Applications & Pathways

In the modern world zero-carbon society has become a new buzzword of the era. Many projects have been initiated to develop alternatives not only to the environmental crisis but also to the shortage of fossil fuels. With successful projects in automobile technology hydrogen fuel is now being tested and utilized as a sustainable green fuel in the aviation sector which will lead to zero carbon emission in the future. From the mid-20th century to the early 21st numerous countries and companies have funded multimillion projects to develop hydrogen-fueled aircraft. Empirical data show positive results for various projects. Consequently large companies are investing in various innovations undertaken by researchers under their supervision. Over time the efficiency of hydrogen-fueled aircraft has improved but the lack of refueling stations large production cost and consolidated carbon market share have impeded the path of hydrogen fuel being commercialized. In addition the Unmanned Aerial Vehicle (UAV) is another important element of the Aviation industry Hydrogen started to be commonly used as an alternative fuel for heavy-duty drones using fuel cell technology. The purpose of this paper is to provide an overview of the chronological development of hydrogen-powered aircraft technology and potential aviation applications for hydrogen and fuel cell technology. Furthermore the major barriers to widespread adoption of hydrogen technology in aviation are identified as are future research opportunities.

The electrification of heavy-duty trucks stands as a critical and challenging cornerstone in the low-carbon transition of the transportation sector. This paper employs the total cost of ownership (TCO) as the economic evaluation metric framed within the context of China’s ambitious goals for heavy truck electrification by 2035. A detailed TCO model is developed encompassing not only the vehicles but also their related energy replenishing infrastructures. This comprehensive approach enables a sophisticated examination of the economic feasibility for different deployment contexts of both fuel cell and battery electric heavy-duty trucks emphasizing renewable energy utilization. This study demonstrates that in the context where both fuel cell components and hydrogen energy are costly fuel cell trucks (FCTs) exhibit a significantly higher TCO compared to battery electric trucks (BETs). Specifically for a 16 ton truck with a 500 km range the TCO for the FCT is 0.034 USD/tkm representing a 122% increase over its BET counterpart. In the case of a 49 ton truck designed for a 1000 km range the TCO for the FCT is 0.024 USD/tkm marking a 36% premium compared to the BET model. The technological roadmap suggests a narrowing cost disparity between FCTs and BETs by 2035. For the aforementioned 16 ton truck model the projected TCO for the FCT is expected to be 0.016 USD/tkm which is 58% above the BET and for the 49 ton variant it is anticipated at 0.012 USD per ton-kilometer narrowing the difference to just 4.5% relative to BET. Further analysis within this study on the influences of renewable energy pricing and operational range on FCT and BET costs highlights a pivotal finding: for the 49 ton truck achieving TCO parity between FCTs and BETs is feasible when renewable energy electricity prices fall to 0.022 USD/kWh or when the operational range extends to 1890 km. This underscores the critical role of energy costs and efficiency in bridging the cost gap between FCTs and BETs.

System durability is crucial for the successful commercialization of polymer electrolyte fuel cells (PEFCs) in fuel cell electric vehicles (FCEVs). Besides conventional electrochemical cycling durability during long-term operation the effect of operation in cold climates must also be considered. Ice formation during start up in sub-zero conditions may result in damage to the electrocatalyst layer and the polymer electrolyte membrane (PEM). Here we conduct accelerated cold start cycling tests on prototype fuel cell stacks intended for incorporation into commercial FCEVs. The effect of this on the stack performance is evaluated the resulting mechanical damage is investigated and degradation mechanisms are proposed. Overall only a small voltage drop is observed after the durability tests only minor damage occurs in the electrocatalyst layer and no increase in gas crossover is observed. This indicates that these prototype fuel cell stacks successfully meet the cold start durability targets for automotive applications in FCEVs.

