Hydrogen fuel-cell traction

Compressed hydrogen stored in high-pressure tanks is fed into a fuel-cell stack, where it meets oxygen drawn from the surrounding air. The two combine electrochemically — not by burning — and the reaction releases electrons, producing direct current, water and heat. That current drives the train's electric traction motors, exactly as current from an overhead wire would. Surplus electricity is banked in onboard lithium-ion batteries and drawn on during acceleration; regenerative braking returns further energy to those batteries. Because there is no combustion, there is no carbon dioxide, no oxides of nitrogen and no particulate matter at the tailpipe, and the train is markedly quieter than a diesel unit. The technology's real value is on non-electrified track — hill, heritage and thin-traffic branch lines where stringing overhead equipment is uneconomic and diesel is the only present alternative.