http://www.ballard.com/be_a_customer/power_generation/fuel_cell_powergen/airgen/airgen_fuel_options

AirGen™ fuel options

The AirGen™ fuel cell generator is fueled by hydrogen that can be supplied through industrial cylinders (for commercial and industrial use).

Industrial cylinders are available in a number of sizes and are sold separately with a cylinder adapter kit for the AirGen™ unit.

The bus thing might be good just to improve city air quality. But the thermal efficiency is not on the side of fuel cells without a compelling reason--like city air pollution.