China, People’s Republic

The imperative to address traditional energy crises and environmental concerns has accelerated the need for energy structure transformation. However the variable nature of renewable energy poses challenges in meeting complex practical energy requirements. To address this issue the construction of a multifunctional large-scale stationary energy storage system is considered an effective solution. This paper critically examines the battery and hydrogen hybrid energy storage systems. Both technologies face limitations hindering them from fully meeting future energy storage needs such as large storage capacity in limited space frequent storage with rapid response and continuous storage without loss. Batteries with their rapid response (90%) excel in frequent short-duration energy storage. However limitations such as a selfdischarge rate (>1%) and capacity loss (~20%) restrict their use for long-duration energy storage. Hydrogen as a potential energy carrier is suitable for large-scale long-duration energy storage due to its high energy density steady state and low loss. Nevertheless it is less efficient for frequent energy storage due to its low storage efficiency (~50%). Ongoing research suggests that a battery and hydrogen hybrid energy storage system could combine the strengths of both technologies to meet the growing demand for large-scale long-duration energy storage. To assess their applied potentials this paper provides a detailed analysis of the research status of both energy storage technologies using proposed key performance indices. Additionally application-oriented future directions and challenges of the battery and hydrogen hybrid energy storage system are outlined from multiple perspectives offering guidance for the development of advanced energy storage systems.

The hydrogen energy industry as one of the most important directions for future energy transformation can promote the sustainable development of the global economy and of society. China has raised the development of hydrogen energy to a strategic position. Based on the patent data in the past two decades this study investigates the collaborative innovation relationships in China’s hydrogen energy field using complex network theory. Firstly patent data filed between 2003 and 2023 are analyzed and compared in terms of time geography and institutional and technological dimensions. Subsequently a patent collaborative innovation network is constructed to explore the fundamental characteristics and evolutionary patterns over five stages. Furthermore centrality measures and community detection algorithms are utilized to identify core entities and innovation alliances within the network which reveal that China’s hydrogen energy industry is drifting toward alliance innovation. The study results show the following: (1) the network has grown rapidly in size and scope over the last two decades and evolved from the initial stage to the multi-center stage before forming innovation alliances; (2) core innovative entities are important supports and bridges for China’s hydrogen energy industry and control most resources and maintain the robustness of the whole network; (3) innovation alliances reveal the closeness of the collaborative relationships between innovative entities and the potential landscape of China’s hydrogen energy industry; and (4) most of the innovation alliances cooperate only on a narrow range of technologies which may hinder the overall sustainable growth of the hydrogen energy industry. Thereafter some suggestions are put forward from the perspective of an industrial chain and innovation chain which may provide a theoretical reference for collaborative innovation and the future development and planning in the field of hydrogen energy in China.

Coastal regions have abundant off-shore wind energy resources and surrounding areas have large-scale liquefied natural gas (LNG) receiving stations. From the engineering perspectives there are limitations in unstable off-shore wind energy and fluctuating LNG loads. This article offers a new energy scheme to combine these 2 energy units which uses surplus wind energy to produce hydrogen and use LNG cold energy to liquefy and store hydrogen. In addition in order to improve the efficiency of utilizing LNG cold energy and reduce electricity consumption for liquid hydrogen (LH2) production at coastal regions this article introduces the liquid air energy storage (LAES) technology as the intermediate stage which can stably store the cold energy from LNG gasification. A new scheme for LNG-LAES-LH2 hybrid LH2 production is built. The case study is based on a real LNG receiving station at Hainan province China and this article presents the design of hydrogen production/liquefaction process and carries out the optimizations at key nodes and proves the feasibility using specific energy consumption and exergy analysis. In a 100 MW system the liquid air storage round-trip efficiency is 71.0% and the specific energy consumption is 0.189 kWh/kg and the liquid hydrogen specific energy consumption is 7.87 kWh/kg and the exergy efficiency is 46.44%. Meanwhile the corresponding techno-economic model is built and for a LNGLAES-LH2 system with LH2 daily production 140.4 tons the shortest dynamic payback period is 9.56 years. Overall this novel hybrid energy scheme can produce green hydrogen using a more efficient and economical method and also can make full use of surplus off-shore wind energy and coastal LNG cold energy.

To cope with climate change emerging fuels- hydrogen ammonia and methanol- have been proposed as promising energy carriers that will replace part of the liquefied natural gas (LNG) in future maritime scenarios. Energy efficiency is an important indicator for evaluating the system but the maritime supply system for emerging fuels has yet to be revealed. In this study the energy efficiency of the maritime supply chain of hydrogen ammonia methanol and natural gas is investigated considering processes including production storage loading transport and unloading. A sensitivity analysis of parameters such as ambient temperature storage time pipeline length and sailing time is also carried out. The results show that hydrogen (2.366%) has the highest daily boil-off gas (BOG) rate and wastes more energy than LNG (0.413%) with ammonia and methanol both being lower than LNG. The recycling of BOG is of great importance to the hydrogen supply chain. When produced from renewable energy sources methanol (98.02%) is the most energy efficient followed by ammonia with hydrogen being the least (89.10%). This assessment shows from an energy efficiency perspective that ammonia and methanol have the potential to replace LNG as the energy carrier of the future and that hydrogen requires efficient BOG handling systems to increase competitiveness. This study provides some inspirations for the design of global maritime supply systems for emerging fuels.

The urgency to mitigate greenhouse gas emissions from maritime vessels has intensified due to the increasingly stringent directives set forth by the International Maritime Organization (IMO). These directives specifically address energy efficiency enhancements and emissions reduction within the shipping industry. In this context hydrogen is the much sought after fuel for all the global economies and its applications for transportation and propulsion in particular is crucial for cutting down carbon emissions. Nevertheless the realization of hydrogen-powered vessels is confronted by substantial technical hurdles that necessitate thorough examination. This study undertakes a comprehensive analysis encompassing diverse facets including distinct variations of hydrogen fuel cells hydrogen internal combustion engines safety protocols associated with energy storage as well as the array of policies and commercialization endeavors undertaken globally for the advancement of hydrogen-propelled ships. By amalgamating insights from these multifaceted dimensions this paper adeptly encapsulates the myriad challenges intrinsic to the evolution of hydrogen-fueled maritime vessels while concurrently casting a forward-looking gaze on their prospective trajectory.

In this paper a two-layer optimization approach is proposed to facilitate the multi-energy complementarity and coupling and optimize the system configuration in an electric-hydrogen-integrated energy system (EH-IES). Firstly an EH-IES with virtual energy storage is proposed to reduce the cost of physical energy storage equipment. Secondly a two-layer optimal allocation method is proposed under a multi-timescale strategy to examine the comprehensive evaluation index of environmental protection and economy. The upper layer utilizes the NSGA-II multi-objective optimization method for system capacity allocation while the lower layer performs economic dispatch at the lowest cost. Ultimately the output includes the results of the equipment capacity allocation of the EH-IES that satisfies the reliability constraint interval and the daily scheduling results of the equipment. The results demonstrate that the electric-hydrogen-integrated energy system with the coupling of multiple energy equipment not only enhances the utilization of renewable energy sources but also reduces the usage of fossil energy and improves the system’s reliability.

