Why is hydrogen
used as a fuel? Hydrogen has the highest energy content per unit weight
of any known fuel-52,000 Btu/lb (120.7 kJ/g). It burns cleanly. When hydrogen
is burned with oxygen, the only byproducts are heat and water. When burned with
air, which is about 68% nitrogen, some oxides of nitrogen are formed. The process
of converting hydrogen to energy using engines or fuel cells is much more efficient
than the comparable gasoline counterparts.
is the octane rating of hydrogen? Short answer: "130+"
according to a study done by the College of the Desert and Sunline Transit Agency
answer: The octane rating of gasoline tells you how much the fuel can be compressed
before it spontaneously ignites. When gas ignites by compression rather than because
of the spark from the spark plug, it causes "knocking" in the engine.
Knocking can damage an engine, so it is not something you want to have happening.
Lower-octane gas (like "regular" 87-octane gasoline) can handle the
least amount of compression before igniting compared to higher octane grades (like
"super" 93-octane gasoline).
The compression ratio of your engine
determines the octane rating of the gas you must use in the car. One way to increase
the horsepower of an engine of a given displacement is to increase its compression
ratio. So a "high-performance engine" has a higher compression ratio
and requires higher-octane fuel. The advantage of a high compression ratio is
that it gives your engine a higher horsepower rating for a given engine weight
-- that is what makes the engine "high performance." The disadvantage
is that for gasoline, it costs more.
Hydrogen has an octane rating of 130
because it can be compressed more than gasoline and 100% octane before the fuel
automatically ignites in the engine. (Gasoline with 87-octane has 87% octane,
a special kind of hydrocarbon that makes up gasoline and other fuels).
How is hydrogen produced? One of the great advantages of hydrogen is that it can be made from a variety
of domestic feedstocks like water, biomass, coal and natural gas. Because hydrogen
exists in many different forms, in any one region, there are a variety of local
feedstocks from which the hydrogen can be extracted.
Today, over 95%
of the hydrogen produced in the U.S. comes from steam reforming natural gas. As
hydrogen moves from its role primarily as an industrial gas to a consumer purchased
fuel, we expect other production technologies to add to the mix so that hydrogen
is produced using the most cost-effective and environmentally sound method available
for a specific region. Some options are: renewable or nuclear electricity and
electrolysis; gasification of biomass and other hydrocarbons like coal; and using
nuclear reactor heat for high-temperature electrolysis or thermo-chemical production
How does an electrolyzer produce
hydrogen from water? An
electrolyzer uses an electric current to separate water into its components-hydrogen
and oxygen. The electricity enters the water at the cathode, a negatively charged
electrode, passes through the water and exists via the anode, the positively charged
electrode. The hydrogen is collected at the cathode and oxygen is collected at
much water is used to make hydrogen? Electrolysis does not require significant
amounts of water. The hydrogen extracted from a gallon of water using a hydrogen
generator could drive a hydrogen fuel cell vehicle as far as gasoline vehicles
travel today on a gallon of gasoline.
How much water would the U.S.
use to fuel the entire light-duty vehicle fleet (cars and small trucks) with hydrogen?
Conversion of the current U.S. light-duty fleet (some 230 million vehicles)
to fuel cell vehicles would require about 100 billion gallons of water/year to
supply the needed hydrogen (1).
For comparison, the U.S. uses about 300
billion gallons of water/year for the production of gasoline (2), about three
times the amount needed for hydrogen, and about 70 TRILLION gallons of water/year
for thermoelectric power generation (3). Domestic personal water use in the United
States is about 4800 billion gallons/year.
John A., "Sustainable Hydrogen Production" Science, Vol 305, Issue 5686,
972-974, 13 August 2004 1) For an estimate of the amount of water needed for
hydrogen-powered fuel cell vehicles, assume a vehicle fuel economy of 60 miles
per kg of H2, that vehicle miles traveled = 2.6 X 10^12 miles/year (found at http://www.bts.gov/
and that 1 gallon of water contains 0.42 kg of H2. Total water required for the
U.S. fleet = (2.6 X 10^12 miles/year)(1 kg of H2/60 miles)(1 gal H2O/0.42 kg of
H2) = 1.0 X 10^11 gallons of H2O/year. This represents the water used directly
for fuel. If one considers all water uses along the chain; for example, from construction
of wind farms to the electrolysis systems (life cycle assessment), then the total
water use would be in the range of 3.3 X 10^11 gallons H2O/year.
is a life cycle analysis (M. Mann and M. Whitaker, unpublished data). The United
States used about 126 billion gallons of gasoline in 2001 [see link above].
How much energy is required to produce
hydrogen via electrolysis of water? The energy required to produce hydrogen
at atmospheric pressure via electrolysis (assuming 1.23 V) is about 32.9 kWh/kg.
