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Record gas prices are making road trips more expensive than ever. But what if, instead of gas, your car ran on the most abundant element in our universe?
On first glance, hydrogen seems to be the ideal fuel for automobiles and other vehicles. It doesn't seem like one could get any cleaner burning, since hydrogen burns (oxidizes) to form simply water vapor. No pollution!
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What a seeming advancement over our current internal combustion engines that put thousands of tons of pollutants into the Earth's atmosphere, as well as giving off massive amounts of heat that contribute to global warming, and many other environmental problems.
Hydrogen (H2) plus Oxygen (O) makes H2O, water, or actually, water vapor, at higher temperatures. And Hydrogen is actually capable of nearly meeting those high expectations.
But the reality is that right now, gasoline-powered motors are still easier on the wallet than hydrogen fuel cells. These battery-like devices inside hydrogen vehicles convert hydrogen and oxygen into water, in the process producing electricity and heat that can power a motor. But hydrogen fuel cells cost ten times more than gasoline engines.
Hydrogen Fuel
Since the early 19th century, scientists have recognized hydrogen as a potential source of fuel. Current uses of hydrogen are in industrial processes, rocket fuel, and spacecraft propulsion. With further research and development, this fuel could also serve as an alternative source of energy for heating and lighting homes, generating electricity, and fueling motor vehicles. When produced from renewable resources and technologies, such as hydro, solar, and wind energy, hydrogen becomes a renewable fuel.
Environmental Impact
There are a couple minor environmental issues. Our Earth's atmosphere is not pure Oxygen, but it is a mixture of gases, with around 4/5 of it being Nitrogen and around 1/5 being Oxygen, and a lot of other gases in small amounts. When Hydrogen (or any other fuel) burns in our atmosphere, a lot of heat is generated (which is sort of the whole point!) When the Nitrogen in the air, it also can oxidize. It can combine with the nearby Oxygen atoms in a variety of ways, such as NO2, NO3, N2O5, and many others. These new compounds are collectively referred to as NOx, and they generally are considered to cause an assortment of health problems in people and other living things.
In addition to NOx production, if the device in which the burning occurs has any lubricants, like oil, there are also oxidation products of the Carbon in them, which can contain CO, carbon monoxide. When Hydrogen is burned in a decently designed device, these environmental problems are fairly minor and they are rarely considered to be any great danger.
Logistics
Hydrogen does have some more significant drawbacks. One of the most difficult to deal with is that it is such a light gas! A pound of Hydrogen contains around 61,000 Btus of latent energy in it, which seems like a lot! For comparison, a pound of regular gasoline only contains around 20,500 Btus in it! Sounds good!
However, a pound of Hydrogen is HUGE! At standard atmospheric pressure and temperature, it takes up around 190 cubic feet of space. In contrast, that pound of gasoline only takes up about 1/50 of a cubic foot.
We can say this same thing in terms of "gallons". A gallon of gasoline contains around 6 pounds, or 125,000 Btus of energy in it. A gallon of hydrogen (gas) only contains around 40 Btus in it. Quite a difference! Instead of a two cubic foot gasoline tank (15 gallons) in your car, you would need a tank more than 3,000 times bigger, over 6,000 cubic feet, for the equivalent Hydrogen! That's a little more than TWO standard semi trailers (8'wide x 8'high x 45' long or 2900 cubic feet each). Pretty big gas tank!
Well, that is obviously not going to happen! So, the many ongoing explorations into using Hydrogen as a fuel always involve carrying COMPRESSED Hydrogen in very thick, heavy tanks. If you have ever seen the kinds of tanks used for the Oxygen for a worker's oxyacetylene cutting torch, that's the kind. Such tanks can hold Hydrogen at around 100 times atmospheric pressure, or 1500 PSI, an extremely high pressure.
Well, at 100 times atmospheric pressure, the Ideal Gas Law tells us that the Hydrogen would now only take up 2900/100 or 29 cubic feet. That works out to around 60 of those high pressure storage tanks (to match the effective capacity of the 15 gallon gasoline tank.). Each tank is very massive to withstand the very high pressure, and each weighs nearly 100 pounds empty. (And around 1/4 pound more when filled with Hydrogen!) So the normal American car which presently weighs around 2800 pounds would have around an extra 6,000 pounds added, so the vehicle would now weigh more than three times as much as current cars! (This tremendously affects acceleration and other performance, and it would be like that car pulling a huge 6,000 pound trailer behind it.
