Cleaner skies with liquid hydrogen

Climate-harming contrails, the trails left behind by planes that contribute to global warming, could become significantly less impactful thanks to new research from the Department of Chemical Engineering and Biotechnology (CEB).

Research led by Paula Mendoza-Moreno and George Fulham, under the supervision of Dr Ewa Marek, has developed a method to enhance the energy efficiency and practicality of liquid hydrogen (LH₂) production, a fuel with significant potential to decarbonise aviation among  industry. This approach offers a promising pathway to reducing aviation’s environmental impact as, although contrails could still form due to water vapour emissions, they would be free of carbon-based particulates that contribute significantly to their warming effects.

The study – published in Cell Reports Sustainability – examines the ortho-para isomeric conversion of hydrogen molecules. The process occurs during liquefaction and accounts for up to 57% of the energy required. The findings highlight a practical path to reducing these costs while maintaining LH₂’s viability as a fuel.

The research proposes optimising the extent of ortho-para conversion rather than pursuing near-total conversion to para-hydrogen, which has traditionally been viewed as ideal but is energy-intensive and impractical at scale. By targeting para-hydrogen levels between 83% and 95%, the team demonstrated energy savings of 8% to 13% while ensuring effective storage for up to seven days. This approach aligns more closely with the practical limitations of industrial liquefaction systems, addressing issues such as boil-off, gas replenishment, and potential leaks, all of which are tied to the degree of conversion.

Liquid hydrogen is increasingly viewed as a potential solution for decarbonising the aviation industry due to its ability to replace hydrocarbon fuels without producing CO₂ emissions. The study demonstrates its potential through a specific case: a Boeing 787–9 flight between London and New York powered by LH₂ would reduce harmful emissions by at least 92% compared to conventional jet fuel. Such applications could transform the environmental footprint of major air routes and provide a practical alternative for reducing aviation’s contribution to climate change.

“By rethinking how we approach the ortho-para conversion process, we’ve shown it’s possible to reduce the energy costs of liquid hydrogen production while maintaining its effectiveness as a fuel,” said lead author Paula Mendoza-Moreno. “This offers a realistic pathway to integrating hydrogen into aviation and other industries.”

The study situates these findings within the broader context of hydrogen as a sustainable fuel source. It highlights the importance of designing hydrogen production systems that balance efficiency with practical constraints, offering insights that could accelerate the adoption of LH₂ not just in aviation but across energy-intensive sectors.

This work underscores the importance of addressing specific technical challenges to unlock hydrogen’s potential as a cleaner, more sustainable fuel.