SusChEM: Solar Energy Storage via Photoredox Chemistry at Single Crystal and Porous Semiconductor Electrodes

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PI: Bruce A. Parkinson Proposal Number: 1512551The production of electricity by solar energy is inherently an intermittent process because solar cells do not generate electricity at night. Therefore, at some point, grid-scale energy storage systems will be needed to collect some of the solar energy and convert it to a form that can be converted back to electricity at night. One way is to use a portion of the electricity generated by solar cells to re-charge batteries, which are discharged at night. This project will develop and study the performance a novel solar-driven storage device that will convert the sun?s photons directly to electrochemical energy. This battery uses a flowing electrolyte which stores light energy in the form of electrochemical energy using one type of electrode during the day, and then reverses the flow to regenerate the electrolyte and generate electricity using a different type of electrode at night. By this process, the need for extra solar cells to generate electricity for re-charging the batteries, as well as the battery itself, is eliminated. As part of the education and outreach activities of this project, the principal investigator will expand the successful Solar Hydrogen Activity Research Kit (SHARK) program, where undergraduates and high school students are recruited to help discover new electrode materials that could be useful for the light-driven electrolysis of water to hydrogen gas or for use in the device described above.This project describes a new concept to collect and store solar energy as electrochemical energy in a flow battery configuration ? the solar driven redox flow battery. The goal of this proposed research is to characterize the behavior of semiconductor/redox electrolyte interfaces in the dark and under illumination to optimize photo-driven redox reactions. Single crystal n- and p-type semiconductor electrodes such as Si, GaAs, GaP and InP will be investigated for their ability to photo-oxidize highly oxidizing (n-type) or photo-reduce highly reducing (p-type) redox species. The use of n- and p-type semiconductors in a tandem configuration enables light energy to be stored as electrochemical potential energy that can be recovered by operating the same electrodes under accumulation with the complementary redox couple. These electrode materials are usually unstable when illuminated in aqueous solution, and so atomic layer deposition (ALD) will be used to coat their surface with thin layers of titanium dioxide. The current voltage behavior of these stabilized semiconductors will be measured using both cyclic voltammetry and hydrodynamic methods in the dark and under illumination and with a series of redox electrolytes. These experiments will elucidate the electron transfer kinetics as well as light flux and mass transport limitations of photocurrent generation. The behavior of the dark electrode reactions with redox couples will also be investigated. The light and dark behavior will then be compared to the physical models developed for these processes.