The interface created between an active metal and an oxide support is known to affect the catalytic performance because of the charge transfer process. However, oxide−oxide interfaces produced by supported spinel oxide catalysts have been less studied owing to their complex interface structures and synthetic challenges. Herein, a synthetic strategy for Co 3 O 4 , Mn 3 O 4 , and Fe 3 O 4 nanocubes (NCs) with a controlled CeO 2 layer enables investigation of the role of the interface in catalytic oxidation. Notably, CeO 2 -deposited Co 3 O 4 NCs exhibited a 12times higher CO oxidation rate than the pristine Co 3 O 4 NCs. In situ characterization demonstrates that the deposited CeO 2 prevents the reduction of Co 3 O 4 by supplying oxygen. The maximized interface resulting from Co 3 O 4 NCs with three facets covered by CeO 2 layers was found to exhibit the highest CO oxidation rate even under O 2 -deficient conditions, which resulted from the versatile variation in the oxidation state. This study provides a comprehensive understanding of the Mars−van Krevelen mechanism occurring on the nanoscale at the Co 3 O 4 −CeO 2 interfaces. The same activity trend and hot electron flow are observed for H 2 oxidation reactions using catalytic nanodiodes, thereby demonstrating that the origin of the activity enhancement is charge transfer at the interface.

We present the design of a three-dimensional Pt/mesoporous TiO2 Schottky nanodiode that can capture hot electrons more effectively, compared with a typical two-dimensional Schottky diode. Both chemically induced and photon-induced hot electrons were measured on the three-dimensional Pt/mesoporous TiO2 Schottky nanodiode. An increase in the number of interfacial sites between the platinum and support oxide affects the collection of hot electrons generated by both the catalytic reaction and light injection. We show that hot electrons flowing 2.5 times higher are detected as the current in the mesoporous system, compared with typical two-dimensional nanodiode systems that have a planar Schottky junction. Identical trends for the chemicurrent and photocurrent in the mesoporous system demonstrate that the enhanced hot electrons are attributed to the larger interface area between the metal and the mesoporous TiO2 support fabricated by the anodization process. This three-dimensional Schottky nanodiode can provide insights into hot electron generation on a practical catalytic device.

A novel three-dimensional catalytic nanodiode composed of a Pt thin film on TiO nanotubes was designed for the efficient detection of the flux of hot electrons, or chemicurrent, under hydrogen oxidation. We verify a significant increase in the chemicurrent from the fast transport of electrons across the ordered supporting oxide layer. This study demonstrates the direct detection of hot electrons on well-ordered TiO nanotubes during the catalytic reaction.

Mechanistic understanding of hot electron dynamics at inverse oxide/metal interfaces from a new catalytic nanodiode that exhibits nanoscale metal–oxide interfaces.