Posted on 08/16/2007 11:18:54 AM PDT by Uncledave
Researchers Developing Nanotube Arrays to Produce Hydrogen From Visible Light 15 August 2007
A research group headed by Professor of Electrical Engineering Craig Grimes at Penn State University is developing an inexpensive and easily scalable technique for water photoelectrolysis—the splitting of water into hydrogen and oxygen using light energy.
In a paper published online in Nano Letters, lead author Gopal K. Mor, along with Haripriya E. Prakasam, Oomman K. Varghese, Kathik Shankar, and Grimes, describe the fabrication of thin films made of self-aligned, vertically oriented titanium iron oxide (Ti-Fe-O) nanotube arrays that demonstrate the ability to split water under natural sunlight.
Previously, the Penn State scientists had reported the development of titania nanotube arrays with a photoconversion efficiency of 16.5% under ultraviolet light. Titanium oxide (TiO2), which is commonly used in white paints and sunscreens, has excellent charge-transfer properties and corrosion stability, making it a likely candidate for cheap and long lasting solar cells. However, as ultraviolet light contains only about 5% of the solar spectrum energy, the researchers needed to finds a means to move the materials band gap into the visible spectrum.
They speculated that by doping the TiO2 film with a form of iron called hematite, a low band gap semiconductor material, they could capture a much larger portion of the solar spectrum. The researchers created Ti-Fe metal films by sputtered titanium and iron targets on fluorine-doped tin oxide coated glass substrates. The films were anodized in an ethylene glycol solution and then crystallized by oxygen annealing for 2 hours. They studied a variety of films of differing thicknesses and varying iron content. In this paper they report a photocurrent of 2 mA/cm2 with a sustained, with a time-energy normalized hydrogen evolution rate of 7.1 mL/W·hr and a photoconversion rate of 1.5%, the second-highest rate achieved with an iron oxide related material.
The team is now looking into optimizing the nanotube architecture to overcome the low electron-hole mobility of iron. By reducing the wall thickness of the Ti-Fe-O nanotubes to correspond to the hole diffusion length of iron which is around 4nm, the researchers hope to reach an efficiency closer to the 12.9% theoretical maximum for materials with the band gap of hematite.
As I see it, we are a couple of problems away from having something that will revolutionize the field of hydrogen generation by use of solar energy. —Craig Grimes
In which case the headline should read “...to Produce Hydrogen From Water, Using Visible Light”
My opinion - God put the wealth of oil under the lands of the Muslims to show the world that their culture and religion causes squalor and suffering despite being given all the wealth the could ever need.
Just think how bad it will be for them when we can legitimately say we don’t even want their oil.
The still haven’t explained how they’re gonna store H2 for automobile usage. Gasoline, at least, is a liquid at room temperature.
I agree about the significance, but I don’t believe that hydrogen will ever be a significant private transportation fuel. Instead, it will be a feedstock for synthesis of hydrocarbon fuel very similar to what we use today. The other inputs will be energy and a carbon source, which might be CO2 extracted from the air or industrial processes.
What follows is something I wrote back in May about hydrogen as a transportable vehicle fuel.
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Hydrogen is perhaps the most difficult stuff to store and transport in existence (except for highly radioactive stuff) because of its immutable physical characteristics.
It cannot be liquified at any reasonable temperature (or cost) for general use, and cannot be solidified. It will form an explosive mixture in air over the widest concentration range of almost every other gas, making it extremely dangerous in closed areas.
As a metal (electron donor) it penetrates and dissolves (embrittles) metal tanks and pipes. As the physically lightest molecule, it has the highest average velocity, and diffuses through any flaw or weakness in containment. And an indicator gas, such as is added to natural gas to warn of leaks, would not penetrate the same flaws to provide such a warning.
