Cet article est également disponible en français : Les nanosciences au coeur des technologies propres
The University of California at Berkeley is a leader in research on clean technologies, as recently witnessed by a visiting French delegationof representatives from the solar industry.
This excellence is primarily the result of many years of research in the development of nanoscience. These years of research are the foundation of a number of important advances in energy, the value of which is seen today as part of local initiatives (e.g. the CarbonCycle 2.0 program of Berkeley Lab) and federal initiatives relating to the challenges of the development of renewable energy sources, energy efficiency, pollution control and sustainable development.
It is this observation that has been the motivating factor behind the Office of Science and Technology’s organization of a symposium at the crossroads of nanoscience and clean technology. In partnership with UC Berkeley and Lawrence Berkeley National Lab, the Young Engineers and Scientists Symposium (YESS) proposes to cover, on March 20th to 22nd 2012, a range of topics relating to nanoscience and clean technology, and enable the development of collaborations between the American and French researchers in these fields.
What are the major applications of nanotechnology in the field of clean technologies today?
Demand for new types of technology storage is becoming increasingly urgent. Storage is necessary, both to allow us to move around in zero-emission vehicles and to succeed in smoothing out the fluctuations in output of intermittent renewable energy. However the technical specifications are not all the same for different applications: power, lightness and compactness for the first, the cyclability, low cost and high volumes for the second.
'Expectations in mobile usage thereby encourage taking advantage of smaller and more compact size , as well as new physical phenomena, that the material offers on a nanometer scale.
Recent research has yielded results on the impact of crystallography on the properties of a electrolithic cell. What is the influence of the interface property on the behavior of a battery’s electrodes? (Robert Kostecki, LBNL) What shape is the most conducive to the stability of the cathode and gives the best performance? (Guoying Chen, LBNL) What is the effect of anion substitutions or cations on the electrochemical characteristics of the cathodes? (A. Manthiram, U. Texas, Austin)
In addition, new ideas for nanoscale mechanical structures are emerging: the team of Yi Cui at Stanford has shown that lithium can be stored in "forests" of silicon nanowires, so that they do not fracture as would crystallites or thin film. Pulickel Ajayan at Rice University has shown that cell energy storage can be manufactured, into what consists of a single nanowire. A final example is the construction of a sandwich of silicon and graphene by A. Dillon from the NREL and the S. Whittingham of SUNY Binghamton.
In addition to changes in structure or shape, changing the type of atomic constituents can multiply the possibilities. Projects have simulated properties for more than 20,000 chemical compositions possible for a cathode. Research has an impressive number of possibilities to explore.
According to Cédric Philibert of the International Energy Agency, in 2060 most of the world's electricity could come from solar energy. Photovoltaics, one of the two solar technologies available now, is undergoing a huge development. In fact, the Prometheus Institute noted as early as 2005 the benefits of the use of nanotechnology and listed entities working in this direction in the United States. Nanotechnology makes very promising ideas to improve the photovoltaic conversion efficiency conceivable, for example:
1) Exploiting the excess energy of the electron-hole pairs resulting from the conversion of photons whose energy is greater than the "band gap " of a photovoltaic material. This could increase the current density or voltage across the cell.
2) Introducing intermediate energy levels in the band gap in order to capture carriers generated by photons with energies below the band gap.
A recent Cleantech Republic article mentioned recently some research undertaken in Canada on the engineering spectrum and photo-conversion using nano-tubes. Further south, in California, Professor Ali Javey of the University of Berkeley received in September 2011 the prize of scientific innovation awarded by APEC (Asian-Pacific Economic Cooperation) for his contribution to scientific progress on photovoltaics. His research group is studying the growth on aluminum substrates of optically active cadmium sulfide semiconductors in nano-pillar networks, incorporated into a thin film of cadmium telluride. An article published in November details the advantages of using three-dimensional structures rather than planar cells, including optimizing the collection of current carriers and the alleviation of stress on quality materials.
