Judith L. Jenkins
Population growth and rapidly increasing energy consumption necessitate innovative materials for energy conversion and storage. Gains in solar electricity and battery technologies are evidenced by the availability of commercial products. However viable solar fuel platforms—where the energy in sunlight is used to form storable fuels such as hydrogen gas—have not yet been realized, motivating the work presented here. In order to produce hydrogen gas from sunlight and water, a photocatalyst is required. The ideal photocatalyst for hydrogen gas generation absorbs solar photons (sunlight), producing high-energy electrons necessary for the reduction of hydrogen ions in water. The host nanocrystal studied here, zinc sulfide (ZnS), can reduce hydrogen ions to form hydrogen gas, but this material does not absorb very much sunlight. Our research focusses on increasing the amount of sunlight absorbed by the nanocrystals so that more high energy electrons are generated. We use a technique called cation exchange to substitute copper ions into the ZnS crystal; the resulting material will absorb more sunlight. Systematic control of the amount of copper incorporated into the ZnS is necessary. We hypothesize that by varying the size, shape, and flexibility of the copper source, we can sterically control the availability of copper to the ZnS nanocrystal, thereby affording controlled incorporation of copper. The experiments presented here demonstrate the synthesis and characterization of several copper sources. Preliminary cation exchange results demonstrate progress towards functional photocatalytic materials. Energy sources such as these—which have the potential to be clean, affordable, and abundant—simultaneously help solve societal energy challenges and provide opportunities for further innovation and job growth in the energy sector. The work presented here represents concrete ways that Kentucky’s students and academic institutions actively contribute towards the development and implementation of clean energy technologies in meaningful ways.