|Fig. 1: A systems integration view of the hydrogen economy.  (Courtesy of the U.S. Department of Energy.)|
The use of the term "hydrogen economy" originates from a talk given by John Bockris at the General Motors (GM) technical center in 1970, and it refers to the vision of using hydrogen as a low-carbon fuel source in order to displace conventional fossil fuels. [1,2] Hydrogen is often seen as more attractive than the conventional fuels because whether it is used in a fuel cell with air to produce electricity or burned to produce heat the only by product is water rather than carbon dioxide or other greenhouse gases and particulates.  Another reason hydrogen might be seen as more attractive than say gasoline is because there is an abundant quantity and not a finite limit like the petroleum derived gasoline. There are, however, various challenges to the idea and the future of the hydrogen economy both technical and economic in nature. Fig. 1 displays a systems integration view of the hydrogen economy as envisioned by the National Renewable Energy Laboratory.
The production of hydrogen is a growing industry and produced about 57 million metric tons in 2004, 11 million of which were produced in the United States.  Throughout the early 2000's the annual value of the hydrogen produced worldwide has been increasing steadily. Today, hydrogen is used in two main ways: in the Haber process to produce ammonia, which is ultimately used to make fertilizers or it is used to convert petroleum into more commonly used fuels, a term known as hydrocracking.  Hydrocracking represents an interesting and large growth area because with rising oil prices and rising demand for oil, companies are being forced to locate, drill and extract from less refined sources which require hydrogen. The current use of hydrocracking in the United States is approximately 4 Mt per year.  It is estimated that if the U.S. were to use 37.7 Mt annually this would be enough to convert domestic coal to liquid form and eliminate the United States' dependence on foreign oil, and at about half of this amount it would eliminate the dependence on Middle Eastern oil.
Currently hydrogen around the world is produced from four main sources: coal, oil, natural gas, and water electrolysis. Coal accounts for approximately 18% of global hydrogen while oil accounts for approximately 30%. Natural gas accounts for approximately 48% while water electrolysis provides only 4% of global hydrogen production.  Of these four methods it is estimated that a power plant using the natural gas combined cycle (NGCC) produces the most efficient hydrogen by using a special chemical pathway and combining usable waste heat energy.
Hydrogen as a fuel source has a number of obstacles and challenges that currently limit its viability as a serious replacement for fossil fuels. These include, but are not limited to, hydrogen storage issues, the purity requirement for hydrogen (when used in fuel cells), the infrastructure required, safety and environmental concerns.
|Fig. 2: An example timeline of the hydrogen economy.   (Courtesy of the U.S. Department of Energy.)|
One of the main challenges to hydrogen is the issue of storing it. If using it as a direct fuel to a vehicle it must be stored on board and must be pressurized (in some cases to five or ten-thousand psi) or liquefied to have an appropriate driving range.  You can also store hydrogen underground caves or depleted oil fields, which has largely been done without incident by Imperial Chemical Industries for years.  Another issue with hydrogen is that when using it as part of a fuel cell, you require ultra high purity hydrogen at levels up to 99.999%. One of the main challenges to the hydrogen economy is the infrastructure needed to develop it. It has been theorized that a hydrogen infrastructure would consist of industrial sized underground pipes and filling stations across the country, which would form a so-called "Hydrogen Highway".  Those stations, which were not located near a pipeline, would have to receive their hydrogen from delivery trucks and trailers or make their own hydrogen onsite. Although there is already a well-established network of natural gas pipeline, expensive treatments would have to be done in order to retrofit them for hydrogen. In a city like Los Angeles, where there are already some hydrogen fueling stations, the goal would be to have a station every five or so miles and have them on the road between Los Angeles and other major cities in the South West portion of the country. As can be imagined the cost of this would be monumental and is currently infeasible.
Another of the main challenges to the hydrogen economy is the safety and environmental concerns. Hydrogen is extremely flammable and explosive when in the presence of air such that a hydrogen leak in the presence of air will lead to an explosion when sparked or ignited.  This makes hydrogen extremely dangerous in enclosed areas such as underground tunnels or parking.  Hydrogen flames are almost invisible to the naked eye and hydrogen is also odorless which further presents challenges for safety and detection. There have also been environmental concerns because as of current technology hydrogen is made primarily from fossil fuel reformation. This would lead to a higher rate of carbon dioxide emissions than if the fossil fuels were used directly. 
The idea of using hydrogen as fuel source in order to reduce greenhouse gas emissions is an ambitious and altruistic notion. It is not, however, without its challenges ranging anywhere from the current technology and cost, to infrastructure and safety. With the increase and demand for oil, there has been a higher market and greater interest in alternative, cheaper, and safer means for hydrogen production. Research is being done all across the United States and the world to find inexpensive and safe ways to produce hydrogen to proliferate the dream of the hydrogen economy. Fig. 2 is a sample timeline developed by the U.S. Department of Energy for some of the possible goals and dates for completion of milestones.
© David Llanos. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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 "Hydrogen Posture Plan," U.S. Department of Energy, December 2006.