NANO2021-Nanoteknologi og nye materiale

Through the project MOC@SUPCAP the partners NTNU, SINTEF and IST from Portugal have developed materials to be used in supercapacitors. The materials are based on a mixture of metal oxides and carbon materials, which is a step further in the development of capacitors which are currently based on carbon materials from coconut shell. The project has been funded by the respective funding agencies through the m-ERA.net, a sub program of Horizon 2020. Energy can be stored in a supercapacitors by either storing electrical charge on the high surface available (carbon) or through a redox reaction in the metal oxide. State of the art electrochemical capacitors store energy using electrical charge. Since the charge is only stored on the surface there is no chemical reaction, but only a surface reaction the capacitor will have close to unlimited charge and discharge cycles compared to e.g. a battery where a chemical reaction occur and change the materials during cycling. However, these devices have suffer from low energy storage capability. To increase the storage capacity it is possible to add in a metal oxide. These oxides have a metal ion (cation e.g. manganese, nickel, cobalt) which can have different valence. These combination of these materials are called hybrid materials and development of these hybrid materials have been one of MOC@SUPCAPs goal. The goal is challenging since a controlled mixture of carbon with very high surface area and a metal oxide with correct particle size, composition and purity. MOC@SUPCAP has been successful in developing different hybrid materials mainly using two different synthesizing routes; electrochemical deposition of metal oxides on a nano porous carbon material and different wet chemical synthesis routes. Both methods are inexpensive and is possible to scale up. IST has been responsible for the electrochemical deposition and SINTEF for the wet chemical routes. The different routes have each their pro and cons. Electrochemical deposition have demonstrated better capacitance, while the wet chemical routes with spray coating to prepare electrodes are more applicable for commercial processing. Both methods have resulted in materials with several thousand cycles. SINTEF has also evaluated which composition (carbon/metal oxide) of the hybrid material results in best capacitance. Throughout the project period there have been good cooperation and especially when it comes to different characterization techniques which are necessary to understand and improve the materials. A detailed and fundamental understanding of the electrochemical processes which occurs during charge and discharge have been carried out by the PhD student at NTNU. In the study, focus has been on MnO2 materials where high capacitance has been demonstrated in addition to cycling for thousands of cycles. This has been achieved by optimizing both the structure of MnO2 and selection of electrolyte, e.g. electrolyte based on two valent cations. The most stable electrode show highest crystallinity and it has been shown that secondary phases convert to MnO2 during repeatedly charge/discharge cycles which enhance the stability. Mathematical models for impedance spectra for porous structures of manganese oxides has been developed. The model can be used to understand impedance spectra, e.g. when the composition of electrolyte changes. The PhD studies are still ongoing when the project ends and several publications are foreseen after the PhD dissertation. One of the goals in the project has been to develop an asymmetric supercapacitor cell where different type of electrodes is used in the same cell; one electrode using high surface area carbon materials and another electrode using a hybrid electrode based on a mixture of metal oxides and carbon. SINTEF has prepared electrodes with realistic loading to achieve sufficient energy density. There is still improvement for significant enhanced properties, but important knowledge has been gained to carry out this work later. Through the project period several meetings between all partners have been arranged, both physically and face-to-face in Lisboa and Trondheim. This has been necessary to keep up necessary progress and cooperation in the project. The results from the project have been presented at international conferences and journals (latter, mainly from IST) and towards industry when possible. The project has not resulted in any patents or contributed to any commercial products, but this was not expected during the project period. However, significant enhanced competence on supercapacitors has been developed and this will be used for future development of energy storage.

The project aims at designing and fabricating a new class of high performance hybrid composite electrodes for supercapacitors by combining carbon materials and metal oxides. These electrodes are expected to have a higher specific capacitance than conventi onal double-layer (carbon based) electrodes due to the additional contribution of redox pseudocapacitance, characteristic of metal oxides. The development of these new materials will be a step forward on achieving supercapacitor devices with enhanced powe r and energy densities at competitive. The innovation of the MOC@SUPCAP project is based on using simple, low-cost fabrication routes to create a new class of higher performance electrodes for supercapacitors contributing beyond the state-of-the-art and c reating alternatives to the conventional systems existing in the market. The project is on the edge of advanced materials research and is foreseen to contribute to breakthrough advances. The topic is highly relevant today and the project partners have the expertise to develop a successful project. The expected results are new hybrid materials with enhanced capacitance fabricated by simple and low-cost routes, able to meet the demands of the energy storage sector. Moreover, the results can be transferred f or the private sector, due to the foreseen simplicity of the explored fabrication routes. The high quality of the expected results will contribute to high level scientific publications and have a high impact for the society as a whole.