1. Petroleum hydrocarbons are the second most abundant source of hydrogen on Earth, after the oceans.
2. Gasoline is a mixture of hydrocarbons - chemically similar molecules, all with a straight or branched chain of carbon atoms, plus a number of attached hydrogen atoms. Collectively, all can be represented by the generic formula:
H - (CH2)n - H
where “n” can be any number up to perhaps 40 or so. The lightest is Methane (CH4), the major component of natural gas. Carbon has an atomic weight of 12 and Hydrogen 1, so Methane has a molecular weight of 12 + 4 = 16, 25% of which (by weight) is Hydrogen.
3. Propane, which can be liquefied at ambient temperatures and relatively low pressure, is C3H8, with a molecular weight of 12 x 3 + 8 = 44, and is 18% Hydrogen by weight. This light hydrocarbon is produced as a byproduct of petroleum refining.
4. Gasoline is a mixture of medium weight liquid hydrocarbons, but can reasonably be represented (on average) by Octane, C8H18, which has a molecular weight of 8 x 12 + 18 = 114, and is 15.8% Hydrogen by weight.
5. One “mole” of Hydrogen gas at Standard Temperature and Pressure (STP = 68F, 14.7PSI) has a volume of 22.4 liters (5.92 gallons) and weighs 2 grams. Liquid Hydrogen has a specific gravity of 0.070. This means 1 liter would weigh 70 grams, and 22.4 liters would weigh 1568 grams.
6. 5.92 (we will use 6) gallons of gasoline would weigh approximately 6 x 8 x .75 = 36 pounds, x 16 oz/lb x 25.4 grams/oz = 14,360 grams. 14,360 x .158 = 2269 grams of Hydrogen, in the same space, without compression.
7. 2269 / 2 = 1135, x 14.7 = 16,677 PSI pressure required to achieve the same density of Hydrogen in the same size tank. This would be 2269 / 1568 = 1.45 times as dense as LIQUID Hydrogen, and far beyond current production technology.
8. Low molecular weight hydrocarbons are the most efficient way to store Hydrogen that God ever designed, and if you want something better, you should ask Him to do it. According to His rules, the fuel of the future will not be much different from what we use today, whether we continue to find and refine it, or manufacture it from other sources of Carbon and Hydrogen.
NOTE: I realize that I used a mixture of units, but I wanted to use familiar terms and measures where possible for clarity, while using constants and characteristics that would be easy to verify.
Car and aircraft manufacturers obsess about weight, and adding hundreds to thousands of pounds to each vehicle is futile. It might work for trains, boats, trucks, and buses.
Not quite correct. What is really the case is that "currently" (no pun intended), the cost of the necessary electricity is too high. If the cost of photovolataic cells drops enough, then electrolysis is a feasible option.
I agree that there would be a longer ways to go for Hydrogen to become a feasible vehicle/transportation fuel.
I see a lot of hybrids on the road today, and my hunch is that the electrical production for such vehicles will become much simpler if we get something like this hydrolysis technique to work on an enterprise scale.
I wonder if a suitable carbon source might be coal, since it’s so abundant in the U.S.
Also, similar techniques are used to break up ocean water into its components as a purification process (similar to reverse osmosis). So this kind of technology holds promise on two of the most pressing issues — energy and water.
It appears to be a photovoltaic cell who's output current is used to directly break the hydrogen oxygen bond of water (electrolysis). Which begs the question of separating the two gasses as they are evolved and storing them under pressure.
Regards,
GtG
read the thread *sigh*
hematite is iron oxide (Fe2O3). Rust is primarily hydrated hematite (Fe2O3 with some water molecules attached)
It would have been more accurate to say that the titania (TiO2) and rust were combined...
Iron is a metallic conductor; carbon as diamond is indeed a wide bandgap semiconductor (or insulator), although graphite is a conductor. There are differences between a low bandgap semiconductor and a metal in terms of the electrical properties as a function of temperature, etc.
Interesting work, actually - too bad the writer of the article mucked it up...
Intersting take.....
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