Hydrogen and Fuel Cells - Production
If hydrogen is to be the energy alternative of the next century and thus the next millennium, we must examine whether hydrogen production can possibly keep pace with the incredible energy needs of our ever expanding international economy.
According to the United States Department of Energy Office of Power, the most daunting problem associated with current hydrogen production is the energy needed to produce it and to provide for energy losses in the hydrogen-to-application chain. Using existing conventional technology, "hydrogen requires at least twice as much energy as electricity twice the tonnage of coal, twice the number of nuclear plants, or twice the field of PV panels to perform an equivalent unit of work. Most of today's hydrogen is produced from natural gas, which is only an interim solution since it discards 30% of the energy in one valuable but depletable fuel (natural gas) to obtain 70% of another (hydrogen). The challenge is to develop more appropriate methods based on sustainable energy sources, methods that do not employ electricity as an intermediate step."
The most cost-efficient method currently employed in the industrial manufacture of hydrogen is steam hydrocarbon reforming, where natural gas is treated with high temperature steam, causing a chemical breakdown of the natural gas releasing hydrogen. Other methods start with the gasification of low sulfur coal in an extremely high temperature industrial furnace, and the subsequent chemical "scrubbing" of this gas to extract hydrogen, along with carbon monoxide and carbon dioxide. Both of these technologies produce hydrogen at an acceptable price for the role hydrogen currently plays in manufacturing, but are not nearly competitive with gasoline or natural gas in terms of providing economic energy for transportation or any other energy-oriented application. In industrial applications where extremely pure hydrogen is needed, electrolysis is the preferred method of production. Using electricity to chemically decompose water into its component elements of hydrogen and oxygen, electrolysis is very energy intensive and cannot compete economically on a large scale with other methods at this time due to the cost involved in generating electricity for the process.
It is clear that significant technological and economic barriers must be overcome before hydrogen can become the energy solution for our global future. Several alternative production methods are presently being explored in hopes of bringing down the cost of manufacturing hydrogen.
Foremost among the production methods being considered is what has become known as solar hydrogen. Solar hydrogen refers to any method of production that uses the power of the Sun to produce and collect usable hydrogen. This can be accomplished by various methods. The most likely approaches are:
Energy collection by solar "gensets," parabolic solar collectors that focus and concentrate the light energy of the Sun
Applying the collected energy to a Stirling-cycle heat engine, which in turn drives an electricity-producing generator to power an electrolysis system
Using the heat from collected solar energy to "crack" hydrogen directly from hydrogen bearing sources like water, natural gas, and organic bio-mass, such as municipal and agricultural waste.
Solar hydrogen offers the greatest potential at this time for pollution free, totally renewable energy. The primary methods of hydrogen production today, while representing a very small fraction of the total spectrum of hydrocarbon pollution worldwide, nevertheless contribute further carbon monoxide and carbon dioxide to the atmosphere, as well as sulfur dioxides that exacerbate acid rain. In contrast, solar hydrogen applications promise an unending source of clean usable energy along with the benefits of non-polluting collection. As current methods further deplete diminishing fossil fuel resources, solar hydrogen will use the limitless power of the Sun to manufacture hydrogen from sea water, recycled water, and even from the garbage that threatens to overflow landfills worldwide.
Other than solar hydrogen, there are several other extraction technologies being studied for their potential to produce hydrogen on a massive scale while still maintaining the integrity of our environment. This would allow remaining hydrocarbon fuel sources to be used for purposes other than energy use, such as the manufacture of plastics, synthetic fibers like nylon and polyester, and other durable goods.
The cost of producing the electricity to extract hydrogen has been a stumbling block on the path toward greater availability of hydrogen as an energy resource. One potential solution to this problem is solar generation of electric power to fuel the electrolysis process, described technically as photoelectrochemical technology, facilitated either by solar gensets or photovoltaic solar panel stacks. Another possible solution is the linking of hydrogen production and hydroelectric power, which has the lowest cost associated with producing electricity on the scale necessary to manufacture hydrogen for industrial as well as energy uses. Other emerging renewable technologies such as wind generation and tidal wave energy are also possibilities that may have application in this area in the future.
Producing hydrogen by means other than electrolysis means extracting hydrogen without the use of electricity. Again, there are several approaches being studied that may develop into promising production strategies.
One hydrogen collection method that does not involve the use of electricity is a process known as photolysis. This is a process where strains of blue green algae have been provided with proper temperature and light conditions so that the chlorophyll and enzymes within the algae can chemically split sea water into hydrogen and oxygen. Known as photobiological production, this is a very environmentally friendly process, with no need for external energy, other than perhaps maintaining the ambient temperature ranges necessary to promote the process.
Another photobiological option is the use of genetically manipulated bacteria and enzymes to "crack" seawater. The major problem to be overcome is that the bacteria that most efficiently separate water into its component elements are anaerobic bacteria, meaning that they work most efficiently in an oxygen-free environment. This causes an obvious problem, as one of the component elements released in the dissociation of water is oxygen. Here is where genetic engineering comes into play, and continued research has begun to produce strains of bacteria that are capable of sustaining their photobiological action in the presence of oxygen, increasing the likelihood that this could become a useful production method.
