Fuel cells have a bright future as emission free sources of energy. A fundamental understanding of fuel cell catalysis is required to target existing manufacturing challenges. While the oxidation of pure hydrogen is not considered a technical hurdle in fuel cells, the power loss at the cathode during the electroreduction of oxygen is found to be significant. Pt is currently the most promising catalyst material, providing the best compromise in terms of performance and durability, but unfortunately it is costly. It is essential to carefully examine the mechanistic pathway of the oxygen reduction reaction (ORR), and to identify a catalyst with improved performance for the electroreduction of oxygen in order to improve fuel cell efficiency and to reduce manufacturing costs.
Using x-ray spectroscopic techniques, including XPS and XAS, we have focused on the oxygen reduction reaction on Pt(111). The ORR reaction occurs at the triple phase boundary where gas, water containing electrolytes, and catalytic metal particles contact to form both humid and dry regions on the surface of the catalyst. We have found evidence that the role of water in the ORR reaction is two-fold; it can act to both promote and impede the chemical reaction. Additionally, hydrogen peroxide is formed as a by-product during the fuel cell operation and initiates the degradation of the ion exchange membrane. We have searched for a potential pathway of peroxide formation on Pt(111) and found that adsorbed hydrogen plays an important role.
|