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Designing and fabricating highly active and thermally stable catalysts with minimal noblemetal loading is crucial for solid oxide fuel cells that operate with direct methane fuel. In this study, ultralow-loading Ru catalysts (<10 μg cm −2 ) are fabricated using plasma-enhanced atomic layer deposition (PEALD) on a samaria-doped ceria (SDC) backbone for a methane oxidation electrode. The Ru catalyst with a high surface area and a high triple-phase boundary density shows electrochemical performance superior to that of its sputtered counterpart despite a 95% reduction in noble-metal loading. Furthermore, the PEALD Ru catalyst demonstrates more stable operation at elevated temperatures with less morphological degradation in comparison to the sputtered catalyst and mitigates carbon coking. Such improvements are ascribed to the nature of PEALD, which can make Ru particles conformally on porous SDC with highly dense and intimate interfaces.

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Atomic layer deposition (ALD) has the advantage of being able to deposit various materials as nanometer-scale thin films at low temperatures, and to precisely control thickness and doping levels. Due to these advantages, ALD has been applied in various fields including solid oxide fuel cells (SOFCs). SOFC is an echo-friendly next-generation energy conversion device that has high efficiency and fuel-flexibility. However, due to the high operating temperature (1000 ℃) of conventional SOFCs, problems such as thermal degradation and material selection occur. In order to solve this problem, low temperature SOFCs (LT-SOFCs) that can be operated below 500 ℃ are being studied. However, as the operating temperature decreases, oxygen reduction reaction (ORR) at cathodes of SOFCs also slows down. Therefore, engineering cathode surface, where ORR takes place, is important to improve the performance of LT-SOFCs. In this study, we deposited an ultra-thin film (~ 5nm) yttria-stabilized zirconia (YSZ) overlayer on the Pt cathode surface of LT-SOFC through ALD. In addition, the effect of doping level on the performance and thermal stability of LT-SOFC was studied by varying the cycle ratio of zirconia and yttria. The doping level of the YSZ overlayer was controlled to be 6, 13, 16 and 23 mol%, which were confirmed through XPS analysis. The performance of the cell with 16 mol% -doped YSZ overlayer at 450 ℃ showed the highest maximum power density, which was 70 % higher than that of cell without the overlayer. In addition, the activation resistance, which is mostly from ORR, was also reduced by 27 %. In addition, in the prolonged operation for 5 hours at 450 ° C, it was found that the performance of the cell without the overlayer was reduced by 80 %, while that of the cell with 16 mol%-doped ALD YSZ overlayer was reduced by 40 %. This result shows that the thermal stability was also improved when the ALD YSZ overlayer was deposited.