Molecular Complexes at Electrode Interfaces for Sustainable Energy Applications Public Deposited

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Last Modified
  • March 20, 2019
Creator
  • Lapides, Alexander
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • The development of sustainable, carbon-neutral energy sources is necessary to offset the environmental harm caused by the consumption of CO2-releasing fossil fuels. Although solar irradiation is sufficient to satisfy worldwide energy demand, storage of this energy remains problematic. One storage method is the photolysis of water into oxygen and hydrogen. Burning hydrogen in the presence of oxygen unleashes the energy stored in its chemical bonds, forming only water as a byproduct. Long-term applications require the stable integration of molecules with semiconductor materials to facilitate photolysis. One method for attaching molecules to surfaces is reductive electropolymerization, in which vinyl-functionalized monomers are electrochemically reduced, inducing C–C bond formation. These polymers precipitate on the electrode surface – attached by physical adsorption. Substitutive coordination chemistry, influenced by electrochemical potential and the electrolytic solution, is possible in these polymer environments. Electropolymerization is applicable in the formation of multi-component films as well. Electrochemical reduction of a semiconductor-bound, vinyl-derivatized chromophore in a solution containing a distinct vinyl-functionalized molecule results in spatially-separated, covalently-linked assemblies on the semiconductor surface. Transient absorption spectroscopy demonstrated that the chromophore undergoes electron injection to the semiconductor and hole transfer to the second molecule. The polymer overlayer improves the photochemical interfacial stability of the underlying chromophore by ~30-fold. Multi-component film formation via electropolymerization allows for the incorporation of a molecular water oxidation catalyst as the outer layer. Chromophore-catalyst assemblies thusly formed demonstrate impressive electrochemical- and photo-stability with high electrocatalytic activity for oxygen formation. Atomic layer deposition (ALD) of a metal oxide is known to stabilize covalent binding of molecules to semiconductor surfaces by “burying” the bonds; here it is demonstrated that embedding a chromophore in a metal oxide, attaching a catalyst, and additional metal oxide deposition is a method of forming stable chromophore-catalyst “mummies” that produce oxygen photoelectrochemically over multiple hours. Core/shell semiconductors with mismatched conduction band potentials are constructed using ALD. Sub-nanosecond injection and recombination processes are investigated, as are the effects of annealing on the core/shell interface. These findings are compared to device measurements.
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Rights statement
  • In Copyright
Advisor
  • Brookhart, Maurice
  • Templeton, Joseph
  • Waters, Marcey
  • Meyer, Thomas
  • Miller, Alexander
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2016
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