Industry is the biggest sector of energy consumption and greenhouse gas emissions whose decarbonisation is essential to achieve the Sustainable Development Goals. Carbon capture energy efficiency improvement and hydrogen are among the main strategies for industrial decarbonization. However novel approaches are needed to address the key requirements and differences between sectors to ensure they can work together to well integrate industrial decarbonisation with heat CO2 and hydrogen. The emerging Calcium Looping (CaL) is attracting interest in designing CO2-involved chemical processes for heat capture and storage. The reversibility relatively high-temperature (600 to 900 ◦C) and high energy capacity output as well as carbon capture function make CaL well-fit for CO2 capture and utilisation and waste heat recovery from industrial flue gases. Meanwhile methane dry reforming (MDR) is a promising technology to produce blue hydrogen via the consumption of two major greenhouse gases i.e. CO2 and CH4. It has great potential to combine the two technologies to achieve insitu CO2 utilization with multiple benefits. In this paper progresses on the reaction conditions and performance of CaL for CO2 capture and industrial waste heat recovery as well as MDR were screened. Secondly recent approaches to CaL-MDR synergy have been reviewed to identify the advantages. The major challenges in such a synergistic process include MDR catalyst deactivation CaL sorbents sintering and system integration. Thirdly the paper outlooks future work to explore a rational design of a multi-function system for the proposed synergistic process.

Proton exchange membrane fuel cells (PEMFCs) are attracting attention for their green energy-saving and high-efficiency advantages becoming one of the future development trends of renewable energy utilization. However there are still deficiencies in the gas supply system control strategy that plays a crucial role in PEMFCs which limits the rapid development and application of PEMFCs. This paper provides a comprehensive and in-depth review of the PEMFC air delivery system (ADS) and hydrogen delivery system (HDS) operations. For the ADS the advantages and disadvantages of the oxygen excess ratio (OER) oxygen pressure and their decoupling control strategies are systematically described by the following three aspects: single control hybrid control and intelligent algorithm control. Additionally the optimization strategies of the flow field or flow channel for oxygen supply speeds and distribution uniformity are compared and analyzed. For the HDS a systematic review of hydrogen recirculation control strategies purge strategies and hydrogen flow control strategies is conducted. These strategies contribute a lot to improving hydrogen utilization rates. Furthermore hydrogen supply pressure is summarized from the aspects of hybrid control and intelligent algorithm control. It is hoped to provide guidance or a reference for research on the HDS as well as the ADS control strategy and optimization strategy

One of the major challenges in harnessing energy from renewable sources like wind and solar is their intermittent nature. Energy production from these sources can vary based on weather conditions and time of day making it essential to store surplus energy for later use when there is a shortfall. Energy storage systems play a crucial role in addressing this intermittency issue and ensuring a stable and reliable energy supply. Green hydrogen sourced from renewables emerges as a promising solution to meet the rising demand for sustainable energy addressing the depletion of fossil fuels and environmental crises. In the present study underground hydrogen storage in various geological formations (aquifers depleted hydrocarbon reservoirs salt caverns) is examined emphasizing the need for a detailed geological analysis and addressing potential hazards. The paper discusses challenges associated with underground hydrogen storage including the requirement for extensive studies to understand hydrogen interactions with microorganisms. It underscores the importance of the issue with a focus on reviewing the the various past and present hydrogen storage projects and sites as well as reviewing the modeling studies in this field. The paper also emphasizes the importance of incorporating hybrid energy systems into hydrogen storage to overcome limitations associated with standalone hydrogen storage systems. It further explores the past and future integrations of underground storage of green hydrogen within this dynamic energy landscape.

All diesel-only trains in the UK will be phased out by 2040. Hydrogen and ammonia emerge as alternative zerocarbon fuel for greener railway. Solid Oxide Fuel Cells (SOFCs) provide an alternative prime mover option which efficiently convert zero-carbon fuels into electricity without emitting nitrogen oxides (NOx) unlike traditional engines. Superior to Proton Exchange Membrane Fuel Cells (PEMFCs) in efficiency SOFCs fulfil MW-scale power needs and can use ammonia directly. This study investigates innovative strategies for integrating SOFCs into hybrid rail powertrains using hydrogen or ammonia. Utilizing an optimization framework incorporating Particle Swarm Optimization (PSO) the study aims to minimize operational costs while considering capital and replacement expenditures powertrain performance and component sizing. The findings suggest that hybrid powertrains based on ammonia-fueled SOFCs may potentially reduce costs by 30% compared to their hydrogen counterparts albeit requiring additional space for engine compartments. Ammonia-fueled SOFCs trains also exhibit a 5% higher efficiency at End-of-Life (EoL) showing less performance degradation than those powered by hydrogen. The State of Charge (SoC) of the batteries in range of 30–70% for both cases is identified as most costeffective.

The seal and weight of the Type IV hydrogen storage vessel are the key problems restricting the safety and driving range of fuel cell vehicles. The boss as a metal medium connecting the inner liner of the Type IV hydrogen storage vessel with the external pipeline affects the sealing performance of the Type IV hydrogen storage vessel and there is no academic research on the weight of the boss. Therefore according to the force characteristics of the boss this paper divides the upper and lower areas (valve column and plate). The valve column with seal optimization and light weight is manufactured with a 3D printing additive while the plate bearing and transferring the internal pressure load is manufactured by forging. Firstly a two-dimensional axisymmetric simulation model of the sealing ring was established and the effects of different compression rates on its seal performance were analyzed. Then the size and position of the sealing groove were sampled simulated and optimized based on the Latin Hypercube method and the reliability of the optimal seal structure was verified by experiments. Finally the Solid Isotropic Material with Penalization (SIMP) topology method was used to optimize the weight of the boss with optimal sealing structure and the reconstructed model was checked and analyzed. The results show that the weight of the optimized boss is reduced by 9.6%.

Power-to-gas technology provides an emerging pathway for promoting green and lowcarbon transformation of energy systems. Through the processes of electrolyzing water and the methanation reaction it converts surplus renewable energy into hydrogen and natural gas offering an effective approach for large-scale integration of renewable energy sources. However the optimization of existing integrated energy systems has yet to finely model the operational characteristics of power-to-gas technology severely limiting the energy conversion efficiency of systems. To address this issue this paper proposes an integrated energy system operation strategy considering the slow dynamic response characteristics of power-to-gas. Firstly based on the technical features of power-to-gas an operational model for electrolyzing water to produce hydrogen is constructed considering the transition relationships among cold start-up hot start-up and production states of a methanation reaction thereby building a power-to-gas operation model considering slow dynamic response characteristics. This model finely reflects the impact of power-to-gas operational states on methanation facilitating accurate representation of the operational states of methanation. Then considering the energy conversion constraints and power balance of various coupled devices within integrated energy systems an optimization model for the operation of the integrated energy system is constructed with the total daily operation cost of the system as the optimization objective. Finally simulation comparisons are conducted to demonstrate the necessity of considering the slow dynamic response characteristics of power-to-gas technology for integrated energy system operation. The case study results indicate that the proposed power-to-gas operation model can accurately simulate the methanation process facilitating the rational conversion of surplus renewable energy into natural gas energy and avoiding misjudgments in system operation costs and energy utilization efficiency.

