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    Drones are used for various applications such as air survey, disaster recovery, and delivering. Despite attracting attention as a new growth area, the biggest problem of drones is its small battery capacity and limited flight time of less than an hour. A fuel cell developed by Prof. Gyeong Man Choi (Dept. of Materials Science and Engineering) and his research team at POHANG UNIVERSITY OF SCIENCE & TECHNOLOGY (POSTECH) can solve this problem.

    fuelcellsrep22443-f1

    Fig 1: Schematics of fabrication process of micro-SOFC supported on LSTN-YSZ/STS substrate.

    Miniaturized solid oxide fuel cell (SOFC)

    Prof. Choi and his Ph.D. student Kun Joong Kim have developed a miniaturized solid oxide fuel cell (SOFC) to replace lithium-ion batteries in smartphones, laptops, drones, and other small electronic devices. Their results were published in the March edition of Scientific Reports, the sister journal of Nature. Their achievement has been praised because it can be utilized, not only for a small fuel cell, but also for a large-capacity fuel cell that can be used for a vehicle.

    The SOFC, referred to as a third-generation fuel cell, has been intensively studied since it has a simple structure and no problems with corrosion or loss of the electrolyte. This fuel cell converts hydrogen into electricity by oxygen-ion migration to fuel electrode through an oxide electrolyte. Typically, silicon has been used after lithography and etching as a supporting component of small oxide fuel cells. This design, however, has shown rapid degradation or poor durability due to thermal-expansion mismatch with the electrolyte, and thus, it cannot be used in actual devices that require fast On/Off.

    The research team developed a new technology that combines porous stainless steel, which is thermally and mechanically strong and highly stable to oxidation/reduction reactions, with thin-film electrolyte and electrodes of minimal heat capacity. Performance and durability were increased simultaneously. In addition, the fuel cells are made by a combination of tape casting-lamination-cofiring (TLC) techniques that are commercially viable for large scale SOFC.

    The fabrication process is simpler than for other micro-SOFCs because it does not use complicated lithography, etching or templating. A dual-layer substrate is prepared using conventional tape-casting and lamination . Then the green dual-layer is co-fired in reducing gas ) to avoid oxidation of STS. To ensure suitable nanostructure, the dual-layer substrate is characterized after firing. The LSTN-YSZ contact layer (thickness ~40 μm) has pore size of ~500 nm and surface root-mean-square roughness (RMS) of 44 nm ). An area porosity ε of LSTN-YSZ surface obtained from binary images, increased from 14 to 18% after surface polishing and a RMS value decreased from ~44 nm to ~21 nm after surface polishing ), thus the porosity and surface roughness are appropriate for deposition of 2-μm-thick and dense electrolyte.

    The fuel cells exhibited a high power density of ~ 560 mW cm-2 at 550C. The research team expects this fuel cell may be suitable for portable electronic devices such as smartphones, laptops, and drones that require high power-density and quick on/off. They also expect to develop large and inexpensive fuel cells for a power source of next-generation automotive.

    With this fuel cell, drones can fly more than one hour, and the team expects to have smartphones that charge only once a week.

    Reference

    This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology.

    http://www.postech.ac.kr/

    http://www.nature.com/articles/srep22443

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