Safety Considerations
There are obvious safety considerations in trying to drive a 9,000 pound vehicle down the road. Handling and stopping would be very seriously affected. But there is a bigger concern.
Those 60 very high pressure tanks present another complication. If industrial workers ignore proper safety rules when working with a high pressure Oxygen tank, it could fall over. As the hundred pound tank falls over, it quickly develops a lot of momentum. If there should happen to be something in the way on the floor, where the neck and valve of the tank hit it, the neck and/or valve tends to just snap off. Suddenly, 1500 PSI of compressed gas has an easy way out, and it all goes out almost immediately. Isaac Newton told us about the Law of Action and equal Reaction. The hundred pound body of the tank then zooms off at extremely high speed in the other direction. There have been many industrial accidents where such Oxygen tanks flew many hundreds of feet through the air and passed completely through many concrete walls.
Most suppliers of industrial Oxygen display photographs of vehicles where ONE such Oxygen tank had not been strapped down properly and the neck wound up snapping off. Usually, the vehicles shown in those pictures are hard to tell as being vehicles, except for maybe a tire somewhere in the picture.
Get the point? Imagine having 60 such tanks in a car. Either one vibrates loose from its clamps, or the guy who last replaced them didn't strap them all down properly, or an accident occurs where you hit another vehicle or a tree. If even one of those tanks ruptures, bad things would result. And have you ever even seen what happens to any car when a semi hits it?
Notice that this issue is not actually related to any hazard of Hydrogen itself, but rather the fact that it would have to be stored at extremely high pressures due to its very low density. Whether it was a high-pressure Oxygen tank or a high-pressure Hydrogen tank, this danger is virtually the same, and is entirely due to the pressure that the gas is compressed to.
Because of this extraordinary safety hazard, which is only due to the very high pressures involved and really has nothing to do with the Hydrogen itself, there is no imaginable way that the US Government would ever allow such vehicles to be licensed. It would conceivably be safer to drive a dynamite truck!
Cost Considerations
It would be wonderful if massive amounts of compressed Hydrogen were easily available. In that case, except for the safety and size considerations just discussed, Hydrogen would be a nearly ideal fuel for vehicles. However, no compressed gas of any kind exists naturally and so mechanical compression is required. An air compressor that can commonly be bought for $300 can compress air to around 100 PSI, around seven times natural atmospheric pressure. However, compressors that are capable of 1500 psi or 100 times atmospheric pressure are very large, very complex, and VERY expensive. In addition, every pipe and every fitting used must also be able to safely withstand such pressures. (Normal pipes would just burst.) In addition, whoever operated such a compressor would have to be very extensively trained, to keep all of its parts from bursting from the pressure and killing someone. The point: People are not ever likely to have their own Hydrogen compressors, and so they would certainly always have to buy the Hydrogen from some large corporation. Logically, it figures that that corporation will be the very same ones that now own all the oil and gasoline companies!
However, even if there was some way to do all that compression, it takes a good amount of electricity for the compressor motor to drive the compressor. A significant cost would be involved for that compression, even if you somehow had your own compressor.
In addition, free Hydrogen does not exist. All of the Hydrogen that might be collected is now in various compounds. The simplest to deal with is water. If you had Chemistry in High School, then you hooked up some electricity to an apparatus that contained water, and you saw little bubbles of Hydrogen form in one upside down test tube and Oxygen form in the other. That is called Electrolysis, or the Dissociation of water. It is obviously pretty easy to do.
But those are just little bubbles of Hydrogen that you collect. Remember that you are going to need an amount of Hydrogen that would more than fill two semi trailers, to just equal one tank of gasoline! It is possible to calculate the amount of electricity needed for that, but you must get the idea that it is a LOT of electricity! So, you get to pay your electric company for that, too.
So, you would wind up paying for the electricity to Dissociate the water in the first place, plus the cost of the electricity needed for the extreme compression. Of course, all of this would be after you bought the necessary equipment!
