Inexhaustible, clean and attractive in terms of energy: right now, hydrogen seems to have it all. But is it possible to base an entire economy on the use of this gas and ultimately replace CO₂-generating fossil fuels?

Hydrogen has the simplest atomic structure and consequently is the lightest of all elements in the periodic table of elements. It is gaseous at ambient temperature and becomes a liquid at -253 °C. On Earth, hydrogen is almost everywhere, particularly in water (each water molecule has two hydrogen atoms bonded to an oxygen atom). With oceans covering 70% of the globe, hydrogen is widely spread across our planet. Hydrogen is also found in hydrocarbons which, as the name indicates, are formed from a combination of carbon and hydrogen atoms. Not to mention biomass, another potential source of hydrogen, which is contained in all living matter, whether animal or vegetable.

Despite its abundance, hydrogen is practically non-existent in the natural state as it is always bonded with oxygen (water) or carbon (hydrocarbons, biomass). It is partly because it is so abundant that hydrogen is so attractive, but it is also because the combustion of hydrogen with oxygen in the air produces only heat and water, and therefore no pollution. These arguments are so persuasive that some foresee an economy in which hydrogen would replace existing fuels and at the same time serve as a source of electricity. Indeed, hydrogen and electricity go well together: one can go from one to the other with water-electrolysis systems and fuel cells. Water electrolysis breaks water down into hydrogen and oxygen; in the other direction, hydrogen combustion with oxygen gives water back.

How is hydrogen produced?

Hydrogen is not a primary source of energy. It is what the specialists call an "energy vector": in other words, energy that is not directly usable – unlike oil – but which must be extracted or produced before being transported, stored and used. Just like electricity, to produce hydrogen as a source of available energy first requires expending… energy! The hydrogen must already have been extracted from water, by electrolysis for example. Luckily, hydrogen has the advantage of being a storable energy vector and, on top of that, does not generate greenhouse gases. These remarkable qualities have not gone unnoticed.

Currently, most hydrogen (95 to 96%) is produced using fossil fuels – mainly natural gas – through "reforming" Though inexpensive, the drawback of this process is that it gives off a large amount of CO₂. The other production process, electrolysis, is advantageous when low-cost electricity is used. This method is not used very often right now (only 1 to 2% of the hydrogen produced) and only when a high level of purity is required. However, in the longer term (2030 – 2050) water molecules will be dissociated directly using heat from new-generation, high-temperature nuclear reactors.

A variety of uses

For now, hydrogen is more a chemical product than an energy vector. The energy aspect is limited to space-age satellite launchers like Europe's Ariane 5, which consumes 25 metric tons of it every time it is launched, or the space shuttle, which uses 617 metric tons.

The petrochemical industry is the biggest user of this gas, primarily to hydrogenate heavy oils that are too rich in carbon during the refining process, or to produce low sulfur fuels. Hydrogen is also one of the raw materials for the chemical industry, where it is used to produce ammonia and methanol, as well as dyes and hydrogen peroxide. It is also used to treat water, to disinfect food wrapping on packaging machinery and as an antiseptic. The other main areas of use are in the metallurgical, electronics (microprocessors), pharmaceutical and glass industries, and even in the food processing industry. It is also used in the production of industrial soaps, paints and varnishes. Each year, 45 to 50 million metric tons of the gas are produced to meet industrial demand. Were it to be used as an energy vector, its production would have to be multiplied 100-fold.

Difficult to store

Technically speaking, hydrogen storage is costly due to its very low density and its very low liquefaction temperature. Large quantities (when used as rocket fuel, for example) must be stored in the liquid state, whereas pressurized storage in gaseous form is preferable for quantities of a few tens of kilograms. This is how it would be stored if it were used as fuel for automobiles, so it would have to be storable in the gaseous state as routinely and safely as if it were butane. To keep tank size down, the hydrogen would have to be compressed at a pressure of 700 bar. Such tanks have been developed for several years and are undergoing certification.

But even under these conditions, it takes no less than 4.6 liters of hydrogen to get as much energy as with 1 liter of gasoline! The risk of a leak must also be taken into consideration, given the flammable and explosive nature of this gas under certain containment conditions. Indeed, due to the molecule's small size, hydrogen can pass through many materials, including certain metals. This hazard should be put into perspective, however: though the gas can escape easily, it is also quickly dispersed in air – four times faster, in fact, than natural gas.

Centralized or decentralized distribution?

Like the system currently used for oil-based fuels, hydrogen distribution must make the fuel widely available in a convenient and completely safe way and at an affordable price. This requires the creation of suitable transportation and distribution infrastructures.

There are two possibilities. The first is the so-called "centralized" mode, with external production and transport by road, rail or pipeline. Pipeline distribution networks for hydrogen already exist (about 1,000 km in France, Germany and the Benelux) and are supplying the chemical and petrochemical industries. So there is good experience with hydrogen transport, but it costs about 50% more than for natural gas. The so-called "decentralized mode", on the other hand, requires the construction of special filling stations that produce the fuel on-site. Before this can happen, some remaining technical problems must be resolved, particularly relating to safety, to ensure that the user's risk is no greater than for a conventional gasoline pump. There are already about forty pilot hydrogen filling stations (both pressurized and cryogenic) around the world, primarily in the United States, Japan, Germany, Spain, France and Iceland. The average cost of a hydrogen filling station is estimated at about €200,000.

Pending more widespread use of such filling stations, some carmakers plan to use hybrid fuels with hydrogen. The hydrogen would be produced directly aboard the vehicle by reforming methanol, gasoline or diesel, an easier process. But, in that case, these would not really be hydrogen vehicles, especially since reforming would produce carbon dioxide.

Research programs underway

Many countries around the world are engaged in hydrogen and fuel cell research and development. This is true in Germany (Daimler Chrysler, Siemens), the United States, Canada (Ballard), Japan and France (CEA and CNRS in particular), where companies such as Helion are already building prototypes. Work currently focuses mainly on the production mode, storage and safety. Tank designs that are as compact and lightweight as they are safe and affordable will be decisive, for it is their storage potential that makes hydrogen attractive compared with electricity. One storage alternative would be to use certain carbon-based materials or metal alloys capable of absorbing the hydrogen and returning it on demand. With regard to the explosion risk, work is underway at Ineris and CEA in France and at Linde in Germany.

Various programs to promote hydrogen to the general public are being led around the world, especially in the United States via the California Fuel Cell Partnership (CaFCP), in Canada (Ballard), in Japan (MITI's We-Net program) and in Germany. Associations such as the French Hydrogen Association or Alphea in France and the European Hydrogen Association (EHA) at the European level, are also working in this direction.

A decision that is as political and strategic as it is technical

In the United States, the Strategic Plan for Hydrogen received funding of $30 million in 2001 and, in January 2003, President George W. Bush announced that $1.2 billion would be allocated to hydrogen research. In the European Union, the 7th Framework Programme for research and development (FP7) will receive €2.8 billion in public and private funding over 10 years. In April 2002, the city of London created London Hydrogen Partnership, an organization that plans to put into service three buses equipped with fuel cells. With the research currently underway, the first market for hydrogen-based electricity and heat production is expected in 2008, and the first fleets of cars by 2010 – 2015.

The fact that nations and municipalities are involved alongside industry suggests that hydrogen will take on a significant role in the not too distant future, due as much to political decisions as to technological advances.

Many people already believe that hydrogen will be the best energy vector in the future and that the technological, safety, regulatory and social issues associated with its development will be solved within the next ten years, especially in the transportation sector. Of course, the complete transition to a «hydrogen economy» will take a few more decades. But when that happens, we will have entered a new era.