SOLAR HYDROGEN PRODUCTION

The conversion of light energy into applicable and useful, nonpolluting clean energy is one of the most important challenges in science. The first energy crisis in the early 1970s made the photochemical conversion and storage of solar energy a top priority concern.
Sunlight in the near-infrared, visible and ultraviolet regions give off a tremendous amount of energy and intensity, so that solar energy would contribute significantly to our electrical and chemical needs. It would, thus, be of great importance to develop effective systems able to absorb and operate efficiently under solar energy.
At least two systems have been considered for the conversion of sunlight into other energy sources:
1) Silicon solar cell that would convert sunlight into electricity that you read it in past post in this weblog
2) Artificial photosynthesis for the conversion and storage of solar energy into safe and useful chemical energy, e.g., for the photodecomposition of water to produce hydrogen.
The consumption of hydrogen will continue to increase dramatically in future, however, at this moment; we do not have any useful systems to produce hydrogen in an environmentally harmonious way so that such a clean and safe procedure from water can be considered vital to our future.
It is well recognized that alternatives to fossil-fuel-based energy are needed due to supply,environmental, and security issues. An alternative energy carrier being proposed is Hydrogen. However, the primary method of producing hydrogen as fuel involves stripping the hydrogen from hydrocarbons in a process called steam reforming. This process generates significant quantities of CO2, an undesirable greenhouse gas. Many researchers and also our Laboratory have been working to develop and improve a process termed photoelectrochemical hydrogen production.
This process has the potential to provide for economical and environmentally sound production of hydrogen by splitting water with sunlight using a semiconductor catalyst. However, the process,while proven, is currently not economical due to shortcomings in the semiconductor’s material properties. The researches are undegone and many interesting updates have released up to now.

Solar Energy Conversion

Solar Cells
In 1886, the American solar cell pioneer Charles Fritts concluded that,
“…the supply of solar energy is both without limit and without cost and will continue to stream down on earth after we exhaust our supplies of fossil fuels.”
This statement seems of more importance nowadays than ever before even though we know that the technology for harvesting solar energy is neither without limits nor without costs.

Solar Cell History

Alexandre-Edmond Becquerel is usually credited as the first to demonstrate the photovoltaic effect. Becquerel was interested in photographic images and his pioneering photoelectric experiments in 1839 were done with liquid and not solid state devices. Platinum electrodes, coated with AgCl or AgBr, were illuminated in acidic solution and a small photocreated voltage was registered. It would take almost 50 years from Bequerel’s first photovoltaic observation until the first solar cell was designed. It was the American inventor Charles Fritts who fabricated a solar cell in 1883 based on the photosensitive material selenium.
The efficiency was low, less than 1% but there was a market for the device in light sensors for cameras. The real breakthrough for solar cells came from researchers at the Bell Laboratories in 1954.

Based on their results they concluded that, “The direct conversion of solar radiation into electrical power by means of a photocell appears more promising as a result of recent work on silicon p-n junctions”. An overall solar energy efficiency of 6% was achieved, which was the real start for photovoltaics as a power generator. Since then considerable effort has been made to boost the efficiency and lower the fabrication cost of solar cells. In 1961 Shockley and Queisser published an analysis that has been described as the most elegant theoretical work in photovoltaics to date that puts an upper limit on the performance of solar cells with one extraction mechanism. The limit is fundamental and originates from the fact that photons with energy less than the bandgap are not absorbed and the excess energy in photons with energy larger than the band gap is lost to phonon vibrations (heat). This upper solar-to-electrical conversion efficiency is 32% at room temperature, regardless of likely future improvements in material quality or device design of photovoltaics with one extraction mechanism.

Today we are indeed aware that fossil fuels such as coal, oil and natural gas are finite resources. Excessive worldwide usage has also introduced conflicts and modern concepts such as global warming and smog alerts. Currently, as much as 80% of all energy consumed comes from chemical energy stored in fossil reserves.
Any major changes in energy consumption are not foreseen in the near future. Instead, the global energy demand is expected to increase by up to 60% and CO2 emissions by 70% by 2020.
This is going to put further pressure on an already stressed energy system. Therefore, it is of great importance to develop new alternative energy sources not based on fossil fuels. Solar energy has many advantages; it is an abundant resource and it is renewable. The most sophisticated and favorable form of solar energy is solar photovoltaic. Solar photovoltaic, which means “light-electricity”, is the direct conversion of sunlight into electricity without moving parts, pollution or noise.

