Metal oxide nanomaterials based on first-row transition metals are particularly attractive for applications in renewable energy technologies because (i) they absorb visible light, (ii) they are thermodynamically capable of performing desired photoredox chemistry, such as water oxidation and reduction of protons or carbon dioxide, and (iii) they are composed of inexpensive, earth-abundant, nontoxic elements. Complete synthetic control of the size, shape, and crystal structure of first-row transition metal oxide nanomaterials combined with a thorough understanding of their electrochemical and photophysical behavior is required to optimize their function in photocatalytic applications. This talk focuses on recent results from two ongoing areas in our group. The first area investigates the role of organic ligands, solvent, and precursor chemistry in controlling the size, shape, composition, and crystal phase of first-row transition metal oxide nanocrystals synthesized at elevated pressure using solvothermal methods. The second project combines thermal difference and resonance Raman spectroscopy with DFT calculations to explore the dynamics and electronic structure of photoexcited states of nanostructured thin films of alpha-Fe2O3 (hematite). These data indicate that polarons (quasiparticles that comprise a charge-carrier self-trapped in a potential well formed by nuclear displacements of the surrounding lattice) form directly upon photoexcitation of a thermally activated lattice. This newly recognized mechanism of photoinduced polaron formation has significant implications for the use of hematite in light-conversion technologies such as photoelectrochemical water oxidation.
Kathryn Knowles (University of Rochester)