IsoPROPEL enables zero-emission waterborne transport through a waste-free energy cycle using renewable isopropanol to power fuel cells. Made from CO2 and green hydrogen, isopropanol can be produced through an electrified process and used directly in next-generation fuel cells that generate power without emitting CO2. Tested in inland waterway transport, this innovative closed-loop system could pave the way for clean, circular fuels that drive the decarbonisation of heavy-duty mobility.