Fuel cells in aviation: challenges to power the future of flight

The aviation sector is currently transitioning towards hybrid electric aircraft, driven by sustainability imperatives and technological progress. This article examines fuel cells' potential to meet aeronautical power demands, analyzing the state of the art to identify key performance indicators (KPIs) and research challenges in advancing hydrogen-based aviation. Several technologies, including proton exchange membrane and solid oxide fuel cells, are evaluated as candidates for on-board installation. Then, the following research areas are identified and discussed: design, control, thermal management, and degradation. These interconnected tasks are essential for advancing the state of the art, a goal achievable through effective modeling approaches at the individual component and system levels. One of the KPIs requiring substantial improvement is the system's mass-to-power ratio. This metric largely relies on the integration of advanced materials and manufacturing techniques at the stack level, aimed at reducing the bipolar plates mass and optimizing membrane electrode assembly performance to increase the operating temperature, thus leading to lighter and more compact thermal management systems. At system level, enhancing the hydrogen storage tank's gravimetric capacity is a priority in keeping the aircraft's maximal take-off mass (MTOM) within acceptable limits. Moreover, the integrated sizing of the fuel cell system alongside energy storage (e.g., batteries) and the development of multi-level control strategies can help mitigate MTOM increase, optimize performance, and enhance the durability of hydrogen-based devices. Finally, the original equipment manufacturers of fuel cell systems for the transportation sector, particularly aviation, are identified to offer insights into ongoing efforts towards achieving net-zero aviation.