(581c) Electrostatic Manipulation of Lewis Acidity in Ultrathin Catalytic Films Via Programmable Catalytic Condensers

Programmable catalysts offer precise control of active site electron density, providing a design strategy for enhancing catalyst performance by tuning catalyst properties to elementary reaction kinetics.^[1] One type of programmable catalyst is a metal oxide graphene catalytic condenser, where charge in the catalytic layer can be tuned via application of an electrical bias across the device stack. We recently demonstrated that an alumina-graphene catalytic condenser can reduce the unimolecular dehydration barrier of 2-propanol by ~0.2 eV with only +3 V applied bias, which corresponded to ~0.1 excess hole density per pentacoordinate Al site.^[2]

Herein, we extend the catalytic condenser design to a titania-based catalytic layer. Titania is a Lewis acid catalyst and semiconductor with a ~3.2 eV bandgap, making it a suitable candidate for thin-film electronic devices in which the conductivity is varied by orders of magnitude. We use atomic layer deposition (ALD) to fabricate titania-based catalytic condensers by depositing ultrathin (< 10 nm) films of TiO_x on graphene and dielectric substrates. These devices exhibit capacitance increases over bare graphene, large differences in on/off state conductivities, and electron mobilities commensurate with tunable electronic characteristics; together, these suggest that the electronic occupation of titania is readily manipulated by our device architecture. Due to the ultrathin nature of the TiO_x films, these changes in electronic occupation impact the Lewis acidity of the catalytically-accessible surface, which was characterized using temperature programmed desorption (TPD) of Lewis basic probe molecules in an ultra-high vacuum (UHV) reactor.

These findings extend the applicability of catalytic condensers to titania-based designs. While we focus on electrostatic tuning of Lewis acidity in ultrathin films, this device will be generally applicable for controlling both thermal and electrocatalytic chemistries.

[1] ACS Catal. 2020, 10(21), 12666.

[2] JACS Au, 2022, in press.