Hydrogen is an emerging technology changing the context of heating with cleaner combustion than traditional fossil fuels. Studies indicate the potential to repurpose the existing natural gas infrastructure offering consumers a sustainable economically viable option in the future. The integration of hydrogen in combined heat and power systems could provide residential energy demand and reduce environmental emissions. However the widespread adoption of hydrogen will face several challenges such as carbon dioxide emissions from the current production methods and the need for infrastructure modification for transport and safety. Researchers indicated the viability of hydrogen in decarbonizing heat while some studies also challenged its long-term role in the future of heating. In this paper a comprehensive literature review is carried out by identifying the following key aspects which could impact the conclusion on the overall role of hydrogen in heat decarbonization: (i) a holistic view of the energy system considering factors such as renewable integration and system balancing; (ii) consumer-oriented approaches often overlook the broader benefits of hydrogen in emission reduction and grid stability; (iii) carbon capture and storage scalability is a key factor for large-scale production of low-emission blue hydrogen; (iv) technological improvements could increase the cost-effectiveness of hydrogen; (v) the role of hydrogen in enhancing resilience especially during extreme weather conditions raises the potential of hydrogen as a flexible asset in the energy infrastructure for future energy supply; and finally when considering the UK as a basis case (vi) incorporating factors such as the extensive gas network and unique climate conditions necessitates specific strategies.

Proton Exchange Membrane Fuel Cells (PEMFCs) are seen as an alternative for heavy-duty transportation electrification. Powered by a green hydrogen source they can provide high efficiency and low carbon emissions compared to traditional fuels. However to be competitive these systems require high reliability when operated in real-life conditions as well as safe and efficient operating management. In order to achieve these goals the X-in-the-loop (also called model-based design) methodology is well suited. It has been largely adopted for PEMFC system development and optimisation as they are complex multi-component systems. In this paper a systematic analysis of the scientific literature is conducted to review the methodology implementation for the design and improvement of the PEMFC systems. It exposes a precise definition of each development step in the methodology. The analysis shows that it can be employed in different ways depending on the subsystems considered and the objectives sought. Finally gaps in the literature and technical challenges for fuel cell systems that should be addressed are identified.

There is renewed interest in hydrogen as an alternative fuel for aero engines due to their perceived environmental and performance benefits compared to jet fuel. This paper presents a cycle thermal performance energy and creep life assessment of hydrogen compared with jet fuel using a turbofan aero engine. The turbofan cycle performance was simulated using a code developed by the authors that allows hydrogen and jet fuel to be selected as fuel input. The exergy assessment uses both conservations of energy and mass and the second law of thermodynamics to understand the impact of the fuels on the exergy destruction exergy efficiency waste factor ratio environmental effect factor and sustainability index for a turbofan aero engine. Finally the study looks at a top-level creep life assessment on the high-pressure turbine hot section influenced by the fuel heating values. This study shows performance (64% reduced fuel flow rate better SFC) and more extended blade life (15% increase) benefits using liquefied hydrogen fuel which corresponds with other literary work on the benefits of LH2 over jet fuel. This paper also highlights some drawbacks of hydrogen fuel based on previous research work and gives recommendations for future work aimed at maturing the hydrogen fuel concept in aviation.

Decarbonisation of heavy haul rail is an essential contributor to a zero-emissions future. However the transition from diesel to battery locomotives is not always practical given the unique characteristics of each haul. This paper demonstrates the limitations of state-of-the-art batteries using real-world data from multiple locomotives operating in Australian rail freight. An energy model was developed to assess each route’s required energy and potential regenerated energy. The tractive and regenerative battery energy mass and cost were determined using data from the energy model coupled with battery specifications. The feasibility of implementing lithium iron phosphate (LFP) nickel manganese cobalt (NMC) and lithium titanium oxide (LTO) chemistries was explored based on cost energy density cycle lifespan and locomotive data. LFP was identified as the most suitable current battery solution based on current chemistries. Further examination of the energy demands and associated mass/volume constraints concluded that three platforms are required for heavy haul rail decarbonisation i) a battery electric locomotive for low-energy demands which can be coupled with either ii) a battery electric tender for medium energy demands or iii) a hydrogen fuel cell electric tender for higher energy demands. A future-looking techno-economic assessment of battery and hydrogen fuel cell platforms concludes that the lowest cost solution for low-energy hauls is a battery-only system and for high-energy hauls a battery-hydrogen system.

