Ever since the beginning of time, mankind has been dependant on Mother Nature to provide them with various energy sources for cooking, staying warm, and powering machines. At first, this energy source was wood. Then, as technology increased, man found other things to burn, such as coal, oil and gas. As the need for greater energy sources increased, man started looking around them. They found water, light, and wind. Still in need of energy, man looked smaller instead of bigger. They soon harnessed the power of the nucleus, and the atomic age was born. Now, a new age is being born. An age where mere power is not the whole issue, but how it is produced, the effects it has on the environment, and long-range productivity capabilities. The other energy sources are being depleted or are simply not making the grade on the economical scale. Now, a new technology must be harnessed, and I believe that the answer to our problems is something that has been around forever, right under our noses for centuries and yet completely ignored.
This mystery solution is actually water. Not so much the water in and of itself, but the hydrogen and the oxygen that combine to produce it. There is enough power in a glass of water to run the city of Chicago for a week. There is enough water in the first 10 feet of all the oceans in the world to power the world for over a million years. The best part about it is that the process of turning water into hydrogen power is that it is 100% clean and pollution free. We have in front of us, a solution to the world's power problems without the uncertain future that is bound to other power producing methods of the past.
Some may agree that, yes hydrogen does sound like an interesting and possibly viable future energy source, but why bother? We already have a successful economy based on fossil fuels. We have used these fuel sources for over a hundred years. Why should we change now? The answer is simple. There are five main reasons that an economy dependent on fossil fuels is an economy that will eventually fail.
2. Non-Renewable resource
4. International Dependency
5. Monopoly on the market
Fossil fuels (i.e., petroleum, natural gas and coal), which meet most of the world's energy demand today, are being depleted rapidly. Also, their combustion products are causing global problems, such as the greenhouse effect, ozone layer depletion, acid rains and pollution, which are posing great danger for our environment, and eventually, for the total life on our planet. Many engineers and scientists agree that the solution to all of these global problems would be to replace the existing fossil fuel system with the Hydrogen Energy System. Hydrogen is a very efficient and clean fuel. Its combustion will produce no greenhouse gases, no ozone layer depleting chemicals, and no acid rain ingredients and pollution. Hydrogen, when produced from renewable energy sources (solar, wind, bio-chemical), would result in a permanent energy system, which we would be completely independent and renewable.
A particular mess involving the fossil fuels is the environmental damage being caused by the fossil fuels and their combustion products. Technologies for fossil fuel extraction, transportation, processing and particularly their end use (combustion), have harmful impact on the environment, which cause direct and indirect negative effects on the economy. Excavation of coal devastates the land, which has to be reclaimed and is out of use for several years. During the extraction, transportation and storage of oil and gas, spills and leakages occur, which cause water and air pollution. Refining processes also have an environmental impact. However, most of the fossil fuel environmental impact occurs during the end use. The end use of all fossil fuels is combustion, despite the final purpose of its use (i.e., heating, electricity production or power for transportation). The main constituents of fossil fuels are carbon and hydrogen, but also some other ingredients, which are originally in the fuel (sulfur), or are added during refining (lead, alcohols). Combustion of the fossil fuels produces various gases, which are all released into the atmosphere and cause air pollution. Air pollution is defined as the presence of some gases and particulates, which are not a natural constituent of the atmosphere, or even the presence of the natural constituents in an abnormal concentration. Air pollution causes damage to human health, animals, crops, structures, and reduces visibility.
Once in the atmosphere, triggered by sunlight or by mixing with water and other atmospheric compounds, these pollutants may undergo chemical reactions, and change their form and become secondary pollutants like ozone, aerosols, peroxyacyl nitrates, and other various acids. Precipitation of sulfur and nitrogen oxides, which have dissolved in clouds and in rain droplets to form sulfuric and nitric acids, is called acid rain. Acid dew, acid fog and acid snow have also been recorded. Acid deposition (wet or dry) causes soil and water acidification, resulting in damages to the aquatic and terrestrial ecosystems, affecting humans, animals, vegetation and structures.
