Control and assembly of new cobalt functionalised materials towards water oxidation catalysis

Martin Sabi, Mercè (2017) Control and assembly of new cobalt functionalised materials towards water oxidation catalysis. PhD thesis, University of Glasgow.

Abstract

The rational design of Transition Metal Substituted Polyoxometalates (TMSPs) structures is one of the biggest challenges of synthetic chemists working in the field. Even though it is known that certain factors such as the pH of the reaction or ratio of starting materials can determine the structure of the most commonly synthesised Polyoxometalates (POMs), total structural control is not yet achieved. This exposes the difficulty of rational TMSP design, which is an extremely important goal towards targeting certain structures with specific properties. In the work presented here, the design of a specific building block, the {PW6} unit, is examined. The connectivity of this moiety allows the introduction of curved features into a structure. Herein, different cobalt containing structures which possess the Keggin type {PW6} fragment in their framework are reported. These structures were synthesised using {P2W15} as a building block, and such a Dawson to Keggin transformation is unprecedented.
Water oxidation catalysis is of extreme importance, as it is an energetically demanding step in the water splitting process, where hydrogen as a clean fuel can be obtained. Most Water Oxidation Catalysts (WOCs) still use precious metals. However, a few earth-abundant TMSPs-WOCs exist. The most used strategies when it comes to optimising these catalysts are based on changing the heteroatom, the transition metal or the whole structure itself. It was decided to investigate whether the tungsten framework of a given catalyst could be modified by doping with molybdenum. It was found that different amounts of molybdenum could be doped into the tungsten framework of the structure, and the process also gave rise to two types of crystal for each molybdenum to tungsten ratio. These two crystal types were due to cationic differences alone.
During electrochemical analysis of these compounds it was decided to investigate the effect of two different experimental setups to determine not only if the composition of the catalyst contributed to the overall behaviour, but also if the nature of the working electrode had a significant effect. Both methods demonstrated that the molybdenum doped materials synthesised in this work were WOCs and were more efficient than the tungsten parent.
The reason for investigating the setup is that in the literature no two electrochemical setups of TMSPs WOCs are consistent, which is worth exploring. It was found that the setup did have a significant effect as when carbon paste electrodes (CPEs) were used the compound with less molybdenum content had the best water oxidation catalysis properties. Whereas with the Nafion ink preparation the inverse was true. This calls into question how accurately different WOCs tested on different setups can be compared.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Polyoxometalates, POMs, cobalt transition metal POMs, water oxidation, electrocatalysis, molybdenum, cobalt, tungsten, self-assembly, inorganic synthesis.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Supervisor's Name: Cronin, Professor Leroy
• Date of Award: 2017
• Embargo Date: 20 December 2021
• Depositing User: M Martin Sabi
• Unique ID: glathesis:2017-8646
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 21 Dec 2017 11:31
• Last Modified: 04 Jan 2021 07:39
• URI: https://theses.gla.ac.uk/id/eprint/8646