Understanding the Coordination Dynamics of Platinum in Fuel Cell Catalysts

The study of platinum (Pt) catalysts plays a crucial role in the advancement of fuel cell technology. One important aspect of this research involves analyzing the coordination number and the distance between neighboring atoms, which inform us about the catalyst's structural integrity during varying potentials. For instance, at a low potential of 0.1 V, a well-reduced Pt particle exhibits approximately 7.5 Pt neighbors at a distance of 2.76 Å, with no adjacent oxygen (O) neighbors. This indicates a clean Pt surface, crucial for efficient catalytic activity.

As the potential rises, the behavior of Pt and O neighbors changes significantly. At a higher potential of 1.2 V, the concentration of Pt neighbors diminishes while the O neighbors increase, reflecting a transition from a reduced to an oxidized state. This transformation is essential for understanding the electrochemical processes that dictate the performance of fuel cell catalysts. Despite this change, the face-centered cubic (fcc) structure of bulk platinum remains intact, suggesting that only a thin oxide layer forms on the surface, which thickens with increasing potential.

Recent studies have provided valuable insights into the hysteresis observed in the coordination number of Pt neighbors when the potential sweep is reversed. This phenomenon, demonstrated by Yoshitake et al., mirrors the behavior seen in voltammograms, showcasing how dynamic the interactions between Pt and other species can be under different electrical conditions. The proposed schematic model illustrates the influence of potential on the structural changes occurring in carbon-supported Pt particles, highlighting both surface oxide growth and roughening.

The impact of adsorbed hydrogen on Pt's coordination dynamics has also been extensively studied. Research by Mukerjee and McBreen, for example, indicates a significant decrease in the coordination number as the potential increases, implying a shift from a spherical to a flatter, raft-like morphology of the Pt particles. This morphological change is critical, as it can affect the catalyst's activity and stability under operational conditions.

To further our understanding of the kinetics of oxide formation and removal on Pt/C electrodes, energy dispersive extended X-ray absorption fine structure (EXAFS) techniques have been employed. These methods allow for rapid data collection, capturing the dynamic changes in coordination numbers over time. Research has shown that both the formation and reduction of oxide can be modeled using different mathematical functions, providing insights into the rates at which these processes occur under varying potentials.

In conclusion, the intricate dynamics of platinum coordination in fuel cell catalysts reveal vital information that can inform future advancements in fuel cell technology. By examining how Pt neighbors and surrounding oxide layers interact under different electrical conditions, researchers can optimize these catalysts for improved performance and efficiency.