PhotoelectrochemistryProducing Hydrogen from Solar Power I. Introduction A. Producing fuel with solar power B. The problems C. The solution II. Process of Splitting Water A.
Electrolysis B. Disadvantages of electrolysis III. Using Solar Power to produce electrical Energy A. The process IV. The Problems with Solar Power A.
Compatibility of semiconductors B. Energy range C. The expense V. The Solution A. Single device to perform task 1. Eliminates the loss of energy B.
More efficient semiconductors developed VI. Summary VII. Conclusion It s the ultimate in clean energy: Generate fuel from water using only the power of sunlight, and when the fuel burns, it gives off nothing but water. As outlandish as it sounds, the dream was accomplished decades ago by using solar energy to split water into its components, oxygen and hydrogen-a powerful fuel that can be used to run everything from power plants to cars. But as a commercial proposition, the process has been a nonstarter because it s so inefficient and expensive. The two steps involved-generating electricity from sunlight and using it to split water-normally take place in separate devices, and energy is lost in between.
Now, researchers at the National Renewable Energy Laboratory (NREL), have come up with a single device that accomplishes both tasks and has set a world record in efficiency for converting photons 1, found in sunlight, to fuel (4).
... power the world. Solar energy producers fall into two separate categories: thermal solar collectors and photovoltaic panels. Thermal solar energy collectors are “a source of hot water ... call boxes, and “solar photovoltaic cells can easily provide power to these remote devices, eliminating the need for ... is still fairly expensive. Solar energy is a viable option to replace fossil fuels because it is ...
This new solar powered water splitter, built by NREL chemists John Turner and Oscar Khaselev, converts about 12. 5% of the energy in sunlight to gaseous fuel-nearly double the previous record achieved by a conventional two step process (10).
Process of Splitting Water Splitting water to create gaseous hydrogen and oxygen is quite simple. First, stick a pair of metal electrodes into water.
Then, apply an electric current to them, and the oxygen gas attracts to one electrode and hydrogen gas to the other. The process, known as electrolysis is commonly used to produce pure hydrogen for making everything from food oils to computer chips (6).
But it s expensive and requires fossil fuels to generate the electricity that powers the process. So energy researchers have long dreamed of using solar energy to drive the electrolysis. Using Solar Power The basic principle of generating electricity from sunlight is, again, well known. When photons from sunlight strike normally static electrons in some semiconductor materials, they push the electrons into a higher energy level, allowing them to roam about.
Left behind are electron holes, or vacancies, that act like positive charges that can also move through the material. Additional semiconductor layers on either side of the absorbing layer then channel the electrons and holes in opposite directions, creating an electric current that can perform work or be stored in a battery (1).
But unfortunately, combining this so called photovoltaic 2 effect with electrolysis in a single device isn t simple. The Problems with Solar Power First, there s a compatibility problem. Solar cells must be placed in water in order to split it into hydrogen and oxygen, but semiconductors that are efficient light absorbers are often unstable in water. Also, a water molecule splits into hydrogen and oxygen atoms only if each atom absorbs electrical charges that have very precise, and different, amounts of energy.
In conventional electrolysis, the metal electrodes carry electrical charges with a wide energy range, allowing those with just the right amount of energy to catalyze the split, but semiconductors are more finicky and charges in these materials can exist only at well-defined energy levels (10).
The materials used in solar hot water systems must be carefully chosen to ensure that the unit will be efficient but also affordable. The efficiency of the conversion of sunlight energy to heat energy of the water depends on the materials of construction and the efficiency of heat transfer of the materials. Solar hot water systems use the processes of conduction to transfer the heat absorbed from ...
Unfortunately, the only semiconductor materials known to produce electrical charges at just the right levels to generate both hydrogen and oxygen are very poor absorbers of sunlight. Looking at a Solution To overcome these problems, Turner and Khaselev constructed a single device that contains two different semiconductor materials. One, made from gallium indium phosphide, which absorbs ultraviolet and visible light and produces mobile electrons with the right energy to produce hydrogen.
The other, made from gallium arsenide, that absorbs in fared light and produces holes with the right amount of energy to produce oxygen. Gallium indium phosphide is stable in water, so it can be used directly as an electrode. Gallium arsenide, however, is unstable in water, but in order to counter this problem the material is shielded by a special epoxy coating, and the holes are driven to a separate platinum electrode (4).
Although the new device appears to be efficient and stable, it is estimated that the cost of producing hydrogen in bulk would be three times that of the cheapest method, in which hydrogen atoms are stripped from natural gas by super heated steam (1 and 6).
Scientists are currently trying to engineer cheaper semiconductors to perform the water-splitting reaction. If they succeed, the energy of the future may finally find its way to the present. In summary of this report, the ability to use solar energy to split water, may revolutionize the world as we know it. It is very likely to serve as an unlimited fuel, one that is harmless to our environment, to power our automobiles, power plants, and possibly even our homes. It may also prove to be useful in the production of the vast materials that are already made from hydrogen. This new technology, certainly appears likely to be of great benefit to us in the future, if only we are able to work out the problems of expense in production, as well as the inefficiency of the process as a whole.
Nevertheless, the chances of solving these problems seem very good, as scientists continue diligently researching and developing the processes involved, and it s very likely that changes may be seen, very soon, in our lives as a result of this technology. References 1. A. Heller, Science 223, 1141 (1984) 2. J. R.
Throughout the entire history of mankind, the technological advancements that civilisations have made have always been tied in with the development of energy sources. The first human energy technology was fire, along with human labour as the major energy source. This has bee supplemented by animals for agriculture and transportation since at least the dawn of agriculture some 10, 000 years ago. ...
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