Chem. Lett. 11, 438 (2020) Most elements heated in air form a metal oxide (+) Relatively stable; (-) Band gaps typically too large Distribution of carrier effective masses for 5548 metal oxides m*h > m*e m*e m*h n-type oxide semiconductors ZnO, In2 O3 , SnO2 , TiO2 … p-type oxide semiconductors Cu2 O, SnO, NiO, BiVO4 …
Band s2 and d0 cations: (Sn, Sb, Pb, Bi)(Ti, W, V, Nb, Ta)Ox Metal s2 Exact band structure depends on the nature of chemical bonding and crystal structure
Study: Bismuth Vanadate A. Walsh et al, Chem. Mater. 21, 547 (2009) (Bi 6s + O 2p) Simplified two-level coupling scheme Matches valence band XPS APL 98, 212110 (2011) Electronic density of states (DFT/PBE) Stereochemical and electronic activity of Bi in BiIIIVVO4 involves Bi 6s – O 2p interactions
Solid State Chem. 196, 157 (2012) SnII 2 TiIVO4 is more suitable for visible-light solar fuel applications than rutile (SnIV,TiIV)O2 Sn2 TiO4 isostructural to mixed-valence minum (PbII 2 PbIVO4 ) Electron density at the upper valence band (DFT/PBEsol) Eg exp~1.6 eV
and A. Walsh, Nature Comm. 1, 4379 (2025) Noise Chemeleon can run on a laptop Text-guided denoising diffusion model: “Suggest a crystal structure for Bi2 TiWO8 ” Sample
Nature Comm. 7, 13706 (2016) Values depend on the specific reaction Photoelectrochemical solar to hydrogen Some factors: • Non-radiative processes • Necessary overpotential • Faradaic efficiency
Mq+h+→Mq+1 Small hole polaron Conduction Band Polaron = charge carrier coupled to a structural distortion Irreversible loss (excess energy lost thermally)
a high symmetry coordination environment that reduces the band gap Kanta Ogawa et al, J. Am. Chem. Soc. 146, 5806 (2024) IPs from photoelectron yield spectroscopy (PYS) Electron density at the upper valence band BiY
NbO8 Cl and Bi6 NbWO14 Cl Kanta Ogawa et al, Chem. Mater. 35, 5532 (2023) Bi4 NbO8 X (n = 1) Bi O X a Bi/Ba O Ti Bi5 BaTi3 O14 X (n = 3) c Bi Nb/W Bi6 NbWO14 X d Ba2 Bi3 Nb2 O11 X (n = 2) b Bi Bi/Ba Ba O X Nb O Bi4 NbO8 X (n = 1) Bi O X a Bi/Ba O X Ti Bi5 BaTi3 O14 X (n = 3) c X Bi Nb/W Bi6 NbWO14 X d Ba2 Bi3 Nb2 O11 X (n = 2) b Bi Bi/Ba Ba O X Nb O Electronic structure is influenced by chemical interactions within and between the polyatomic building blocks
determines relative band energies Kanta Ogawa and Aron Walsh, J. Am. Chem. Soc. 147, 821 (2025) Upper valence band Lower conduction band Modular approach to engineer band gaps, energies, carrier transport ∆𝑉𝑖𝑛𝑡𝑒𝑟 = 𝑄𝑙𝑎𝑦𝑒𝑟 𝑑 2𝜀𝑆 charge distance area
chemical principles for band engineering of metal oxides. Multi-component photoelectrodes offer potential to tailor performance The presentation contained work from: Kanta Ogawa, Lucas Garcia-Verga, Liam Harnett Thanks to my collaboration network, in particular: James Durrant (ICL) and Ernest Pastor (CNRS-Rennes)