Introduction to Hydrogen PowerUpdated June 2, 2022 Energy Science
At present, the United States produces 100 billion cubic feet of hydrogen annually for various industrial applications as well as the continued use by NASA. In the U.S. alone, 50 million pounds of hydrogen are used daily in industrial processes, with many millions of pounds used internationally.
Hydrogen is used in the manufacture of gasoline and heating oil, as well as in the manufacture of ammonia, which is then used to make fertilizer and other chemical products. Hydrogen gas is used in welding, to hydrogenate vegetable oil and peanut butter. Hydrogen is a part of the formula for the rocket fuel that put a man on the moon, and continues to launch the ongoing Space Shuttle missions. Used in the manufacture of glass and industrial lubricants, semiconductor circuits, and some cosmetic products, it is apparent that the safe and efficient use of hydrogen is already taking place here in the U.S. and around the world every day.
Advantages of Hydrogen Energy
Hydrogen as a fuel source for energy, whether used to produce electricity via a hydrogen fuel cell or used as a primary fuel to drive generators and automobile engines, has many positive advantages, balanced with very few negative consequences or drawbacks. The foremost of these advantages, particularly when compared with the use of hydrocarbon fossil fuels for electricity production and transportation, is that among all of its potential applications, hydrogen's only waste or byproduct is H2O pure water.
While hydrocarbon fuels produce massive amounts of carbon dioxide, a greenhouse gas, as well as acid rain, hydrogen fueled combustion engines actually clean the air they pass through. Fuel cell powered electric vehicles produce only water from their exhaust pipes, along with trace amounts of oxides of nitrogen which occur naturally in the Earth's atmosphere.
Comparing the pros and cons of using hydrogen as opposed to nuclear fission for electric production, the balance falls again heavily in favor of hydrogen. Fission reactors use a fuel whose availability is limited and production dangerous, while even the least efficient hydrogen technology provides cleaner power with almost no risk assumed in production, especially when taking into account that the technology for renewable sources of hydrogen production is already a current reality.
In terms of waste management, the burden of continued use of fissionable materials creates highly toxic spent fuel that must be handled with the most stringent safety protocols for over 20,000 years.
Hydrogen Fuel Cells
Hydrogen fuel cells have been in development since Sir William Grove's time. From the working systems developed by Francis Bacon to the research and development crucible of NASA, efforts have been made to adapt fuel cells to varied industrial and commercial tasks, as well as provide power for transportation in the form of electric vehicles.
The workings of the hydrogen fuel cell are surprisingly simple, comprising no moving parts, and they can produce electricity for a wide variety of uses, from the smallest generator or engine to industrial and commercial levels commensurate with the largest power plants currently operating.
The energy exchange that takes place in the hydrogen fuel cell begins with a chemical reaction between the hydrogen introduced to the cell, and the anode, or negative terminal of the fuel cell. The anode is covered with a material that chemically reacts with hydrogen, causing the hydrogen atoms to release some of their available electrons, leaving behind the positively charged protons in the nucleus of the hydrogen atoms.
A membrane divides the fuel cell, and on the other side, is the positively charged element or cathode. The cathode reacts with the oxygen available in the air, causing another chemical reaction that leaves the cathode with a positive potential. As electrons are drawn to the cathode side of the cell by its positive charge, they are absorbed by the oxygen atoms on the cathode side of the cell, producing negatively charged particles called oxygen anions. By providing an external circuit from the negatively charged anode side of the cell to the positive cathode side, a usable electric current is formed.
The real magic of the hydrogen fuel cell then takes place inside, as the only particles that can pass through the membrane dividing the cells are the positively-charged protons from the anode side. Protons drawn through the membrane combine with the negatively charged oxygen anions on the cathode side, producing once again H 2 O. The oxygen is expelled on the cathode side, priming the cell for further oxygen absorption. A small amount of heat is released by the chemical reactions within the fuel cell, varying according to the size and design of the cell.
Hydrogen fuel cells are commonly used in multiple sets, which can produce vast amounts of electric power. Cell designs vary from small cells the size of a car battery to larger industrial size cells, which may someday power entire cities.
Hydrogen Powered Automobiles
Currently, fuel cells are being used in several automobile applications, and these cars are becoming commercially available in the U.S. and Europe. In Reykjavik, Iceland, the city's commercial bus service is being converted to non-polluting electric motors driven by hydrogen fuel cells. The cities of Chicago and Vancouver are both examining using fuel cell powered buses as part of their transportation systems.
Daimler Chrysler has developed the Necar 4, a zero-emission vehicle with an electric motor powered by hydrogen fuel cells, and hopes to introduce the car to the U.S. market as soon as 2004. The Necar 4 has a top speed of 90 mph and has a 280-mile range, comparable to most gasoline-powered cars.
Fuel cell design varies according to the power demands of a given system, and the operating temperatures that best suit that particular application. Higher operating temperatures allow the use of less pure hydrogen sources, as fuel cells are capable of chemically extracting hydrogen from a variety of fuels like methanol, and even fossil fuels like oil and natural gas. Different materials are used for the fuel cell membrane, allowing only specific particles to penetrate to the other side of the cell. Cell design also varies as to the material that coats the electrodes within the cell.