The remaining products of combustion in the atmosphere, mainly carbon dioxide, together with other so-called greenhouse gases (methane, nitrogen oxides and chlorofluorocarbons), result in thermal changes by absorbing the infrared energy the earth radiates into the atmosphere, and by re-radiating some back to earth, causing global temperatures to increase. The effects of a temperature increase are melting of the ice caps, rising sea levels and climate changes, which could include heat waves, droughts, floods, stronger storms, and more wildfires.
Using the studies of scores of environmental scientists, the above stated damages have been calculated for each of the fossil fuels. Table 1 shows the results for each type of damage in 1998 U.S. dollars. It can be seen that the environmental damage for coal in 1998 is $14.51 per GJ(Giga-Joule 10^9 Joules) of coal consumed; for petroleum in 1998, $12.52 per GJ of petroleum consumed; for natural gas in 1998, $8.26 per GJ of natural gas consumed, and the weighted mean damage in the world is 1998, $12.05 per GJ of fossil fuel consumption. These damage costs are not included in the prices of fossil fuels, but are paid for by the people, directly or indirectly, through taxes, health expenditures, insurance premiums, and through a reduced quality of living. In other words, today's fossil fuels are heavily subsidized. If the respective environmental damages were included in the fossil fuel prices, it would force earlier introduction of cleaner fuels, such as hydrogen, with many benefits to the economy and the environment.
Table 1: Environmental Damage Caused by Each of the Fossil Fuels
Type of Damage (n) Environmental Damage 1998 $ per GJ
Coal Petroleum Natural Gas
Effect on Humans 5.16 4.19 3.09
Premature deaths 1.75 1.42 1.05
Medical expenses 1.75 1.42 1.05
Loss of working efficiency 1.66 1.35 0.99
Effect on animals 0.75 0.63 0.45
Loss of domestic live stock 0.25 0.21 0.15
Loss of wildlife 0.50 0.42 0.30
Effect on Plants and Forest 1.99 1.61 1.20
Crop yield reduction - ozone 0.25 0.21 0.15
Crop yield reduction - acid rains 0.13 0.10 0.07
Effect on wild flora (plants) 0.77 0.62 0.46
Forest decline (economic value) 0.27 0.22 0.16
Forest decline (effect on biological diversity) 0.53 0.43 0.33
Loss of recreational value 0.04 0.03 0.03
Effect on aquatic ecosystems 0.26 1.55 0.16
Oil spills 0.26 1.55 0.16
Underwater tanks leakages 0.90
Liming lakes 0.04 0.03 0.03
Loss of fish population 0.04 0.03 0.03
Effect on biological diversity 0.18 0.15 0.10
Effect on man-made structures 1.66 1.34 0.983
Historical buildings and monument degradation 0.18 0.15 0.10
Detriment to building and houses 0.37 0.30 0.22
Steel construction corrosion 0.99 0.80 0.59
Soiling of clothing, cars, etc. 0.12 0.09 0.07
Other air pollution costs 1.45 1.16 0.88
Visibility reduction 0.30 0.23 0.18
Air pollution abatement costs 1.15 0.93 0.70
Effect of strip mining 0.73
Effect of climactic changes 2.04 1.66 1.22
Heat waves - effects on humans 0.27 0.22 0.16
Agricultural losses 0.16 0.13 0.10
Livestock losses 0.13 0.10 0.07
Forest losses 0.16 0.13 0.10
Wild flora and fauna losses 0.93 0.75 0.56
Water shortage and power production problems 0.25 0.21 0.15
Floods 0.07 0.06 0.04
Storms, hurricanes, tornadoes 0.07 0.06 0.04
Effect of sea level rise 0.47 0.38 0.28
TOTALS 14.51 12.52 8.26
In order to see the worldwide dimensions of the fossil fuel environmental damage, see Table II. 37% of the total damage is caused by coal while the coal consumption is 31% of the total fossil fuel consumption. On the other hand, only 20% of the damage is caused by natural gas, which has a market share of 29%. It is clear that increasing the natural gas consumption, at the expense of coal and petroleum, would be environmentally beneficial. This would also prepare the way for greater public acceptance of gaseous fuels, which would result in a smoother changeover to hydrogen, also a gaseous fuel.
