Enhancement of ammonia oxidation activity over Y2O3-modified platinum surface: Promotion of NH2,ad dimerization process

In recent years, increasing attention has been focused on the utilization of ammonia as a fuel for anion exchange membrane fuel cells (AEMFCs) due to the significant development of anion exchange membranes (AEMs). Although the improvement in catalytic activity for ammonia oxidation reaction was achieved for some Pt-based electrocatalysts, no effective methods were established to enhance the tolerance toward the catalyst poisoning, which is known as the major issue for the utilization of ammonia as a fuel. In this paper, first, the additive effect of Y2O3 was intensely investigated by in situ ATR-IR spectroscopy. For the Y2O3-modified Pt surface, the IR band area of N2H4,ad species, which is the intermediate species of ammonia oxidation reaction, was distinctively increased, suggesting the promotion of NH2,ad dimerization process. This effect of Y2O3 was then accurately clarified by applying the Y2O3 modification for Pd surface. Despite that Pd was inactive for the NH2,ad dimerization reaction, the IR band of N2H4,ad species was clearly detected only in the case of Y2O3-modified Pd surface. This is the strong evidence that the Y2O3 additive itself promotes the NH2,ad dimerization reaction. Furthermore, the electrocatalytic performance of Y2O3-modified Pt/C electrocatalyst was evaluated using the commercial AEMFC system. A twofold increase in both maximum power density and tolerance toward the catalyst poisoning was confirmed as compared to the cell with the conventional Pt/C electrocatalyst. These results clearly show the applicability of our catalyst design strategy to improve the performance of the real-world electrocatalyst for the ammonia oxidation reaction.