Green liquid hydrogen (LH2) could play an essential role as a zero-carbon aircraft fuel to reach long-term sustainable aviation. Excluding challenges such as electrolysis transportation and use of renewable energy in setting up hydrogen (H2) fuel infrastructure this paper investigates the interface between refueling systems and aircraft and the impacts on fuel distribution at the airport. Furthermore it provides an overview of key technology design decisions for LH2 refueling procedures and their effects on the turnaround times as well as on aircraft design. Based on a comparison to Jet A-1 refueling new LH2 refueling procedures are described and evaluated. Process steps under consideration are connecting/disconnecting purging chill-down and refueling. The actual refueling flow of LH2 is limited to a simplified Reynolds term of v · d = 2.35 m2/s. A mass flow rate of 20 kg/s is reached with an inner hose diameter of 152.4 mm. The previous and subsequent processes (without refueling) require 9 min with purging and 6 min without purging. For the assessment of impacts on LH2 aircraft operation process changes on the level of ground support equipment are compared to current procedures with Jet A-1. The technical challenges at the airport for refueling trucks as well as pipeline systems and dispensers are presented. In addition to the technological solutions explosion protection as applicable safety regulations are analyzed and the overall refueling process is validated. The thermodynamic properties of LH2 as a real compressible fluid are considered to derive implications for airport-side infrastructure. The advantages and disadvantages of a subcooled liquid are evaluated and cost impacts are elaborated. Behind the airport storage tank LH2 must be cooled to at least 19 K to prevent two-phase phenomena and a mass flow reduction during distribution. Implications on LH2 aircraft design are investigated by understanding the thermodynamic properties including calculation methods for the aircraft tank volume and problems such as cavitation and two-phase flows. In conclusion the work presented shows that LH2 refueling procedure is feasible compliant with the applicable explosion protection standards and hence does not impact the turnaround procedure. A turnaround time comparison shows that refueling with LH2 in most cases takes less time than with Jet A-1. The turnaround at the airport can be performed by a fuel truck or a pipeline dispenser system without generating direct losses i.e. venting to the atmosphere.

The production storage and use of hydrogen for energy purposes will become increasingly important during the energy transition. One way to use hydrogen is to apply it to power vehicles. This green technological solution affects low-emissions transport which is beneficial and important especially in cities. The authors of this article analyzed the use of hydrogen production infrastructure for bus propulsion in the city of Katowice (Poland). The methods used in the study included a greedy algorithm and cost methods which were applied for the selection of vehicles and identification of the infrastructure for the production storage and refueling of hydrogen as well as to conduct the economic analysis during this term. The article presented the complexity of the techno-economic analysis of the infrastructure and its installation. The key element was the selection of the number of vehicles to the hydrogen production possibilities of an electrolyser and capabilities of the storage and charging infrastructure.

Power-to-X technologies that convert renewable electricity to chemically stored energy in “X” may provide a gaseous liquid or solid fuel that can be used in winter to provide both heat and electricity and thus replace fossil fuels that are currently used in many countries with cold winters. This contribution compares two options for power-to-X technologies for providing heat and electricity supply of buildings with high solar photovoltaic coverage at times of low solar availability. The option “compressed hydrogen” is based on water electrolysis that produces hydrogen on-site. This hydrogen is subsequently compressed and stored at high pressure (350 bar) for use in winter by a fuel cell. The option “aluminium redox-cycle” includes an inert electrode high temperature electrolysis process that is carried out at industrial scale. Produced aluminium is subseqeuntly transported to the site of use and converted to hydrogen and heat – and finally to electricity and heat - by aluminium-water reaction in combination with a fuel cell. Results of cost and LCA analysis show that the overall energetic efficiency of the compressed hydrogen process is slightly higher than for the aluminium redox cycle. However the aluminium redox-cycles needs far less on-site storage volume and is likely to become available at lower investment cost for the end user. Total annual cost of ownership and global warming potential of the two options are quite similar.