Table II. Worldwide Fossil Fuel Consumption and Environmental Damage for 1998.
Fossil Fuel Consumption
World coal consumption
World petroleum consumption
World natural gas consumption (1018 J per year)
Environmental Damage Estimate
Damage due to coal
Damage due to petroleum
Damage due to natural gas
Total Damage (1998 billion $)
It can be seen from Table II that the annual worldwide environmental damage caused by fossil fuels in 1998 is $4,345 billion, or equal to 11% of the gross world product. This is a very large figure. Conversion to a cleaner fuel, such as hydrogen, would enable the world to save this enormous sum, and perhaps use it to improve the quality of life worldwide.
An often over-looked aspect of petroleum energy is the international dependency factor. At the moment, the United States get over half of its petroleum energy from foreign markets. Of these foreign markets, over half comes from Middle Eastern countries, where there is a lot of political unrest and anti-American sentiment. It would make foreign relations a lot easier if the US didn't have to depend on those countries for vital economical support. Besides foreign relations, our domestic economy would be strengthened because we would no longer have to spend money on foreign markets, and would instead push our money into domestic markets, thereby strengthening our economy.
Energy researchers are looking at the possible sources of energy to replace the fossil fuels. There are quite a number of primary energy sources available, such as thermonuclear energy, solar energy, wind energy, hydropower, geothermal energy, ocean currents, tides and waves.
As far as your average consumer is concerned, about one-quarter of the primary energy is used as electricity and three-quarters as fuel. The other previously mentioned energy sources must, therefore, be converted to these energy carriers needed by the consumer. Compared to fossil fuels, none of the newer primary energy sources could be used directly as a fuel for air or land transportation. Consequently, they must be used to manufacture fuels, as well as to generate electricity.
There are many candidates for a new fuel source, such as synthetic gasoline, synthetic natural gas (methane), methanol, ethanol and hydrogen. The fuel of choice must satisfy the following conditions:
It must be convenient fuel for transportation.
It must be versatile or convert with ease to other energy forms at the user end.
It must have high utilization efficiency.
It must be safe to use.
It must be environmentally friendly and supportable in the economy.
Vehicles and airplanes carry their fuel for a certain distance before replenishing their fuel supply. In the case of space transportation, the space vehicles must carry their fuel, as well as the oxidant necessary for their scheduled range. As a result, it is important that the transportation fuel be as light as possible and also takes up as little space as possible. We can combine these requirements in a dimensionless number, called the motivity factor:
Where E is the energy generated by the fuel, M the mass of the fuel, V the volume of the fuel, and subscript h refers to hydrogen. The higher the motivity factor, the better the fuel for transportation. Table III will list the important properties of popular fuels, as well as the motivity factors calculated using the above equation. It can be seen that among liquid fuels, LH2 has the best motivity factor, while methanol has the lowest motivity factor. Among the gaseous fuels, GH2 has the best motivity factor.
Consideration of the utilization efficiency advantage of hydrogen further improves hydrogen's standing as the best transportation fuel. Of course, this is one of the reasons why hydrogen is the fuel of choice for the space programs around the world, even though presently, it is more expensive than fossil fuels.
At the user end, all fuels must be converted through a process (such as combustion) to other forms of energy such as thermal, mechanical and electrical energy. If a fuel can be converted through more than one process to various forms of energy at the user end, it becomes more versatile and more convenient to use for the consumer. Table IV lists various fuels and processes by which they can be economically converted to other forms of energy. It can be seen that all the fuels, except hydrogen, can be converted through one process only: combustion. Hydrogen, however, can be converted to other forms of energy in five different ways. In addition to flame combustion, it can be converted directly from steam, converted to heat through catalytic combustion, act as a heat source and/or heat sink through chemical reactions, and converted directly to electricity through electrochemical processes (fuel cell). In other words, hydrogen is the most versatile, and useful fuel.
In comparing fuels, it is important to take into account the utilization efficiencies. For use by the user, fuels are converted to various energy forms, such as mechanical, electrical and thermal. Studies show that in almost every instance of utilization, hydrogen can be converted to the desired energy form more efficiently, and economically than other fuels.