An alternative, of course, would be to buy (rent actually) tanks of industrial Hydrogen that is already compressed. Current prices for Industrial Hydrogen (the lowest purity available) are around $42 for a large, very high pressure tank which contains 197 standard cubic feet of Hydrogen, plus a monthly rental fee for the tank. The 2900 cubic feet that we had earlier determined were equal to one 15 gallon tank of gasoline, would therefore be around 15 of these tanks, which would cost around $630 for the compressed Hydrogen plus the monthly rental of around $150 for the tanks themselves.
We complain today at paying $2 per gallon for gasoline, which would be $30 for our 15 gallon tank. How many people would be willing to pay $630 and more for the same trip?
Flame Speed
Even if all the other hurdles are overcome regarding using Hydrogen as a fuel, it seems to have yet another disadvantage, one that it shares with most other gaseous fuels: the speed at which a flame front travels is rather slow for the purposes of conventional engines. With an ideal Hydrogen-air mixture, a flame front can travel at around 8 feet/second. For comparison, a gasoline-air mixture creates a flame front speed that ranges from around 70 feet/second up to around 170 feet/second in normal engines.
Consider the inside of an engine cylinder in a normal car engine traveling down the highway. The engine may be rotating at 2,000 rpm, or 33 revolutions per second. The piston must therefore move upward and downward 33 times every second, and its speed in the middle of its stroke is around 45 feet/second. If a fuel burning in the cylinder is to actually push down on the piston, in order to do actual work in propelling the vehicle, the fuel-air mixture needs to burn at a speed faster than the piston is moving! Otherwise, the slow-burning mixture would actually act to SLOW DOWN the piston! It would not only not do productive work, but it would require work FROM the piston.
The fact that a Hydrogen-air mixture has a flame-front speed of around 1/10 that of a gasoline-air mixture seems to indicate that only a very slowly moving mechanism could be used. That might be possible, but it suggests that yet another hurdle might lie in front of Hydrogen ever becoming a common motor fuel.
Composition of Hydrogen
Hydrogen is the simplest and most common element in the universe. It has the highest energy content per unit of weight—52,000 British Thermal Units (Btu) per pound (or 120.7 kilojoules per gram)—of any known fuel. Moreover, when cooled to a liquid state, this low?weight fuel takes up 1/700 as much space as it does in its gaseous state. This is one reason hydrogen is used as a fuel for rocket and spacecraft propulsion, which requires fuel that is low?weight, compact, and has a high energy content.
In a free state and under normal conditions, hydrogen is a colorless, odorless, and tasteless gas. The basic hydrogen (H) molecule exists as two atoms bound together by shared electrons. Each atom is composed of one proton and one orbiting electron. Since hydrogen is about 1/14 as dense as air, some scientists believe it to be the source of all other elements through the process of nuclear fusion. It usually exists in combination with other elements, such as oxygen in water, carbon in methane, and in trace elements as organic compounds. Because it is so chemically active, it rarely stands alone as an element.
When burned (or combined) with pure oxygen, the only by products are heat and water. When burned (or combined) with air, which is about 68% nitrogen, some oxides of nitrogen (or NOx) are formed. Even then, burning hydrogen produces less air pollutants relative to fossil fuels.
Producing Hydrogen
Hydrogen bound in organic matter and in water makes up 70% of the earth's surface. Breaking up these bonds in water allows us produce hydrogen and then to use it as a fuel. There are numerous processes that can be used to break these bonds. Described below are a few methods for producing hydrogen that are currently used, or are under research and development.
Most of the hydrogen now produced in the United States is on an industrial scale by the process of steam reforming, or as a byproduct of petroleum refining and chemicals production. Steam reforming uses thermal energy to separate hydrogen from the carbon components in methane and methanol, and involves the reaction of these fuels with steam on catalytic surfaces. The first step of the reaction decomposes the fuel into hydrogen and carbon monoxide. Then a "shift reaction" changes the carbon monoxide and water to carbon dioxide and hydrogen. These reactions occur at temperatures of 392? F (200 ? C) or greater.
Another way to produce hydrogen is by electrolysis. Electrolysis separates the elements of water—H and oxygen (O)—by charging water with an electrical current. Adding an electrolyte such as salt improves the conductivity of the water and increases the efficiency of the process. The charge breaks the chemical bond between the hydrogen and oxygen and splits apart the atomic components, creating charged particles called ions. The ions form at two poles: the anode, which is positively charged, and the cathode, which is negatively charged. Hydrogen gathers at the cathode and the anode attracts oxygen. A voltage of 1.24 Volts is necessary to separate hydrogen from oxygen in pure water at 77? Fahrenheit (F) and 14.7 pounds per square inch pressure [25? Celsius (C) and 1.03 kilograms (kg) per centimeter squared.] This voltage requirement increases or decreases with changes in temperature and pressure.
