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Synthesis of metallic metal oxide nanofibers through electrospinning for electrochemical catalysts

Synthesis of metallic metal oxide nanofibers through electrospinning for electrochemical catalysts
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대학원 화학·나노과학과
이화여자대학교 대학원
In this study, electrospinning was used as one of the most facile methods to obtain considerable amounts of 1-dimensional nanostructures which were called nanofibers. It is simple to attain uniform extended metal oxide fibers with specific diameters of nanoscale via electrospinning from a mixed solution of precursors. In general, nanostructures have more advanced electrochemical and catalytic ability than microstructures. Thus, it is possible for the synthesized nanofibers to be applied to nanosized capacitors, electrochemical electrodes and catalysts. First, iridium oxide (IrO2) nanofibers are prepared by a simple and easy method with electrospinning. The high electrochemical activity of iridium oxide nanofibers is shown in the oxidations of biological species including L-ascorbic acid (AA), 4-acetamidophenol (AP), dopamine (DA), glucose, β-nicotinamide adenine dinucleotide (NADH) and uric acid (UA). Compared to bare glassy carbon electrode, IrO2 nanofibers facilitate AA oxidation most significantly. The amperometric response of IrO2 nanofibers is linearly proportional to the AA concentration, indicating high sensitivity, fast response, low detection limit, and exclusive selectivity over AP, DA, glucose, NADH, and UA at their physiological levels. In addition, excellent potential resolution of IrO2 nanofibers which is sufficient to differentiate AA, DA, NADH, and UA is verified by differential pulse voltammetry. The results support that IrO2 nanofibers are good potential sensing materials selectively for AA in complex biological samples. Second, rhodium oxide (Rh2O3) nanofibers are synthesized via facile electospinning process. After that, single crystalline ruthenium oxide (RuO2) nanorods are grown onto electrospun Rh2O3 nanofibers hierarchically by the thermal annealing process of the amorphous Ru(OH)3 precursor. The growth of hetero-nanostructures on electrospun nanofibers is facilitated by nucleation on the rough surface of particle-like polycrystalline nanofibers. The morphology and structure of RuO2 nanowires on Rh2O3nanofibers is characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrum and transmission electron microscopy (TEM). Electrochemical measurements suggest that prepared Rh2O3 nanofibers and RuO2 nanorods–Rh2O3 nanofibers exhibit different electroactivities toward H2O2 electrochemical reaction: RuO2nanorods–Rh2O3nanofibersenhance H2O2 reduction more favorably compared to Rh2O3nanofibers. Furthermore, RuO2 nanorods–Rh2O3 nanofibers generate a higher current conducted by H2O2 reduction than bare Rh2O3nanofibers so that RuO2 nanorods–Rh2O3 nanofibers are more sensitive to H2O2. Lastly, it is reported that ruthenium oxide (RuO2) is a great material as electrodes in electrochemical devices because of their high electrical conductivity, chemical stability, and characteristics. Also, rhenium oxide (ReO3) is the interesting material as a sensor for electroactive species and they have high electrical conductivity. Thus, it is a task of great significance to synthesize these two metal oxide composite nanofibers in nanoscale since nanostructures have more improved electrochemical and catalytic ability than large scale structure. Electrospinning is the facile synthetic technique for RuO2-ReO3 composite nanofibers to make uniform fibers of nanoscale. The RuO2-ReO3 nanofibers with various atomic ratio of Re are prepared from mixed solution of ruthenium precursors and rhenium precursors by electrospinning following thermal annealing process. The electrochemical applications of RuO2-ReO3 composite nanofibers are investigated as capacitors. Specific capacitance is remarkably influenced depending on the amount of Re increased. Among the compositions of RuO2-ReO3(n) nanofibers (n = 0.0, 0.07, 0.11, and 0.13), where n denotes the relative atomic ratio of Re to the sum of Ru and Re, RuO2-ReO3(0.11)/GC represents the highest performances.;이 논문은 전기방사법을 이용하여 나노 섬유를 합성하고 이 물질들을 나노 크기의 축전기나 촉매제, 전기화학적 생체 주요 물질들의 농도 측정 전극 등에 활용 가능함을 보이고자 연구하였다. 첫 번째 장에서는 이리듐옥사이드 나노 섬유를 전기방사법을 통해 합성하였다. 전기방사법은 손쉬운 방법으로 활용 가능한 양의 나노 섬유를 합성할 수 있는 방법이다. 이러한 방법으로 합성한 나노 섬유는 아스코르브산의 농도 측정에 주목할 만한 전기화학적 특성을 보였다. 또한 다른 생체 주요 물질들이 있음에도 아스코르브산의 측정이 방해 받지 않음을 확인하였다. 비교적 긴 시간의 반응 동안에도 안정한 이리듐옥사이드 나노 섬유를 아스코르브산 농도 측정 전극 물질로 적합하였다. 두 번째 장에서는 전기방사법을 이용하여 합성한 로듐옥사이드 나노 섬유 위에 금속성의 루테늄옥사이드 나노 막대를 계층적인 구조로 합성하였다. 이러한 나노 구조는 표면적을 증대하여 전기화학적 촉매 효과를 증대시켜 유망한 복합 나노 구조체 역할을 한다. 합성한 계층적인 나노 구조를 이용하여 만든 전극이 과산화수소 반응에 전기화학적 반응을 일으킴을 확인하였다. 또한 과산화수소 측정 전극으로 적용 가능함을 실험을 통해 보였다. 세 번째 장에서는 루테늄옥사이드와 레늄옥사이드 복합체의 나노 섬유를 전기방사법을 이용하여 쉽게 합성하였다. 전구체가 포함된 용액의 구성에 따라 다양한 비율의 복합체 나노 섬유를 얻을 수 있었다. 이러한 복합 나노 구조는 축전기로 이용될 수 있는 여러 물질들을 존재하게 하여 전기화학적 특성을 증대 시킬 수 있다. 합성한 물질을 이용하여 실제 축전기에 적용 시킬 수 있는지 전기화학적 실험을 통해 확인하였으며, 뛰어난 축전기로서의 성능을 확인할 수 있었다.
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