A kilogram is about 2.2 lb. For 1 mole (2 g) of hydrogen the energy is about 0.0660
kWh/mole. Compressing or liquefying the hydrogen would take additional energy.
One company produces hydrogen through electrolysis at about 7,000psi at an energy
usage of about 60kWh/kg H2.
Because a Watt is Voltage x Current,
this is equivalent to Power x Rate x Time. The power in this case is the voltage
required to split water into hydrogen and oxygen (1.23 V at 25?C). The rate is
the current flow and relates directly to how fast hydrogen is produced. Time,
of course, is how long the reaction runs. It turns out that voltage and current
flow are interrelated. To run the water splitting reaction at a higher rate (generating
more hydrogen in a given time), more voltage must be applied (similar to pushing
down on the accelerator of a car; more gas is used to make the car go faster.)
For commercial electrolysis systems that operate at about 1 A/cm2, a voltage of
1.75 V is required. This translates into about 46.8 kW-hr/kg, which corresponds
to an energy efficiency of 70%.
Lowering the voltage for electrolysis,
which will increase the energy efficiency of the process, is an important area
Doesn't it take too much energy to make hydrogen?
Is it worth doing? Like all fuels, it takes energy to produce hydrogen
and deliver it to a vehicle. The amount of energy required depends on how the
hydrogen is made. Some methods require more energy than others.
it may take more energy to produce and deliver hydrogen than it takes to produce
and deliver gasoline or natural gas, the hydrogen fuel is used more efficiently
in hydrogen vehicles. Most hydrogen internal combustion engines (ICEs)
are about 25% more efficient than their gasoline counterparts and fuel cells are
100-200% (2-3 times) more efficient. In many cases, the overall "well-to-wheels"
energy usage can be much lower for hydrogen vehicles than for gasoline or natural
gas vehicles using a conventional internal combustion engine.
National Hydrogen Association
much hydrogen is produced each year? The world economy currently consumes
about 42 million tons of hydrogen per year. About 60 percent of this becomes feedstock
for ammonia production and subsequent use in fertilizer (ORNL, 2003). Petroleum
refining consumes another 23 percent, chiefly to remove sulfur and to upgrade
the heavier fractions into more valuable products. Another 9 percent is used to
manufacture methanol (ORNL, 2003), and the remainder goes for chemical, metallurgical
and space purposes (Holt, 2003). Some recent worldwide hydrogen
production totals are shown below:
hydrogen does the U.S. use? Each year, the United States uses more than
9 million tons (about 90 billion normal cubic meters, 3.2 trillion standard cubic
feet) of hydrogen, 7.5 million tons of which are consumed at the place of manufacture.
The remaining 1.5 million tons are considered to be "merchant" hydrogen,
or hydrogen that is sold. Today, most of this hydrogen is used as a chemical,
rather than a fuel, in a variety of commercial applications:
fixation of nitrogen from the air to produce ammonia for fertilizer (about two-thirds
of commercial hydrogen is used for this)
Hydrogenation of fats and
oils, in which vegetable oils are changed from liquids to solids; shortening is
an example of a hydrogenated oil
Methanol production, in hydrodealkylation,
hydrocracking, and hydrodesulphurization
Metallic ore reduction
and the study of superconductivity (liquid hydrogen)
oxidation in the manufacturing of semi-conductors
(hydrogen transfers heat very well)
Hydrogen's main use as a fuel
is in the space program. Today hydrogen fuels both the main engine of the Space
Shuttle and the onboard fuel cells that provide the Shuttle's electric power.
How much does hydrogen cost? The estimated costs for
producing and delivering hydrogen to the fueling station using todays
technologies vary from $2.10/gallon of gasoline equivalent (gge) to $9.10/gge.
These hydrogen costs do not include highway taxes and do include the increased
fuel efficiency of fuel cell vehicles compared to gasoline-powered hybrid electric
vehicles. That is, the driver of a fuel cell vehicle would pay the same amount
to travel 100 miles on hydrogen as the driver of a gasoline-powered hybrid electric
vehicle would pay for gasoline if the price was between $2.10/gallon to $9.10/gallon
to travel that same distance.
Source National Academy of Engineering,
"The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs"(2004),
Projected costs using future technology if current R&D
efforts are successful would reduce the cost of hydrogen to the range between
$1.75/gge to $4.25/gge. Thus hydrogen is expected to be competitive with gasoline
per mile driven.
Source National Academy of Engineering, "The
Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs"(2004),
In addition, some NHA member companies are projecting that
they can produce and deliver hydrogen economically to fueling stations at costs
as low as $1.20/gallon of gasoline equivalent, again untaxed. After adding the
average US highway taxes (federal and state) of $0.43/gallon, hydrogen would still
be less expensive than gasoline per mile traveled.