A solar cell can be described as a device that under illumination is charged and works as a “battery” as long as the solar cell is kept under illumination.
No matter what materials are used in the solar cell, the origin of this effect is the same. The incoming light is absorbed by the semiconductor and electrons are excited from a low-energy state to a high-energy state. To prevent the excited electron to recombine back to its initial energy state it is crucial that the excitation is followed by a lateral selective extraction. The excited electrons are transported from the high-energy state to the high electron energy contact (negative potential) simultaneously as the vacated low-energy states are replenished from the low energy (positive) contact. These two basic mechanisms, absorption and extraction, create the necessary potential difference over the device and under load are the driving force for the photocurrent.

Solar Cells Today
Today, after 50 years of research, the solar cell market is totally dominated by silicon cells due to their good efficiency and stability. However, they are still too expensive to be a good competitor to conventional electricity generation. The cost for a complete grid connected photovoltaic system of 12.5% is about 5.5 USD per peak Watt, a price that must be reduced by at least one order of magnitude to be competitive. The high cost is mainly due to high-energy demand for purifying SiO2 o high quality Si, which in combination with low material yield during fabrication leads to a high fabrication cost. There are three types of silicon solar cells, single crystal.

My Academic Background & Research Interests

In my BSc. Thesis project, I had done a comprehensive study on the Processes of converting of refinery heavy Oil residues to light products on the title of “Upgrading of Petroleum Heavy Residue to Gasoline " in Sharif University of Technology, Tehran, IRAN, that is the more famous and competitive Iranian university specially in engineering and Technology field. In that study I Proposed to use the hydrofining of residues in among all of the hydrogen assisted processes and other various thermal and cracking processes.

My MSc. undergone in wellknown Faculty of Engineering of Tehran University and Dissertation Work entitled as: "Preparation Technology of Nano sized Inorganic salts" In my master thesis, I tried to prepare fine powders by preparing a microemulsion of a precursor and freeze-drying the frozen microemulsions. I have mainly focused on investigating the dependence of morphology and size of nanoparticles on preparation condition and type of surfactant/co-surfactant.
Besides studying Master course at Tehran University and after I finished my general and theoretical courses I started to work in "Iranian Agricultural Engineering Research Institute" that is a well-known Iranian Research Institute and therefore they support some part of my Master Thesis.

I’m attempting to evolve techniques that, can be run in our lab and be operational, This has served to sharpen my inclination to engage in active research within this area.
In these nine and half years of working, I have strived to maintain an approach of expending independent effort in all my endeavors. Learning by me and sharing my knowledge with others has been most worthwhile, when comprehending a concept.
Over the past Four years, I have developed an interest in the areas of Nano powder.
In conclusion, I would like to add that the essence of University education lies in the synergetic relationship between the student and his department. I feel that graduate study at Osaka Prefecture University will be the most logical extension of my academic pursuits and a major step towards achieving my objectives.
I would be grateful to you if I’m accorded the opportunity to pursue my graduate studies with financial assistance at your institution and am able to justify your faith in me.
Photoelectrochemistry is a general category encompassing light induced electrochemical reactions of semiconductors in contact with liquid electrolytes arising from the primary generation of minority carriers.
Photoelectrochemical processing has been a subject of considerable recent interest.
When immersed in an electrolyte, a semiconductor undergoes an exchange of electrons with the liquid at the interface to equalize the work functions of the two phases.
Thus, when light of energy greater than the band gap strikes the interface and is absorbed by the semiconductor, electrons and holes are produced, with minority carriers being swept to the semiconductor surface.
My interests in NanoScience and technology lie in the area of Nanopowders, thin films and physical Chemistry.

I also believe that my serious intention for study and research, my past experience and academic background in various areas of Nanopowders, Chemistry and Project management will be beneficial for my graduate studies.
I have chosen Osaka Prefecture University for continuing my education because as I know it provides excellent opportunities for doing a worldwide cooperation with other scientists as well as for the research in the area of my interests.
I believe all of these are beside presence of a globally distinguished Professor Like Prof. Anpo should be attainable.
This Photo always reminds me fascination memories with my coworkers in Graduate School of Engineering, Osaka Prefecture University, Physical Chemistry lab.

