Can we use water as a fuel

Can we use water as a fuel

To save you a lot of embarrassment, I’ll talk of hydrogen.

Hydrogen is fuel.

Water contains hydrogen, but bonded with oxygen.

If the hydrogen can be liberated from water (by a process known as dissociation), you can use it as fuel. Actually, you need to make water conductive by making it an electrolyte; quite a simple and inexpensive process.

You do not even need the oxygen from water; enough oxygen is freely available in the atmosphere.

At the heart of hydrogen's promise lie two key qualities.

First, supplies of it are virtually limitless. Since it is a primary constituent of water, an economical method of extracting it is the only thing needed to produce literal oceans of energy.

Second, burning hydrogen does no harm to the environment. It simply returns the gas to the form of water.

Hydrogen is also a uniquely flexible medium for the storage and distribution of energy. It is easily converted into electricity through the use of a fuel cell, and electricity can be turned back into hydrogen by electrolyzing water.

Transmitted through pipelines similar to those used for natural gas, it can carry energy from large, remote powerplants to individual homes and factories as electricity now does—but with far greater efficiency.

And unlike electricity, hydrogen can be kept in tanks to fuel vehicles, or to store power for periods of peak demand.

In the words of Peter Hoffman, editor and publisher of The Hydrogen Letter: "Hydrogen is the fuel at the end of the line when everything else has been depleted, found unworkable or environmentally objectionable."

To most people, the word hydrogen immediately conjures up the spectre of the Hindenburg dirigible, exploding over the New Jersey countryside.

▲The model LZ-129 Hindenburg burning at Lakehurst, New Jersey

Yet, a more objective analysis reveals that hydrogen is no more dangerous than other flammable materials used as fuels, and even has some significant safety advantages.

Ironically, a case in point is the Hindenburg incident itself.

Although it exploded hundreds of feet off the ground, 62 of the air ship's 97 passengers survived, partly because the lightweight gas rose clear of the craft as it burned, and was consumed in a relatively brief explosion.

Kerosene jet fuel would have clung to the wreckage and burned furiously for a long time, likely killing everyone in the vicinity.

Still, the Hindenburg remains a real obstacle to hydrogen's acceptance among the general public.

From a practical point of view, however, the real problems have to do with engineering and economics.

In an important new development in the electrolysis of water, a thin plastic-like sheet is actually the electrolyte, a solid-polymer material that is a much better ion conductor than the liquid potassium hydroxide electrolyte used with water in conventional electrolysis.

The result? More hydrogen for the same amount of electrical energy used.

It's just one of a variety of advances being made in the field of hydrogen production.

Others include:

• An electrolysis system that splits water when the sun shines on its electrodes.

• An electrolysis process that uses powdered coal and water, requiring only half the amount of electricity needed in conventional electrolysis. • Biological organisms and materials that split water when exposed to sunlight.

• Thermochemical cycles that induce water-splitting through intense heat.

Why all the intensive research into hydrogen production?

Two reasons.

One, hydrogen is widely used industrially as a chemical feedstock for many manufacturing processes. Most hydrogen today comes from natural gas and petroleum, which are in relatively short supply.

Two, when that short supply becomes no supply, we'll need other sources of hydrogen and other sources of fuel.

Fortunately, nature's safe contains a virtually inexhaustible supply of hydrogen. We just have to find the combination to unlock it.

Seventy-five percent of the earth's surface is covered with water.

Every molecule of water has two atoms of hydrogen and one of oxygen.

If we can learn to economically extract the hydrogen trapped in that water, our fuel worries will be over.

Hydrogen is a better fuel than gasoline.

Pollution-free, it turns back into water when burned.

It packs more energy per pound than any fuel—for example, 19,000 Btu of potential heat energy for a pound of gasoline, 61,000 for a pound of liquid hydrogen.

The biggest single problem standing in the way of a hydrogen economy is cost.

Those two hydrogen atoms are very friendly with that oxygen atom.

Splitting them apart takes energy.

With electrolysis of water—the standard commercial way of splitting water, used for decades—that energy comes from expensive electricity.

"Electrolytic hydrogen today costs in the neighborhood of $15—$25 per million Btu," says Al Mezzina at Brookhaven National Laboratory. "Gasoline is something like $6—$8 per million Btu."

Because of its expense, electrolytic hydrogen constitutes only about one percent of all hydrogen produced.

It is used where especially pure hydrogen is needed—in metal processing and semiconductor manufacturing processes, for example.

But the future is not entirely bleak.

Some or all of the systems just mentioned may one day play an important role in hydrogen production.

Take a closer look at them.

Advances in electrolysis

Conventional electrolysis applies a DC voltage across two electrodes submerged in a solution of water and potassium hydroxide. When current flows, an exchange of ions and electrons occurs between the electrodes. Hydrogen atoms collect at the negative electrode (cathode) and oxygen atoms at the positive electrode (anode). A separator between the electrodes separates the gases.

