Chemistry has a key role to play in the development of many of tomorrow’s technological solutions, especially in the energy field, both in production and storage and the deployment of new energy sources. Chimie ParisTech, in addition to training future specialists in this field, is exploring several areas of research related to this field.
Energy production by electrical conversion: the example of a new generation of photovoltaic cells
The photovoltaic sector is in rapid evolution with, on the one hand, strong needs on the application side given the large production volumes and, on the other hand, a maturation of dominant technologies that are reaching their performance limits; crystalline silicon, for example, is at 90% of its theoretical performance. And if there is one thing that all chemists agree on, it is the importance of photovoltaic cells in the production of renewable energy.
Since 2013, Dr. Pauporté’s Optoelectronics, Photovoltaics and Nanostructures group has been interested in perovskite photovoltaic solar cells. Perovskite is a crystalline structure that can integrate organic molecules in an inorganic network: these semiconductor materials have optoelectronic properties that can be modulated by chemistry. The cells studied by the team consist of a layer of perovskite sandwiched between two layers that provide selective contact and that allow the separation of charges: holes and electrons(1). In particular, the group studied and optimized the integration of ZnO oxide nanostructures for electronic transfer within the cell. It is also developing complex perovskites with multiple cations that display a great efficiency and stability; low-cost organic semiconductors for hole separation. The peak performance achieved by Dr. Pauporté’s group to date is 20.6%.
Chimie ParisTech is also home to a laboratory dedicated to photovoltaic energy: the IPVF (Institut Photovoltaïque d’Ile de France), headed by Jean François Guillemoles, is part of the Instituts pour la Transition Energétique (ITE), which emerged from a partnership with many industrialists such as EDF, Total and Air Liquide and which has been selected by the Investment Plan for the Future. The UMR IPVF is working on several fronts: fundamental issues (process for ultimate photovoltaic conversion yields), important questions for applications (improving the reliability and sustainability of solar technologies) and innovations (development of new materials and devices for a competitive technology that will enable the industry to grow in Europe).
The conversion of solar energy into electricity remains a reliable way to produce energy and can still be improved, but other less known types of conversion such as chemical conversion are being studied.
Chemical conversion used to optimize a city’s gas production from farm waste
One of the main environmental issues is to limit greenhouse gas emissions. Carbon dioxide, hydrocarbons or nitrous oxide are the main causes of global warming. As we continue to produce them in greater quantities than nature can degrade them, finding ways to convert them, especially into re-usable energies, appears to be the best long-term solution.
In that frame of mind, Vincent Piepiora, a former student of Chimie ParisTech, had the idea of using plasma technology to convert CO2 and H2 from farm digesters to CH4, which is then reinjected into a network or compressed into NGV. These digesters produce raw biogas by digestion with anaerobic bacteria(2) and are already present on farms. However, the conversion is not absolute and it is difficult to separate the compound from residual H2 and CO2. Furthermore, a legal limit has been set on the amount of injectable H2 in a network; set at 5%, this system would reach it easily. How does this technology work?
For several years, the 2PM (Processes, Plasmas and Microsystems) team, which is led by Professor Tatoulian at Chimie ParisTech, has been developing plasma processes based on the use of a gas that is completely or partially ionized by applying an electric field to it (electronic impact). It is very reactive because it contains many radical and ionic species. Usually used in surface treatments (etching, functionalization, polymerization), they can also be used as vectors and reagents for chemical reactions.
The natural progression was for Vincent Piepioria and the 2PM team to co-found the first integrated start-up at Chimie ParisTech, ENERGO (of which PSL holds 10% of the company’s shares). From their collaboration came the homonymous module, which achieves the catalytic conversion of CO2 and H2 into CH4 using plasma technology. Installed after the digesters, it complements the conversion of the biogas as well as releases the reused heat to give bacteria a temperature of 50°C, which they need to work. There are many advantage to using this method:
- simple integration into existing systems, additional revenues for operators,
- a re-usable source of heat and oxygen, not to mention a significant reduction in its environmental impact.
The targeted market is small farms, especially because of the system’s relatively low flow rate (currently about 20 m3/h). It is a great example of innovative research used to meet current societal challenges.
While energy production methods are widely studied by researchers, what about energy storage?
Energy storage, or how to develop alternative lithium solutions in mobile systems
The first alkali metal on the periodic table, lithium is commonly used in batteries to store energy via an electrochemical accumulator system. There are three main types:
- The lithium-ion battery, the most used, delivers the most energy.
- The lithium-polymer battery, a viable variant of the lithium-ion, is much safer but produces less energy.
- The lithium-metal battery, less often used because of the high reactivity of lithium metal, especially in moisture.
Researchers from the MIM2 (Materials, Interfaces and Soft Matter) team joined in the race to improve Li-ion batteries, testing a new methodology opposed to the traditional and popular “trial and error” method. Their starting point was to create new electrolytes by modeling, before selecting the best structures to synthesize them and analyze them to assess their performance.
Lithium is not a rare element (in 2009, the US Geological Survey Institute estimated that there is 11 million tons of lithium on earth); however, its exploitation is bound to explode in the coming years, especially because of the development of electric cars. Faced with this observation, this project was stopped and the team, backed by funding from the ANR (Agence Nationale de la Recherche), has set itself a new course: the creation and development of new electrolytes “Beyond Lithium” for batteries to eventually replace lithium in some energy storage systems.
Special consideration has been given to stationary systems, which can for example be positioned at the base of wind turbines or on mobile systems (phones, computers, etc.), for which the constraints are very different. Maximizing the safety and longevity of the battery is indeed very important for these systems, while such constraints as mass and power should be less of a focus. Redox-flow batteries seem to be a particularly interesting solution for these mobile systems. This new generation of rechargeable batteries use a chemical element (such as vanadium) under different oxidation states to store energy as chemical potential. Their excellent lifespan, the fact that they can be recharged and their relative inertia regardless of temperature (in a reasonable range) are but a few of their advantages. In order to develop them, the MIM2 team partnered with a start-up, AZA, not in order to compete with Li-ion batteries with “short” storage, but rather to focus on the “long” storage capacity mentioned above.
Creating the energy of tomorrow
Chimie ParisTech researchers are tackling all energy-related issues, from energy production by solar and chemical conversion, to battery storage and development of new technologies. In addition to the sector’s need for innovation to meet current environmental and societal challenges, advances are paving the way for ever cleaner technologies. To achieve this, we are developing new collaborations between academic researchers and industries or start-ups, which can only strengthen the quality and relevance of the projects we are undertaking.
After all, what is better than to be inventing the energy of tomorrow?
Auteur : Thomas Moragues
Engineering student at Chimie ParisTech - Class of 2020.
Describes a molecule with a carbon-metal bond. These molecules are widely used because this bond induces a negative polarization of the carbon, turning it nucleophilic.
(2) Anaerobic bacteria
Bacteria whose chemical digestion cycle happens in the absence of oxygen. In this case, they digest CO2 and H2 in CH4. The opposite of an anaerobic cycle is an aerobic cycle, which requires an oxygen-rich atmosphere.