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For years, hydrogen gas has been exciting researchers and "green" enthusiasts alike for its potential as a pollution-free, energy-efficient fuel.
Among several advantages of hydrogen over other fuels is its byproducts: burning hydrogen in air just produces water. Unfortunately, hydrogen brings along several drawbacks that prevent its widescale adoption.
The most glaring of these is scarcity. H2 gas molecules are so light that they can easily escape the earth's gravitational pull, leaving little of the pure gas in the atmosphere.
In order for hydrogen to be a viable fuel source, scientists need to invent a cheap, efficient method for generating hydrogen.
Fortunately, many top research groups are focusing on this problem, and it seems they are bringing the cost of generating hydrogen down to a viable level. Read below to learn about some of the most recent hydrogen generation technologies.
Image: Flickr - Fuel Cell
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Producing Hydrogen from Natural Gas
Today's technique for producing hydrogen from natural gas is highly inefficient, requiring high temperatures and pressures.
An exciting new paper from Mohamed Halabi, a scientist working at Eindhoven University of Technology, shows an intriguing solution to the problems posed by using natural gas to make hydrogen.
Halabi unveiled his new technique in his PhD. dissertation in May, 2011, entitled "Sorption Enhanced Catalytic Reforming of Methane for Pure Hydrogen Production -- Experimental and Modeling."
Halabi's technique uses a catalyst based on Rhodium, a transition metal. The process also generates CO2, which is then absorbed by a sorbent based on Hydrotalcite. Halabi's design incorporates the materials into a bed reactors and, according to him, operates at temperatures of 400 - 500 oC and pressure of 4.5 bar (450 kPa).
In comparison, the conventional techniques require temperatures as high as 850 oC and pressures of 25 bar (2500 kPa). In addition, the conventional technique is a multi-stage affair, including extensive processing to remove carbon dioxide and other contaminates.
The new technique produces 99.5% pure hydrogen gas at much lower temperature and pressure; the reactor size is much reduced as well. These improved characteristics represent a potentially large increase in energy efficiency.
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Several species of bacteria and algae are capable of photosynthesis, in which an organism turns CO2, H2O, and sunlight into sugars. Though these sugars do serve as fuel, they aren't the kind of fuel humans are looking for: they don't burn well.
However, research shows that some species of bacteria can produce hydrogen directly under certain conditions. Two different enzymes are independently responsible for generating hydrogen: hydrogenase and nitrogenase.
Researchers have known of this ability for years, but had been unable to create hydrogen in useful quantities. This is unfortunate, because methods using microorganisms require only ordinary pressures and temperatures, meaning a much lower energy input.
Now, researchers have demonstrated that they can metabolically engineer certain species of bacteria to maximize hydrogen production by either photosynthesis or fermentation. The review by Vardar-Schara, Maeda, and Wood, linked at the end of this article, discusses several species of bacteria and algae showing hydrogen-producing capability. It also goes into great depth on the enzymes and genes involved in hydrogen production.
Image: Flickr - Cyanobacteria Cells
Bioengineered bacteria and algae certainly represent an exciting possibility due to their expected efficiency and low energy intensivity. They might, one day, even find use in interplanetary missions to provide fuel on far-flung outposts. The viability of this method looks to be several years away at the very least, though.
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Making Hydrogen from Biomass
The final method we will look at is for generating hydrogen from biomass.
The process, which is similar to that used to generate ethanol, requires large volumes of plant matter. The fuel for this process is glucose, which engineers must derive from the plant matter.
Researchers Randy Cortright, James Dumesic, and Rupali Davda, all from the University of Wisconsin, have published a paper in the journal Nature describing their method for creating hydrogen. Their method relies on a platinum-based catalyst.
Researchers say they can use cheap materials such as wood waste and paper mill byproducts to create hydrogen from glucuse. The process described by the Wisconsin group takes place at just 227 oC. The pressure used is high enough that the water in the process never vaporizes, creating a substantial energy savings.
Another advantage to this process is that its byproducts contain only very low concentrations of carbon monoxide. Carbon monoxide ruins the electrodes used in low-temperature fuel cells, and has been a major problem in hydrogen generation.
Further research is needed to find cheaper catalysts and ways to increase hydrogen yields, but biomass seems to be a promising future generator of hydrogen.