Electrocatalytic Hydrogen Evolution Reaction by a Pyrene-Appended Copper Complex

The observed continuous increase in greenhouse gas concentrations is due to ongoing large-scale combustion of fossil fuels. In recent years researchers have been actively developing alternative carbon-neutral, or better yet, carbon-zero future fuels to replace the use of fossil fuels. Future fuels should be generated using electricity derived from geothermal, hydro, solar and wind renewable resources. Green hydrogen (H₂) is a promising future fuel, as its production by water splitting utilising electricity generated from renewable sources produces zero carbon emissions. Water splitting by electrolysis is known to be an energy intensive process, therefore, catalysts are required to catalyse the conversion of water into H₂ and O₂ molecules. In this thesis, a pyrene-appended copper(II) complex is synthesised and studied for its electrocatalytic hydrogen evolution reaction (HER) activity.

Chapter 1 provides an overview of an ongoing environmental crisis, which is global climate change. It also introduces the potential of hydrogen as a carbon-zero fuel to replace the extensive use of fossil fuels in the industrial and transport sectors, along with its current production (brown/grey, blue and green hydrogen). A brief description of the key concepts of the hydrogen evolution reaction is also provided.

Chapter 2 describes the multistep synthesis of diphenylamine-2,2’-dicarboxyaldehyde using previously reported literature protocols. Then the 1:1 condensation reaction with diethylenetriamine is then carried out to prepare the [1+1] N₄-donor Schiff-base macrocycle HL^Et. Finally, pyrene functionalisation of the alkyl NH of H^LEt was carried out with 1-bromomethylpyrene, yielding the pyrene functionalised macrocycle HLpyrene. These compounds were characterised using ESI-MS spectrometry and ¹H NMR spectroscopy.

In Chapter 3, the [Cu^II(L^pyrene)]BF₄ complex is prepared by reacting HL^pyrene with copper(II) tetrafluoroborate in the presence of triethylamine in DCM/MeOH, to avoid pyridine contamination. Vapour diffusion in Et₂O yielded orange single crystals of [Cu^II(L^pyrene)]BF₄·0.5H₂O which were characterised using ESI-MS and X-ray crystallography.

In Chapter 4 HER electrocatalysis testing is carried out on the synthesised [Cu^II(L^pyrene)]BF₄·0.5H₂O complex. The results of this study were then compared to two previously reported literature copper(II) catalysts by the Brooker group. A literature review on the importance of pre-treatment and polishing of the working electrode is included.

Finally, Chapter 5 summarises the key findings and provides an outlook towards future directions for this study.