Impact of Pt(hkl) Electrode Surface Structure on the Electrical Double Layer Capacitance

Area of Science:

• Electrochemistry
• Surface Science
• Computational Materials Science

Background:

• Classical electrical double-layer (EDL) theory lacks consideration of electrode surface structure.
• Experimental validation of EDL theory is limited to ideal systems like mercury electrodes.
• Solid electrode EDL properties are crucial for electrochemical energy applications but poorly predicted by classical theory.

Purpose of the Study:

• To investigate the relationship between platinum (Pt) surface structure and electrical double-layer capacitance.
• To elucidate the role of surface defects, such as steps, on EDL properties.
• To bridge the gap between theoretical EDL models and experimental observations for solid electrodes.

Main Methods:

• Combined *ab initio* molecular dynamics (AIMD) simulations with electrochemical experiments.
• Utilized flat, stepped, and kinked Pt single crystal facets as model systems.
• Employed acidic HClO4 media for interfacial studies.

Main Results:

• Surface defects, specifically steps on Pt surfaces, significantly reduce EDL capacitance near the potential of zero charge (PZC).
• AIMD simulations revealed distinct water dipole orientations across different Pt facets.
• Experimentally measured capacitance exhibited an inverse volcano-shaped dependence on surface step density.

Conclusions:

• Electrode surface structure, including atomic arrangement and defects, is a critical determinant of EDL capacitance.
• The orientation of water molecules at the interface is facet-dependent and influences capacitance.
• This study provides a mechanistic understanding for optimizing EDL properties in electrochemical systems by controlling surface morphology.