During the past two years, eight ETH mechanical and electrical engineering students have developed a four-seated electric aircraft with modular battery system, based on the Sling TSi, as part of an ETH focus project. The aircraft is the world's first certified four-seated electric aircraft and it has already completed its first flights. In parallel, as a part of a new project called e-Sling Project H2, a functioning prototype of a hydrogen-powered fuel cell system was developed. The follow-up project Cellsius Project H2 aims to build a hydrogen fuel-cell/battery hybrid powertrain to be installed in a new, manned aircraft. The vision of the new project is to expand the maximal flight time of the zero emission flight, which is possible through the high energy density of the hydrogen compared to batteries. The prospective first hydrogen take-off date is summer 2024.