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Title: Novel electrocatalysts for ammonia synthesis and hydrogen evolution
Author: Sudmeier, Tim
ISNI:       0000 0004 9351 6208
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2020
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This thesis explores the activity of single atom metal catalysts on graphene-like support (SACs) and metal nitrides for the nitrogen reduction reaction (NRR). Furthermore, extensive analysis of HER activity and in-situ characterisation are carried out to derive a structure-activity relationship of SACs in the hydrogen evolution reaction (HER). To that end, a library of single atom transition metals on nitrogen-doped graphene (M-NGs) with comparable compositions is synthesised by a carbon backbone method. Their HER activity is assessed showing Ru-NG and Co-NG to be highly active. The data is correlated with the φ factor, a computationally suggested descriptor for electron density on the metal site constituting the first experimental substantiation of this design principle. Additionally it is found that HER activity on cobalt-containing SACs can be further tuned by changing the coordination environment of the metal via the inclusion of oxygen into the first coordination shell. In in-situ XANES and IR spectroelectrochemical thiocyanate poisoning experiments three distinct active sites are observed and it is suggested that distortion from the square planar Co-N₄ environment caused by axial oxygen ligands leads to decreased HER activity. In the second part of this thesis Co₃Mo₃N was identified as a potential electrocatalyst for the direct reduction of N₂ to N³- in molten chloride eutectics. Based on experimental evidence and previous literature reports, a Mars van Krevelen-type mechanism is suggested for the reaction in which Li⁺ ions facilitate the activation of dinitrogen, as well as enable participation of the lattice nitrogen of Co₃Mo₃N.
Supervisor: Tsang, Edman Sponsor: Engineering and Physical Sciences Research Council ; Royal Commission for the Exhibition of 1851
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available