Today, researchers and scientists at Brookhaven are working on an experimental system that is similar to a conventional electrolysis system, except that it eliminates the need for man-made electricity. As with conventional electrolysis, the system uses two electrodes. The difference is that the anode is a special light-sensitive semiconductor made of iron oxide.

"It is coated with a thin film of titanium dioxide to prevent it from corroding in its solution of water and potassium hydroxide," says Dr. Chiang Yang, one of the scientists involved in the experiment. When sunlight shines on the system, an electrical potential is created at the anode, causing current to flow. An electron and ion exchange occurs, much as it does in a conventional electrolysis system.

"You can think of what happens at the anode in this way," Yang explains. "When sunlight strikes the semiconductor electrode, some electrons become highly excited and change their position, sort of like individuals at a theater getting up to let other people have their seats. This leaves holes to be filled. Other electrons from the water move in to occupy the holes. This results in water-splitting. But sometimes the excited electrons move back into the holes they vacated before other electrons from the water can move in, much as if many of those people in the theater got up out of their seats, thought better of it, and sat back down again. This is wasted motion, which produces nothing but heat. We call it recombination. We want to reduce recombination to a minimum, which is another way of saying we want to increase our efficiency."

So far the system exists only as a small laboratory model.

Decreasing the recombination rate is just one of the many problems that must be solved before it progresses beyond that stage.

And Dr. Yang cautions against undue optimism. "In the overall scheme of photoelectrolysis, what we have done is not a breakthrough," he says. "But it's an important step along the road to developing practical photoelectrolytic cells. However, this and other similar systems that use sunlight and semiconductor electrodes must be explored fully. If we can work out the bugs, they may play a significant role in hydrogen production."

An experimental photochemical approach to electrolysis is also being pursued by a group at Caltech, led by Prof. Harry B. Gray. The experimenters do not use solid electrodes but instead a unique, man-made molecule (an organic complex with the metal rhodium at its core). When dissolved in water and exposed to sunlight, the chemical splits water molecules, releasing hydrogen. "It's far too early to tell if this will ever be commercially practical," says Dr. Virginia Houling, a member of Gray's research team. "We are on the very edge of technology with these systems.”

Harry B. Gray | www.cce.caltech.edu

Another promising approach to electrolysis is the GE solid-electrolyte system developed in Wilmington, Mass. The solid-polymer material is 10 mils thick and is coated on both sides with a thin film of electrode material. "This system is important in various ways," says Jack Russell, GE program manager for solid-polymer-electrolyte electrolysis programs. "It is more efficient than comparable conventional systems, which essentially means you can produce more hydrogen for the same amount of electricity. And it uses no caustic liquid electrolytes."

Still another electrolysis system is in very early experimental stages at the University of Connecticut. Prof. Robert Coughlin uses a conventional electrolyzer and a water solution of sodium hydroxide or acid. But he also adds finely powdered coal—the type of coal electric utilities burn for their turbines. The powdered coal has the interesting effect of reducing by 50 percent the amount of electricity needed to produce a given amount of hydrogen. The coal oxidizes and is consumed in the process, but the energy generated by oxidation reduces the amount of electrical energy needed for electrolysis.

What the end results of his initial lab work will be, Coughlin isn't sure.

"But when you have the possibility of reducing electrical costs by 50 percent," he says, "you've got to check it out. And we do have vast supplies of coal."

Few experts doubt that some form of electrolysis, perhaps various forms in different regions, will eventually play an important role in hydrogen production.

For example, says Brookhaven's Mezzina, "As research in photovoltaic cells develops to the point where they are cheap enough and practical, electrolyzers in the Sun Belt might be powered by solar cells. In areas where there's not a lot of sun but plenty of hydroelectric power, hydroelectric plants may supply water-splitting energy. In still other places, nuclear power plants may supply the electricity."

Splitting water with heat

Nuclear plants could also supply heat for a different approach to water-splitting—thermochemical dissociation.

Researchers have known for a long time that if water is heated to 3,700 degrees F it spontaneously breaks up into oxygen and hydrogen.

There are problems with this method, though—not the least of which is lack of container materials that can withstand such temperatures over a sustained period.

Also, there is no practical way to obtain such temperatures.

However, if certain inorganic compounds are added to the water—sulfur dioxide and iodine, for example—the water breaks up through a series of chemical reactions at a much lower temperature: 1,400 degrees F.

At the end of the process, the inorganic compounds are regenerated, and the process is ready to start again. Still highly experimental, the thermochemical cycles used so far have derived their heat from conventional laboratory furnaces.

"We're still years away from actual hook-up to a nuclear reactor," says Dr. Giovanni Caprioglio, manager of chemistry at General Atomic Corp. in San Diego, Calif.

General Atomic is one of the leaders in thermochemical research.

