How Does solar energy convert into hydrogen energy(II)
Hydrogen is a high quality source of energy. Decomposition in water or any other ways in which solar energy can be converted to hydrogen energy, hydrogen production from solar energy, it is mainly as follows:
(1) solar-hydrogen from electrolysis of water. Hydrogen from electrolysis of water is now more widely used and more mature, more efficiently (75%-85%), but the power in both conventional hydrogen, from the energy use of gain. Therefore, only after the significant drop in the cost of solar power, large-scale hydrogen from electrolysis of water can be achieved.
(2) solar thermal hydrogen production from water decomposition. Water or steam heated to above 3000K, the hydrogen and oxygen in the water can break down. Efficient hydrogen production by this method, but requires a high concentration can achieve high temperatures, hydrogen production are generally not used in this way.
(3) the solar thermochemical cycle for hydrogen production. In order to reduce the high temperature solar direct thermal water splitting for hydrogen production requirements, developed a thermochemical cycle for hydrogen production methods, that is, in the middle of adding one or more water, then heated to a lower temperature, going through various stages of response, ultimately splitting water into hydrogen and oxygen, and intermediate consumption, recyclable. Thermochemical cycle decomposition temperature along the lines of 900-1200K, it was a rotating parabolic mirror concentrator for easy temperature, decomposition of water efficiency in the 17.5%-75.5%. Intermediate restores are the main problems that exist, even if restoring by 99.9%-99.99%, and would also like to add a 0.1%-0.01%, which will affect the price of hydrogen, and environmental pollution.
(4) solar photochemical hydrogen production from water decomposition. This hydrogen thermochemical cycle for hydrogen production with such similarities, adding a photosensitive substance in water as a catalyst, increasing long wavelength absorption of light energy to the Sun, use of photochemical reactions of hydrogen. Japan people use iodine sensitivity to light, devised including photochemical, thermal response an integrated hydrogen production processes, hydrogen 97 liters per hour, efficiency of up to 10% per cent.
(5) the solar photoelectrochemical cells hydrogen production from water decomposition. 1972, Japan this more health first people uses n type Titania semiconductor electrode for anode, and to Platinum black for cathode, made solar photoelectric chemical battery, in too Sun irradiation Xia, cathode produces hydrogen, anode produces oxygen, two electrode with wire connection will has current through, that photoelectric chemical battery in too Sun of irradiation Xia while achieved has decomposition water system hydrogen, and system oxygen and obtained power. Scientists around the world attach great importance to this experimental result, considered to be a breakthrough in solar technology. However, photoelectrochemical cells hydrogen production efficiency is very low, only 0.4%, only absorb ultraviolet light from the Sun, and near ultraviolet light, and electrode corrosion-prone, inconsistent performance, it has yet to meet the practical requirements.
(6) solar hydrogen production by catalytic decomposition of water by complexation. Since 1972, scientists found three adjacent pethidine nail of the excited state complexes with electron transfer capacity and charge transfer reaction catalyzed by complex, made use of this process for hydrogen production by photocatalytic decomposition of water. This complex is a catalyst, its role is to absorb light energy, charge separation and charge transfer and Assembly, and through a series of coupled processes, leading to split water into hydrogen and oxygen. Hydrogen production by catalytic decomposition of water by complexation was premature, the research is continuing.
(7) the bio-hydrogen production by photosynthesis. Green algae under anaerobic conditions for more than 40 years ago, after exposure to the Sun can evolve hydrogen; more than 10 years ago, also found that many algae, blue-green algae in an oxygen-free environment to adapt over time, photosynthetic hydrogen under certain conditions. At present, due to the mechanism of photosynthesis and algal hydrogen have so much to learn, algae, hydrogen is inefficient, to achieve engineering there is a considerable gap between the hydrogen. It is estimated that such as algal photosynthesis biohydrogen efficiency to 10%, 9 grams of algae per square metre per day hydrogen molecules, received 50,000 square kilometers of solar, through photosynthetic hydrogen engineering meets United States of all the fuel needs.