NSF-BSF: Engineering alpha-SnWO4 Photoanode Interfaces for Efficient Solar-to-Fuel Conversion

This project will explore materials that can be used to convert low value feedstocks such as carbon dioxide and wastewater into high-value products such as fuels. The research will focus on alpha-phase tin-tungsten oxide, which is readily available in the U.S. This material has a layered atomic structure that gives it an unusual property — the ability to absorb light and move electrical charge. The charge can then be used to initiate chemical reactions. This property is a powerful tool for boosting efficiency. However, it is difficult to make this material without defects. The research team will solve this problem by using computer simulations that guide experimental synthesis. The project will use advanced manufacturing techniques that combine plasma growth processes with ultrafast light heating pulses. These techniques will enable the controlled growth of high-quality thin films of materials. The project’s outcome will be new materials design and manufacturing methods for advanced semi-conductor materials for energy and chemical manufacturing applications. The central premise of this research is that the photoelectrochemical performance of α-SnWO₄ is governed by a strong, underexplored anisotropy in its electronic structure and charge transport, arising from its layered orthorhombic crystal structure. Density functional theory calculations predict that different crystallographic facets of α-SnWO₄ exhibit substantially different bandgaps, band edge positions, and water oxidation activities, offering a powerful tuning knob for photoelectrode design. However, exploiting this anisotropy requires the ability to grow phase-pure α-SnWO₄ films with controlled crystallographic orientation, which has been impeded by inherent synthesis challenges including Sn²⁺ oxidation and disproportionation reactions that typically yield secondary phases or randomly oriented polycrystalline films. The research team will overcome these challenges through a non-equilibrium synthetic approach combining pulsed laser deposition, ion beam-assisted substrate texturing, and rapid photonic heating. The synthetic and structural work will be tightly coupled with first-principles calculations of facet-dependent surface stability, polaron localization, and water oxidation thermodynamics and kinetics. The project will establish quantitative facet-polaron-reactivity relationships that provide design principles transferable to the broader class of anisotropic multinary metal-oxide photoelectrodes for fuel production. 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.