Preparation of Electrocatalysts for Oxygen Reduction and Water Oxidation Reactions, and Construction of Photoanodes with Covalently Bonded Chromophores

• Author / Creator

  Wang, Chao

• Renewable fuels are essential to meet the future energy demands of our society and to alleviate the impact of the anthropogenic CO2 on the environment. Energy conversion devices like fuel cells, water electrolyzers, and photoelectrochemical cells are the key components in the transformation to a renewable energy dependent society. This dissertation describes the synthesis and characterization of active electrocatalysts for fuel cells and water electrolyzers, as well as a novel method to prepare stable chromophore–semiconductor photoelectrodes.
  Due to the sluggish kinetics at the fuel cell cathode, active oxygen reduction reaction electrocatalysts are required. The first part of the thesis describes the preparation and the oxygen reduction activity of the electrodeposited, conformal Pt overlayers on glancing angle deposited Ni nanopillar catalysts that could potentially be applied in fuel cells. Up to 30-fold enhancement in the Pt mass-normalized oxygen reduction reaction activity was observed compared to Pt directly deposited on glassy carbon substrates.
  Water electrolysers are crucial devices in the long-term storage of sustainable energy as hydrogen. The water oxidation reaction at the anode of the electrolysers is kinetically sluggish, and requires active electrocatalysts. A simple bench-top aqueous synthetic method was developed to prepare extremely active water oxidation electrocatalysts for water electrolyzers. The Ir0.89Ni0.11 and Ir0.89Cu0.11 hydrous oxide nanoparticles prepared using this method are among the most active and stable water oxidation catalysts in acid published to date. The Ni0.75Fe0.25 layered double hydroxides prepared are among the most active alkaline water oxidation catalysts. The electrocatalysts were characterized using X-ray diffraction, transmission electron microscopy, cyclic voltammetry, and X-ray photoelectron spectroscopy. Mechanisms for the water oxidation activities were proposed.
  Photocatalytic water oxidation and carbon dioxide reduction reactions favors the use of alkaline conditions, but common anchoring groups, like phosphonic ester groups and carboxylic ester groups, between the visible-light chromophores and the semiconductor surfaces are only stable in acidic solutions. In this dissertation, Ru- and Ir- chromophores on semiconductor surfaces were prepared with a novel diazonium reduction and metalation method, and the bonding was between the C5 of the 1,10-phenathroline ligand of the chromophores and the ITO or TiO2 surfaces. The chromophore–semiconductor photoelectrodes prepared using this method were active and relatively stable to photoelectrochemical oxidation of hydroquinone and triethylamine under neutral and basic conditions and potentially can be paired with electrocatalysts to carry out the photocatalytic water oxidation and carbon dioxide reduction reactions.

• Subjects / Keywords

  • Water oxidation reaction
  • Photoelectrode
  • Oxygen reduction reaction

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R39G5GW2S

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.