About the Seminar:

Metastable semiconductors have been discovered in many chemical systems that have desirable properties for driving fuel-producing redox reactions from sunlight, including broad visible-light absorption, optimal band edge energies, defect tolerance, and functional carrier mobilities. These photoelectrochemical properties have frequently been found to be associated with their metastable nature, e.g., from specific features in their crystal structures leading to their thermodynamic instability with respect to phase segregation. Recent results will be presented on new mixed-metal oxides that unveil flux-mediated synthetic approaches for kinetic stabilization in this growing class of semiconductor systems.^1-4 Their syntheses have been achieved by reactions that leverage the exothermic formation of stable salt side products as well as shortened reaction diffusion pathways and lowered reaction temperatures. Kinetic stabilization of the products has also been enhanced via the application of a) high cohesive energies of an underlying substructure that is maintained during the reaction, and b) solid-solution compositions which help to inhibit phase segregation while also providing for percolation pathways.  These approaches have yielded, e.g., the first known Sn(II)-perovskites that are isoelectronic to widely commercialized Pb(II)-containing piezoelectrics.¹  Photocatalysis of these semiconductors will primarily be described for light driven H₂O-splitting or CO₂-reduction reactions when in aqueous solutions under ultraviolet and visible-light irradiation.^2,3

References:
1) Switching Lead for Tin in PbHfO₃: Noncubic Structure of SnHfO₃. Gabilondo, E. et al. Angew. Chem. Int. Ed. 2023, e202312130(1-9).
2) Metastability and Photoelectrochemical Properties of Two Cu(I)-Based Oxides with Delafossite Structures. O’Donnell, S. et al. Chem. Mater. 2023, 35, 1404-1416.
3) Capturing Metastable Oxide Semiconductors for Applications in Solar Energy Conversion. Maggard, P.A. Acc. Chem. Res. 2021, 54, 3160-3171.
4) Renaissance of Topotactic Ion-Exchange for Functional Solids with Close Packed Structures. Maggard, P.A. et al. Chem. Eur. J. 2022, 28, e202200479(1-6).

About the Speaker: 

Paul A. Maggard earned his Ph.D. in solid-state materials chemistry at Iowa State University in Ames, Iowa.  Following a post-doctoral stint at Northwestern University in Evanston, IL, he accepted a faculty position in the Department of Chemistry at North Carolina State University.  Current research efforts in his laboratory focus on the flux and hydrothermally- mediated syntheses of crystalline metal oxides and chalcogenides, transition-metal halides, carbon nitrides, and metal-oxide/organic hybrids and investigations of their physical properties. He has received the NSF CAREER award, Beckman Young Investigator award and a Research Corporation for Science Advancement (Scialog) award.