Date on Master's Thesis/Doctoral Dissertation
12-2024
Document Type
Doctoral Dissertation
Degree Name
Ph. D.
Department
Chemistry
Degree Program
Chemistry, PhD
Committee Chair
Grapperhaus, Craig A.
Committee Co-Chair (if applicable)
Buchanan, Robert M.
Committee Member
Gupta, Gautam
Committee Member
Ramezanipour, Farshid
Committee Member
Zamborini, Francis P.
Author's Keywords
Hydrogen evolution reaction; electrocatalysis; N2S2 chelate ligands; nickel electrocatalysts; carbon substrates; pencil electrode
Abstract
Hydrogen is an important energy storage alternative to fossil fuels due to its high energy density. Currently, most hydrogen is produced through petroleum feedstocks, which produce large amounts of carbon dioxide. However, a more eco-friendly method is the electrocatalytic splitting of water into hydrogen and oxygen. Efficient catalysts for the hydrogen evolution reaction (HER) are typically platinum group metals, which are rare and expensive. There is growing interest in developing HER electrocatalysts with earth-abundant metals for water electrolysis. Nickel, which lies in the same group in the periodic table as Pt and has similar chemical properties, is explored extensively for HER electrocatalysis. Moreover, other metals or non-metals have been incorporated in Ni derivatives to enhance the activity and achieve a higher surface area to facilitate HER. Ni-based molecular catalysts have also been designed to mimic the HER activity of natural hydrogenases that catalyze the reversible reduction of protons to hydrogen. This dissertation explores different nickel-based molecular and binary catalysts for homogeneous and heterogeneous HER. Systematic changes in the structure of the diacetyl-bis(4-methyl-3-thiosemicarbazone) (ATSM) ligand were introduced to obtain bis(thiosemicarbazonato) (BTSC), hybrid thiosemicarbazonato-alkylthiocarbamato (TSTC), and bis(alkylthiocarbamato) (BATC) ligands. The six square planar Ni(II) complexes featuring an N2S2Ni core with redox-active ligands demonstrate a notable modulation of reduction potential and basicity upon variations in the electronic structure of the ligands. These complexes are stable under acidic conditions or reductions but decompose under homogenous HER conditions, limiting their use as homogenous electrocatalysts. Inks of the Ni-complexes were drop cast on glassy carbon electrodes to determine the heterogenous HER activity of these complexes in an aqueous acidic medium. The Ni-complexes with high basicity and small methyl groups in the ligand backbone show low overpotential. In contrast, those with lower basicity and/or a bulky phenyl group in the ligand backbone require higher overpotentials. One of the best catalysts was taken as a representative to study the effect of change in carbon support on the activity of the catalyst. We demonstrate that the HB pencil is a viable disposable carbon support that can be used to study HER catalysts in a comparable manner to GCEs. Carbon nanocage-encapsulated Ni2P was also explored as a stable and efficient heterogeneous electrocatalyst for producing green hydrogen using water splitting.
Recommended Citation
Paudel, Mohan, "Nickel electrocatalysts on carbon supports for the hydrogen evolution reaction." (2024). Electronic Theses and Dissertations. Paper 4481.
Retrieved from https://ir.library.louisville.edu/etd/4481
Included in
Catalysis and Reaction Engineering Commons, Inorganic Chemistry Commons, Materials Chemistry Commons