Nanopilars of CdS embedded in a CdTe thin film
On the corporate side and still in California, Nanosolar choses to deposit layers of Copper-Indium-Gallium-Selenide (CIGS) with machines that look like printing presses. The ink here is composed of nanoparticles of about 100 nm in diameter and has the advantage of intrinsically possessing the stoichiometry of the CIGS material to be deposited - this very accurate proportion represents the main difficulty encountered by conventional methods of printing of CIGS. EDF EN, EDF's subsidiary dedicated to the development of renewable energy, has been for several years a "strategic partner" of Nanosolar and the installation of 6 MW of additional projects was announced in mid-November.
On the U.S. east coast Konarka, a company and in which the company Total has invested, is working on organic photovoltaic cells using a polymer invented by the company’s co-founder and Nobel prize laureate Dr. Heeger. The polymer can be deposited on a flexible substrate. Among the publications of the company, is found work on the nanomorphology and changes induced in the heterojunctions by changing the element (carbon or silicon) used as a "bridge" in polymers.
In 2010, the DOE awarded a cash prize of $ 122 million over 5 years for the creation of the Joint Center for Artificial Photosynthesis (JCAP), on the Berkeley and Caltech campus’. The ambitious goal of this center is to develop affordable solutions of a generation of “solar” fuels - that produce fuel from water, CO2 and light - using abundant materials , and 10 times more effective then plants.
To achieve this, JCAP faces many technological challenges, ranging from the nanoscale components to the macroscale of the integrated systems. The proposed approach follows three themes:
1) The "accelerated" discovery: the objective is to increase the number of discoveries in abundant materials that can capture and transform light energy into usable chemical fuels.
2) The passage from theory to practice: assemble the pieces of the puzzle at the nanoscale level (absorbers, catalysts, membranes) in units of functional photosynthesis and multiply these units in larger and larger systems, which operate at room temperature and over long periods of time.
3) The development of testing techniques that measure in record time millions of candidates for the absorbers, catalysts, etc. ... new assessments of the performance of components and complete systems. It will also be necessary to develop new theoretical tools, guiding by modeling the discovery of innovative materials.
The subject of Bioenergy is predominant on the Berkeley campus with the presence of two very important research centers: the Biosciences Energy Institute and the Joint Bioenergy Institute. How to link the issues of bioenergy and nanotechnology? Some tools in synthetic biology may be similar to nanotechnologies (when dealing with biological sensors to regulate metabolic pathways in plants for example).
Even if the subject of bioenergy seems a little far from nanotechnology, recent advances have proved crucial for the microbial bioenergy synthesis and nanotechnologies are seen as a key in the next generation of biofuels. Indeed, nanoparticles, nanotubes, nanofibers and nanoporous materials serve as efficient tools for processing raw materials, genetic engineering, biofuels and for bioelectrochemical systems.
Thus, with the development of materials and technologies, nanomaterials are doomed to be part of the bioenergy sector, such as for example the topic of efficient harvesting of biofuels: in effect on this subject the versatile nature of nanomaterials has allowed us to imagine the development of new absorbent materials and membranes that make harvesting biofuels easier and less expensive. More recently in a DoE laboratory nanoparticles have been developed that are capable of recovering the oil produced by algae without denaturing and destroying them. Thus these particles are able to slip between the membrane and cell wall and recover oil in their nanopores without causing cell death, which may have a significant impact on the sustainable development of the biofuel industry based on algae.
Much of the world’s electricity is generated by thermodynamic cycles that convert heat into mechanical energy and then electricity. Most of this heat is not converted, but lost and dissipated in the environment. If a small part of this lost heat could be converted into electricity, the impact on global energy consumption would be enormous. Many industrial processes are also generating major heat loss, just as the engine heat from our cars.
Thermoelectric materials, which have the particularity to convert heat into electricity, could be used to capture this wasted heat. According to the website “Techniques of an Engineer”, good thermoelectric material that is composed of large mass chemical elements, will have high mobility of the carriers (high relative permittivity elements: selenium, tellurium, antimony, semiconductor band gap), and low thermal conductivity.
Thus, an inverter or a cooling system could use thermoelectric materials to improve their effectiveness. This could also be applied to current converters, solar cells, etc ... However the main problem of thermoelectric components is that they are generally constructed of rare and expensive materials, making the commercial offer unattractive at the moment.