Experiments are performed in hydrogen-oxygen mixtures at the cryogenic temperature of 77 K with the equivalence ratio of 1.5 and 2.0. The optical fibers pressure sensors and the smoked foils are used to record the flame velocity overpressure evolution curve and detonation cells respectively. The 1st and 2nd shock waves are captured and they finally merge to form a stronger precursor shock wave prior to the onset of detonation. The cryogenic temperature will cause the larger expansion ratio which results in the occurrence of strong flame acceleration. The stuttering mode the galloping mode and the deflagration mode are observed when the initial pressure decreases from 0.50 atm to 0.20 atm with the equivalence ratio of 1.5 and the detonation limit is within 0.25-0.30 atm. The heat loss effect on the detonation limit is analysed. In addition the regularity of detonation cell is investigated and the larger post-shock specific heat ratio !"" and the lower normalized activation energy # at lower initial pressure will cause the more regular detonation cell. Also the detonation cell width is predicted by a model of = ($) ⋅ Δ# and the prediction results are mainly consistent with the experimental results.

To reduce carbon sulfur dioxide (SO2) and nitrogen oxide (NOX) emissions from the integrated energy system (IES) a low carbon optimization strategy for the IES is proposed taking into account carbon SO2 and NOX emissions. Firstly hydrogen production storage and use equipment such as methane reactor electrolysis tank hydrogen fuel cell and hydrogen energy storage are added to the traditional IES to build a multi-energy complementary system of electricity gas cooling thermal and hydrogen. Then this paper introduces a stepped carbon trading mechanism and the model of the emissions of SO2 and NOX. Finally to further reduce its pollutant emissions the model of combined heat and power units and hydrogen fuel cells with adjustable thermoelectric ratio is built. To compare and account for the impact of air pollutant emissions on the optimal low-carbon operation of IES this paper construsted three scenarios with the lowest cost of carbon trading the lowest penalty cost for SO2 and NOX emissions and total operation cost as objective functions respectively The results show that the strategy is effective in reducing air pollutant emissions from integrated energy systems and the outputs of CHP and HFC with adjustable thermoelectric ratios are more flexible and can effectively achieve carbon reduction and pollutant emission reduction.

With the increasing concern about global energy crisis and environmental pollution the integrated renewable energy system has gradually become one of the most important ways to achieve energy transition. In the context of the rapid development of hydrogen energy industry the proportion of hydrogen energy in the energy system has gradually increased. The conversion between various energy sources has also become more complicated which poses challenges to the planning and construction of park-level integrated energy systems (PIES). To solve this problem we propose a bi-level planning model for an integrated energy system with hydrogen energy considering multi-stage investment and carbon trading mechanism. First the mathematical models of each energy source and energy storage in the park are established respectively and the independent operation of the equipment is analyzed. Second considering the operation state of multi-energy coordination a bi-level planning optimization model is established. The upper level is the capacity configuration model considering the variable installation time of energy facilities while the lower level is the operation optimization model considering several typical daily operations. Third considering the coupling relationship between upper and lower models the bi-level model is transformed into a solvable single-level mixed integer linear programming (MILP) model by using Karush–Kuhn–Tucker (KKT) condition and big-M method. Finally the proposed model and solution methods are verified by comprehensive case studies. Simulation results show that the proposed model can reduce the operational cost and carbon emission of PIES in the planning horizon and provide insights for the multi-stage investment of PIES.

Hydrogen is the most promising alternative fuel in the field of engines. Exhaust heat assisted methanol dissociation is an attractive approach for generating hydrogen. In this work simulations are conducted on a compression ignition engine fueled with different proportions of diesel-dissociated methanol gas (DMG) blends at intermediate engine speed full load and 0% EGR ratio. The results reveal that the indicated thermal efficiency and indicated mean effective pressure are greatly enhanced combustion efficiency is increased and regular emissions of CO HC and soot are reduced while NOx emissions are reduced with increased DMG substitution. In addition a simulation is conducted at an intermediate engine speed full load 15% DMG substitution ratio and varying EGR ratios of 0–20%. The results indicate that the dual-fuel engine outperforms the original engine with respect to power fuel economy and regular emissions once an optimal EGR rate is adopted.

As a versatile energy carrier hydrogen possesses tremendous potential to reduce greenhouse emissions and promote energy transition. Global interest in producing hydrogen from renewable energy sources and transporting storing and utilizing hydrogen is rising rapidly. However the high costs of producing clean hydrogen and the uncertain application scenarios for hydrogen energy result in its relatively limited utilization worldwide. It is necessary to find new promising technological paths to drive the development of hydrogen energy. As part of technological innovation emerging technologies have vital features such as prominent impact novelty relatively fast growth etc. Identifying emerging hydrogen-energy-related technologies is important for discovering innovation opportunities during the energy transition. Existing research lacks analysis of the characteristics of emerging technologies. Thus this paper proposes a method combining the latent Dirichlet allocation topic model and hydrogen-energy expert group decision-making. This is used to identify emerging hydrogen-related technology regarding two features of emerging technologies novelty and prominent impact. After data processing topic modeling and analysis the patent dataset was divided into twenty topics. Six emerging topics possess novelty and prominent impact among twenty topics. The results show that the current hotspots aim to promote the application of hydrogen energy by improving the performance of production catalysts overcoming the wide power fluctuations and large-scale instability of renewable energy power generation and developing advanced hydrogen safety technologies. This method efficiently identifies emerging technologies from patents and studies their development trends. It fills a gap in the research on emerging technologies in hydrogen-related energy. Research achievements could support the selection of technology pathways during the low-carbon energy transition.

Arguably one of the most important issues the world is facing currently is climate change. At the current rate of fossil fuel consumption the world is heading towards extreme levels of global temperature rise if immediate actions are not taken. Transforming the current energy system from one largely based on fossil fuels to a carbon-neutral one requires unprecedented speed. Based on the current state of development direct electrification of the future energy system alone is technically challenging and not enough especially in hard-to-abate sectors like heavy industry road trucking international shipping and aviation. This leaves a considerable demand for alternative carbon-neutral fuels such as green ammonia and hydrogen and renewable methanol. From this perspective we discuss the overarching roles of each fuel in reaching net zero emission within the next three decades. The challenges and future directions associated with the fuels conclude the current perspective paper.

