Development of molecular catalysts for H2 evolution and modified copper catalyst for CO2 reduction

• Main Author: Ho, Xian Liang
• Other Authors: Richard D. Webster
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Science::Chemistry
• Online Access: https://hdl.handle.net/10356/139947
• Institution: Nanyang Technological University

In the first part of the thesis, a series of first row transition metal complexes have been synthesized in order to study their mechanism and efficiency as a H2 evolution catalyst. The H2 produced can served as an alternative clean fuel to tackle the issue on climate change. A comprehensive characterisation of the electrochemical and spectroscopic properties of these complexes has been performed. The efficiency and the mechanism of these materials and complexes have been studied. In Chapter 3, the effects of the first coordination sphere on H2 evolution was explored. A new Co and Ni tetraamido macrocyclic ligand (TAML) complexes were synthesised and their reactivity for electrocatalytic proton reduction were studied. The metal complexes have been extensively characterized with various spectroscopic techniques. The Co TAML complex appeared to be active for electrocatalytic H2 evolution initially. However, detailed mechanistic studies revealed that Co nanomaterials were responsible for the catalysis. In Chapter 4, the effect of the second coordination sphere modification on H2 evolution activity was explored. An active Ni salicylaldimine catalyst was synthesized and found to be able to incorporate into a molecular photocatalytic H2 evolution system with [IrIII(ppy)2(dtbbpy)(]PF6) (ppy = 2-phenylpyridinato; dtbbpy = 4,4’-di-tert-butyl- 2,2’-bipyridine, [Ir]+) as a light-harvester and triethylamine (TEA) as a sacrificial electron donor and reductive quencher. This new Ni complex possess a pair of peripheral ether arms in the second coordination sphere of the molecule. Various spectroscopic techniques such as nanosecond transient absorption spectroscopy (TAS), transient emission spectroscopy (TES) and, electron paramagnetic resonance (EPR), supported by intermediate isolation studies and density functional theory (DFT) calculations suggest the possible influence of balancing ligand redox noninnocence and second coordination sphere effects to effect H2 evolution activity. In the second part of the thesis, the surface modification on oxide-derived copper (OD-Cu) and its influence on the products distribution of CO2 reduction on Cu were investigated. In Chapter 6 of the thesis, it was found that the majority of the crystal facets in the polycrystalline OD-Cu can dictate the major products formed and can greatly reduce the overpotentials for CO2 reduction.