CAREER: Aligned Tandem Semiconductor Microwire Slurries for Low-cost, High Efficiency Solar Hydrogen Generation

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Solar energy be used to photochemically "split" water into hydrogen and oxygen gases. Hydrogen can be used as a fuel to power fuel cells or as a building block molecule for the manufacture of chemical products and materials. This research project will study novel catalysts and reactor designs for producing solar water-splitting semiconductor microparticles that are capable of solar-to-hydrogen conversion efficiencies at a level that could make slurry reactor designs practical for commercial solar hydrogen production. The resulting discoveries will help advance solar energy technology along a path towards low-cost solar energy storage and sustainable fuel production. Such technologies potentially can revolutionize the energy industry and greatly enhance the energy independence of the United States. The research project is complemented by an educational and outreach plan that engages undergraduate and graduate students, as well as the wider community, in learning activities related to solar energy and renewable resources.In this research project, a design approach will be pursued for monolithic single-particles of ideally matched top and bottom cell bandgaps materials. The objective is to maximize light absorption and quantum efficiency while minimizing the deleterious ohmic resistances and back reactions. The specific research objectives are to: (1) Produce a tandem semiconductor photoelectrode on a base of silicon microwires capable of unassisted water-splitting under 1 Sun solar energy flux, and demonstrate a tandem single-particle slurry reactor at greater than 1 percent solar-to-hydrogen efficiency for more than 24 hours; (2) Investigate the fundamental effects of particle alignment and light scattering on the efficiency of a tandem single-particle slurry reactor by invoking variable levels of magnetic alignment and back reflection during operation; (3) Investigate the effects of particle density and single-particle current density on water-splitting back-reaction rates and co-evolved hydrogen and oxygen concentration with variable illumination intensity and carrier gas flow rate; (4) Perform mesoscale modeling via multi-physics simulations of tandem single particles to predict current distribution as a function of particle alignment and light scattering, as well as hydrogen and oxygen concentrations in the electrolyte as a function of particle current density and carrier gas flow rate, and validate the modeling by experimental results; (5) Incorporate a ternary III-V semiconductor of optimized bandgap as the top sub-cell in the tandem particles to produce a slurry reactor capable of solar-to-hydrogen in excess of 8 percent, and utilize a protective TiO2 coating to extend the particle lifetime beyond 24 hours. The educational activities will feature solar and renewable energy course development and broad dissemination, the incubation of a materials and energy science master’s degree program and certificate program, and direct inclusion of underrepresented undergraduates into the research process.This project is jointly funded by the Catalysis and Electrochemical Systems programs and the Established Program to Stimulate Competitive Research (EPSCoR).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.