Table III. Energy Densities (HHV) and Motivity Factors for Liquid and Gaseous Fuels
Fuel Chemical Formula Energy per unit Mass
J/kg Energy per unit Volume
J/m Motivity Factor
CÃÂ£ 20 HÃÂ£ 42
Table V shows the utilization efficiency factors, defined as the fossil fuel utilization efficiency divided by the hydrogen utilization efficiency, for various applications.
Table V. Utilization Efficiency Comparisons of Fossil fuels and Hydrogen
Application Utilization Efficiency Factor
Internal Combustion Engines
Fuel Cells/Electric Motor
Subsonic Jet Transportation 0.84
Supersonic Jet Transportation
Hydrogen Utilization Efficiency Factor
Fossil Fuel Utilization Efficiency Factor 0.72
There are two safety aspects concerning fuels. The first is toxicity, and the other is flammability. In addition to the toxicity of their combustion by-products, the fuels themselves can be toxic. The toxicity increases as the carbon-to-hydrogen ratio increases. Hydrogen as well as its main combustion product, water or water vapor, are not toxic. However, Nitric Oxide (NOX), which can be produced through the flame combustion of hydrogen (as well as through the combustion of fossil fuels) displays toxic effects.
Table VI lists the characteristics of fuels related to fire hazards. Lower density makes a fuel safer, since it increases the buoyancy force for speedy dissipation of the fuel in case of a leak. For the same reason, higher diffusion coefficients are helpful. Higher specific heat causes a fuel to be safer, since it slows down the temperature increases for a given heat input. Wider ignition limits, lower ignition energies, and lower ignition temperatures make the fuels less safe, as they increase the limits in which a fire could start. Higher flame temperature, higher explosion energy, and higher flame emissivity make a fuel less safe as well, since its fire would be more damaging.
Table VII compares the safety of fuels. For each of the toxic elements and fire hazard characteristics, it ranks the fuels from 1 to 3, 1 being the safest and 3 the most dangerous. These rankings have been summed up for each fuel in order to arrive at an overall ranking. The total rankings have been given safety factors, defined as the ratio of the total ranking for hydrogen to that of a given fuel. It can be seen that hydrogen becomes the safest fuel, while gasoline is the least safe, and methane in between the two.
Table VI. Characteristics Related to Fire Hazard of Fuels
Property Gasoline Methane Hydrogen
Diffusion Coefficient In Air3 (Cm2/Sec)
Specific Heat at Constant Pressurea (J/Gk)
Ignition Limits In Air (vol %)
Ignition Energy In Air (Mj)
Ignition Temperature (oC)
Flame Temperature In Air (oC)
Explosion Energyb (G TNT/kj)
Flame Emissivity (%) 4.40
1.0 - 7.6
228 - 471
34 -43 0.65
5.3 - 15.0
25 -33 0.084
4.0 - 75.0
a At normal temperature and pressure.
b Theoretical maximum; actual 10% of theoretical.
Table VII. Safety Ranking of Fuels
Gasoline Methane Hydrogen
Toxicity Of Fuel
Toxicity Of Combustion
Flame Emissivity 3 2 1
3 2 2
3 2 1
3 2 1
3 2 1
1 2 3
2 1 3
3 2 Q
3 1 2
3 2 1
3 2 1
Totals 30 20 16
Safety factor f s 0.53 0.80 1.00
1, safest; 2, less safe; 3, least safe
When we look at the fuel options critically under all the criteria given above, it becomes clear that hydrogen is the best transportation fuel, the most versatile fuel, the most efficient fuel and the safest fuel. Summed up, hydrogen is the best fuel period.
It is clear that it is extremely important to manufacture hydrogen using any and all "primary energy sources", in order to make up for their shortcomings. This energy system would be called the "Hydrogen Energy System".