The smallest amount of electricity necessary to electrolyze one mole of water is 65.3 Watt-hours (at 77? F; 25 degrees C). Producing one cubit foot of hydrogen requires 0.14 kilowatt-hours (kWh) of electricity (or 4.8 kWh per cubic meter).
Renewable energy sources can produce electricity for electrolysis. For example, Humboldt State University's Schatz Energy Research Center designed and built a stand-alone solar hydrogen system. The system uses a 9.2 kilowatt (KW) photovoltaic (PV) array to provide power to compressors that aerate fish tanks. The power not used to run the compressors runs a 7.2 kilowatt bipolar alkaline electrolyzer. The electrolyzer can produce 53 standard cubic feet of hydrogen per hour (25 liters per minute). The unit has been operating without supervision since 1993. When there is not enough power from the PV array, the hydrogen provides fuel for a 1.5 kilowatt proton exchange membrane fuel cell to provide power for the compressors.
Steam electrolysis is a variation of the conventional electrolysis process. Some of the energy needed to split the water is added as heat instead of electricity, making the process more efficient than conventional electrolysis. At 2,500 degrees Celsius water decomposes into hydrogen and oxygen. This heat could be provided by a concentrating solar energy device. The problem here is to prevent the hydrogen and oxygen from recombining at the high temperatures used in the process.
Thermochemical water splitting uses chemicals such as bromine or iodine, assisted by heat. This causes the water molecule to split. It takes several steps—usually three—to accomplish this entire process.
Photoelectrochemical processes use two types of electrochemical systems to produce hydrogen. One uses soluble metal complexes as a catalyst, while the other uses semiconductor surfaces. When the soluble metal complex dissolves, the complex absorbs solar energy and produces an electrical charge that drives the water splitting reaction. This process mimics photosynthesis.
The other method uses semiconducting electrodes in a photochemical cell to convert optical energy into chemical energy. The semiconductor surface serves two functions, to absorb solar energy and to act as an electrode. Light-induced corrosion limits the useful life of the semiconductor.
Researchers at the University of Tennessee and U.S. Department of Energy's (DOE) Oak Ridge National Laboratory are researching ways to use photosynthesis to produce hydrogen from sunlight. The researchers extracted two photosynthetic complexes from spinach plants; called Photosystem I and Photosystem II. The two work together to produce carbohydrates for the plant. By attaching platinum atoms to the Photosystem I complexes, the researchers were able to produce hydrogen from visible light. Unfortunately, the process required the use of an added chemical that makes the overall process impractical, but the achievement shows potential. The researchers are working to combine the platinum-Photosystem I complexes with the Photosystem II complexes, forming a molecular system that can convert light and water directly into hydrogen, without help from an added chemical.
Biological and photobiological processes can use algae and bacteria to produce hydrogen. Under specific conditions, the pigments in certain types of algae absorb solar energy. The enzyme in the cell acts as a catalyst to split the water molecules. Some bacteria are also capable of producing hydrogen, but unlike algae they require a substrate to grow on. The organisms not only produce hydrogen, but can clean up pollution as well.
Research funded by DOE has led to the discovery of a mechanism to produce significant quantities of hydrogen from algae. Scientists have known for decades that algae produce trace amounts of hydrogen, but had not found a feasible method to increase the production of hydrogen. Scientists from the University of California (UC), Berkeley, and the U.S. DOE's National Renewable Energy Laboratory found the key. After allowing the algae culture to grow under normal conditions, the research team deprived it of both sulfur and oxygen, causing it to switch to an alternate metabolism that generates hydrogen. After several days of generating hydrogen, the algae culture was returned to normal conditions for a few days, allowing it to store up more energy. The process could be repeated many times. Producing hydrogen from algae could eventually provide a cost-effective and practical means to convert sunlight into hydrogen.
