Hydrogen is the most abundantly available element in the universe. It is environmentally friendly with its non-polluting nature. It has every reason to dominate the fuel market. Yet, it fails to fossil fuels, which is currently the driving force of our automobiles. Some have heralded hydrogen as the ‘Energy of the Future’, but sceptics say it will always be just that – A future fuel, which never makes it out of test cars. But this was until DaimlerChrysler came up with an innovative idea – SOAP to fuel the future automobiles.

The Sodium borohydride Fuel

What's been holding back development of fuel-cell cars is the storage tanks that such vehicles require, which are so big, that there's hardly room for passengers, let alone cargo. The DaimlerChrysler ‘Natrium’ vehicle gets round this by storing the hydrogen as sodium borohydride, a non-toxic solution that can be pumped in and out of the vehicle safely and cleanly. The fuel is elusive hydrogen stored in a mixture of 75-percent water and 25-percent glorified soap powder. It is something like a soap factory under the hood. It involves simple borate - a chemical mined from the ground and used as laundry detergent. The fuel cell runs on hydrogen taken from sodium borohydride - a man-made chemical. What's left is borax soap in the tank. The only emission from the tailpipe is steam.

Sodium borohydride (NaBH4) is the most benign fuel under consideration. It is a compound of sodium, boron, and hydrogen. It is used in a variety of chemical industries, including the paper and pulp industries (as a bleach), in wastewater processing and in pharmaceutical synthesis. Sodium borohydride is hydrogenated sodium borate (NaBO2), chemically equivalent to borax - a substance used as a laundry detergent ingredient. The sodium borate (NaBO2) is not consumed in the process, but merely acts as a carrier for the hydrogen. The system is completely safe since it produces the dangerous hydrogen gas only when needed. Once the flow of sodium borohydride over the catalyst stops, so does the production of hydrogen.

NaBH4 + 2 H2O catalyst 4 H2 + NaBO2

The only other reaction product, sodium metaborate is water-soluble and environmentally benign. The reaction is exothermic - so there is no need to supply external heat to access the hydrogen. The heat generated is sufficient to vaporize some of the water present, and as a result the hydrogen is supplied at 100% relative humidity. This co-generated moisture in the H2 stream is an added benefit both for fuel cells and for internal combustion engines.

The idea of using sodium borohydride as a fuel is not new – it has long been known that boron hydrides store more energy than similar hydrocarbons. Back in the 1960s, work on the fuel was abandoned because at that time the fuel was intended for combustion, which represented an insurmountable engineering challenge. The development of ‘the catalyst‘ technology for controlled release of hydrogen have allowed engineers to take a fresh look at this possibility. Besides it’s infrastructure issues are less challenging that with other fuels proposed for fuel cell vehicles.