In the Hydrogen Energy System, hydrogen (and oxygen) is produced in large industrial plants where the energy source (solar, nuclear, and even fossil) and water (H2O), the raw material, are available. For large-scale storage, hydrogen could be stored underground in old mines, caverns and/or aquifers. Hydrogen is then transported by means of pipelines or super tankers to cities and other places where energy is used. It is then used in electricity, transportation, industrial, residential and commercial zones as a fuel and/or an energy carrier. The by-products are water or water vapor. If combustion of hydrogen is used, then some NOx is also produced, but a lot lower than similar combustion methods of fossil fuels. Water and water vapor is recycled back, through rain, rivers, lakes and oceans, to make up for the water used in the first place to manufacture hydrogen, thereby creating a completely renewable resource.
One of the great advantages to this system over current systems is power grid usage. Today, power centers all hook up to a national grid of power lines, and power is routed at great loss across the country due to friction in the lines. This is also a reason for the recent New York blackout. When one generator goes out, all of the other generators work harder to compensate for the missing generator. All of the generators in the world run at 60 hertz, and if a generator goes out, then that frequency is reduced, forcing the others to raise it back up. If enough generators go out, then the remaining working ones can't compensate and they all go off-line, creating rolling blackouts. With the Hydrogen System, each individual building and home would have its own Fuel Cell that would not only generate enough electricity for the building, but also provide heat and water. There would be no grid for blackouts to roll across. There would be no primary target for terrorists. Today, you could crash a plane into a nuclear power plant and cause nuclear fallout as well as no power for a massive area. Since every building has its own power source with hydrogen, there is no centralized power plant to attack.
The oxygen produced in the industrial plant making hydrogen could either be released into the atmosphere, or could be shipped or piped to industrial and city centers for use in fuel cells (instead of air) for electricity generation. This would have the advantage of increasing the utilization efficiency. The oxygen could be used by industry for non-energy applications, and also for rejuvenating the polluted rivers and lakes, or speeding up sewage treatment.
It should be noted that in the hydrogen energy system, hydrogen is not a primary source of energy. It is an intermediary or secondary form of energy, or an energy carrier. Hydrogen complements the primary energy sources, and presents them to the consumer in a convenient form at the desired location and time.
Table VIII lists the pollutants for the three competing energy systems described. It can be seen that the coal/synthetic fossil system is the worst from the environmental point of view, while the solar-hydrogen energy system is the best. The solar-hydrogen system will not produce any CO2, C, Sox, hydrocarbons or particulates, except some NOx. However, the solar-hydrogen-produced NOx is much less than that produced by the other energy systems. This is due to the fact in the solar hydrogen energy system only the flame combustion of hydrogen in air will generate NOx. The other utilization processes (such as direct steam generation, use of hydrogen in fuel cells, hydriding processes, etc.) will not produce any NOx .
Table VIII. Pollutants Produced by Three Energy Systems
Pollutant Fossil fuel
** Only in combustion methods
Table IX presents the environmental damage per gigajoule of the energy consumed for each of the three energy systems considered, and also for their fuel components in 1998 US dollars, as well as environmental compatibility factors, defined as the ratio of the environmental damage due to the hydrogen-energy system to that due to a given energy system. The environmental damage for the solar-hydrogen energy system is due to the Nox produced. It can be seen that the solar-hydrogen energy system is environmentally the most compatible system.
Hydrogen also has the answer to the depletion of the ozone layer, mainly caused by chlorofluorocarbons. Refrigeration and air-conditioning systems based on the hydriding property of hydrogen do not need chlorofluorocarbons, but need hydrogen, and any hydrogen leak would not cause ozone layer depletion. Such refrigeration systems are also very quiet, since they do not have any moving machinery.
Table IX. Environmental Damage and Environmental Compatibility Factors
Energy System and Fuel Environmental Damage
(1998 $/GJ) Environmental
Compatibility Factor, f E
Fossil Fuel System
Natural Gas 12.47
Coal/Synthetic Fossil Sys.
Solar-Hydrogen Energy Sys.
In economic considerations, it is also important to compare the future costs of hydrogen (which will be considerably lower than they are today because of the assumed market and technology development), with fossil fuels, both internal and external, which, unavoidably, will be higher than today's prices due to depletion, international conflicts and the environmental impact).
