The aviation sector is a significant player in the realm of the global energy crisis and climate change. Since the 1980s, CO2 emissions from aviation have increased by 3.6% per year. As a result, aviation currently accounts for 12% of transport-related CO2 emissions and 2–3% of all anthropogenic emissions with a steadily increasing influence. In order to tackle this challenge, the European Commission formulated reduction targets in the “Flight Path 2050”: 75% CO2 reduction per passenger kilometer relative to the capabilities of typical new aircraft in 2000, as well as 90% NOx and 65% perceived noise reduction. Similarly, two US government agencies, IATA and ICAO, pursue an average improvement in fuel efficiency of 1.5% per year until 2020, a cap on net aviation CO2 emissions from 2020 (carbon-neutral growth) and a 50% CO2 reduction until 2050. A tenable solution would be the use of hydrogen as fuel. Because its gravimetric energy density is three times higher, using hydrogen can reduce overall weight of the aircraft. This effect is pronounced in fuel-intensive aircraft like long-distance, large passenger number, and hypersonic aircraft. Once hydrogen is used as a fuel, there is no better converter than a fuel cell. The increased efficiency of a fuel cell leads to a further reduction of the fuel load. Fuel cells enable further advantages of electric aircraft such as distributed propulsion, which increases the aerodynamic efficiency. Furthermore, multifunctional integration of the fuel cell into aircraft via harvesting by-products, such as water, heat or oxygen-depleted exhaust air, allows for using the fuel cell to provide vital processes like de-icing, cabin air conditioning, water supply or fire suppression of luggage compartment or fuel tanks.

Defense forces look forward to self-sufficiency in every situation and location. Power and energy supply must be robust, reliable and versatile. Batteries are in wide use by the Army for their forward area detachments and by the Air force and Navy for autonomous vehicles and remote operation fields. The concept of fuel cell has undergone numerous innovative up gradations and has got adapted and diversified into several types. Low acoustic signature, low thermal signature, practically no chemical emission, improved specific energy, high energy density, reduced recharging cycle times etc., are important features of fuel cells weighing against the best of battery choices, as far as the military segment is concerned. These features are of significance to the civil sector as well. Fuel cells are power on demand devices based on electrochemical energy conversion. In batteries the stored chemical energy is released as electrical energy. Once the reactants are consumed, the battery stops delivering power and needs to be recharged using electrical energy from external sources. In fuel cells, though electrical energy is generated through electrode reactions, the reactants per say are not stored in the cells and can continue to give a rated power output as long as supply of the fuel and oxidant could be maintained.