Solar energy is the primary source of energy on Earth. Its transformation provides the chemical energy ensuring the development of the vast majority of living beings. Fossil fuels – oil, gas, coal – are not as well as derivatives. The effective recovery, processing and storage of solar energy is a major challenge but this energy would be a perfect answer to current energy needs. Photovoltaic systems can harvest solar energy and transform it into electricity. But this latter form of energy has the disadvantage of being difficult to store.
The natural chemical processes mastered the solar energy through the process of photosynthesis. The perfect solution would be to get the energy produced by photosynthesis in plants directly. Or we should be able to copy this process that billions of years of evolution have perfected in order to convert solar energy into chemical energy as hydrogen, which is easier to store than electricity.
In the process of photosynthesis, solar energy is used to split water and produce oxygen molecules, protons and electrons. To produce an electric current, the electrons produced by the reaction have to be recovered. This is what a team of Stanford University researchers has succeeded to do by using nano-gold electrodes. A nano-electrode is stuck inside a cell of algae. First of all the task is to create an electrode small enough to be introduced into a cell and, secondly, to puncture the cell and to maintain the electrode in place without causing death of the algae. Once in place, this electrode directly receives the electrons produced in the energy factories of plant cells that have chloroplasts.
However, this took place not only in a single cell and the resulting current is extremely low: a picoamperes. To be effective, it should be possible to improve the recovery of electrons within cells and multiply the number of cells tethered by about a thousand billion. Not to mention the possibility that the “energy theft” is also the cause of the premature death of cells. The authors are nevertheless confident. They believe that this approach would potentially produce more energy from plants through combustion. If these results highlight the possibility of recovering the energy directly from the source, other researchers propose to mimic natural structures in order to reproduce the process of photosynthesis.
The evolution has produced structures that make the process of photosynthesis very effective: why not copy? In a sheet, the different structures are intended to guide the solar energy to the chloroplasts where it will be transformed, providing excellent performance. The development of nanotechnology allows scientists to have a bottom-up construction of these structures, that is to say, playing with Legos and building material, piece by piece, the structure. Imaging methods and characterization can get the plans. The advantage of the researcher is that it can choose the materials he uses, so that biological materials are available in limited variety.
In the first attempt to produce an artificial inorganic leaf Chinese researchers injected the titanium oxide in the leaf of a plant, using the leaf as a mold. They obtained a structure eight times more productive than in hydrogen the same amount of titanium dioxide. By coating the platinum foil, they multiplied the productivity of the structure 10. These results were presented last March at the 239th National Meeting of the American Chemical Society, held in San Francisco. Copy the entire structure may seem like a good way to copy the process to recover hydrogen to fuel cell fuels. However, it is also considered to reproduce only the chemical process of decomposition of the water molecule.
Copy the chemical mechanisms
A team from the Massachusetts Institute of Technology (MIT) proposed a new method to realize the dissociation of water molecule using solar energy. They have thus reproduced the reaction taking place during photosynthesis without using the same materials as those used in nature. Although. They are in fact used a virus which is capable of binding catalytic materials (iridium oxide) and organic pigments. This is then included in a matrix of micro-gel creating a tangle to ensure the progress of the reaction. Pigments capture light energy, catalysts ensure the realization of the reaction. The virus is now staging the structural components and also ensures the transfer of energy.
However, this structure allows for the time being to ensure the least interesting part of the reaction: production of oxygen via the oxidation of the water molecule. It remains to change the structure to ensure the recombination of proton and electron products for the hydrogen atoms. Another drawback of the structure is related to the cost of iridium. In considering an industrial application, it will be necessary to find another less expensive catalyst.
A booming area
If this research were somewhat original, yet there are groups working on the subject. Less than a month ago the program Catalytix Sun caused a stir by promising to provide such equivalent electricity consumption of a house (30kw / h) through a water bottle. Since the project is supported by ARPA-E to the tune of $4 million. The technology used is based on a new catalyst discovered in the laboratory at MIT led by Daniel Nocera. His research focuses on the use of abundant elements on Earth to generate hydrogen and oxygen through fresh water or clean sea water. In the words used by the ARPA-E this technology provides a method of versatile, inexpensive, efficient, scalable storage of renewable energy. The system should cost a tenth of the price of conventional systems. The photo-electrochemical cells are also capable of converting sunlight and water into hydrogen for the production of synthetic fuels.
Similarly, the Helios Project is an initiative with a goal to develop solar energy at the Lawrence Berkeley National Laboratory (LBNL) in collaboration with UC Berkeley. The primary goal of this effort is the storage of energy from the sun. Scientists are focusing on several approaches such as generation of biofuels from biomass or algae and direct conversion of water and CO2 into fuel by the rays of light. The latter is particularly interesting because it contained what the researchers call “artificial photosynthesis”. To achieve this goal, the researchers repeated the process of photosynthesis using advanced materials and new molecules. The light is thus collected by the photovoltaic elements and then used to form chemical reactions to create fuel using only water and carbon dioxide. Researchers expect this process more efficient than that obtained by natural photosynthesis.
The natural structures offer solutions to current problems, particularly in the field of energy. The capacity analysis, comprehension and reproduction of structures and reactions observed at the molecular level have reached sufficient maturity to open new perspectives. The intensity of research in order to master the photosynthesis is an example.