At first glance, hydrogen appears to be the perfect solution to a carbon intensive transportation infrastructure. Hydrogen is an abundant element, and the only bi-product of hydrogen fuel cell vehicles is H2O – water. However, as pure hydrogen is not found on earth, it must be produced using energy, such as electricity or natural gas, and often generates significant CO2 emissions. And, as with electricity, hydrogen is not a fuel in itself, but is only an energy carrier. Unfortunately, in the near term, hydrogen will never exceed the efficiency of using electricity directly due to the energy losses involved in the production of hydrogen.
Hydrogen-fuel vehicles include both internal combustion engines and fuel-cell vehicles (FCVs). Plumbing an internal combustion engine (ICE) for hydrogen isn’t too difficult, but getting hydrogen fuel is difficult due to the few fuel stations. Ford and BMW have a small fleet of hydrogen powered cars in the U.S. Fuel-cell vehicles are a number of years off due to the high cost of the materials in the proton exchange membrane. Fuel cell vehicles are electric vehicles driving by the electricity from the fuel cell or they can be a hybrid, with a battery pack that stores energy in the car that then drives the wheels.
Hydrogen is a potential transport fuel both for ICEs and for FCVs. Fuel cells use hydrogen as a fuel to generate electricity on board the vehicle, which is then used to power an electric motor that drives the wheels and supports other vehicle functions. The hydrogen can also be produced on board the vehicle, for example from ethanol or other liquid fuels containing hydrogen. However, current costs and maturity level of hydrogen technology limits its availability and affordability for the general public.
Hydrogen can be produced from fossil fuels or from nuclear or renewable energy by a number of processes. These include water electrolysis, natural gas reforming, gasification of coal and biomass, water splitting by high-temperature heat, photoelectrolysis, and biological processes.
While the electricity sector is still highly carbonized, the production of hydrogen using electrolysis produces slightly more CO2 than running a vehicle on petrol or diesel. And, running vehicles on hydrogen produced by electrolysis requires twice as much electricity as running them on battery electric power. As the electricity sector continues to de-carbonize, it may become less CO2 intensive to produce hydrogen.
Infrastructure will also be needed to distribute, store and deliver hydrogen to vehicles. The overall investment cost for this infrastructure, worldwide, is likely to be in the trillions of US dollars. Overall, the retail price of hydrogen for transportation users, reflecting all feedstock, capital and operating costs, appears likely to remain well above USD 1.00/L of gasoline equivalent for the foreseeable future. Fundamentally, fuel cells have the potential to reduce GHG emissions by nearly 100% compared with conventional gasoline-powered vehicles, if the hydrogen used is produced from a renewable source.
Platinum is a key ingredient in hydrogen fuel cells, and is a very rare and expensive metal. Due to this constraint, the hydrogen industry is currently investigating materials to replace platinum in hydrogen vehicle fuel cells. The amount of platinum needed to produce a fuel cell vehicle is constantly reducing and platinum can also be recovered from the fuel cell at the end of its life.
For more information on fuel cell technology, please visit the Union of Concerned Scientists
To see an illustration of how a fuel cell works, click here.