How do hydrogen vehicles work? There
are two main kinds, fuel cell vehicles and hydrogen internal combustion engine
Fuel cell vehicles are electric cars. Hydrogen is pumped
into a tank in the car, just as with gasoline. The hydrogen gas is then fed into
the fuel cell where it is electrochemically converted into electricity -- with
no combustion, no moving parts, and no emissions other than water vapor. The electricity
is used to power the vehicle. A fuel cell is also 2-3 times more energy efficient
than a gasoline engine.
Hydrogen ICE vehicles use a regular combustion
engine modified to use gaseous hydrogen instead of liquid gasoline (much like
a natural gas vehicle is modified). They burn hydrogen, but since there is no
carbon in hydrogen, there are no CO2 emissions and only trace amounts
of NOx (oxides of nitrogen--the air we breathe is 79% nitrogen). Hydrogen ICE
vehicles are typically about 30% more efficient than comparable gasoline vehicles.
types can be hybridized for additional gains in efficiency, by adding an electricity
storage device like a battery or capacitor.
Source Q&A with
Dan Sperling, director of the Institute of Transportation Studies; associate director
of the Energy Efficiency Center and professor of Transportation Engineering and
Environmental Policy at the University of California, Davis.
all cars ran on hydrogen, and all hydrogen was made from water, would we run out
of water? Conversion of the current U.S. light-duty fleet (some 230 million
vehicles) to fuel cell vehicles would require about 100 billion gallons of water/year
to supply the needed hydrogen (1). Domestic personal water use in the
United States is about 4800 billion gallons/year.
The U.S. uses about
300 billion gallons of water/year for the production of gasoline (2),
and about 70 trillion gallons of water/year for thermoelectric power generation
Solar and wind power do not require water for their
electricity generation. So not only do these resources provide sustainable carbon-free
energy, they reduce the water requirements for power generation.
1) For an estimate of the amount of water needed for hydrogen-powered fuel
cell vehicles, assume a vehicle fuel economy of 60 miles per kg of H2, that vehicle
miles traveled = 2.6 X 10^12 miles/year (found at ),and that 1 gallon of water
contains 0.42 kg of H2. Total water required for the U.S. fleet = (2.6 X 10^12
miles/year)(1 kg of H2/60 miles)(1 gal H2O/0.42 kg of H2) = 1.0 X 10^11 gallons
of H2O/year. This represents the water used directly for fuel. If one considers
all water uses along the chain; for example, from construction of wind farms to
the electrolysis systems (life cycle assessment), then the total water use would
be in the range of 3.3 X 10^11 gallons H2O/year.
2) This is a life cycle
analysis (M. Mann and M. Whitaker, unpublished data). The United States used about
126 billion gallons of gasoline in 2001 [see link above].
How viable are hydrogen vehicles
as an alternative to gasoline-powered cars? In many ways, they are more
viable than gasoline. A fuel cell electric vehicle is better suited to modern
vehicles that increasingly use electrical systems in place of mechanical and hydraulic
to steer, brake, and control the various functions of the vehicle. Also, in a
fuel cell vehicle, the entire powertrain can be consolidated into a flat "skateboard"
chassis, providing automakers much design freedom in latching all sorts of different
vehicle bodies on to the chassis -- without having to work around a protruding,
heat-producing engine and large mechanical driveline. A fuel cell is also 2-3
times more energy efficient than a gasoline engine.
Other vehicles that
use hydrogen in a regular combustion engine are also very viable. They use existing
engine technology, modified to use gaseous hydrogen. Hydrogen ICE vehicles are
about 30% more efficient than comparable gasoline vehicles and produce ultra-low
emissions, with no CO2.
Source Q&A with Dan Sperling,
director of the Institute of Transportation Studies; associate director of the
Energy Efficiency Center and professor of Transportation Engineering and Environmental
Policy at the University of California, Davis and the National Hydrogen Association
What happens to the tank in my car if I get
tanks, whether they are filled with gaseous or liquid hydrogen are incredibly
strong-MUCH stronger than the gasoline tanks found in vehicles today. For example,
this car was dropped on its back end from 90 feet (reaching 52 mph as it hit the
ground), with a hydrogen tank secured in the trunk. The tank was undamaged and
no hydrogen was leaked.
Source Sandia National Laboratories
Will I ever be able to buy a hydrogen-powered
vehicle? Every major automaker is developing hydrogen fuel cell vehicles,
although some are focusing on internal combustion engines instead of fuel cells.
Existing cars can be converted to run on hydrogen, and several major car companies
either have demonstration hydrogen cars or are due to release them in the next
few years. The successful development of advanced hydrogen storage systems will
accelerate the introduction of truly clean fuel cell vehicles.
at least one automaker planning to begin selling them to the public at a reasonable
price as early as 2009, and several aiming for a few years after that. But this
depends on fuel suppliers building more hydrogen fueling stations and the government
offering incentives to buyers (as they do now for hybrid vehicles).