The effective cost of a fuel can be calculated using the following relationship:
Where Ci is the internal cost or the conventional cost of the fuel, Ce the external cost, including the environmental damage caused by the fuel hfk the fossil fuel utilization efficiency for application k, and hsk the synthetic fuel (including hydrogen) utilization efficiency for the same application, or the end use.
In order to evaluate the overall cost (Co) to society, the three scenarios considered earlier will be used. This cost can be calculated from the relationship
where an is the fraction of energy used by the energy sector n, such as electricity generating, heat producing, surface transportation, subsonic air transportation, and supersonic air transportation. Since it is a fraction, their sum is
Substituting Eq. (2) for Eq. (3), one obtains
Using Equations. (2)-(5), Tables X-XII have been prepared for the three energy scenarios: The fossil fuel system, the coal/synthetic fossil fuel system, and the solar-hydrogen energy system. Comparing the results, it becomes clear that the solar-hydrogen energy system is the most cost-effective energy system, and results in the lowest effective cost to society.
Table X. Effective Cost of Fossil Fuel System
Application Fuel Energy Consumption
Fraction Effective Cost
(1998 U.S. $/GJ)
Thermal Energy Natural Gas
Electric Power Coal 0.30 17.25
Surface Transportation Gasoline 0.20 31.61
Air Transportation Jet Fuel 0.10 25.98
TOTAL OF FRACTIONS 1.00
OVERALL EFFECTIVE COST 22.11
*Average for residential and industrial sector.
Table XI. Effective Cost of Coal/Synthetic Fuel System
Application Fuel Energy
Fraction Effective Cost
(1998 U.S. $/GJ)
Thermal Energy Coal
Electric Power Coal 0.30 17.25
Surface Transportation SNG
Air Transportation Syn-jet fuel 0.10 45.45
TOTAL OF FRACTIONS 1.00
OVERALL EFFECTIVE COST 27.55
Table XII. Effective Cost of Solar-Hydrogen Energy System
Fraction Effective Cost
(1998 U.S. $/GJ)
Internal Combust Engines
TOTAL OF FRACTIONS 1.00
OVERALL EFFECTIVE COST 19.23
3 It has been assumed that 1/3 of hydrogen will be produced from hydropower and/or wind-power, and 2/3 from solar.
The advantages of hydrogen versus fossil fuels can be listed as follows:
Liquid hydrogen is the best transportation fuel when compared with liquid fuels such as gasoline, jet fuel and alcohols; and gaseous hydrogen is the best gaseous transportation fuel.
1. While hydrogen can be converted to useful energy forms (thermal, mechanical and electrical) at the user end through five different processes, fossil fuels can only be converted through one process: flame combustion. In other words, hydrogen is the most versatile fuel.
2. Hydrogen has the highest utilization efficiency when it comes to conversion to useful energy forms (thermal, mechanical and electrical) at the user end. Overall, hydrogen is on average 39% more efficient than fossil fuels. In other words, hydrogen will save primary energy resources.
3. When fire hazards and toxicity are taken into account, hydrogen becomes the safest fuel.
4. When the environmental impact is taken into consideration, the solar hydrogen energy system becomes the most environmentally compatible energy system. It will not produce greenhouse gases, ozone layer damaging chemicals, oil spills, climate change and little or no acid rain ingredients and pollution. It will actually reverse the global warming and bring the earth back to its normal temperatures by decreasing the CO2 in the atmosphere to its pre-industrial revolution level.
5. The solar hydrogen energy system has the lowest effective cost when environmental damage and higher utilization efficiency of hydrogen are taken into account.
In order to better explain the processes by which hydrogen is utilized, some methods are described in detail below. Data is taken from the Clean Energy Research Institute from the University of Miami:
Direct steam generation by hydrogen/oxygen combustion
Hydrogen combusted with pure oxygen results in pure steam:
2H2 + O2 = 2H2O
The above reaction would develop temperatures in the flame zone above 3,000 ÃÂ°C, therefore, additional water has to be injected so that the steam temperature can be regulated at a desired level. Both saturated and superheated vapor can be produced.
