Tandem Semiconductor Microwire Slurries for Solar Hydrogen Generation

Abstract

Meeting the industry goal of $2/kg for solar H2 is a daunting task that will require novel, highly efficient systems which eliminate many of the components and balance-of-systems costs inherent with photovoltaics + electrolyzers. Technoeconomic models have consistently shown that a photoactive slurry reactor for water-splitting could offer the cheapest route to storing solar energy as hydrogen fuel. However, abundant challenges with this approach have thus far limited such particle-based reactors to prohibitively low efficiencies. This talk will highlight our progress toward the development of a tandem semiconductor particle system designed to address the weaknesses of slurry reactors and achieve a high solar-to-hydrogen (STH) efficiency for particle systems. A proof-of-concept tandem structure uses silicon microwires as the base of the particle, with a wider bandgap TiO2 layer grown on top to gain the additional photovoltage necessary to split water. Semiconductor architecture development and performance will be discussed along with early modeling efforts. In-situ magnetic alignment of the particles has been demonstrated for possible improved tandem light management. In addition, slurry optical characterization and photoelectrochemical performance will be discussed as a function of slurry parameters including bubble flowrate, particle concentration, spectral conditions, and light management strategies. Slurry conditions for minimizing back reactions will be discussed as well.