Ferroelectric Modulation of Surface Electronic States in BaTiO₃ for Enhanced Hydrogen Evolution Activity

Abstract

Ferroelectric nanomaterials offer the promise of switchable electronic properties at the surface, with implications for photo- and electrocatalysis. Studies to date on the effect of ferroelectric surfaces in electrocatalysis have been primarily limited to nanoparticle systems where complex interfaces arise. Here, we use MBE-grown epitaxial BaTiO3 thin films with atomically sharp interfaces as model surfaces to demonstrate the effect of ferroelectric polarization on the electronic structure, intermediate binding energy, and electrochemical activity toward the hydrogen evolution reaction (HER). Surface spectroscopy and ab initio DFT+U calculations of the well-defined (001) surfaces indicate that an upward polarized surface reduces the work function relative to downward polarization and leads to a smaller HER barrier, in agreement with the higher activity observed experimentally. Employing ferroelectric polarization to create multiple adsorbate interactions over a single electrocatalytic surface, as demonstrated in this work, may offer new opportunities for nanoscale catalysis design beyond traditional descriptors.

Nanoscale Surface Structure of Nanometer-Thick Ferroelectric BaTiO3 Films Revealed by Synchrotron X-ray Scanning Tunneling Microscopy: Implications for Catalytic Adsorption Reactions

“…The consistent decrease at different edges suggests a clear effect of ferroelectric polarization on the number of photoelectrons emitting from the surface to the tip in tunneling mode. Previously, a downward polarization in ferroelectric BaTiO 3 thin films was shown to lead to a decreased electron density at the surface of the films due to an upward band bending . Therefore, a decreased probability for tunneling of photoelectrons at the downward-poled surface may underlie the consistent decrease in X-ray absorption across all three edges.…”

“…It was soon realized that tuning ferroelectric layers in heterojunctions and superlattices can add significant functionality to even more diverse architectures, which has in turn triggered extensive research on the interfacial properties of ferroelectrics . A focus on interfaces led to an intense investigation of ferroelectrics in related fields, including photovoltaics , and catalysis, − where switchable interface properties are of significant importance. Throughout, a critical challenge in investigating ferroelectric interfaces has remained the simultaneous probing of the effect of polarization on both surface structure and chemistry at the atomic scale.…”

Energy Interplay in Materials: Unlocking Next‐Generation Synchronous Multisource Energy Conversion with Layered 2D Crystals

“…SMEC 2D crystals could also be used as advanced electrocatalysts that are enhanced by multiple energy sources and high surface area-increased kinetics. [118] An example of potential ferroelectric 2D crystals with multiple energy conversion mechanisms is described in a recent report on 2D copper indium thiophosphate, CuInP 2 S 6 (CIPS), crystals. [55] These crystals exhibited an enhanced BPVE effect that was two orders of magnitude higher than typical bulk ferroelectric perovskite oxides due to the nanoscale thickness of the material being smaller than the electron mean free path.…”

“…Yet, this external input is challenging to deliver in many applications. Recent M → E energy harvesting [14,95,138] and ferroelectric materials [118] can directly activate catalysts and eliminate the need for externally applied active energy inputs. SMEC materials can combine these phenomena and capture different types of energy to provide an "adaptive" catalyst that functions for a significantly expanded timespan.…”

“…SMEC 2D crystals could also be used as advanced electrocatalysts that are enhanced by multiple energy sources and high surface area‐increased kinetics. [ 118 ]…”