Biomass is a relatively recent term that means any organic material that may contain usable fuel compounds. Examples of biomass materials are wood pulp waste associated with paper manufacture, agricultural waste such as grasses and crop byproducts like corn stalks, and what is somewhat pristinely labeled MSW in the industry; municipal solid waste, a.k.a. garbage. These biomass sources can be broken down biologically by various microbes to produce usable hydrogen. This represents another non-electrical method of producing hydrogen, while at the same time offering new ways of using materials that were previously discarded into our environment, often with deleterious effects.
Biomass presents other opportunities for non-electric production of hydrogen, such as the process of pyrolysis. Using a renewable energy source such as parabolic solar collectors to concentrate heat energy from the Sun, a high temperature thermochemical reaction is established, separating biomass materials into hydrogen bearing vapors and a carbon-rich residue called char. By burning the char residue, further heat is created and used in the generation of high temperature steam. This steam is then applied to the hydrogen bearing gases in a conventional hydrocarbon reforming process, similar to that used in the extracting of hydrogen from natural gas. While this technology is still in its infancy, many researchers believe it holds great promise for energy production in the future, as well as providing options for the disposal of biomass wastes.
The perceived dangers of transporting hydrogen, with the lingering association of the Hindenburg tragedy, need to be addressed. Allaying these fears will play a role in determining whether governmental agencies, leaders of industry, and the public at large can align themselves to seek workable energy solutions for a common future.
Since gaseous hydrogen is 14 times lighter than air, if the gas escapes containment, it immediately disperses into the atmosphere with no toxic consequences. With improved storage mediums being developed, the likelihood of accidental release, already small, becomes an even lesser possibility. Metal hydrides, a chemical bonding of hydrogen with various metallic alloys, preclude the uncontrolled release of hydrogen, as heat energy must be applied to the hydrogen-bearing alloy to release its hydrogen load. Some types of hydride storage at ambient room temperatures can store larger amounts of hydrogen than an equal volume of liquid hydrogen. A new storage method using an experimental material known as activated carbon shows promise of storing ever greater volumes of hydrogen in smaller spaces. This is even more efficient than metal hydrides as a given volume of activated carbon can safely store 2.4 times the amount of hydrogen as the same volume of compressed gas stored at 3,000 PSI. Other ways of storing hydrogen, such as pressurized glass microspheres and new carbon materials called Bucky balls and whisker scrolls are also being studied and tested, in hopes of even further increasing the volume of hydrogen stored while increasing safety.
Applications: Present Into the Future
It remains to be seen how scientists, engineers, governments and their tax-paying consumer populations will adjust to the energy realities of the future. Many of the technologies we have discussed already exist, but if they are to be applied on the massive scale necessary to meet the ever-growing energy needs of an expanding world population, there is much work to be done.
Hydrogen power is only one of many alternative energy options being currently experimented with. The actual solutions that are adopted as hydrocarbon and nuclear fuels become further depleted will most likely embrace several of these options. While investigations continue into solar power, geothermal energy, wind and wave power generation, as well as nuclear fusion, the Earth continues to absorb the consequences of our past technological decisions. This adds impetus to the growing international movement toward cleaner, safer, affordable energy that will need to be available for the ever increasing numbers of future generations.
Economic factors will have perhaps the greatest influence on when and how energy alternatives are implemented, as modern consumer economies become a reality for more and more of the emerging nations across the globe. At present, fossil fuel being the cheapest and most easily available energy medium, consumption in the form of gasoline, diesel fuel, heating oil, coal and natural gas continues to grow. While this growth facilitates modernization and more opportunity for economic development in the present, it could be viewed as shortsighted, when some of the other less obvious factors are considered.
One way to illustrate this problem is to examine the use of hydrocarbon deposits for fuel versus the manufacture of durable goods from those same deposits. Petroleum products are used in the manufacture of many items used daily by people everywhere from plastics to synthetic fibers, from semi-conductors that fueled the computer revolution to medicines, cosmetics, industrial chemicals, and lubricants. When the cash value of these durable goods is assessed and compared to the cash value of fuels produced from the same amount of hydrocarbon material, especially when the dwindling nature of these materials is also considered, the disparity in value is staggering. The resale value of those durable goods, which due to their chemical nature may also be capable of being recycled, is over 30 times the value of the fossil fuel, which is burned once, and after the energy is used, gone forever. It does not take an economist or an accountant to see that dramatic economic opportunities are lost every day as we continue to let these potential profits go up in smoke.
Viewed in this light, it is evident that our energy choices are part of a many faceted international economic equation, and that it will take continued optimism to face the challenges ahead. Looking forward with a more future-oriented vision, we can perhaps glimpse some of the possibilities that lie before us, especially within the context of the applications for hydrogen energy.