Understanding the Chemical Dynamics of PtRu Catalysts in Fuel Cells

Fuel cell technology has garnered significant attention for its potential in clean energy solutions, particularly through the use of bimetallic catalysts like platinum-ruthenium (PtRu). Recent studies have delved into the intricate behaviors of these catalysts under varying electrical potentials, revealing crucial insights into their operational efficiency and stability.

Research conducted by O’Grady et al. indicates that variations in the distance between metal neighbors in PtRu catalysts can be subtle. They noted that at a potential of 0.8 V vs RHE, no platinum-oxygen (Pt-O) neighbors were detected, while ruthenium-oxygen (Ru-O) neighbors appeared at approximately 1.8 Å. This phenomenon has been attributed to the preferential leaching of ruthenium from the alloy at elevated potentials, a process that can significantly influence catalyst performance.

The role of adsorbates, such as methanol, is another critical factor influencing the behavior of PtRu catalysts. Studies by Mukerjee and O’Grady showed that at 0.0 V vs RHE, methanol adsorption decreased the broadening of the white line in X-ray absorption near-edge structure (XANES) data. This suggests a reduction in hydrogen adsorption, a vital aspect of electrochemical reactions in fuel cells. In the absence of methanol, an increase in the intensity of the white line was observed with increasing potential, indicating a rise in the d band vacancy, which is essential for catalytic activity.

Interestingly, the presence of methanol appears to suppress this increase in vacancy, hinting that methanol or its derivatives may be contributing electrons to platinum under high-potential conditions. Further investigations revealed that at intermediate potentials, the formation of carbon monoxide (C1) species on the catalyst surface initially increases the d band vacancies, but higher potentials lead to a decrease due to the formation of oxy-hydroxides that displace carbon fragments.

Beyond PtRu catalysts, other platinum alloys, such as those containing molybdenum (PtMo), have also shown promise in enhancing carbon monoxide tolerance in proton exchange membrane (PEM) fuel cells. These catalysts exhibit distinct peaks in CO stripping voltammograms, indicating varying electrochemical behaviors that can facilitate better performance in fuel cell operations.

The ongoing exploration of these catalytic systems underscores the complex interplay of various factors, including metal interactions, adsorbate dynamics, and operational conditions. These insights are crucial for optimizing fuel cell technology and advancing its role in sustainable energy solutions.