Ammonia a molecule that is gaining more interest as a fueling vector has been considered as a candidate to power transport produce energy and support heating applications for decades. However the particular characteristics of the molecule always made it a chemical with low if any benefit once compared to conventional fossil fuels. Still the current need to decarbonize our economy makes the search of new methods crucial to use chemicals such as ammonia that can be produced and employed without incurring in the emission of carbon oxides. Therefore current efforts in this field are leading scientists industries and governments to seriously invest efforts in the development of holistic solutions capable of making ammonia a viable fuel for the transition toward a clean future. On that basis this review has approached the subject gathering inputs from scientists actively working on the topic. The review starts from the importance of ammonia as an energy vector moving through all of the steps in the production distribution utilization safety legal considerations and economic aspects of the use of such a molecule to support the future energy mix. Fundamentals of combustion and practical cases for the recovery of energy of ammonia are also addressed thus providing a complete view of what potentially could become a vector of crucial importance to the mitigation of carbon emissions. Different from other works this review seeks to provide a holistic perspective of ammonia as a chemical that presents benefits and constraints for storing energy from sustainable sources. State-of-the-art knowledge provided by academics actively engaged with the topic at various fronts also enables a clear vision of the progress in each of the branches of ammonia as an energy carrier. Further the fundamental boundaries of the use of the molecule are expanded to real technical issues for all potential technologies capable of using it for energy purposes legal barriers that will be faced to achieve its deployment safety and environmental considerations that impose a critical aspect for acceptance and wellbeing and economic implications for the use of ammonia across all aspects approached for the production and implementation of this chemical as a fueling source. Herein this work sets the principles research practicalities and future views of a transition toward a future where ammonia will be a major energy player.

Solid-state hydrogen storage technology has emerged as a disruptive solution to the “last mile” challenge in large-scale hydrogen energy applications garnering significant global research attention. This paper systematically reviews the Chinese research progress in solid-state hydrogen storage material systems thermodynamic mechanisms and system integration. It also quantitatively assesses the market potential of solid-state hydrogen storage across four major application scenarios: on-board hydrogen storage hydrogen refueling stations backup power supplies and power grid peak shaving. Furthermore it analyzes the bottlenecks and challenges in industrialization related to key materials testing standards and innovation platforms. While acknowledging that the cost and performance of solid-state hydrogen storage are not yet fully competitive the paper highlights its unique advantages of high safety energy density and potentially lower costs showing promise in new energy vehicles and distributed energy fields. Breakthroughs in new hydrogen storage materials like magnesium-based and vanadium-based materials coupled with improved standards specifications and innovation mechanisms are expected to propel solid-state hydrogen storage into a mainstream technology within 10–15 years with a market scale exceeding USD 14.3 billion. To accelerate the leapfrog development of China’s solid-state hydrogen storage industry increased investment in basic research focused efforts on key core technologies and streamlining the industry chain from materials to systems are recommended. This includes addressing challenges in passenger vehicles commercial vehicles and hydrogen refueling stations and building a collaborative innovation ecosystem involving government industry academia research finance and intermediary entities to support the achievement of carbon peak and neutrality goals and foster a clean low-carbon safe and efficient modern energy system.

This paper provides a comprehensive review of the research progress current state-ofthe-art and future research directions of energy storage systems. With the widespread adoption of renewable energy sources such as wind and solar power the discourse around energy storage is primarily focused on three main aspects: battery storage technology electricity-to-gas technology for increasing renewable energy consumption and optimal configuration technology. The paper employs a visualization tool (CiteSpace) to analyze the existing works of literature and conducts an in-depth examination of the energy storage research hotspots in areas such as electrochemical energy storage hydrogen storage and optimal system configuration. It presents a detailed overview of common energy storage models and configuration methods. Based on the reviewed articles the future development of energy storage will be more oriented toward the study of power characteristics and frequency characteristics with more focus on the stability effects brought by transient shocks. This review article compiles and assesses various energy storage technologies for reference and future research.

A compact wireless near-field hydrogen gas sensor is proposed which detects leaking hydrogen near its source to achieve fast responses and high reliability. A semiconductor-type sensing element is implemented in the sensor which can provide a significant response in 100 ms when stimulated by pure hydrogen. The overall response time is shortened by orders of magnitude compared to conventional sensors according to simulation results which will be within 200 ms compared with over 25 s for spatial concentration sensors under the worst conditions. Over 1 year maintenance intervals are enabled by wireless design based on the Bluetooth low energy protocol. The average energy consumption during a single alarm process is 153 µJ/s. The whole sensor is integrated on a 20 × 26 mm circuit board for compact use.

Hydrogen energy is regarded as an ideal solution for addressing climate change issues and an indispensable part of future integrated energy systems. The most environmentally friendly hydrogen production method remains water electrolysis where the electrolyzer constructs the physical interface between electrical energy and hydrogen energy. However few articles have reviewed the electrolyzer from the perspective of power supply topology and control. This review is the first to discuss the positioning of the electrolyzer power supply in the future integrated energy system. The electrolyzer is reviewed from the perspective of the electrolysis method the market and the electrical interface modelling reflecting the requirement of the electrolyzer for power supply. Various electrolyzer power supply topologies are studied and reviewed. Although the most widely used topology in the current hydrogen production industry is still single-stage AC/DC the interleaved parallel LLC topology constructed by wideband gap power semiconductors and controlled by the zero-voltage switching algorithm has broad application prospects because of its advantages of high power density high efficiency fault tolerance and low current ripple. Taking into account the development trend of the EL power supply a hierarchical control framework is proposed as it can manage the operation performance of the power supply itself the electrolyzer the hydrogen energy domain and the entire integrated energy system.

The core of carbon neutrality is the energy structure adjustment and economic structure transformation. Hydrogen energy as a kind of clean energy with great potential has provided important support for the implementation of the carbon peaking and carbon neutrality goals of China. How to achieve the large-range safe and reliable transportation of hydrogen energy with good economic benefits remains the key to limiting the development of hydrogen energy. Using the existing natural gas pipeline network can save many infrastructure construction costs to transport hydrogen-blended natural gas. However due to great differences in the physical and chemical properties of hydrogen and natural gas the transportation of hydrogen-blended natural gas will bring safety risks to the pipeline network operation to a certain extent. In this paper the influences of pipeline transportation of hydrogen-blended natural gas on existing pipelines and parts along the pipelines are analyzed from two aspects of pipe compatibility and hydrogen blending ratio and the safety of pipeline transportation of hydrogen-blended natural gas is summarized from two aspects of leakage and accumulation as well as combustion and explosion. In addition the integrity management of hydrogen-blended natural gas pipelines and the existing relevant standards and specifications are reviewed. This paper points out the shortcomings of current hydrogen-blended natural gas pipeline transportation and gives some relevant suggestions. Hopefully this work can provide a useful reference for developing a hydrogen-blended natural gas pipeline transportation system.

