Solar Energy Storage Using Earth-Abundant Materials
Roske, Christopher W.
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Among alternative energy technologies, solar is well suited to meet the grand energy challenge ahead if we can overcome the intermittent supply of sunlight.1,2 Storing solar energy in chemical bonds serves as an attractive technical solution that requires selecting suitable chemical reactions and building tailored systems.3 Many research groups are aiming to electrochemically reduce carbon dioxide to a solar fuel, such as ethanol, or split water into hydrogen and oxygen gas, but these groups have been unable to design efficient and cheap systems that navigate these complex multi-step chemical transformations without encountering significant parasitic overpotentials.4 While we fully expect further advances to eventually solve these issues, in the intervening time parallel investigations should also focus efforts on alternative reactions, which more immediately address the growing demand for continuously supplied clean energy. The vision of the system we have requires complete integration of light collection by a semiconductor made from abundant materials, efficient conversion of solar energy facilitated by inexpensive catalysts, and storage of the energy by reversible chemical reactions matched to the light absorber of interest. The aim of our work is to perform experiments that could lead to such a device, and in the process, advance the field of artificial photosynthesis as a whole. Our project began by the simulation and modeling of different materials and reactions to identify a candidate semiconductor and chemical reaction combination to more closely explore. Then, we identified a candidate cathode catalyst material, constructed a prototype photocathode assembly, and finally, initiated work on the photoanode. We hypothesized that hydrobromic acid splitting driven with two illuminated silicon electrodes would serve as an appropriate goalpost.