Another source of hydrogen produced through natural processes is methane and ethanol. Methane (CH4) is a component of "biogas" that is produced by anaerobic bacteria. Anaerobic bacteria occur widely throughout the environment. They break down or "digest" organic material in the absence of oxygen and produce biogas as a waste product. Sources of biogas include landfills, and livestock waste and municipal sewage treatment facilities. Methane is also the principal component of "natural gas" (a major heating and power plant fuel) produced by anaerobic bacteria eons ago. Ethanol is produced by the fermentation of biomass. Most fuel ethanol produced in the United States is made from corn.
Chemical engineers at the University of Wisconsin-Madison have developed a process to produce hydrogen from glucose, a sugar produced by many plants. The process shows particular promise because it occurs at relatively low temperatures, and can produce fuel-cell-grade hydrogen in a single step. Glucose is manufactured in vast quantities from corn starch, but can also be derived from sugar beets or low-cost waste streams like paper mill sludge, cheese whey, corn stover or wood waste.
The United States, Japan, Canada, and France have investigated thermal water splitting, a radically different approach to creating hydrogen. This process uses heat of up to 5,430?F (3,000?C) to split water molecules.
Potential Uses for Hydrogen
When properly stored, hydrogen as a fuel burns in either a gaseous or liquid state. Motor vehicles and furnaces can be converted to use hydrogen as a fuel. Hydrogen has actually been used in the transportation, industrial, and residential sectors in the United States for many years. Many people in the late 19th century burned a fuel called "town gas," which is a mixture of hydrogen and carbon monoxide. Several countries, including Brazil and Germany, still distribute this fuel. Hydrogen was used in early "hot-air" balloons, and later in airships (dirigibles) during the early 1900's. Gaseous hydrogen was used in 1820 as fuel for one of the earliest internal combustion engines. The U.S. Air Force had a secret, multi-million dollar program during the 1950's, code-named "Suntan," to develop hydrogen as a fuel for airplanes. Currently, industries use large quantities of hydrogen for refining petroleum, and for producing ammonia and methanol. The Space Shuttle uses hydrogen as fuel for its rockets. Automobile manufacturers have developed hydrogen-powered cars.
Burning hydrogen creates less air pollution than gasoline or diesel. Hydrogen also has a higher flame speed, wider flammability limits, higher detonation temperature, burns hotter, and takes less energy to ignite than gasoline. This means that hydrogen burns faster, but carries the danger of pre-ignition and flashback. While hydrogen has its advantages as a vehicle fuel it still has a long way to go before it can be used as a substitute for gasoline. This is mainly due to the investment required to develop a hydrogen production and distribution infrastructure.
However, things are getting started in this regard. Vehicle manufacturers Honda and BMW have set up hydrogen fueling stations as part of their efforts to develop fuel cell powered cars. At Honda's research and development center in Torrance, California, a PV array electrolyses hydrogen from water. The array generates enough hydrogen to power one fuel-cell vehicle. Additional power from the power grid is used to increase the hydrogen production capacity. The new station is supporting Honda's fuel cell vehicle development program for hydrogen production, storage, and fueling. Honda and a fuel cell developer are also working together on a "home" hydrogen refueling system for fuel cell vehicles. BMW opened a hydrogen fueling station at the company's engineering and emissions control test center in Oxnard, California. BMW is taking a different approach than most car companies, burning hydrogen directly in advanced internal-combustion engines, and is testing these vehicles at the Oxnard facility.
The California Fuel Cell Partnership (CaFCP) is also building a hydrogen infrastructure. The CaFCP commissioned its first "satellite" hydrogen fueling system in late October 2002, in Richmond, California, about 70 miles from the CaFCP headquarters and a primary refueling facility in West Sacramento. This extends the range over which the CaFCP's prototype fuel cell vehicles can be driven. The fueling system uses electrolysis to generate hydrogen from water and includes a storage unit capable of holding 104 pounds (47 kilograms) of hydrogen. It is capable of fueling a small fleet of vehicles and requires only one or two minutes per refueling.
In November 2002, the world's first hydrogen energy station that can provide fuel for vehicles and also produce electricity opened in Las Vegas Nevada. The station is located in the city's vehicle maintenance and operation service center. It combines an on-site hydrogen generator, compressor, liquid and gaseous hydrogen storage tanks, dispensing systems, and a stationary fuel cell. It is capable of dispensing hydrogen, hydrogen-enriched natural gas, and compressed natural gas. DOE is also working with the city to convert municipal vehicles to operate on hydrogen.