One problem is that the only kind of reactor that can provide heat at the 1,400-degree temperature needed is the gas-cooled nuclear reactor". And there are only two of them working in the world," Caprioglio says. "One is in Colorado, and the other is in Germany."

Heat from a solar collector might also work. Georgia Tech has built a solar collector that is capable of providing the needed heat. "But the efficiency may not be as great as it would be with a nuclear reactor," Caprioglio says.

"At this point, no one can say with absolute certainty that, even if the technical problems (such as heat-resistant materials) are solved, we can bring the cost and efficiencies to a reasonable level," says Caroline Mason of Los Alamos National Scientific Laboratories, where research is also being done on thermochemical cycles. "But we must pursue it to find out."

Caprioglio agrees. "If everything goes as planned," he says, "there will be some substantial chemical-engineering demonstration processes, and we'll start collecting data and putting down some serious efficiency and cost-analysis figures."

Biological water-splitting

There are creatures on Earth that split water without electricity, heat, high technology, or effort. They are, of course, the green plants. Using the greenish compound, chlorophyll, they capture the energy of sunlight to turn water and carbon dioxide into the oxygen we breathe and energy-rich compounds containing carbon, hydrogen, and oxygen—the carbohydrates.

The process, photosynthesis, is the basis for most life on Earth.

This observation has stimulated some researchers to follow what is probably the most exotic—and far-off—of all the experimental paths to water-splitting: modifying the plants' own photosynthetic process so that hydrogen is freed, rather than trapped in carbohydrates.

At Oak Ridge National Laboratory, experimenters are investigating the use of both spinach chloroplasts (the disc-like structures where photosynthesis occurs in green plants) and fresh-water algae to generate hydrogen. Oak Ridge Lab's Dr. Elias Greenbaum said: "There is a chance that photobiological hydrogen production may be able to take its place among the new energy sources that have been and will be developed when fossil fuels become too expensive or unavailable."

No one can really predict what the outcome of all this research will be.

Many scientists and researchers in the field of hydrogen production, strongly voiced two themes :

1) We must explore all possible areas of hydrogen production, even if many prove to be too costly, inefficient, or impractical. That's the only way real progress can be achieved.

2) Hydrogen will be the fuel of the future.

The only questions are when and how it will be produced.

We can. It's just that it's not economical.

Using water as fuel requires it to react with something abundant everywhere. Most abundant thing that is the same everywhere is air. Therefore it should either:

• React with oxygen (we know it doesn't happen)
• React with nitrogen (it doesn't happen either)

So much for water.

So, if we still insist on using it as fuel, most logical way to do it is to split it into hydrogen and oxygen. This is called electrolysis, and requires energy.

But the energy obtained from burning hydrogen to obtain water is the same as hydrolizing water to split it. This is called “enthalpy of formation of water”.

The basic principle of universe is that “energy can neither be created nor destroyed”, so it holds true in this case as well. If you want to split up water, you have to put in the equal amount of energy so the atoms forming water can be “convinced” to break their bonds. This doesn't leave us any free energy that we can harness.

Some “geniuses” may say that “yeah but using a catalyst it can be done”. No. Here's the reason:

This is a representative exothermic (heat liberating) reaction graph. In our example, hydrogen is on the left hand side. When you burn it to obtain water, you obtain the energy shown as delta G on the graph. In order to split it to hydrogen and oxygen, you'll need to put in the same amount of energy.

The only difference a catalyst makes is that it lowers the “activation energy” (Ea) required for the reaction to take place, nothing more.

In order for us to be able to efficiently use water as fuel, we need a catalyst that completely nullifies the activation energy so that the water splits into hydrogen and oxygen as soon as it comes in contact with it, at least in theory. There's no such thing as of this writing, despite the fact that at least two decades of research has been put into it.

Another option is to find vast natural hydrogen reserves somewhere in the world and, cheap and safe methods to extract and transport it globally. So far, no such resource has been discovered.

Even if we can, the combustion systems we use today (engines, boilers, etc.) should all be redesigned as hydrogen is difficult to handle and loves to explode (does the word “Hindenburg” ring a bell?) So a tiny leak somewhere in your engine can turn it into a fireball in the blink of an eye.

This is exactly why we don't synthesize fuels even today, though we know how to, because the total energy to be gained is zero or less, considering the losses. We only extract and distill what has already been formed through natural processes, because it's cheaper.

Hope this helps.

As might be expected, these last two questions raised considerable disagreement among the experts, but less than might be expected.

Most generally agreed that it will be another 20 years before we see hydrogen making any significant contribution to the energy picture. Calvin says, "Within 25 years, 10 percent of the U.S. will be on the so-called hydrogen economy."

Hydrogen is the most promising fuel for the future. All the experts believe we'll learn to produce it economically. The question nobody can answer, though, is how soon.

Plenty more research is needed.

Image source Google

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