Doctor of Philosophy
Institute for Superconducting and Electronic Materials
Downsizing and atomically dispersing metal species particles on a carrier substrate has emerged as a new frontier of heterogenous catalysis, which can achieve maximize the utilization efficiency of metal element, in structures such as single atom catalysts (SACs), dimer, cluster and nanoparticle catalysts. Moreover,benefitting from the optimized geometric and electronic structure, the adsorption and desorption ability for different reaction intermediates can be optimized. Over the past decades, numerous atomic-level electrocatalysts have been designed and successfully applied in the field of electrocatalysis, including nitrogen reduction reaction (NRR), hydrogen evolution rection (HER), oxygen reduction reaction (ORR), oxygen evolution reaction (OER) etc. In addition, with the advancement of characterization technologies and quantum computational chemistry, such as scanning transmission electron microscopy (STEM), X-ray absorption spectroscopy (XAS) and density functional theory (DFT), the atomic structure of catalytic sites and reaction mechanisms during reactions has been revealed and provides guidance for the further rational design of atomic-level electrocatalysts. However, catalytic performance is highly sensitive to the coordination environment of active metal sites, thus optimizing the electronic structure of the metal centre by introducing a properly-coordinated atom is essential for good catalytic performance. Moreover, for different complex reactions or dual-metal catalysts, there remains substantial room for exploring the actives sites and real reaction mechanisms. Herein, three strategies have been developed for designs of three kinds of atomic-level electrocatalysts for specific reactions.
For the NRR system, the catalytic performance and Faradaic efficiency is limited by the competing HER reaction and other side reactions. To address the issue of low yield rate and low efficiency, a dual-metal FeMo dimer was dispersed on a nitrogen-doped carbon layer (denoted as FeMo@NG) to accelerate the NRR kinetics and circumvent the HER. The dual-metal catalytic centre was investigated by STEM, XAS and DFT and the NRR performance was evaluated by a electrochemical method. Surprisingly, the FeMo dimer catalysts exhibit higher catalytic activity than their Fe or Mo single atom counterparts owing to a combination of ligand, geometric and synergistic effects, with a yield rate of 14.95 µg h-1 mg-1 at -0.4 V (vs. RHE) and a Faradaic efficiency of 41.7 % at -0.2 V (vs. RHE). Based on experimental and simulated results, the FeMoN6 (FeMoN6 ??) was identified as the real active site for further mechanism study. The DFT result further reveals that FeMoN6 active sites can not only weaken N≡N bonds, but also efficiently catalyses nitrogen reduction through the distal pathway without N2H4 formation.
Li, Yang, Advanced Atomic-level Material for Electrocatalysis, Doctor of Philosophy thesis, Institute for Superconducting and Electronic Materials, University of Wollongong, 2020. https://ro.uow.edu.au/theses1/1301
FoR codes (2008)
0303 MACROMOLECULAR AND MATERIALS CHEMISTRY, 0306 PHYSICAL CHEMISTRY (INCL. STRUCTURAL), 0307 THEORETICAL AND COMPUTATIONAL CHEMISTRY
Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.