With the large-scale integration of intermittent renewable energy generation presented by wind and photovoltaic power the security and stability of power system operations have been challenged. Therefore this article proposes a control strategy of a hydrogen production system based on renewable energy power generation to enable the fast frequency response of a grid. Firstly based on the idea of virtual synchronous control a fast frequency response control transformation strategy for the grid-connected interface of hydrogen production systems for renewable energy power generation is proposed to provide active power support when the grid frequency is disturbed. Secondly based on the influence of VSG’s inertia and damping coefficient on the dynamic characteristics of the system a VSG adaptive control model based on particle swarm optimization is designed. Finally based on the Matlab/Simulink platform a grid-connected simulation model of hydrogen production systems for renewable energy power generation is established. The results show that the interface-transformed electrolytic hydrogen production device can actively respond to the frequency disturbances of the power system and participate in primary frequency control providing active support for the frequency stability of the power system under high-percentage renewable energy generation integration. Moreover the system with parameter optimization has better fast frequency response control characteristics.

Hydrogen–gasoline hybrid refueling stations can minimize construction and management costs and save land resources and are gradually becoming one of the primary modes for hydrogen refueling stations. However catastrophic consequences may be caused as both hydrogen and gasoline are flammable and explosive. It is crucial to perform an effective risk assessment to prevent fire and explosion accidents at hybrid refueling stations. This study conducted a risk assessment of the refueling area of a hydrogen–gasoline hybrid refueling station based on the improved Accident Risk Assessment Method for Industrial Systems (ARAMIS). An improved probabilistic failure model was used to make ARAMIS more applicable to hydrogen infrastructure. Additionally the accident consequences i.e. jet fires and explosions were simulated using Computational Fluid Dynamics (CFD) methods replacing the traditional empirical model. The results showed that the risk levels at the station house and the road near the refueling area were 5.80 × 10−5 and 3.37 × 10−4 respectively and both were within the acceptable range. Furthermore the hydrogen dispenser leaked and caused a jet fire and the flame ignited the exposed gasoline causing a secondary accident considered the most hazardous accident scenario. A case study was conducted to demonstrate the practicability of the methodology. This method is believed to provide trustworthy decisions for establishing safe distances from dispensers and optimizing the arrangement of the refueling area.

Under the background of the power system profoundly reforming hydrogen energy from renewable energy as an important carrier for constructing a clean low-carbon safe and efficient energy system is a necessary way to realize the objectives of carbon peaking and carbon neutrality. As a strategic energy source hydrogen plays a significant role in accelerating the clean energy transition and promoting renewable energy. However the cost and technology are the two main constraints to green hydrogen energy development. Herein the technological development status and economy of the whole industrial chain for green hydrogen energy “production-storage-transportation-use” are discussed and reviewed. After analysis the electricity price and equipment cost are key factors to limiting the development of alkaline and proton exchange membrane hydrogen production technology; the quantity scale and distance of transportation are key to controlling the costs of hydrogen storage and transportation. The application of hydrogen energy is mainly concentrated in the traditional industries. With the gradual upgrading and progress of the top-level design and technology the application of hydrogen energy mainly including traffic transportation industrial engineering energy storage power to gas and microgrid will show a diversified development trend. And the bottleneck problems and development trends of the hydrogen energy industry chain are also summarized and viewed.

This paper presents a review of system design and analysis control strategy optimization and heat and mass integration of integrated solid oxide fuel cell (SOFC) and reciprocating internal combustion engine (ICE) system. Facing the future power-fuel-power path both SOFC and ICE can adapt to a variety of fuels which is one evidence that ICE is amenable to integration with SOFC while SOFC is more efficient cleaner and quieter than ICE. Different system topologies are classified whose dynamic performances are also analyzed. In addition the heat and mass integration of system is discussed. Moreover the combustion modes of ICE which can be applied to steady combustion high efficiency and low emissions are analyzed and compared. Meanwhile the potential and methods of system waste heat recovery are discussed. The exergy analysis energy density and techno-economy are discussed. Finally the results are discussed in the last section with the final conclusion that SOFC-ICE systems are very suitable for long-distance transportation such as maritime and aviation which can also solve problems of the carbon and pollutant emissions with the background of engine cannot be replaced in maritime while the system can adapt a variety of alternative fuels.

Wind and solar energy are the important renewable energy sources while their inherent natures of random and intermittent also exert negative effect on the electrical grid connection. As one of multiple energy complementary route by adopting the electrolysis technology the wind-solar-hydrogen hybrid system contributes to improving green power utilization and reducing its fluctuation. Therefore the moving average method and the hybrid energy storage module are proposed which can smooth the wind-solar power generation and enhance the system energy management. Moreover the optimization of system capacity configuration and the sensitive analysis are implemented by the MATLAB program platform. The results indicate that the 10-min grid-connected volatility is reduced by 38.7% based on the smoothing strategy and the internal investment return rate can reach 13.67% when the electricity price is 0.04 $/kWh. In addition the annual coordinated power and cycle proportion of the hybrid energy storage module are 80.5% and 90% respectively. The developed hybrid energy storage module can well meet the annual coordination requirements and has lower levelized cost of electricity. This method provides reasonable reference for designing and optimizing the wind-solar-hydrogen complementary system.

Magnesium-based hydrogen storage alloys have attracted significant attention as promising materials for solid-state hydrogen storage due to their high hydrogen storage capacity abundant reserves low cost and reversibility. However the widespread application of these alloys is hindered by several challenges including slow hydrogen absorption/desorption kinetics high thermodynamic stability of magnesium hydride and limited cycle life. This comprehensive review provides an in-depth overview of the recent advances in magnesium-based hydrogen storage alloys covering their fundamental properties synthesis methods modification strategies hydrogen storage performance and potential applications. The review discusses the thermodynamic and kinetic properties of magnesium-based alloys as well as the effects of alloying nanostructuring and surface modification on their hydrogen storage performance. The hydrogen absorption/desorption properties of different magnesium-based alloy systems are compared and the influence of various modification strategies on these properties is examined. The review also explores the potential applications of magnesium-based hydrogen storage alloys including mobile and stationary hydrogen storage rechargeable batteries and thermal energy storage. Finally the current challenges and future research directions in this field are discussed highlighting the need for fundamental understanding of hydrogen storage mechanisms development of novel alloy compositions optimization of modification strategies integration of magnesium-based alloys into hydrogen storage systems and collaboration between academia and industry.

As a key link in the application of hydrogen energy hydrogen refueling stations are significant for their safe operation. This paper established a three-dimensional 1:1 model for a seaport hydrogen refueling station in Ningbo City. In this work the CFD software FLUENT was used to study the influence of leakage angles on the leakage of high-pressure hydrogen through a small hole. Considering the calculation accuracy and efficiency this paper adopted the pseudo-diameter model. When the obstacle was far from the leakage hole it had almost no obstructive effect on the jet's main body. Still it affected the hydrogen whose momentum in the outer layer of the jet has been significantly decayed. In this condition there would be more hydrogen in stagnation. Thus the volume of the flammable hydrogen cloud was hardly affected while there was a significant increase in the volume of the hazardous hydrogen cloud. When the obstacle was close to the leakage hole it directly affected the jet's main body. Therefore the volume of the flammable hydrogen cloud increased. However the air impeded the hydrogen jet relatively less because the hydrogen jet contacted the obstacle more quickly. The hydrogen jet blocked by the obstacle still has some momentum. Therefore there was no more hydrogen in stagnation and no significant increase in the volume of the hazardous hydrogen cloud.

