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Engineering of Nanocomposites for a New Energy Conversion Device Joining Fuel Cell and Solar Cell

Final Report Summary - NANO-FCSC (Engineering of Nanocomposites for a New Energy Conversion Device Joining Fuel Cell and Solar Cell)

Clean energy conversion is one of the key issues for the 21st century. Fuel cells (FC) are a promising technology for efficient and clean energy conversion that can have an impact on the global energy and climate challenge. However, in recent year, the development of current FC technology is facing a variety of bottlenecks which severely restrains the commercialization of FC. Thus this Nano-FCSC project intended to explore a new development pathway for current FC technology by utilization of nanotechnology, specifically nanocomposite approach.
The overall aim of the Nano-FCSC project is to develop and engineer functional nanocomposite materials for a novel energy conversion technology, which combines the principle of both fuel cell and solar cell, and investigate scientific principles and device mechanisms, including ion and electron transport. This project is a multidisciplinary and interdisciplinary research encompassing nanotechnology, materials synthesis, materials characterization, thin film fabrication, device fabrication and performance test (fuel cell and solar cell) and modelling activities. Therefore, the experienced researcher will have exposure to a wide range of experts on nanoscience, fuel cell, solar cell, applied physics and modelling during the whole course of project development.
During the duration of the project, the following achievements have been successfully made, and relevant results have been published or submitted to international journals:
(1) The first part of the work has been done on exploration of new effective composite materials that can be used for single component fuel cells (SCFC). A composite of industrial-grade material LaCePr-oxide (LCP) and perovskite La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) was fabricated and investigated for SCFC. The microstructure, morphology, and electrical properties of the LCP, LSCF, and LCP-LSCF composite were investigated and characterized. It is found that the key issue for decent performance of the device is to achieve balanced ionic and electronic conductivities by varying the ratios of LCP to LSCF in the composite. Fuel cell with an optimum ratio of 60 wt% LCP to 40 wt% LSCF reached the highest open circuit voltage (OCV) at 1.01 V and a maximum power density of 745 mW cm−2 at 575 °C, which is much better compared to conventional FCs using an LCP electrolyte layer. Furthermore, the performance stability was validated by continuous 14-h operation. The good performances of EFFCs can be attributed to characteristics including an interfacial mechanism, a junction effect, and the multiple roles of NCAL as an electrode catalyst. These results illustrate the great potential of EFFCs for next-
(2) Regarding to the mechanism study, an important Schottky-junction (SJ) effect was discovered on high performance fuel cells. The nanocomposite semiconductor-ionic material with unique multifunction properties plays a key to realize such junction device. Unlike fuel cells that use an electrolyte separator, the SJ band-gap barrier and built-in electric field prevent the device from short-circuit. Incorporation of the Schottky effect to build the SJ junction can combine both physical and electrochemical processes to drive the devices’ underlying processes. The power densities of 500 -1000 mW/cm2 were achieved at 550 oC. While at this temperature, conventional fuel cell constructed using the anode/electrolyte/cathode in this work, reached less than 400 mW/cm2. The maximum power output of SJ device was enhanced up more than two times. Applying this effect and principle to fuel cells offers several great advantages, including simplicity, low cost of material and technology, light weight, and good performance. These imply great commercial applications of the principle and invention.
(3) The project also integrated the research on fuel cell and solar cell to some extent. Recent success on perovskite solar cell (PSC) not only has made an emergence of new photovoltaics technology, but also inspires a new generation energy conversion. Based on the PSC principle, we have designed and constructed a novel fuel-to-electricity conversion device by using a composite as a core functional layer, which consists of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) perovskite oxide and Sm-Ca co-doped ceria (SCDC) ionic conductor, sandwiched by n- and p-conducting layers. The conversion process makes use of semiconductor energy bands and junctions properties. The physical properties of the junction and alignment of the semiconductor energy band allow for direct ion transport and prevent internal electronic short-circuiting, while at the same time avoiding losses at distinct electrolyte/electrode interfaces typical to conventional fuel cells. The new device achieved a stable power output of 1080 mWcm−2 at 550 °C in converting hydrogen fuel into electricity.
Besides the scientific achievement, the project also accomplished achievement on knowledge transfer and collaboration establishment by the following aspects:establishing a new graduate course at Aalto University on Nanotechnology for advanced energy applications and enhancing EU-Indian cooperation in Nano-energy.