“I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable.” (Jules Verne The Mysterious Island -1874)
HYDROGEN ENERGY IS NOT CHEAP WHEN COMPARED TO OTHER ENERGY SOURCES AT THIS TIME. HOWEVER, HYDROGEN CAN BE THE KEY TO SOLVING THE ENERGY PROBLEMS OF THE WORLD.
One of the most important reasons for the last two world wars was the sharing of energy sources. 60 years on from the last world war, the world is now very close to confronting the same problem. There has been an enormous rise in energy demand since the middle of the last century. This increase has resulted from both rapid industrial development and population growth. As shown in Figure 1 and 2, the world population is 4.8 times greater, and the total energy requirement has increased more than 30 fold from between 1850 and 2000. Many studies have demonstrated that while global demand increases by at least 2-3% per year, the current oil fields are depleting at an average of 3-5% per year. If this demand continues at this rate, we will reach a point of crisis in oil sometime after 2010, and the same will be true for natural gas somewhat later, between 2020 and 2030 [1, 3]. The basic energy source of the world, hydrogen, is a new hope for solving the energy problem. It is likely that this century will be the century of the fuel cell. This technology uses hydrogen as fuel, and offers the prospect of supplying the world with clean, sustainable electrical power.
Hydrogen, which is the simplest element in space, was discovered in the 16th century and its inflammable property was understood in the 18th century. Ninety percent of the known universe consists of this simple element. Hydrogen is colorless, odorless, nonpoisonous, and 14.4 times lighter than air. In its liquid phase it has a temperature of -252.77 Â°C. It is the fuel of the sun and other stars, hence the main energy source of the universe. Hydrogen is not found as a free element in nature, but rather it is found as a compound, particularly as water. Hydrogen has the largest energy amount per unit mass among known fuels. The energy of 1 kg of hydrogen equals 2.1 kg of natural gas and 2.8 kg gasoline. However, its volume per unit energy is higher. It is 1.33 times more efficient compared with fossil fuels as an energy source. When hydrogen is used to produce heat or propulsion, only liquid water or water vapor emerge, making it an extremely clean energy source.
Hydrogen can be used with fuel cells to produce electricity. At the present time, the cost of this method is 3 times more expensive when compared to other fuels. Fuel cells use hydrogen, or hydrogen containing compounds to produce electrical energy and heat. A fuel cell has no moving parts and makes no noise when operating. A single fuel cell contains three layers, as shown in Figure 3. These are the anode-electrode layer, the membrane layer, and the cathode-electrode layer.
There are three types of fuel cells; Polymer Electrolyte Membrane (PEM), Direct Methanol Fuel Cell (DMFC), and Solid Oxide Fuel Cell (SOFC), each named after the material used as fuel. The PEM fuel cell is fueled by pure hydrogen. In the anode, hydrogen is split into its basic elements, a proton and an electron. While the proton migrates through the membrane of the fuel cell, the electron travels around the membrane and goes to the cathode, creating an electrical current. In the cathode-hydrogen proton the electron reacts with oxygen to form water, which is rejected as waste. The basic system is the same for the DMFC and the SOFC fuel cells. The DMFC is fueled by a mixture of methanol and water. Before reaching the anode electrode, the methanol is split into CO2and hydrogen. The SOFC fuel cell can use different kinds of fuels that contain methane and hydrogen. All the reactions are shown in Table 1. One fuel cell can produce 0.6 of a volt. To get enough power, several fuel cells are piled in a stack. The space between fuel cells is filled with gas that helps to distribute the hydrogen and oxygen gas to the membranes.
Although hydrogen energy is a new source, the production of hydrogen is not a new concept. Every year, 500 billion m3 of hydrogen is produced, stored, transported, and utilized in the world. Initially, hydrogen was used for the production of ammonia, but today hydrogen utilization has expanded tremendously to incorporate applications in chemical and petroleum refining, metallurgy, the hydrogenation of edible fats and oils, space and weather programs, fuel cells, and the manufacture of high quality electronic components. The most important consumer is in the petroleum- chemistry industry.
Hydrogen can be obtained by using different methods. Hydrogen can be produced from electricity, using electrolysis to split water into hydrogen and oxygen. Reforming is another method that produces hydrogen. In this method, hydrogen is extracted from a gas with a high concentration of methane, such as natural gas. This process uses hot steam to obtain hydrogen from the methane. When methane gas is mixed with hot water vapor, the gas is split into carbon monoxide and hydrogen.
Although hydrogen can be stored as a gas or liquid, storing and handling hydrogen is difficult as compared to gasoline. While gasoline is a liquid, hydrogen is a gas. At atmospheric pressure at sea level (pressure at sea level is 1.0 atm = 1.01325 bars), hydrogen has a volume 3,100 times greater than gasoline. To decrease the volume of the hydrogen, pressure is used. Hydrogen can be stored under pressure up to 700 bars. At this pressure, hydrogen has a volume 6.4 times greater than that of gasoline.
Another method for storing hydrogen is in the liquid phase. In this phase, hydrogen has a volume 3.6 times greater than gasoline. Liquid hydrogen can be stored under high pressure in steel tubes. Hydrogen should be cooled to -252.77 °C to become liquid. The cooling process requires energy. 25% of hydrogen energy is used for the cooling process. The largest liquid hydrogen tank is at the Kennedy Space Center in Florida. It contains up to 3,400 m3 liquid hydrogen.
Hydrogen can also be stored in metal hydrides. When cooling is applied, the hydrogen atoms diffuse inside the metal hydrides. To release the hydrogen, the reverse process, heating, is needed. Due to the large storage necessary, aluminum and boron hydrides have been used extensively over the last 10 years. In particular, boron hydrides are important as they can be used in liquid conditions. Metal hydride storage is very safe because of the low pressure and the fact that there is little free hydrogen inside the storage tank. Another advantage of this way of storing is that metal hydrides hold hydrogen at very low volumes.
It seems that hydrogen may be the major energy source in the future. Eventually, it will be used to supply the energy needed in the economy, being used for transportation, central and distributed electric power, and combined heat and power for buildings, and industrial processes. However, hydrogen technology is currently in the pre-production stage of development. Hydrogen energy is not cheap when compared to other energy sources at this time. There are some challenges that need to be overcome, such as producing, storing, and using hydrogen efficiently before we use hydrogen instead of fossil fuels. However, hydrogen is the key to solving the energy problems of the world. Hydrogen is available in every country, everywhere. Using hydrogen as an energy source will prevent many conflicts between countries. This energy source will help address concerns about energy security, global climate change, and air quality. It seems that the views of Jules Verne, quoted at the beginning of this article, will be realized one day in the future. And people will thank God not only for water, but also for the hydrogen in it.
1. “Energy Wars” by David Chapman - a director of Bullion Management Services the manager of the Millennium BullionFund (www.bmsinc.ca).
2. Cook B., ‘An Introduction to Fuel Cells and Hydrogen Technology’, Heliocentris, 2001.