Tunable III-Nitride Nanostructures for N=N and C-H Bond Activation
Abstract
Solar photocatalysis is a promising strategy for sustainable synthesis of chemicals and fuels, essential for sustainability and energy independence. An outstanding challenge is the photocatalytic activation of C-H and N=N bonds, critical for field deployment of synthetic processes in applications of nitrogen fixation and generation of liquid fuels. Currently, these reactions require thermo-catalytic processes at centralized industrial facilities, with intensive energy input, and massive carbon emissions. Solar alternatives have so far been hindered by the lack of robust photocatalytic materials that could enable efficient, stable, and selective reactions, as required for generation of liquid fuels and chemicals for DOD applications. Here, we propose fundamental studies of III-nitride (III-N) nanostructures that have recently emerged as ideal material platforms for photocatalysis. III-nitrides are the only known III-V semiconductors whose energy band edges straddle a broad range of redox potentials, under visible and near-IR light, fulfilling an essential requirement to achieve efficient photocatalysis. Furthermore, we observed > 1-year stability for III-N photocathodes for water splitting. Building upon our recently demonstrated solar water-splitting system, and preliminary studies of photocatalytic CH4 and N2 conversion, our team proposes to develop III-N nanostructures as highly efficient and stable photo(electro)catalysts for C-H and N=N activation. Progress in this field has been hindered by a lack of fundamental understanding of the materials structure/property relations, as well as the lack of high-quality materials with broad solar photo-absorption. Our team has the unique ability to overcome these challenges through the growth of high-quality dilute anion III-N nanostructures with control over the energy bandgap from the UV-vis to the IR, overcoming the long-standing challenge of lattice mismatch when synthesizing In-rich InGaN with a narrow bandgap. These materials have the potential to enable substantial enhancements of catalytic efficiency through control of the surface properties, internal fields, lateral heterojunctions via core-shell structures, ballistic transport of electrons/holes and interfacial charge transfer from the semiconductor to the reactants. Therefore, we anticipate the proposed materials can enable the photoinjected carriers to become fully available for bond activation, offering a revolutionary platform to drive efficient, stable, and selective photocatalysis. The MURI program will thus provide a comprehensive theoretical and experimental understanding of dilute anion III-N nanostructures (Ga(In)NX for N=N and C-H bond activation. This will be accomplished through multiple cycles of an iterative approach where computational design of materials with desired optical, electronic and reactivity properties will identify promising surfaces, dopants and co-catalysts, guiding the synthesis of spectrally tunable Ga(In)NX nanostructures, and spectroscopic characterization of carrier dynamics and catalytic reactivity. State-of-the-art epitaxy and surface functionalization by atomically dispersed active sites will provide high-quality photocatalytic platforms. Fundamental studies will characterize the unique structural, optical, electronic, and photocatalytic properties enabled by these novel nanostructures, including N-termination, tunable electronic level alignment, hot carrier dynamics, high oxidation potential, and interfacial polarization fields essential for efficient reactivity. We will establish the emerging field of dilute anion III-N for photocatalytic applications by advancing fundamental understanding of structure/function relations that determine the stability, efficiency, and selectivity. The resulting knowledge will provide guidelines for developing powerful catalytic systems for a wide range of reactions relevant to outstanding challenges in sustainable energy and environment remed
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 07, 2021
- Source ID
- W911NF2110337
Entities
People
- Zetian Mi
Organizations
- Army Contracting Command
- United States Army
- University of Michigan