Fuel cells are a type of technology that use hydrogen to produce useful energy. In fuel cells, electrolysis is reversed by combining hydrogen and oxygen through an electrochemical process, which produces electricity, heat, and water. The U.S. space program has used fuel cells to power spacecraft for decades. Fuel cells capable of powering automobiles and buses have been and are being developed. Several companies are developing fuel cells for stationary power generation. Most major automobile manufacturers are developing fuel cell powered automobiles.
Hydrogen could be considered a way to store energy produced from renewable resources such as solar, wind, biomass, hydro, and geothermal. For example, when the sun is shining, solar photovoltaic systems can provide the electricity needed to separate the hydrogen (as described above regarding Humboldt State University's Research Center). The hydrogen could then be stored and burned as fuel, or to operate a fuel cell to generate electricity at night or during cloudy periods.
Storing Hydrogen
In order to use hydrogen on a large scale, safe, practical storage systems must be developed, especially for automobiles. Although hydrogen can be stored as a liquid, it is a difficult process because the hydrogen must be cooled to -423? Fahrenheit (-253? Celsius). Refrigerating hydrogen to this temperature uses the equivalent of 25% to 30% of its energy content, and requires special materials and handling. To cool one pound (0.45 kg) of hydrogen requires 5 kWh of electrical energy.
Hydrogen may also be stored as a gas, which uses less energy than making liquid hydrogen. As a gas, it must be pressurized to store any appreciable amount. For large-scale use, pressurized Hydrogen gas could be stored in caverns, gas fields, and mines. The hydrogen gas could then be piped into individual homes in the same way as natural gas. Though this means of storage is feasible for heating, it is not practical for transportation because the pressurized metal tanks used for storing hydrogen gas for transportation are very expensive.
A potentially more efficient method of storing hydrogen is in hydrides. Hydrides are chemical compounds of hydrogen and other materials. Research is currently being conducted on magnesium hydrides. Certain metal alloys such as magnesium nickel, magnesium copper, and iron titanium compounds, absorb hydrogen and release it when heated. Hydrides, however, store little energy per unit weight. Current research aims to produce a compound that will carry a significant amount of hydrogen with a high energy density, release the hydrogen as a fuel, react quickly, and be cost-effective.
A company in Utah, Power Ball Technologies, has developed a process in which sodium metal is pelletized and encapsulated with polyethylene plastic. The pellets can then be containerized, transported, and then opened in a patented hydrogen generator to produce hydrogen gas. According to the company, each gallon of these pellets is capable of producing 1,307 gallons of hydrogen gas, which is an equivalent hydrogen storage density more than 7 times greater by volume than a compressed hydrogen tank storing hydrogen at 3,000 psi.
The Cost of Hydrogen
Currently the most cost-effective way to produce hydrogen is steam reforming. According to the U.S. Department of Energy, in 1995 the cost was $7.39 per million Btu ($7.00 per gigajoule) in large plant production. This assumes a cost for natural gas of $2.43 per million Btu ($2.30 per gigajoule). This is the equivalent of $0.93 per gallon ($0.24 per liter) of gasoline. The production of hydrogen by electrolysis using hydroelectricity at off peak rates costs between $10.55 to $21.10 per million Btu ($10.00 to $20.00 per gigajoule).
Conclusion
Yes, fuel cells, which are effective mechanisms for converting Hydrogen and Oxygen into water vapor and releasing a lot of energy, certainly seem to be fascinating potential sources of energy for vehicles. However, it certainly seems that sufficient Hydrogen cannot be stored in a car for any length of trip without compressing it to extremely high pressures. THAT fact causes both cost and safety considerations which seem to make practical use of Hydrogen remain a fascinating dream which will probably never become reality.
Yes, Hydrogen can be demonstrated in experimental vehicles, and they can have impressive acceleration and speed. But that's with a rather small Hydrogen tank aboard. If you ever see an impressive demonstration like that of a Hydrogen powered vehicle, make sure to ask how long that vehicle could continue to perform like that. The answer is certain to be no more than a few minutes at most. So, as a demonstration, Hydrogen can seem quite impressive, because it is! But in actual practical applications, the details probably make it never to be usable in our vehicles.
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