奈米材料的製備及在燃料電池與太陽能電池上的應用

Abstract

本研究主要針對於在尋找新奇的奈米材料並且在燃料電池及太陽能電池上有實質的應用性，例如我們發現在利用控制反應溫度、陽離子與奈米粒子濃度而發生離子交換反應，成功發展出利用離子交換機制之新奇的方法來合成含有Ru與Pt多重合金之奈米粒子，進而由X光吸收光譜來確定其奈米粒子中所進行氧化還原陽離子交換反應之機制。另外我們進而測試此FexPtRu1-x奈米粒子在甲醇催化上的反應特性，其主要是用於測試CO剝除與甲醇催化的效果。利用XAS中的EXAFS數據分析結構及表面組成，並觀察其以旋轉電極測試之CO剝除、甲醇催化與氧氣還原反應的影響。另外在陰極氧氣還原方面，我們成功合成出dendrited-like之FePt奈米粒子，並展現對氧氣有很好的催化活性，並利用理論計算在不同表面，如(111),(200)和(311)平面之surface energy以及其對O2之吸附能的結果來討論其奈米粒子對氧氣還原的催化效果。 另外在太陽能電池的研究方面，我們成功合成出低能隙的二硫化鐵之奈米粒子以提升元件對太陽光譜的吸收能力，本研究利用低能隙的硫化鐵奈米粒子與高分子混掺製備光伏元件，實驗結果顯示添加硫化鐵確實可使元件吸收近紅外光的能量，然而對於最佳化製程和元件效能仍需要未來進一步的探討。最後也展示出以二硫化鐵作為近紅外光偵測器的主動層，並以氧化锌 (ZnO) 作為元件 blocking layer之研究。

The thesis attempts to develop an efficient electrocatalyst for DMFC and a novel material with near infrared absorption for solar cell appication. Following these concepts, the nanomaterials with different functions have been developed and shown their special properties on fuel cell or solar cell applications.

In chapter 3, the new ternary Fe1-xPtMx nanocrystals were tested for their catalytic properties in the anodic electrode of a fuel cell. Their catalytic capability will be discussed elsewhere. Furthermore, the in situ studies of detailed chemical transformation from binary to ternary metal nanocrystals using X-ray absorption spectroscopy were on progress. Overall, our results have demonstrated a simple and rapid route for the syntheses of new catalysts based on metal alloy nanocrystals.

In chapter 4, we have demonstrated that the Fe1-xPtRux NCs with various Fe/Ru ratios and alloying extent were well-controlled via chemical transformation in solid solution phase. Moreover, the solid solution Fe1-xPtRux NCs showed the unique catalytic performance for CO stripping and methanol oxidation in comparison with FePt NCs and commercial J-M PtRu catalysts. The enhanced electrocatalytic properties for methanol oxidation reaction can be attributed to that the electron density of Pt-CO bond in the Fe1-xPtRux NCs becomes weaker due to charger transfer from Fe and Ru to Pt atoms based on the density functional theoretic studies. Overall result has suggested that the chemical transformation reaction of the solid solution NCs is a quite useful method to modify the surface of the NCs and improve the catalytic activity in DMFC applications.

In chapter 5, we have developed FePt alloy nanodendrites with high-index facets. The activity increased in the following order: FePt nanoparticles (111)< FePt nanocube (200) < FePt nanodendrites (311), indicating that the nanostructure with high-facet index possessed higher surface energy and demonstrated higher catalytic activity for ORR. We observe that the different coordination number and surface energy in the FePt hkl facets. The formation of different facets is attributed to the different degrees of surface reconstruction induced by oxygen adsorption. In chapter 6, A soft and biocompatible surface-enhanced Raman scattering (SERS) substrate was fabricated based on a three-dimensional (3D) structure of end-tethered poly(L-lysine) (“t-PLL”) with a brush-like configuration conjugated with silver nanoparticles (Ag NPs) (Ag NPs-t-PLL film). The conjugation procedures were carefully adjusted to generate the films with different interval widths (W) between Ag NPs and diameters (D) of Ag NPs. The resulting film was then characterized by zeta potential, CD spectropolarimeter and scanning electron microscopy. Furthermore, the studies of SERS enhancements using Ag NPs-t-PLL film as a substrate were performed. The significant increases of SERS enhancements have been obtained as W/D was decreased from 0.9 to 0.2. Our results not only afford a facile fabrication of a 3D soft substrate for SERS with high sensitivity and biocompatibility but also offer great potentials for the development of new biosensors. In chapter 7, we use new material for organic IR harvesting solar cells application based on poly(3-hexylthiophene)-iron disulfide (FeS2) nanocrystal(NCs) blend. The devices exhibited high photo-electric current conversion efficiency in infrared region (>700 nm)where the external quantum efficiency was 6.5% at wavelength 650nm and 1% at 700 nm. The photoresponsed measurement also indicated that onset of photogenerated edge was about 900nm, which is contributed by FeS2 NCs. The device power conversion efficiency under AM 1.5 100 mw/cm2 illumination was 0.13%, short circuit current density of 0.7mA/cm2, open circuit voltage of 0.44V and fill factor(FF) about 42.6%. This study also pointed out that FeS2 NCs:P3HT hybrid can provide a low cost, environment friendly and easy process organic solar cells.

In chapter 8, We have demonstrated that solution-processed NIR photodetectors can be conveniently fabricated using films of FeS2 nanocrystals. With the I-V Characteristics and temporal photoresponse achieved, the FeS2-based device is suitable for NIR detector application. At light wavelength above 715 nm, a strong photocurrent is seen, with a photo-to-dark current ratio of 176. The characteristic times for rise and fall of photocurrent are 0.55s and 1.1s, respectively. Our device can work reproducibly in air. Considering the advantages of solution-process fabrication, low cost and environment friendly, the FeS2-based photodetector have high potential for use in near infrared range application