• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.62-62
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• 2018

Pt is still considered as one of the most active electrocatalysts for ORR in alkaline fuel cells. However, the high cost and scarcity of Pt hamper the widespread commercialization of fuel cells. As a strong candidate for the replacement of Pt catalyst, silver (Ag) has been extensively studied due to its high activity, abundance, and low cost. Ag is more stable than Pt in the pH range of 8~14 as the equilibrium potential of Ag/Ag+ being ${\approx}200mV$ higher than that of Pt/PtO. However, Ag is the overall catalytic activity of Ag for oxygen reduction reaction(ORR) is still not comparable to Pt catalyst since the surface Ag atoms are approximately 10 times less active than Pt atoms. Therefore, further enhancement in the ORR activity of Ag catalysts is necessary to be competitive with current cutting-edge Pt-based catalysts. We demonstrate the architectural design of Ag catalysts, synthesized using plasma discharge in liquid phase, for enhanced ORR kinetics in alkaline media. An attractive feature of this work is that the plasma status controlled via electric-field could form the Ag nanowires or dendrites without any chemical agents. The plasma reactor was made of a Teflon vessel with an inner diameter of 80 mm and a height of 80 mm, where a pair of tungsten(W) electrodes with a diameter of 2 mm was placed horizontally. The stock solutions were made by dissolving the 5-mM AgNO3 in DI water. For the synthesis of Agnanowires, the electricfield of 3.6kVcm-1 in a 200-ml AgNO3 aqueous solution was applied across the electrodes using a bipolar pulsed power supply(Kurita, Seisakusyo Co. Ltd). The repetition rate and pulse width were fixed at 30kHz and 2.0 us, respectively. The plasma discharge was carried out for a fixed reaction time of 60 min. In case of Ag nanodendrites, the electric field of 32kVcm-1 in a 200-ml AgNO3 aqueous solution was applied and other conditions were identical to the plasma discharge in water in terms of electrode configuration, repetition rate and discharge time. Using SEM and STEM, morphology of Ag nanowires and dendrites were investigated. With 3.6 kV/cm, Ag nanowire was obtained, while Ag dendrite was constructed with 32 kV/cm. The average diameter and legth of Ag nanowireses were 50 nm and 3.5 um, and thoes values of Ag dendrites were 40 nm and 3.0 um. As a results of XPS analysis, the surface defects in the Ag nanowires facilitated O2 incorporation into the surface region via the interaction between the oxygen and the electron cloud of the adjacent Ag atoms. The catalytic activity of Ag for oxygen reduction reaction(ORR) showed that the catalytic ORR activity of Ag nanowires are much better than Ag nanodendrites, and electron transfer number of Ag nanowires is similar to that of Pt (${\approx}4$).

• 한국광학회지
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• 제28권1호
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• pp.28-32
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• 2017

본 논문에서는 LSPR 센서에 적용하기 위한 제한된 높이 100 nm에서 $TiO_2$, $SiO_2$의 다중층을 이용한 LSPR 센서를 디자인을 제안했다. LSPR 센서의 구조는 유전체 층과 나노 구조가 있는 금속층으로 디자인 하였다. 금속층은 금 박막 40 nm와 높이 40 nm, 주기 600 nm, 선폭 300 nm인 나노와이어 구조체를 올려놓은 구조로 디자인하였다. 유전체 층의 높이를 100nm로 제한하고, $TiO_2$, $SiO_2$가 반복되는 구조로 하여 반복층의 개수를 1~4개로 변경하면서 비교 분석하였다. 파장 가변형 SPR을 디자인하기 위해 각도를 75도로 고정하고 파장을 변화시켜 FEM방식으로 계산하였다. 결과로 굴절율이 고정되어 있을 때 다중층의 개수가 증가할수록 공명 파장이 짧아지는 현상을 확인 하였고, 파장의 변화에 더 민감하게 변화하는 것을 측정하였다. 다만, 다중층의 개수가 3개층 이상이 되면 변화하지 않는 것을 확인하였다.