Speaker
Description
This study explores the epitaxial growth of cobalt oxide (Co₃O₄) thin films on platinum (Pt(100)) single crystals, focusing on the interfacial phenomena that drive the Oxygen Evolution Reaction (OER) in electrochemical water-splitting.1 By systematically varying film thickness, we uncover the delicate interplay between interfacial charge transfer and surface polarization, both critical for catalytic performance.2 The growth process reliably produces structurally stable films across a range of thicknesses, confirmed through Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (LEED).
A Schottky barrier forms at the Pt/Co₃O₄ interface, enabling directional charge transfer facilitated by band bending, as evidenced by X-ray and Ultraviolet Photoelectron Spectroscopy (XPS/UPS). Thinner films demonstrate enhanced charge transfer kinetics and dynamic surface polarization, which are essential for modulating surface states that interact with oxygen intermediates during the OER.3 These reactive surface states, optimally distributed in thinner films, reduce the energy barrier for oxygen adsorption and activation, thereby improving catalytic efficiency. Conversely, thicker films exhibit higher capacitance due to bulk volumetric contributions, highlighting the trade-off between surface reactivity and bulk effects on performance.
Electrochemical analyses, including Mott-Schottky analysis and capacitance-voltage spectroscopy (CVS), reveal dynamic charge behavior at the interface, with distinct regions of accumulation, depletion, and inversion. Key capacitance peaks at 0.5 V (Co²⁺/Co³⁺ transitions) and 0.65 V (subsequent redox transitions), resolved for the first time as distinct events, are associated to surface states from the fuzzy nature of the skin layer formation. These states enhance oxygen adsorption, lower reaction barriers, and improve catalytic efficiency, suggesting a critical film thickness where charge neutralization optimizes electronic structure and reaction kinetics under operational conditions.4 This study establishes a relationship between controlled film thickness, interfacial charge dynamics, and catalytic performance, bridging fundamental surface science principles with practical electrocatalytic applications. The findings provide a pathway for designing high-performance Co₃O₄-based electrodes to enhance water-splitting efficiency and advance sustainable energy technologies.
- Faber, M. S. & Jin, S. Earth-abundant inorganic electrocatalysts and their nanostructures for energy conversion applications. Energy Environ. Sci. 7, 3519–3542 (2014).
- Tong, Y. et al. A metal/semiconductor contact induced Mott-Schottky junction for enhancing the electrocatalytic activity of water-splitting catalysts. Sustain. Energy Fuels 7, 12–30 (2022).
- Sun, Z. et al. Simultaneously Realizing Rapid Electron Transfer and Mass Transport in Jellyfish-Like Mott–Schottky Nanoreactors for Oxygen Reduction Reaction. Adv. Funct. Mater. 30, 1910482 (2020).
- Zhang, B. et al. Encapsulation of Co/Co3O4 hetero-nanoparticles within the inner tips of N-doped carbon nanotubes: Engineering Mott-Schottky nanoreactors for efficient bifunctional oxygen electrocalysis toward flexible zinc-air batteries. Chem. Eng. J. 448, 137709 (2022).