The German Aerospace Research Establishment (DLR) has developed a compact hydrogen/ oxygen steam generator. The steam generator consists of the ignition, combustion and evaporation chambers. In the ignition chamber a combustible mixture of hydrogen and oxygen at a low oxidant/fuel ratio is ignited by means of a spark plug. The rest of the oxygen is added in the combustion chamber to adjust the oxidant/fuel ratio exactly to the stoichiometric one. Water is also injected in the combustion chamber after it has passed through the double walls of the combustion chamber. The evaporation chamber serves to homogenize the steam. The steam's temperature is monitored and controlled. Such a device is close to 100% efficient, since there are no emissions other than steam and little or no thermal loss. The hydrogen steam generator can be used to generate steam for spinning reserve in power plants, for peak load electricity generation, in industrial steam supply networks and as a micro steam generator in medical technology and biotechnology.
Catalytic burning of hydrogen
Hydrogen and oxygen in presence of a suitable catalyst may be combined at temperatures significantly lower than flame combustion (about 500 ÃÂ°C). This principle can be used to design catalytic burners and heaters. Catalytic burners require considerably more surface area than conventional flame burners. Therefore, the catalyst is typically dispersed in a porous structure. The reaction rate and resulting temperature are easily controlled by controlling the hydrogen flow rate. The reaction takes place in a reaction zone of the porous catalytic sintered metal cylinders or plates in which hydrogen and oxygen are mixed by diffusion from opposite sides. A combustible mixture is formed only in the reaction zone and assisted with (platinum) catalyst to burn at low temperatures. The only product of catalytic combustion of hydrogen is water vapor. Due to low temperatures there are no nitrogen oxides formed. The reaction cannot migrate into the hydrogen supply, since there is no flame and hydrogen concentration is above the higher flammable limit (75%). Possible applications of catalytic burners are in household appliances such as cooking ranges and space heaters. The same principle is also used in hydrogen sensors.
Electrochemical electricity generation (Fuel Cells)
Hydrogen can be combined with oxygen without combustion in an electrochemical reaction (reverse of electrolysis) and produce electricity (DC). The device where such a reaction takes place is called the electrochemical fuel cell or fuel cell.
Depending on the type of the electrolyte used, there are several types of fuel cells:
Alkaline fuel cells (AFC) use concentrated (85 wt%) KOH as the electrolyte for high temperature operation (250ÃÂ°C) and less concentrated (35-50 wt%) for lower temperature operation (
Polymer electrolyte membrane or proton exchange membrane fuel cells (PEMFC) use a thin polymer membrane (such as perfluorosulfonated acid polymer) as the electrolyte. The membranes as thin as 12-20 microns have been developed, which are excellent proton conductors. The catalyst is typically platinum with loadings about 0.3 mg/cm2, or, if the hydrogen feed contains minute amounts of CO, Pt-Ru alloys are used. Operating temperature is usually below 100ÃÂ°C, more typically between 60 and 80ÃÂ°C.
Phosphoric acid fuel cells (PAFC), use concentrated phosphoric acid (~100%) as the electrolyte. The matrix used to retain the acid is usually SiC, and the electrocatalyst in both the anode and cathode is Platinum black. Operating temperature is typically between 150-220ÃÂ°C.
Molten carbonate fuel cells (MCFC) have the electrolyte composed of a combination of alkali (Li, Na, K) carbonates, which is retained in a ceramic matrix of LiAlO2. Operating temperatures are between 600-700ÃÂ°C where the carbonates form a highly conductive molten salt, with carbonate ions providing ionic conduction. At such high operating temperatures, noble metal catalysts are typically not required.
Solid oxide fuel cells (SOFC) use a solid, nonporous metal oxide, usually Y2O3-stabilized ZrO2 as the electrolyte. The cell operates at 900-1000ÃÂ°C where ionic conduction by oxygen ions takes place.
A typical fuel cell consists of the electrolyte in contact with a porous electrodes on both sides. A schematic representation of a fuel cell with reactant and product gases, and ions flow directions for the major types of fuel cells are shown below. The electrochemical reactions occur at the three-phase interface - porous electrode/electrolyte/reactants.
