Research

Research Overview

Our research focuses on design, synthesis, and characterization of semiconducting and metallic crystals and polycrystalline electrodes with controlled compositions and morphologies for use in electrochemical and photoelectrochemical devices (e.g. photoelectrochemical cells, solar cells, and electrocatalysis). This research combines disciplines of inorganic chemistry, materials chemistry, electrochemistry, solid state chemistry, and nano-scale science. Our group develops new electrochemical synthetic strategies that can make a significant advancement in constructing polycrystalline electrode materials. We achieve this by combining compositionally versatile electrodeposition methods with various new synthetic concepts/techniques that can allow for morphological control at various length scales. The functional properties we currently investigate in conjunction with compositional and morphological variation include electrochemical, photoelectrochemical, and electrocatalytic properties. By pursuing an in-depth atomic level understanding of structure-composition-property relationships, we attempt to bridge the gap between chemistry and materials engineering.

Electrochemically Grown Cu2O Crystals


(scale bar 1 μm)

Electrochemically Grown Zn Crystals

Synthesis of Semiconductor Electrodes for Solar Energy Conversion

Semiconductor electrodes play a critical role for solar energy conversion as they can generate electron-hole pairs by photon absorption. Developing semiconductor electrodes with optimum bandgap energies in a cost effective manner is essential for constructing commercially viable devices for solar energy conversion. Semiconductors that are intensively investigated for use to date have been limited to only a few types of simple semiconductors (e.g. mostly binary compounds) while there are numerous potentially more promising ternary and quaternary semiconductors. This is mostly because these semiconductors have not been readily available as electrode forms. Our group develops new electrochemical synthesis conditions to produce a variety of solid state materials as high quality polycrystalline electrodes for use in solar energy conversion. When combined with post-deposition chemical and thermal synthesis processes, electrochemical synthesis provides one of the most versatile methods to produce semiconductor electrodes with various compositions and morphologies in a practical and cost-effective manner.

Synthesis of a BiVO4 Electrode

Solar Water Splitting by a BiVO4 Electrode

Catalyst Development for Solar Fuel Production

Photoelectrochemical cells allow for direct utilization of photon-generated electron-hole pairs in a semiconductor electrode to drive redox reactions to form chemical fuels. In order to facilitate desired redox reactions at the semiconductor/electrolyte interfaces, catalysts are often necessary to be coupled with semiconductor electrodes. We study various redox catalysts for use in solar fuel production (e.g. H2 evolution, O2 evolution, and CO2 reduction catalysts). In addition to developing efficient catalysts, our special focus lies in pairing semiconductor electrodes and catalysts in an optimal manner and understanding the semiconductor/catalyst interfaces in order to maximize synergistic interactions between them.

Photoelectrode/Catalyst Interfaces for Solar Water Oxidation

Electrochemical and Photoelectrochemical Biomass Conversion

Biomass conversion and solar energy conversion are two important fields of science that will enable us to be completely independent from the use of fossil fuel reservoirs for the production of fuels and industrially important building block organic molecules. Our group develops various electrocatalytic electrodes that can electrochemically oxidize or reduce biomass intermediates to biofuels and industrially important  building block organic molecules under ambient conditions. These catalysts can further be coupled with semiconductor electrodes to construct photoelectrochemical cells that can use solar energy for biomass conversion.

Development of Materials for Electrochemical Water Desalination

The rapid development of industry and agriculture coupled with steady human population growth have put a strain on the world’s supply of fresh water. Since the vast majority of Earth’s water is contained in oceans, desalination of seawater provides an attractive route to meet growing demands for fresh water. In the Choi group, we are developing materials that can undergo redox reactions and simultaneously remove Na+ or Cl- ions through storage within electrode materials to achieve efficient desalination. In 2015, we discovered that Bi can be used as a cost-effective and efficient Cl-storage material through the reversible conversion of Bi to BiOCl. Since then, Bi has served as a platform for the development of a variety of desalination architectures, including desalination batteries and electrodialysis cells. We employ electrochemistry, solution-based synthesis, and strategies from battery electrode processing to optimize the performance of our desalination cells.

Electrodeposition of Bi Foam Electrodes


 

Operating Scheme of a Desalination Battery