Development of High-efficient Electrocatalysts and Photoelectrocatalysts and Their In-/Ex-situ Analysis

• Main Authors: Sung-Fu Hung, 洪崧富
• Other Authors: Hao Ming Chen
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/pums4r

博士 === 國立臺灣大學 === 化學研究所 === 106 === Photoelectrolysis has been regarded as an effective approach to converting solar energy into chemical fuels. In empirical application, various catalysts can remarkably affect the overall intrinsic catalytic performance. Photocatalysts with superior light absorbing ability frequently exhibit weak surface catalytic ability, while electrocatalyst with the outstanding surface catalytic capability commonly cannot proceed the photoelectric conversion. Hence, the integration of photocatalysts and electrocatalysts can present their superb natures to considerably enhance the entire catalytic activities. Besides, the synergy in the composite system would also influence the activities. By conducting in-situ techniques, the reaction mechanism can be figured out and the catalytic properties can be manipulated and enhanced. This dissertation is focused on the development of new catalysts, the synergy of composite material on photoelectrolysis, and the development of new operando X-ray technique. In this work, the results can be separated into four chapters, including: 1) The development of composite photocatalyst TiO2 NR-Au-IrOx. Plasmonic gold exhibits the superior visible light absorption via localized surface plasmon resonance effect, but its poor surface catalytic ability and the short lifetime of hot holes limit its catalytic performance. Hence, modification of iridium oxide on Au surface would greatly improve the kinetics of hot holes and the catalytic capability by forming tiered energy levels. The results of Ti L-edge of plasmonic electrodes under illumination indicates that the number of injected hot electrons in Au-IrOx is higher than that in pure Au, which is also the reason of high catalytic activity. 2) The development of electrocatalyst with low cost and high activity. As doping iron ions into cobalt oxides, the composite catalyst exhibits superb catalytic ability for oxygen evolution reaction (ηj=10 mA/cm2 = 229 mV). By means of X-ray absorption spectroscopy and electrochemical analysis, it is found that cobalt ions are in charge of the catalytic center, while iron ions primarily confine cobalt ions to the tetrahedral site to restrain the multi-path-transfer of cobalt ions during the dynamic structural transformation between spinel and oxyhydroxide, continuously activating the catalytic behavior of Co2+(Td) ions. 3) The development of operando high-energy resolution fluorescence-detected X-ray absorption spectroscopy. It is found that 3d orbitals of cobalt ions directly interacted with the electrolyte. Instead of involving themselves to interact with the electrolyte, iron ions in the system lead more 3d orbitals of cobalt ions to hybridize with the electrolyte, resulting in the enhancement of intrinsic catalytic activity. 4) The development of high-efficient and low-cost bi-functional electrocatalyst. The synthesized iron-doped cobalt phosphides present high activity in bi-functional performance in alkaline solution with nearly 100% Faradaic efficiency. In-situ transmitted X-ray diffraction identifies that iron ions would stabilize the phosphide phase, restraining the formation of hydroxides that impedes the active substance, and quickly convert into active oxyhydroxide for OER as well as preserve the active phosphide phase for HER to achieve high bi-functional activity.