Hydrogen; From invisible gas to nano energy-saviour
|Terje Berg, Senior Partner, EUCAT
OPINION BY TERJE BERG
Even though Bjørn Lomborg and his colleagues at the Copenhagen Consensus 2004 (www.copenhagenconsensus.com) does not recognize the energy shortage in the world as being among the world’s biggest concerns, there are those who think that if you don’t solve the energy problem, no other concern really matters. Nobel Laureate Richard Smalley is one of the many to point out the following:
We can not supply the peoples of the world with enough energy in the coming decades using current technology. Oil and gas just does not cut it. So what can we use that is both abundant and cheap?
Well, looking at the available resources, why not pick the most abundant resource in the universe? Especially when this turns out to be an excellent energy carrier?
We are—of course—talking about Hydrogen. Hydrogen (like electricity) is the only energy carrier available that can be completely pollution free; in fuel cells the “waste product” it produces is water! Therefore using it not only diminishes greenhouse gas emissions, but also reduces other types of air pollution. Hydrogen also has the highest energy content per unit weight of any known fuel; about 121 kJ/g, for those of you interested in numbers.
Just right for the job then. So what’s stopping us from turning into ‘Hydrogen economies’ on a grand scale? Two things basically: Challenges related to production and storage.
Wait, you might say: How can that be true of the most abundant resource in the universe?
Basically because atomic hydrogen is very reactive and combines with most of the known elements around us. And the tiny amount that does not react or combine is so light that it escapes into space. Therefore we have to find ways of extracting it from hydrogen-rich compounds, and once we have done that, we have to make sure that it is stored in such a way that it does not re-combine or escape before we can use it.
Let’s see how that can be done and how nanotechnology can help us do it.
We’ve basically developed three major types of production technologies: Thermochemical, Electrolytic, and Photolytic.
The main thermochemical methods are:
• Natural Gas Steam Reforming Means adding water to methane and heating it under pressure. Produces Hydrogen and Carbon mono- and dioxide; providing about half of all available hydrogen today
• Partial Oxidation/Ceramic Membrane Reactor Simultaneously separates oxygen from air and partially oxidates methane. This process could result in improved production of hydrogen and/or synthesis gas compared to conventional reformers and will be made more efficient through nanostructuring the membranes involved.
• Biomass Gasification and Pyrolysis Using agricultural or biomass specifically grown for energy uses, hydrogen can be produced via pyrolysis or gasification.
Also produces bio-oils that can be separated into valuable chemicals and fuels. Electrolytic production technologies include:
• Water Electrolysis Used to be the main method for producing hydrogen (and oxygen). Today, however, only provides about 5 percent of commercial hydrogen. But renewed interest and research continues, especially for transportation purposes.
• Reversible Fuel Cells Conventional Fuel Cells (see below) produces electricity from hydrogen, but the processes might be reversed if hydrogen is the desired outcome. Photolytic production technologies
• Photobiological using artificial photosynthesis or certain photosynthetic microbes to produce hydrogen using light energy is an interesting way to go. Especially for the underdeveloped areas in the world where funding is low, but sunlight often abundant. By employing nanocatalysts and engineered systems, hydrogen production efficiency could reach 24%.
• Photoelectrolysis While most traditional (Photovoltaic) Solar Cells produce electricity from sunlight, low-cost designs that produce hydrogen are also being developed, presently at a solar-to-hydrogen efficiency of 7.8%.
Once you have produced the hydrogen it must be stored. Traditionally that has meant putting it into pressurized storage tanks, which has not been to popular amongst the general public, who (falsely) think of these as re-named hydrogen bombs with a high NIMBY-factor (Not In My Back Yard!). Although you can reduce the pressure by liquefying the hydrogen first—using nanocatalysis—the more elegant method at the moment seems to be storing the hydrogen in materials. Two of the main methods for doing this, belongs in the nano realm, and both are being pioneered at the Norwegian Institute for Energy Technology; IFE. These methods are:
• Storing the hydrogen in carbon nano-compounds
Basically means keeping the hydrogen in nano-sized carbon containers, be that fullerenes, nanotubes or nanocones. These methods are still at an early stage, but holds great promise as future hydrogen nano-tanks
• Storage in metal hydrides
These are more near time solutions where you basically put hydrogen atoms in between the crystallic structure of solid metals. IFE presently has the reigning world storage record for hydrogen using this method. By putting the hydrogen atoms 0,16 nanometre apart, they have achieved a hydrogen density more that 8 times higher than liquid pressurised hydrogen. And that in a substance you can keep in a box on your kitchen sink!
Although the metal hydride used by IFE today is too heavy and too costly to be commercially interesting, when you include safety considerations (real or imagined), the metal hydride method seems to be a practical mid-term storage solution securing the position of hydrogen as the main energy carrier for the future.
Having produced and stored the hydrogen, the intended mechanism for its conversion into usable energy, is the Fuel Cell. A fuel cell is a device that uses hydrogen (or hydrogen-rich fuel) and oxygen to create electricity by an electrochemical process. If pure hydrogen is used as a fuel, fuel cells emit only heat and water as a byproduct. Fuel cells are more efficient than combustion-type technologies, and are being developed to power passenger vehicles, commercial buildings, homes, and even small devices such as laptop computers. There are several types of fuel cells under development, and all benefit from our ability to nano-structure materials. But how that is done might be the topic for another article…
OPINIONS EXPRESSED IN THE ARTICLE ABOVE ARE SOLELY THE OPINIONS OF THE AUTHOR