncertainties in estimates of how hydrogen technologies will develop over the course of the next thirty years. Policy recommendations are drawn from these results, and a clear opportunity for future work is outlined. Most notably, the results from this study should be compared with research investigating the investments required to decarbonize the heavy-duty vehicle sectors with alternative technologies such as battery-electric trucks, biodiesel, and catenary systems. Such a comparison would ensure that the most cost effective decarbonization strategy is employed. [ABSTRACT FROM AUTHOR]

Renewable energy is considered the one of the most promising solutions to meet sustainable development goals in terms of climate change mitigation. Today, we face the problem of further scaling up renewable energy infrastructure, which requires the creation of reliable energy storages, environmentally friendly carriers, like hydrogen, and competitive international markets. These issues provoke the involvement of resource-based countries in the energy transition, which is questionable in terms of economic efficiency, compared to conventional hydrocarbon resources. To shed a light on the possible efficiency of green hydrogen production in such countries, this study is aimed at: (1) comparing key Russian trends of green hydrogen development with global trends, (2) presenting strategic scenarios for the Russian energy sector development, (3) presenting a case study of Russian hydrogen energy project «Dyakov Ust-Srednekanskaya HPP» in Magadan region. We argue that without significant changes in strategic planning and without focus on sustainable solutions support, the further development of Russian power industry will be halted in a conservative scenario with the limited presence of innovative solutions in renewable energy industries. Our case study showed that despite the closeness to Japan hydrogen market, economic efficiency is on the edge of zero, with payback period around 17 years. The decrease in project capacity below 543.6 MW will immediately lead to a negative NPV. The key reason for that is the low average market price of hydrogen ($14/kg), which is only a bit higher than its production cost ($12.5/kg), while transportation requires about $0.96/kg more. Despite the discouraging results, it should be taken into account that such strategic projects are at the edge of energy development. We see them as an opportunity to lead transnational energy trade of green hydrogen, which could be competitive in the medium term, especially with state support. [ABSTRACT FROM AUTHOR]

• NH 3 fueling of a modern SI engine was very successful in terms of performance. • Hydrogen blending results in ignition and flame propagation benefits. • Hydrogen blending should be kept low to maximize the indicated efficiency. • The laminar burning velocity describes well the propagation of the flame. • High unburned NH 3 and NOx emissions need to be mitigated by appropriate techniques. The mitigation of climate change requires the increasing use of variable renewable energy sources. Energy storage and transport solutions will contribute to ensure the stability, reliability, and flexibility of the energy systems in that context. Ammonia is a well-known chemical of formula NH 3 and, amongst other electrofuels, a promising energy carrier and carbon-free combustible fuel. In the present experimental study, engine performance, combustion characteristics and pollutant emissions of a recent spark ignition engine fueled with premixed ammonia/hydrogen/air mixtures were assessed. Gaseous ammonia blends in a wide range of hydrogen fuel fractions and equivalence ratios were tested at two different engine loads. Results show performances comparable with conventional fuel operation when the appropriate promotion strategies are used. Specifically, blending up to 20% hydrogen in the fuel by volume improves the cyclic stability and avoids misfires, while granting the best work output and indicated efficiencies near stoichiometry. Higher hydrogen fractions result in depleted efficiency, attributed to higher wall heat losses. The combustion duration is directly correlated to the LBV of the mixtures, thus being accelerated by hydrogen blending. The accelerating effect of hydrogen is particularly remarkable during the initial stage of the combustion. Hydrogen appears therefore mainly as an ignition promoter. Increasing the engine load improves the furnished work and allows to extend the operating boundaries in terms of mixture composition. [ABSTRACT FROM AUTHOR]