A team from Lawrence Berkeley National Laboratory, led by Professor Yang Peidong, recently discovered that rough silicon nanowires could be used to create a thermoelectric material with good performance. Since a low cost production infrastructure already exists for silicon, this material could be available at a relatively affordable price.
Silicon is a low thermoelectric room temperature material, but in the case of its silicon nanowires, the nanoscale diameter and the surface roughness can reduce the thermal conductivity without reducing electrical conductivity, although the mechanism is not yet understood.
In addition, the manufacturing process of a very specific size of these nanowires opens the door to applications in car engines or produced electricity could be used to power the vehicle's electrical system itself.
This technology is the source of developments at the Alphabet Energy startup, honored at the 2009 edition of the competition for startups " Cleantech Open ".
Energy efficiency in electronics
Noting the rapid growth of the share of electricity needed for the uses of information technology (data centers), and the fact that the performance of current integrated circuits have big llimitations, the National Science Foundation (NSF) has decided to open a research center dedicated to energy efficiency in electronics. Directed from the University of Berkeley by the iconic Prof. Eli Yablonovitch, the center aims to reduce energy consumed by transistors by getting as close as possible to the theoretical limits (Landauer limit).
The Research is divided into four themes:
1) Nanoelectronics: conventional transistors require a drive voltage of the Volt, as tensions are managed by a few millivolts. Reducing the operating voltage of a transistor to a few millivolts would result in a gain of power reduction of one million.
2) Nanophotonics: using light instead of electrons for communication requires less energy for long connections. The aim is to further reduce consumption by optical fiber, which is still far from theoretical limits. We must therefore rethink transmitters and detectors.
3) Nanomechanics: to develop nanomechanical switches with very low voltages, a key challenge is the precision of the manufacturing of these mechanisms.
4) Nanomagnetism: nano- magnets are expected to create logical switches which are very energy efficient.
The center will strive to provide the means to work collaboratively among the different teams, , including, through an effort of standardization and integration of new components and circuits.
Geological Carbon Sequestration
On another topic, nanotechnology could be one of the few techniques to verify if the geological sequestration of carbon works. Indeed, the best way to attach and secure CO2 is to attach it to a solid to form a carbonate. This process is a thermodynamically stable long-term solution to sequester CO2, but it takes a lot of time with conventional methods. Now, researchers at Lawrence Berkeley National Laboratory were able to produce magnesium oxide nanocrystals that would accelerate the fixation of CO2. The crystals influence the reaction rate, and control of their size and their surface reaction would increase the rate of CO2 fixed to it.
Instead of waiting for thousands of years to evaluate the process of sequestration as done in the United States and Europe, this discovery can immediately check whether there is formation of carbonates and thus sequestration, allowing on one hand to evaluate the storage space required and on the other the time required to do so.
The main limitation of this technology is that it focuses both on the fears associated with carbon sequestration and those related to the use of nanostructures in the environment. Regulatory agencies such as the Environmental Protection Agency (EPA) will have to set regulations in the coming years.
In addition, other teams at Berkeley closely studying CO2 sequestration in the long term
- within the Center for Nanoscale Control of Geologic CO2, a center named Energy Frontier Research Center by the Department of Energy, which aims to combine experimentation and simulation to understand and control the critical aspects of the geological sequestration of CO2.
- at the Molecular Foundry - a program funded by the DoE to provide support to researchers worldwide whose work can contribute to the study and development of nanoscience - the research is conducted on innovative ways to fix CO2. For example, a new class of polymers mimicking the features of peptides and proteins has been developed as catalysts for the mineralization of CO2.
A French-American symposium on nanoscience and Clean Technology
With the observation that many researchers from the University of Berkeley and Lawrence Berkeley National Laboratory are working on leading issues, the mission for Science and Technology has decided to organize March 20, 21 and 22 in collaboration with UC Berkeley a symposium on nanoscience and clean technologies. With the support of the nanosciences cell of the CNRS and Grenoble Innovation for Advanced New Technologies (GIANT), the Young Engineers and Scientists Symposium (YESS) invites you to participate in sessions on the various themes identified above.
The purpose of the symposium is to promote the meeting of engineers and French and American researchers, juniors and seniors, at the intersection of these topics.
We invite you to visit us at yess2012.org and to contact us if you wish to participate.