Alkaline fuel cells have been used in the space program (Apollo and Space Shuttle) since 1960's. Phosphoric acid fuel cells are already commercially available in container packages for stationary electricity generation. PEM fuel cells are a serious candidate for automotive applications, but also for small scale distributed stationary power generation. High temperature fuel cells, such as molten carbonate and solid oxide fuel cells, have been developed to a pre-commercial/demonstration stage for stationary power generation.
Metal hydrides applications
Hydrogen's property to form metal hydrides may be used not only for hydrogen storage but also for various energy conversions. When a hydride is formed by the chemical combination of hydrogen with a metal, an element or an alloy, heat is generated. Conversely, in order to release hydrogen from a metal hydride heat must be supplied. These processes can be represented by the following chemical reactions:
Charging or absorption: M + xH2 = MH2x + heat
Discharging or de-absorption: MH2x + heat = M + xH2
where M represents the hydriding substance, a metal, an element or an alloy. The rate of these reactions increase with increase in the surface area. Therefore, in general, the hydriding substances are used in powdered form to speed up the reactions.
Elements or metals with unfilled shells or sub-shells of electrons are suitable hydriding substances. Metal and hydrogen atoms form chemical compounds by sharing their electrons in the unfilled sub-shells of the metal atom and the K shells of the hydrogen atoms.
Ideally, for a given temperature, the charging or absorption process and the discharging or de-absorption process takes place at the same constant pressure. However, actually, there is a "hysteresis effect" and the pressure is not absolutely constant - for a given temperature charging pressures are higher than the discharging pressures. The heat generated during the charging process and the heat needed for discharging are functions of the hydriding substance, the hydrogen pressure and the temperature at which the heat is supplied or extracted. Using different metals and by forming different alloys, different hydriding characteristics can be obtained. In other words, it is possible to make or to find hydriding substances which are more suitable for a given application, such as waste heat storage, electricity generation, pumping, hydrogen purification and isotope separation.
Hydrogen can form metal hydrides with some metals and alloys. During the formation of the metal hydride, hydrogen molecules are split and hydrogen atoms are inserted in spaces inside the lattice of suitable metals and/or alloys. In such a way an effective storage is created comparable to the density of liquid hydrogen. However, when the mass of the metal or alloy is taken into account then the metal hydride gravimetric storage density is comparable to storage of pressurized hydrogen. The best achievable gravimetric storage density is about 0.07 kg of H2/kg of metal, for a high temperature hydride such as MgH2 as shown in Table 2. It gives a comparison of some hydriding substances with liquid hydrogen, gaseous hydrogen and gasoline.
Another undeveloped and un-proven theory concerning hydrogen storage is carbon nanotubes. This procedure uses a similar process of bonding hydrogen atoms to an element, in this case, carbon. Scientists think they can develop a nanotube made entirely of carbon atoms. It would be formed of rings of carbon placed on each other, forming a micro tube of carbon atoms. When hydrogen is introduced, it bonds with the carbon atoms to form a hydrogen storage system that is non-volatile, stronger than almost all substances known to man and capable of storing more hydrogen per volume than even liquid hydrogen. This is only theory, but if invented, would revolutionize the industry.
During the storage process (charging or absorption) heat is released which must be removed in order to achieve the continuity of the reaction. During the hydrogen release process (discharging or de-absorption) heat must be supplied to the storage tank.
An advantage of storing hydrogen in hydriding substances is the safety aspect. A serious damage to a hydride tank (such as the one which could be caused by a collision) would not pose fire hazard since hydrogen would remain in the metal structure.
Hopefully, by now, you are convinced of the potential hydrogen has for being the next, and hopefully last energy source needed for mankind. However, as history has shown, things don't get invented until there is a need. We don't realize our potential until a pressing need tests us. Oil and gas reserves are not going to run out for another 25-40 years, and we cannot wait that long for the power of hydrogen to be harnessed. More money needs to be devoted to the research and development of the various technologies that support and influence the implementation of hydrogen into our fossil fuel driven society. Oil and gas are finite resources and the time will eventually come when we will have to switch to something else anyway. That time might as well be now when we still have time to perfect the Hydrogen Energy System before our current energy source runs out.