Aviation and Aerospace (Column)

V. KOPELAS, Advent Technologies, Boston, Massachusetts

The aviation industry has developed—to say the least—since the Wright brothers’ first powered flight in 1903. However, during 2022, the aviation industry was responsible for approximately 2% of global energy-related carbon dioxide (CO₂) emissions and is facing a critical challenge in achieving successful decarbonization, with emissions growing faster in recent decades than rail, road or shipping.¹ To meet the net-zero emissions target by 2050, the aviation industry urgently requires substantial technological advancements for power generation. Embracing new energy sources through innovative technologies is a key enabler to ensure aviation’s cleaner and more sustainable future. 

Among these innovative solutions, proton exchange membrane (PEM) fuel cells present immense promise for clean and efficient power generation across the transportation sector. PEM fuel cells convert chemical energy from hydrogen (H₂) and oxygen to electrical energy, emitting only water and heat as byproducts. Within the realm of PEM fuel cells, there are two main types: low-temperature PEM (LT-PEM) fuel cells and high-temperature PEM (HT-PEM) fuel cells. 

LT-PEM fuel cells operate at relatively low temperatures, typically 80°C–100°C, and require high-purity H₂ to function. While effective in some applications, they face certain challenges in extreme conditions, especially at high altitudes and in hot environments, where dehydration can hinder their performance. Additionally, the need for water in LT-PEM fuel cells can limit their suitability for aviation applications, where weight and efficiency are critical factors. 

Conversely, HT-PEM fuel cells offer a revolutionary solution to the challenges faced by their low-temperature counterparts. Operating at higher temperatures, typically from 120°C–220°C, HT-PEM fuel cells eliminate the need for a water supply, making them ideal for aviation. This is because HT-PEM fuel cells use phosphoric acid as the electrolyte rather than water-assisted membranes, therefore eliminating the need for water balance and other compensating engineering systems. The absence of water in HT-PEM fuel cells addresses the dehydration issue experienced by LT-PEM fuel cells at high-altitude environments, ensuring consistent and reliable performance even at extreme heights. In addition, HT-PEM's resilience to operate in high-temperature conditions at airports with high ground temperatures enables optimal performance without compromising efficiency. 

Compared to battery-powered flights, a fuel cell-powered aircraft using HT-PEM technology and lightweight thin plates could increase range, payload/passenger capacity and the number of trips made on one charge or fill-up. HT-PEM aircraft have the potential to refuel much faster than a typical battery recharge time with the same power output. Additionally, compared to LT-PEM, the high-purity H₂ required by LT-PEM has significant barriers for widespread commercial use, while HT-PEM technology may enable safer H₂ carrier fuels. While HT-PEM can work well with liquid H₂, some are considering H₂ containing fuels such as dimethyl ether and reformed sustainable aviation fuel (SAF) could work just as well due to HT-PEM technology. 

The exceptional adaptability of HT-PEM fuel cells allows them to operate in a wide range of practical conditions, from extreme ambient temperatures as low as -20°C, up to 55°C to humid and polluted environments. In contrast, LT-PEM fuel cells struggle in high-ambient temperatures, are vulnerable to damage in dry climates or polluted air and are intolerant to slight impurities in the H₂ supply. 

In addition to performance advantages, HT-PEM fuel cells offer enhanced system durability with a longer operational life than LT-PEM fuel cells. The ability of an HT-PEM to operate at higher temperatures allows for a simpler cooling system, owing to the higher ambient temperature gradient and, therefore, the efficient transfer of heat away from the fuel cell stack. 

Membrane electrode assembly (MEA) technologies are expected to revolutionize the global fuel cell market by delivering lightweight fuel cells with high-power density, advancing HT-PEM technology throughout the mobility sector. Furthering its commitment to sustainable aviation, the author’s company is in discussions with several aviation companies to accelerate the integration of HT-PEM fuel cells into H₂ aircraft by leveraging its MEA^a technology. 

As the world moves towards a sustainable aviation future, HT-PEM fuel cells are seen as the key enabler. Their ability to operate without water, increased efficiency in extreme conditions, compatibility with various fuels and utilization of existing fuel infrastructure make them the superior choice for the aviation industry. Embracing HT-PEM fuel cell technology brings us closer to achieving net-zero emissions by 2050, ensuring a greener and more sustainable future for aviation and the planet.H₂T

Notes 

^a Ion Pair™ 

About the author

VASILIS KOPELAS is the Vice President of Advent Technologies Holdings Inc., covering corporate strategy and business development in mobility. Kopelas has extensive experience in the automotive and fuel cell industries. Over his 17-yr career, he has held senior positions in R&D, sales and marketing, and business strategy for Toyota Motor Europe and Jaguar Land-Rover in Belgium, Japan, Russia and the UK. Prior to joining Advent, Kopelas served as Manager of Toyota Motor’s fuel cells business group in Brussels, Belgium, where he was responsible for the development and implementation of the company’s corporate fuel cell strategy and the commercialization of fuel cell technology solutions in various sectors and applications, actively contributing to Toyota’s vision toward a H₂ society in the European Union. Kopelas earned MS degrees in automotive product design from Cranfield University in the UK, aeronautical and mechanical engineering from Patras University and a strategic management certificate from the Wharton School of the University of Pennsylvania in the U.S.