Shock-flame interactions (SFI) occur in a variety of combustion scenarios of scientific and engineering interest which can distort the flame extend the flame surface area and subsequently enhance heat release. This process is dominated by Richtmyer-Meshkov instability (RMI) that features the perturbation growth of a density-difference interface (flame) after the shock passage. The main mechanism of RMI is the vorticity deposition results from a misalignment between pressure and density gradients. This paper focuses on the multi-dimensional interactions between shock wave and flame in a hydrogen-air mixture. The simulations of this work were conducted by solving three-dimensional fully-compressible reactive Navier-Stokes equations using a high-order numerical method on a dynamically adapting mesh. The effect of wall friction on the SFI was examined by varying wall boundary condition (free-slip/no-slip) on sidewall. The results show that the global flame perturbation grows faster with the effect of wall friction in the no-slip case than that in the free-slip case in the process of SFI. Two effects of wall friction on SFI were found: (1) flame stretching close to the no-slip wall and (2) damping of local flame perturbation at the no-slip wall. The flame stretch effect leads to a significantly higher growth rate in the global flame perturbation. By contrast the damping effect locally moderates the flame perturbation induced by RMI in close proximity to the no-slip wall because less vorticity is deposited on this part of flame during SFI.

As a clean and renewable energy carrier hydrogen is one of the most promising alternative fuels. Cryogenic compressed hydrogen can achieve high storage density without liquefying hydrogen which has good application prospects. Investigation of the safety problems of cryogenic compressed hydrogen is necessary before massive commercialization. The present study modeled the instantaneous flow field using the Large Eddy Simulation (LES) for cryogenic (50 and 100 K) underexpanded hydrogen jets released from a round nozzle of 1.5 mm diameter at pressures of 0.5-5.0 MPa. The simulation results were compared with the experimental data for validation. The axial and radial concentration and velocity distributions were normalized to show the self-similar characteristics of underexpanded cryogenic jets. The shock structures near the nozzle were quantified to correlate the shock structure sizes to the source pressure and nozzle diameter. The present study on the concentration and velocity distributions of underexpanded cryogenic hydrogen jets is useful for developing safety codes and standards.

Historically it has been a challenge to simulate the experimentally observed cellular structures and marginal behavior of multidimensional hydrogen-oxygen detonations in the presence of losses even with detailed chemistry models. Very recently a quasi-two-dimensional inviscid approach was pursued where losses due to viscous boundary layers were modeled by the inclusion of an equivalent mass divergence in the lateral direction using Fay’s source term formulation with Mirels’ compressible boundary layer solutions. The same approach was used for this study along with the inclusion of thermally perfect detailed chemistry in order to capture the correct ignition sensitivity of the gas to dynamic changes in the thermodynamic state behind the detonation front. In addition the strength of transverse waves and their impact on the detonation front was investigated. Here the detailed San Diego mechanism was applied and it has been found that the detonation cell sizes can be accurately predicted without the need to prescribe specific parameters for the combustion model. For marginal cases where the detonation waves approach their failure limit quasi-stable mode behavior was observed where the number of transverse waves monotonically decreased to a single strong wave over a long enough distance. The strong transverse waves were also found to be slightly weaker than the detonation front indicating that they are not overdriven in agreement with recent studies.

The MC method refuelling protocol in SAE J2601 has been published by the Society of Automotive Engineers (SAE) in order to safely and quickly refuel hydrogen vehicles. For the calculation method of the pressure target to control the refuelling stop we introduced a dual-zone dual-temperature model that distinguishes the hydrogen temperature in the tank from the wall temperature to replace the dual-zone single-temperature model of the original MC method. The total amount of heat transferred by convection between hydrogen and the inner tank wall during the filling process was expressed as an equation of final hydrogen temperature final wall temperature final refuelling time tank inner surface area and the correction factor. The correction factor equations were determined by fitting simulation data from the 0D1D model where hydrogen inside the tank is lumped parameter model (0D) and the tank wall is a one-dimensional model (1D). For the correction factor of the linear equation its first-order coefficient and constant term have a linear relationship with the initial pressure of the storage tank and their R2 values obtained from the fitting are greater than 0.99. Finally we derived a new equation to calculate the final hydrogen temperature which can be combined with the 100% SOC inside the vehicle tank to determine the pressure target. The simulation results show that the final SOC obtained are all greater than 96% using the modified pressure target and the correction factor of the linear equation.

Integrating carbon capture and storage (CCS) technology into an integrated energy system (IES) can reduce its carbon emissions and enhance its low-carbon performance. However the full CCS of flue gas displays a strong coupling between lean and rich liquor as carbon dioxide liquid absorbents. Its integration into IESs with a high penetration level of renewables results in insufficient flexibility and renewable curtailment. In addition integrating split-flow CCS of flue gas facilitates a short capture time giving priority to renewable energy. To address these limitations this paper develops a carbon capture utilization and storage (CCUS) method into which storage tanks for lean and rich liquor and a two-stage power-to-gas (P2G) system with multiple utilizations of hydrogen including a fuel cell and a hydrogen-blended CHP unit are introduced. The CCUS is integrated into an IES to build an electricity–heat–hydrogen–gas IES. Accordingly a deep low-carbon economic optimization strategy for this IES which considers stepwise carbon trading coal consumption renewable curtailment penalties and gas purchasing costs is proposed. The effects of CCUS the twostage P2G system and stepwise carbon trading on the performance of this IES are analyzed through a case-comparative analysis. The results show that the proposed method allows for a significant reduction in both carbon emissions and total operational costs. It outperforms the IES without CCUS with an 8.8% cost reduction and a 70.11% reduction in carbon emissions. Compared to the IES integrating full CCS the proposed method yields reductions of 6.5% in costs and 24.7% in emissions. Furthermore the addition of a two-stage P2G system with multiple utilizations of hydrogen further amplifies these benefits cutting costs by 13.97% and emissions by 12.32%. In addition integrating CCUS into IESs enables the full consumption of renewables and expands hydrogen utilization and the renewable consumption proportion in IESs can reach 69.23%.

This study proposes four kinds of hybrid source–grid–storage systems consisting of pho‐ tovoltaic and wind energy and a power grid including different batteries and hydrogen storage systems for Sanjiao town. HOMER‐PRO was applied for the optimal design and techno‐economic analysis of each case aiming to explore reproducible energy supply solutions for China’s industrial clusters. The results show that the proposed system is a fully feasible and reliable solution for in‐ dustry‐based towns like Sanjiao in their pursuit of carbon neutrality. In addition the source‐side price sensitivity analysis found that the hydrogen storage solution was cost‐competitive only when the capital costs on the storage and source sides were reduced by about 70%. However the hydro‐ gen storage system had the lowest carbon emissions about 14% lower than the battery ones. It was also found that power generation cost reduction had a more prominent effect on the whole system’s NPC and LCOE reduction. This suggests that policy support needs to continue to push for genera‐ tion‐side innovation and scaling up while research on different energy storage types should be en‐ couraged to serve the needs of different source–grid–load–storage systems.