Department of Energy and Q&A with Dan Sperling, director of the Institute
of Transportation Studies; associate director of the Energy Efficiency Center
and professor of Transportation Engineering and Environmental Policy at the University
of California, Davis.
hydrogen safe? Most fuels have high energy content and must be handled
properly to be safe. Hydrogen is no different. In general, hydrogen is neither
more nor less inherently hazardous than gasoline, propane, or methane. As with
any fuel, safe handling depends on knowledge of its particular physical, chemical,
and thermal properties and consideration of safe ways to accommodate those properties.
Hydrogen, handled with this knowledge, is a safe fuel.
Hydrogen has been
safely produced, stored, transported, and used in large amounts in industry by
following standard practices that have been established in the past 50 years.
These practices can be emulated in non-industrial uses of hydrogen to attain the
same level of routine safety.
If hydrogen has
a wider flammability range than gasoline, doesn't that make it unsafe to use? While hydrogen has a wider flammability
range than gasoline, the range is only a piece of the story when considering the
likelihood of a fire resulting from hydrogen escaping into the atmosphere. Each
fuel has different properties that must be considered along with flammability
For example: Gasoline's narrow flammability range is a bit misleading,
since this range can easily and often be reached through normal consumer handling
of gasoline and certainly if spilled. There are of course gasoline fires but,
as we know, fires certainly don't occur every time gasoline vapors are released
to the open air, because the vapors fail to find an ignition source in time.
has a wider flammability range, but because it is lighter than air (50 times lighter
than gasoline vapors and even lighter than helium) and diffuses 12 times faster
than gasoline vapors do, it is very difficult for hydrogen gas to find a suitable
ignition source in an open environment, like a fueling station.
systems used for vehicular fueling are designed to provide public safety just
as gasoline systems are designed to do. While both fueling systems utilize break-away
hoses, shear valves, and monitoring systems, hydrogen systems go a step further.
fuelers are designed as "closed" systems, meaning that the fuel is not
exposed to the atmosphere - unlike gasoline which can be spilled fairly easily
during refueling. This closed system design approach keeps hydrogen always within
proper containment and does not allow oxygen or air to mix with the fuel, thereby
eliminating one of the required combustion elements needed to create a fire. This
further mitigates hydrogen's low ignition energy property, compared to gasoline,
by never allowing a spark or ignition source to have any ability to interact with
the hydrogen gas.
Finally, the National Fire Protection Association (NFPA)
and the International Code Council (ICC) have incorporated hydrogen into their
standards and model codes. These codes reflect the differences in properties between
gasoline and hydrogen (and natural gas as well) through requirements related to
setback distances, control systems, and other public safety elements.
hydrogen harmful to breathe? Accidentally breathing a small amount of
hydrogen won't harm you. Hydrogen is non-toxic to humans, animals and the envionment.
Like other commonly-used gases, hydrogen displaces, or pushes away, oxygen. If
the oxygen you were trying to breathe was displaced by so much hydrogen that you
were breathing very little oxygen, problems could result. Since hydrogen disperses
(rises and spreads out) very quickly, theres a very low risk of breathing
Did hydrogen cause the
Hindenburg accident? The
fire that destroyed the Hindenburg in 1937 gave hydrogen a misleading reputation.
Hydrogen was used to keep the airship buoyant and was initially blamed for the
disaster. An investigation by Addison Bain in the 1990s provided evidence that
the airship's fabric envelope was coated with reactive chemicals, similar to solid
rocket fuel, and was easily ignitable by an electrical discharge. The Zeppelin
Company, builder of the Hindenburg, has since confirmed that the flammable, doped
outer cover is to be blamed for the fire.
burning hydrogen different than the reaction in the H-bomb? Burning hydrogen,
just like burning gasoline, natural gas, or a candle, is a chemical reaction,
which means that electrons get shifted around and new compounds are made, like
water, but the basic atoms remain the same.
The thermonuclear explosion
from a hydrogen bomb is the consequence of a nuclear fusion reaction. During
this reacton, the two isotopes of hydrogen, deuterium and tritium, collide at
very high energy to fuse into helium nuclei, releasing tremendous amounts of energy.
To get these rare isotopes of hydrogen to fuse requires extraordinary
temperatures (hundreds of millions of degrees). These temperatures are supplied
in a thermonuclear weapon (in this case, an H-bomb) by setting off an atomic,
or fission, bomb to trigger the fusion reaction.
commercial hydrogen gas contains no deuterium and no tritium. Without these isotopes,
it is physically impossible for ordinary hydrogen gas to produce a thermonuclear
reaction under any circumstances.