Alkaline fuel cells, first used by Francis Bacon, are the type that NASA uses in its space shuttle missions. The electrolyte, or membrane material, is potassium hydroxide, and the catalyst for the electrode reactions is often platinum, contributing to the high cost that until recently slowed the possibility of commercially developed alkaline fuel cells. Alkaline cells can reach power generating efficiencies of up to 70%, meaning that of the hydrogen consumed in the reaction within the fuel cell, only 30% of its potential heat energy is lost in the chemical reaction converting hydrogen into electricity.
Phosphoric acid (PA) fuel cells are the type which at present have achieved the widest commercial application. These cells have been used where stationary power plants are appropriate, such as in hospitals, nursing homes, office buildings, and utility power plants. With phosphoric acid as the electrolyte and operating temperatures around 400 degrees Fahrenheit, PA fuel cells are also perfect for what is being called cogeneration.
In this process, the steam from the water produced within the cell can be collected and used, raising the potential efficiency of this type of fuel cell to as high as 85%. This is well beyond the normal operating efficiency of over 40%.
PEM Fuel Cells
Proton exchange membrane (PEM) fuel cells are the smallest and lightest of the designs at present, making them the engineer's choice for transportation applications like automobiles and trucks. All of the automobiles that are being readied for the consumer marketplace by major manufacturers worldwide, including GM, Ford, DaimlerChrysler, Honda, and Nissan, are using stacks of PEM fuel cells for their power plants.
Ballard Power Systems of Burnaby, Canada, provides these cells at present. PEM cells also have the lowest operating temperatures, around 200 degrees Fahrenheit, making them ideal for cars and trucks, as lower operating temperatures mean faster start-up times for the internal chemical reactions that power the fuel cells. At these lower temperatures, however, the PEM cell requires pure hydrogen to operate. While the proton exchange membrane fuel cell typically runs at efficiencies in the range of 30%, this will improve as research continues and smaller, lighter designs become a reality.
Solid oxide fuel cells are currently in use in Japan and Europe, promising the type of power needed for large installations such as central electricity generation for utility companies and industrial production facilities. Using a solid ceramic material as opposed to a liquid electrolyte, solid oxide cells operate at the hottest temperatures of any fuel cell, up to 1800 degrees Fahrenheit. This again presents the possibility of cogeneration to take advantage of the excess heat, as well as allowing the use of less pure hydrogen sources.
Finally, molten carbonate fuel cells compete with phosphoric acid cells for commercial applications like hotels and airport terminals. Using a molten mixture of carbonate salts to screen the ions within, and operating at around 1200 degrees Fahrenheit, this fuel cell design allows the use of less pure fuels, even coal- and oil-based hydrocarbon fuel sources.
Research continues on fuel cell technology, and new approaches, designs, and materials are being examined continuously for potential use in this emerging field. Two promising developments are the direct methanol fuel cell, where the cell design allows hydrogen extraction from methanol within the cell, and regenerative fuel cells, where the fuel cell is a closed system, making it a perfect technology for space flight applications.
The other major thrust in hydrogen technology is the use of hydrogen as a directly combustible fuel. While the use of hydrogen, in general, seems to be stigmatized by what has been called the "Hindenburg Effect," its use as a combustible fuel is where hydrogen has the strongest association with past difficulties, hindering public acceptance of this promising area of study.
No major technical innovations are necessary to start using hydrogen as a combustible fuel, as the ability to run existing fossil fuel internal combustion engines on hydrogen is already a reality. Similar to the conversion that allows internal combustion engines to run on natural gas, the conversion is characterized as minor and affordable, and presents many advantages over the use of nonrenewable hydrocarbon fossil fuels.
Technical Challenges of Hydrogen Power
Some technical problems have presented themselves when using hydrogen fuel in an internal combustion engine, mostly having to do with backflushing (where gaseous hydrogen is ignited in the carburetor before it can enter the cylinder) and hot spots within the combustion chamber. Utilizing a direct fuel injection system instead of a carburetor, and installing a water induction system to cool the combustion chamber have significantly reduced backflushing. It has also helped the engine fire at cooler temperatures, reducing formation of oxides of nitrogen from already low levels to practically non-existent.
While the vehicle powered by an internal combustion engine fueled with hydrogen is not totally emission-free, compared to an engine running on hydrocarbon fuel, or even cleaner natural gas, the contrast is striking. While hydrocarbon fuels produce carbon monoxide, carbon dioxide, particulate pollution, and hydrocarbon chemicals that interfere with the Earth's ozone layer, an engine burning hydrogen fuel produces water vapor and small amounts of oxides of nitrogen.
With technical innovations such as water induction systems as well as other pollution control measures, the vehicle powered by an internal combustion engine running on hydrogen fuel actually has the potential to clean the air it runs through while operating. Also, while the number of vehicles currently running on hydrogen fuel is small, it has been noted that running at lower temperatures with this alternative fuel has the potential to extend engine life, as chemical corrosion from hydrocarbon fuel and engine wear due to metal embrittlement are greatly reduced.
Ongoing Experiments With Hydrogen Energy
In Russia, experiments have been done running jet aircraft engines on hydrogen fuel, and Japanese, German and American companies are continuing the research and development of clean-burning hydrogen engines.
Interestingly, it appears that as an interim development, adding hydrogen to natural gas and burning the combination fuel increases the efficiency of the natural gas engine, while reducing its exhaust emissions significantly (up to 50%). This provides an opportunity for hydrogen fuel to become a part of the energy landscape in smaller, easier to accomplish steps.