Liquid hydrogen storage is an important way of hydrogen storage and transportation which greatly improves the storage and transportation efficiency due to the high energy density but at the same time brings new safety hazards. In this study the liquid hydrogen leakage in the storage area of a hydrogen production station is numerically simulated. The effects of ambient wind direction wind speed leakage mass flow rate and the mass fraction of gas phase at the leakage port on the diffusion behavior of the liquid hydrogen leakage were investigated. The results show that the ambient wind direction directly determines the direction of liquid hydrogen leakage diffusion. The wind speed significantly affects the diffusion distance. When the wind speed is 6 m/s the diffusion distance of the flammable hydrogen cloud reaches 40.08 m which is 2.63 times that under windless conditions. The liquid hydrogen leakage mass flow rate and the mass fraction of the gas phase have a greater effect on the volume of the flammable hydrogen cloud. As the leakage mass flow rate increased from 5.15 kg/s to 10 kg/s the flammable hydrogen cloud volume increased from 5734.31 m3 to 10305.5 m3 . The installation of a barrier wall in front of the leakage port can limit the horizontal diffusion of the flammable hydrogen cloud elevate the diffusion height and effectively reduce the volume of the flammable hydrogen cloud. This study can provide theoretical support for the construction and operation of hydrogen production stations.

With the rapid development of hydrogen energy worldwide the number of hydrogen energy facilities such as hydrogen refueling stations has grown rapidly in recent years. However hydrogen is prone to leakage accidents during use which could lead to hazards such as fires and explosions. Therefore research on the safety of hydrogen energy facilities is crucial. In this paper a study of high-pressure hydrogen jet flame accidents is conducted for a proposed integrated hydrogen production and refueling station in China. The effects of leakage direction and leakage port diameter on the jet flame characteristics are analyzed and a risk assessment of the flame accident is conducted. The results showed that the death range perpendicular to the flame direction increased from 2.23 m to 5.5 m when the diameter of the leakage port increased from 4 mm to 10 mm. When the diameter of the leakage port is larger than 8 mm the equipment on the scene will be within the boundaries of the damage. The consequences of fire can be effectively mitigated by a reasonable firewall setup to ensure the overall safety of the integrated station.

In the quest to achieve “double carbon” goals the urgency to develop an efficient Integrated Energy System (IES) is paramount. This study introduces a novel approach to IES by refining the conventional Power-to-Gas (P2G) system. The inability of current P2G systems to operate independently has led to the incorporation of hydrogen fuel cells and the detailed investigation of P2G’s dual-phase operation enhancing the integration of renewable energy sources. Additionally this paper introduces a carbon trading mechanism with a refined penalty–reward scale and a detailed pricing tier for carbon emissions compelling energy suppliers to reduce their carbon footprint thereby accelerating the reduction in system-wide emissions. Furthermore this research proposes a flexible adjustment mechanism for the heat-to-power ratio in cogeneration significantly enhancing energy utilization efficiency and further promoting conservation and emission reductions. The proposed optimization model in this study focuses on minimizing the total costs including those associated with carbon trading and renewable energy integration within the combined P2G-Hydrogen Fuel Cell (HFC) cogeneration system. Employing a bacterial foraging optimization algorithm tailored to this model’s characteristics the study establishes six operational modes for comparative analysis and validation. The results demonstrate a 19.1% reduction in total operating costs and a 22.2% decrease in carbon emissions confirming the system’s efficacy low carbon footprint and economic viability.

Amidst the growing imperative to address carbon emissions aiming to improve energy utilization efficiency optimize equipment operation flexibility and further reduce costs and carbon emissions of regional integrated energy systems (RIESs) this paper proposes a low-carbon economic operation strategy for RIESs. Firstly on the energy supply side energy conversion devices are utilized to enhance multi-energy complementary capabilities. Then an integrated demand response model is established on the demand side to smooth the load curve. Finally consideration is given to the RIES’s participation in the green certificate–carbon trading market to reduce system carbon emissions. With the objective of minimizing the sum of system operating costs and green certificate–carbon trading costs an integrated energy system optimization model that considers electricity gas heat and cold coupling is established and the CPLEX solver toolbox is used for model solving. The results show that the coordinated optimization of supply and demand sides of regional integrated energy systems while considering multi-energy coupling and complementarity effectively reduces carbon emissions while further enhancing the economic efficiency of system operations.

This review aims to summarize the recent advancements and prevailing challenges within the realm of hydrogen storage and transportation thereby providing guidance and impetus for future research and practical applications in this domain. Through a systematic selection and analysis of the latest literature this study highlights the strengths limitations and technological progress of various hydrogen storage methods including compressed gaseous hydrogen cryogenic liquid hydrogen organic liquid hydrogen and solid material hydrogen storage as well as the feasibility efficiency and infrastructure requirements of different transportation modes such as pipeline road and seaborne transportation. The findings reveal that challenges such as low storage density high costs and inadequate infrastructure persist despite progress in high-pressure storage and cryogenic liquefaction. This review also underscores the potential of emerging technologies and innovative concepts including metal–organic frameworks nanomaterials and underground storage along with the potential synergies with renewable energy integration and hydrogen production facilities. In conclusion interdisciplinary collaboration policy support and ongoing research are essential in harnessing hydrogen’s full potential as a clean energy carrier. This review concludes that research in hydrogen storage and transportation is vital to global energy transformation and climate change mitigation.

The influence of hydrogen-enriched natural gas (HENG) and CO2 on the mechanical property of X80 pipeline steel were investigated via fatigue crack growth rate (FCGR) tests and density functional theory (DFT) calculations. The results show that the FCGR in H2 was slightly faster than that in HENG while it was slower than that in the N2/CO2/H2 mixtures. The enhanced FCGR by CO2 further increased with the increasing CO2 content. DFT calculation results show that the adsorbed CO2 on the iron surface significantly increased the migration rate of H atoms from surface to subsurface. This promotes the entry of hydrogen into the steel.

The pressing global challenge of climate change necessitates a concerted effort to limit greenhouse gas emissions particularly carbon dioxide. A critical pathway is to replace fossil fuel sources by electrification including transportation. While electrification of light-duty vehicles is rapidly expanding the heavy-duty vehicle sector is subject to challenges notably the logistical drawbacks of the size and weight of high-capacity batteries required for range as well as the time for battery charging. This Perspective highlights the potential of hydrogen fuel-cell vehicles as a viable alternative for heavy-duty road transportation. We evaluate the implications of hydrogen integration into the freight economy energy dynamics and CO2 mitigation and envision a roadmap for a holistic energy transition. Our critical opinion presented in this Perspective is that federal incentives to produce hydrogen could foster growth in the nascent hydrogen economy. The pathway that we propose is that initial focus on operators of large fleets that could control their own fueling infrastructure. This opinion was formed from private discussions with numerous stakeholders during the formation of one of the awarded hydrogen hubs if they focus on early adopters that could leverage the hydrogen supply chain.