"Photo of Professor Masakazu Anpo's lab Members"

I am sure that my curiosity and research skills will enable me to succeed in the greatly claiming program to become an experimentalist. Eventually, I deeply believe that the excellence of Prof. Anpo’s program, along with my capabilities and motivation, will help me to attain my destination.

I find most appealing about PhotoCatalysyis Science. Keeping up an inquisitive and explorative attitude, I believe, leads to a constant learning process. This approach adds to the already immense potential for innovation that exists in this field.
As a research student in the Physical chemistry lab I did many experiments in Lab, I look to start graduate study in PhD course to refine my knowledge and skills in my areas of interest in the field of photocatalysis with new generation thin and nano films of TiO2.
I believe it will also serve to give direction to my goal of a career as a research professional at an academic or research-oriented organization like my workplace in Iran. I intend to pursue a PhD degree in order to reach that goal.

Hydrogen, Voyager and Pioneer

On the case of Voyager and Pioneer spacecrafts there an important subject about Hydrogen. As you may knew the mentiond Plaque or disc mounted to the exterior of the exploratory spacecraft and etched with information identifying our civilization to alien cultures.

Do you know that The drawing containing two circles in the lower right-hand corner of this is a drawing of the hydrogen atom in its two lowest states? Ther is a connecting line and digit 1 to indicate that the time interval associated with the transition from one state to the other is to be used as the fundamental time scale, both for the time given on the cover and in the decoded pictures.

The Voyager Golden Record
The Voyager Golden Record is a phonograph record included in the two Voyager spacecraft launched in 1977. It contains sounds and images selected to portray the diversity of life and culture on Earth. It is intended for any intelligent extraterrestrial life form, or far future humans, that may find it. The Voyager spacecraft will take about 40,000 years to reach the distance of the star nearest to our Sun called Alpha Centauri, though neither craft is travelling in the correct direction. 'Near' meaning in this case about 4.35 light-years' distance; hence, if other beings do not come in the direction of the spacecraft to meet them, it will take at least that long for the Golden Record to be found.
As the probes are extremely small compared to the vastness of interstellar space, it is extraordinarily unlikely that they will ever be intercepted. If they are ever found by an alien species, it will be far in the future, and thus the record is best seen as a time capsule or a symbolic statement rather than a serious attempt to communicate with aliens.


Pioneer Plaque
This is the diagram that was placed on the pioneer spacecraft in 1973 to communicate our existence to alien life forms
At the top left of the plate is a schematic representation of the hyperfine transition of hydrogen, which is thought to be the most abundant element in the universe. Below this symbol is a small vertical line to represent the binary digit 1. This spin-flip transition of a hydrogen atom from electron state spin up to electron state spin down can specify a unit of length (wavelength, 21 cm) as well as a unit of time (frequency, 1420 MHz). Both units are used as measurements in the other symbols. Note that since the plaque is 229 mm wide, the actual unit of length could have been depicted, although it wasn't.

This is a present from a small, distant world, a token of our sounds, our science, our images, our music, our thoughts and our feelings. We are attempting to survive our time so we may live into yours.
U.S. President Jimmy Carter

Advantages and disadvantages of the various energy sources

The drawbacks of the fossil fuels are well known:

1-Non-renewable energy resource
2-Carbon emissions,
3-The greenhouse effect and global warming
4-Pollution by impurities or additives such as sulphur dioxide and lead compounds
5-Acid rain

Nuclear fission looked very promising in the past (before the Three Mile Island and Chernobyl disasters and concerns about terrorism) and provides a large proportion of energy for some countries, such as France and Korea. In the short-term, it appeared to be non-polluting. Unfortunately, radioactive plutonium is a rather nasty substance.
Clearly, however, an option such as nuclear fission which allows a state with few alternative sources to be less dependent on oil and which has a ‘petroleum sparing’ effect will continue to remain attractive, despite the thorny unresolved issues of disposal of nuclear waste and decommissioning of old nuclear plants (which may end up being encased in concrete and cordoned off for decades at great expense). Furthermore, there is potential for the acquisition of materials by rogue states or terrorists for bomb building or just making ‘dirty’ conventional bombs to spread radioactive dust.

Renewable sources of energy, such as photovoltaic, wind, geothermal, hydroelectric or tidal energy, are tremendously appealing, but are applicable only to specific geographic areas and often with wide fluctuations in availability.

