Citybus in Hong Kong is at the forefront of a hydrogen bus revolution, operating the world's first tri-axle hydrogen double-deck bus, the DD12. Developed in collaboration with Wisdom Motor and Ballard-Weichai, this innovative bus features a fuel cell stack with Ballard's FCgen-LCS technology, boasting a powerful 80 kW output. With a capacity for 91 passengers and a range of 420 km, the DD12 only takes 10 minutes to refuel at Hong Kong's first hydrogen refuelling station in West Kowloon Depot. After successful deployment on Kowloon routes, Citybus plans to expand the use of these hydrogen buses to cross-harbour and long-haul routes. The recent milestone of driving the hydrogen bus through Hong Kong's road tunnels opens up new route possibilities for Citybus. With plans to trial five more hydrogen-powered buses by December, Citybus aims to eventually transition its entire fleet to zero-emission buses by 2045, showcasing its dedication to sustainable public transport solutions.