The rapid growth of global aviation emissions has significantly impacted the environment leading to an urgent need to use carbon reduction methods. This paper analyzes global aviation’s carbon dioxide (CO2) N2O and CH4 emission changes under different hydrogen energy application paths. The global warming potential over a 100-year period (GWP100) method is used to convert the emissions of N2O and CH4 into CO2-equivalent. Here we report the results: if the global aviation industry begins using hydrogen turbine engines by 2040 it could reduce cumulative CO2-equivalent emissions by 2.217E+10 tons by 2080 which is 2.12% higher than starting hydrogen fuel cell engines in 2045. However adopting hydrogen fuel cell engines 10 years earlier shows greater reduction capabilities than hydrogen turbine engines achieving an accumulated reduction of 3.006E+10 tons of CO2-equivalent emissions. Therefore the timing of adoption notably affects hydrogen fuel cell engines more than hydrogen turbine engines. Delaying adoption makes hydrogen fuel cell engines’ performance lag hydrogen turbine engines.

The UK government plans to phase out pure diesel trains by 2040 and fully decarbonize railways by 2050. Hydrogen fuel cell (HFC) trains electrified trains using pantographs (Electrified Trains) and battery electric multiple unit (BEMU) trains are considered the main solutions for decarbonizing railways. However the range of these decarbonization options’ line upgrade cost advantages is unclear. This paper analyzes the upgrade costs of three types of trains on different lines by constructing a cost model and using particle swarm optimization (PSO) including operating costs and fixed investment costs. For the case of decarbonization of the London St. Pancras to Leicester line the electrified train option is more cost-effective than the other two options under the condition that the service period is 30 years. Then the traffic density range in which three new energy trains have cost advantages on different line lengths is calculated. For route distances under 100 km and with a traffic density of less than 52 trips/day BEMU trains have the lowest average cost while electrified trains are the most costeffective in other ranges. For route distances over 100 km the average cost of HFC trains is lower than that of electrified trains at traffic densities below about 45 trips/day. In addition if hydrogen prices fall by 26 % the cost advantage range of HFC trains will increase to 70 trips per day. For route distances under 100 km BEMU trains still maintain their advantages in terms of lower traffic density.

When offshore wind farms are connected to a hydrogen plant with dedicated transmission lines for example high-voltage direct current the fluctuation of wind speed will influence the efficiency of the alkaline electrolyzer and deteriorate the techno-economic performance. To overcome this issue firstly an additional heating process is adopted to achieve insulation for the alkaline solution when power generated by wind farms is below the alkaline electrolyzer minimum power threshold while the alkaline electrolyzer overload feature is used to generate hydrogen when wind power is at its peak. Then a simplified piecewise model-based alkaline electrolyzer techno-economic analysis model is proposed. The improved economic performance of the islanded green hydrogen system with the proposed operation strategy is verified based on the wind speed data set simulation generated by the Weibull distribution. Lastly the sensitivity of the total return on investment to wind speed parameters was investigated and an islanded green hydrogen system capacity allocation based on the proposed analysis model was conducted. The simulation result shows the total energy utilization increased from 62.0768% to 72.5419% and the return on investment increased from 5.1303%/month to 5.9581%/month when the proposed control strategy is adopted.

Innovative approaches on clean alternative energy sources are important for future decarbonization. Electrification and hydrogen energy are crucial pathways for decarbonization in both transportation and buildings. However life-cycle stage-wise carbon intensity is still unclear for both hydrogen- and electricity-driven energy. Furthermore systematic evaluation on low-carbon transition pathways is insufficient specifically within the Internet of Energy that interfaces hydrogen and electricity. Here a generic approach is proposed for quantifying life-cycle stage-wise carbon intensity of both hydrogen- and electricity-driven energy internets. Life-cycle decarbonization effects on vehicle pathways are compared with traditional vehicles with internal-combustion engines. Techno-economic and environmental feasibility of the future advanced hydrogen-driven Internet of Energy is analyzed based on net present value. The region-wise carbon-intensity map and associated decarbonization strategies will help researchers and policymakers in promoting sustainable development with the hydrogen economy.

The depletion and overuse of fossil fuels present formidable challenge to energy supply system and environment. The human society is in great need of clean renewable and sustainable energy which can guarantee the long-term utilization without leading to escalation of greenhouse effect. Hydrogen as an extraordinary secondary energy is capable of realizing the target of environmental protection and transferring the intermittent primary energy to the application terminal while its nature of low volumetric energy density and volatility need suitable storage method and proper carrier. In this context liquid organic hydrogen carrier (LOHC) among a series of storage methods such as compressed and liquefied hydrogen provokes a considerable amount of research interest since it is proven to be a suitable carrier for hydrogen with safety and stability. However the dehydrogenation of hydrogen-rich LOHC materials is an endothermic process and needs large energy consumption which hampers the scale up of the LOHC system. The heat issue is thus essential to be addressed for fulfilling the potential of LOHC. In this work several strategies of heat intensification and management for LOHC system including the microwave irradiation circulation of exhaust heat and direct LOHC fuel cell are summarized and analyzed to provide suggestions and directions for future research.

Hydrogen energy is regarded as a key path to combat climate change and promote sustainable economic and social development. The fluctuation of renewable energy leads to frequent start/stop cycles in hydrogen electrolysis equipment. However electrochemical energy storage with its fast response characteristics helps regulate the power of hydrogen electrolysis enabling smooth operation. In this study a multi-objective constrained operation optimization model for a wind/battery storage/alkaline electrolyzer system is constructed. Both profit maximization and power abandonment rate minimization are considered. In addition some constraints such as minimum start/stop times upper and lower power limits and input fluctuation limits are also taken into account. Then the non-dominated sorting genetic algorithm II (NSGA-II) algorithm and the entropy method are used to optimize the operation strategy of the hybrid energy system by considering dynamic hydrogen production efficiency and through optimization to obtain the best hydrogen production power of the system under the two objectives. The change in dynamic hydrogen production efficiency is mainly related to the change in electrolyzer power and the system can be better adjusted according to the actual supply of renewable energy to avoid the waste of renewable energy. Our results show that the distribution of Pareto solutions is uniform which indicates the suitability of the NSGA-II algorithm. In addition the optimal solution indicates that the battery storage and alkaline electrolyzer can complement each other in operation and achieve the absorption of wind power. The dynamic hydrogen production efficiency can make the electrolyzer operate more efficiently which paves the way for system optimization. A sensitivity analysis reveals that the profit is sensitive to the price of hydrogen energy.