Nitrogen/sulfur-codoped graphene hollow nanoballs as efficient metal-free electro-catalysts for dye-sensitized solar cells

• Main Authors: Yu-Ching Chang, 張鈺靖
• Other Authors: Yit-Tsong Chen
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/8g7k4g

碩士 === 國立臺灣大學 === 化學研究所 === 106 === A huge amount of fossil fuels, such as coal, petroleum, and gas, has been consumed in order to meet the high demand of energy in the world. However, the combustion of these fossil fuels results in not only detrimentally environmental pollution, but also the rapid reduction of fossil resources on the Earth. Recently, several kinds of renewable energy, e.g., fuel cells, wind power, and solar energy, have drawn tremendous attention in academic studies and industrial applications. Among them, solar energy is the most attractive renewable energy; in particular, dye-sensitized solar cells (DSSCs) have the advantages of simple fabrication processes, low cost, flexibility, and semi-transparency. However, if a DSSC possesses low power conversion efficiency and utilizes noble metals, e.g., platinum (Pt) or ruthenium (Ru), as a counter electrode (CE), these disadvantages would hinder this DSSC from wide applications. Therefore, it is an urgent challenge to develop a noble metal-free CE with high power conversion efficiency in DSSCs. Graphene has high carrier mobility, high electrical conductivity, high mechanical strength and flexiblility. In this study, we took advantage of the unique chracteristics of graphene to fabricate high-performance DSSCs by employing different graphene-based CEs, such as graphene hollow nanoballs (GHBs), nitrogen-doped graphene hollow nanoballs (N-GHBs), sulfur-doped graphene hollow nanoballs (S-GHBs), and nitrogen/sulfur-codoped graphene hollow nanoballs (N,S-GHBs). First, we synthesized GHBs on silicon wafers (Si) or carbon cloth (CC) substrates with a chemical vapor deposition (CVD) method. A nitrogen or sulfur precursor, or both, was incorporated in the CVD rection to from N-GHBs, S-GHBs, and N,S-GHBs, respectively. Second, the as-synthesized doped GHBs were used as metal-free CEs to investigate their power conversion efficiencies in DSSCs. The highly curved GHBs could avoid the self-assembly restacking of planar graphene sheets and provide high surface area. In addition, the heteroatomic incorporation in GHBs can reduce the charge-transfer resistance and enhance the catalytic activity of GHBs. We found that pristine GHB (with ∆EP of 698 mV) and heteroatom-doped GHBs (∆EP of 530 mV for N-GHBs and ∆EP of 498 mV for S-GHBs) have different catalytic activities on the I-/I3- reduction reaction and the N,S-GHBs (∆EP of 459 mV) shows the best catalytic performance due to the synergistic effect of electronic and geometric changes. Consequently, the power conversion efficiency of a DSSC with N,S-GHBs as a CE reaches to 9.02 %, comparable to that (8.90 %) of a standard sputtered Pt CE-based cell.