Bio-Hydrogen

Hydrogenases, enzymes involved in the microbial production and consumption of hydrogen gas, were first described in a series of classic papers in the Biochemical Journal by Stephenson and Stickland in the 1930s. The enzymes came to prominence during the fuel crisis of the 1970s, when it became apparent that reserves of fossil fuels were finite and biological hydrogen production offered a sustainable alternative. Since then, the prospect of climate change has spurred the search for sources of hydrogen that do not involve net production of CO2. There has been steady progress in our understanding of hydrogen in the biosphere. Hydrogen is produced by photosynthetic cleavage of water, by fermentation of waste materials, and as a by-product of nitrogen fixation. How we could make this bio-hydrogen into a viable fuel source is certainly a challenge for the future. It will not be possible until we understand, in much more detail, how and why organisms produce hydrogen.
It became obvious early on that economic hydrogen production it is not just a matter of extracting enzymes or growing monocultures of hydrogen-producing organisms and using them like chemical catalysts. Microbes have their own agenda. Hydrogenases are complex enzymes; their synthesis depends on complex multi-step assembly processes, which are now being elucidated. They use complex machinery to transport the hydrogenases, complete with their elaborate nickel- and iron-containing centres, specifically through cell membranes. Moreover organisms in the environment are accustomed to exchanging metabolites, including hydrogen, to optimize their use of energy sources; production of hydrogen and hydrogenases is tightly regulated. Details are emerging of their mechanisms of control of biosynthesis and environmental hydrogen sensing, by regulatory proteins very similar to hydrogenases.

Energy Crisis

Periodic crises in the supply and price of fossil fuels have drawn attention to the fact that renewable energy sources are the only long-term solution to the energy requirements of the world’s population. Molecular hydrogen is a future energy source/carrier that is being actively investigated as an alternative to fossil fuels. It reacts with oxygen, forming only water; hence, it is a clean renewable energy source. It has a high calorific value, and can be transported for domestic consumption through conventional pipelines. Contrary to a widely held belief (the ‘Hindenburg disaster syndrome’), hydrogen gas is safer to handle than domestic natural gas.
When fossil fuels are no longer abundant, or their use is curtailed because of concerns over changes in the atmosphere, the way in which we use energy will be fundamentally changed. For example, the present methods of generating electricity are a compromise between the efficiency of large power stations and the losses in transmission over long distances. It is more efficient to transmit H2 gas through pipelines, than electricity through power lines. Electricity could be produced locally, even domestically, from H2 and air, in fuel cells. The risks of using H2 are offset by the use of lower electric voltages. The switch to a hydrogen economy could be a gradual transition. Hydrogen can be mixed with methane in domestic gas supplies with minimal change to the equipment. But the greatest benefits for H2 will come when exploiting the thermodynamic advantage of fuel cells, converting chemical energy directly to electricity.
A great deal of research is being applied to the use of hydrogen as a fuel in transportation, for cars and airplanes. The goal here is the promise of near-zero emissions.
H2 is also being considered as an alternative to batteries for electronic equipment.
For transport, the difficulties are concerned with finding a compact storage for the low-density fuel; and the expense of the catalysts. Various approaches are being used for storage. One is to store it as a higher-density liquid such as methanol, and reform it to H2 as required. This is somewhat analogous to the biological approach, though it leads to the release of CO2. Other options are to compress the H2, store it as liquid hydrogen at very low temperatures, or combine it with metals to form hydrides from which the gas can be released at will. Another method, which again resembles the biological solution, is to store the H2 in carbon nanotubes, which offer high-density and lightweight storage.
At present most of the H2 is produced industrially by conversion of fossil fuels, either directly or indirectly. This leads inevitably to the net production of the greenhouse gas CO2. New methods will have to involve recycling of organic matter, or direct production of H2 from water using energy sources such as sunlight. This can be achieved either directly in photochemical fuel cells, or by using photovoltaic cells, which use solar radiation to electric current for electrolysis of water into H2 and O2. A great deal of effort has gone into the development of silicon solar cells (photovoltaic) for production of energy from sunlight, which have become less expensive and improved in efficiency.
The costs of production of H2 from the electricity produced are decreasing steadily, but they still involve noble-metal catalysts.