Understanding the Impact of Electrode Potential on AXAFS in Platinum-Based Electrocatalysts

The study of atomic environments in electrocatalysts, particularly those involving platinum (Pt), has revealed that the amplitude of the Atomic X-ray Absorption Fine Structure (AXAFS) is significantly influenced by the applied electrode potential. As the potential increases from 0.00 to 0.54 V and further to 0.74 V, researchers observe an increase in AXAFS amplitude. This relationship has been modeled using the FEFF7 code, which calculates variations in the atomic structure and charge distribution of a Pt cluster, suggesting a charge of approximately 0.05 electrons per surface Pt atom.

However, the interpretation of AXAFS variations remains a topic of debate within the scientific community. The FEFF code employs a muffin-tin approximation for atomic potentials, assuming spherical potentials within a defined radius and negligible values outside of it. While modifications to this model have been proposed to better represent AXAFS features, critics argue that these adjustments do not fully address the limitations of the muffin-tin approximation. Additionally, the chosen Fourier filtering range for data analysis may overlap with signals from neighboring oxygen atoms, complicating the interpretation of results at higher potentials.

In studying platinum-based electrocatalysts, the adsorption of hydrogen and oxide formation significantly affects the X-ray Absorption Spectroscopy (XAS) data, particularly at the Pt L3 edge. The analysis reveals that the dispersion of Pt atoms within typically sized particles (1-5 nm) plays a critical role in how adsorbates influence the spectra. For these particles, the coordination number obtained from Extended X-ray Absorption Fine Structure (EXAFS) data indicates the presence of adsorbates without causing significant restructuring of the metal particle. Low coordination numbers can complicate data fitting processes, highlighting the importance of accurate sample preparation.

To enhance the reliability of parameters associated with Pt-adsorbate bonds, it is crucial to collect XAS data under optimized conditions. This includes ensuring that any excess adsorbate is removed from the sample prior to analysis. Such meticulous approaches have been applied in investigations of underpotential deposition (upd) of various elements, including copper (Cu), on Pt/C electrocatalysts. Studies like those conducted by McBreen and colleagues have shown that controlling the environment around the electrocatalyst, such as excluding oxygen, helps maintain the integrity of the underpotential deposited layer.

These findings underscore the complexity of analyzing and interpreting the interactions between adsorbates and platinum in electrocatalytic systems. Understanding these dynamics not only aids in elucidating the fundamental processes at play in electrocatalysts but also contributes to the development of more efficient materials for energy conversion and storage applications.