Catalysis on oxidized ferroelectric surfaces—Epitaxially strained LaTiO2N and BaTiO3 for photocatalytic water splitting

Abstract

Surface properties of ferroelectrics are promising for catalysis due to the spontaneous electric polarization that can be reversed by an applied electric field. While several theoretical studies show different catalytic activities for differently polarized ferroelectric surfaces at zero electric potential, little work was devoted to catalysis on ferroelectric surfaces at higher electric potentials. Under these conditions that are relevant for photocatalytic experiments and applications, surfaces are usually oxidized. Using density functional theory calculations, we show for LaTiO 2 N and BaTiO 3 that this oxidation heavily impacts and even determines the electronic properties of the catalyst surface and therefore leads to similar reaction free energies for the catalytic steps of the oxygen evolution reaction, irrespective of the bulk polarization. This is opposed to experimental studies, which found different activities for differently polarized catalyst surface domains under oxidizing conditions. We therefore conclude that the experimentally observed activity difference does not originate from the surface polarization following the bulk polarization, but rather from different bulk polarization directions leading to different adsorbate coverages or even surface reconstructions.

Enhancing Oxygen Evolution Reaction Activity by Using Switchable Polarization in Ferroelectric InSnO2N

“…According to the Sabatier principle, if the interaction is too weak, the adsorbate (i.e., the reagent) will be unable to bind to the catalyst, while if the interaction is too strong, the reaction product will fail to desorb. 30,31 Consequently, optimal binding strength corresponds to the maximum OER efficiency and a minimum theoretical overpotential. The density functional theory (DFT) calculations have demonstrated that the four-step OER mechanism is fundamentally limited to a minimum theoretical overpotential of 0.3−0.4 V due to the scaling relation between the binding strength of the OH and OOH intermediates.…”

“…The major obstacle among the water-splitting redox reactions is the low efficiency of the oxygen evolution reaction (OER). − The OER is a multistep reaction involving several intermediates, and every step is vital for the overall conversion efficiency. , The interaction between the catalyst surface and intermediate, strong or weak, will directly affect the reaction activity. According to the Sabatier principle, if the interaction is too weak, the adsorbate (i.e., the reagent) will be unable to bind to the catalyst, while if the interaction is too strong, the reaction product will fail to desorb. , Consequently, optimal binding strength corresponds to the maximum OER efficiency and a minimum theoretical overpotential. The density functional theory (DFT) calculations have demonstrated that the four-step OER mechanism is fundamentally limited to a minimum theoretical overpotential of 0.3–0.4 V due to the scaling relation between the binding strength of the OH and OOH intermediates. , The adsorption strength between the catalyst and intermediate largely depends on the surface electronic states.…”

Narrow Bandgap Inorganic Ferroelectric Thin Film Materials

“…The change in the polarization direction of ferroelectric materials is essentially the result of the inversion of the electric domains. [130,133,135] The hysteresis loop is the most important feature of ferroelectric materials, which describes the hysteresis of the polarization (P) as a function of the external electric field (E). [136] Figure 4a depicts a PFM (Piezoelectric response force microscopy) phase picture of the BFSO film and the possible polarization directions in the unit cell.…”

“…[126][127][128][129] The domains in a ferroelectric material refers to the regions in which the electric dipoles are oriented in a consistent manner. [130][131][132][133][134] Generally, ferroelectric materials are multidomains, which change from multidomains to single domain at an external electric field. The change in the polarization direction of ferroelectric materials is essentially the result of the inversion of the electric domains.…”

“…The change in the polarization direction of ferroelectric materials is essentially the result of the inversion of the electric domains. [ 130,133,135 ] The hysteresis loop is the most important feature of ferroelectric materials, which describes the hysteresis of the polarization ( P ) as a function of the external electric field ( E ). [ 136 ]…”