Seon-Ah Jin

Communication: Enhanced oxygen reduction reaction and its underlying mechanism in Pd-Ir-Co trimetallic alloys

Based on a combined density functional theory and experimental study, we present that the electrochemical activity of Pd3Co alloy catalysts toward oxygen reduction reaction (ORR) can be enhanced by adding a small amount of Ir. While Ir tends to favorably exist in the subsurface layers, the underlying Ir atoms are found to cause a substantial modification in the surface electronic structure. As a consequence, we find that the activation barriers of O/OH hydrogenation reactions are noticeably lowered, which would be mainly responsible for the enhanced ORR activity. Furthermore, our study suggests that the presence of Ir in the near-surface region can suppress Co out-diffusion from the Pd3Co substrate, thereby improving the durability of Pd-Ir-Co catalysts. We also discuss the relative roles played by Ir and Co in enhancing the ORR activity relative to monometallic Pd catalysts.

Combinatorial High-Throughput Screening for Highly Active Pd–Ir–Ce Based Ternary Catalysts in Electrochemical Oxygen Reduction Reaction

A combinatorial library having 66 different ternary compositions of Pd-Ir-Ce was prepared via the impregnation method to find the optimum ternary composition with the highest performance toward oxygen reduction reaction (ORR) in acid media. Its performance in ORR activity of the combinatorial array was evaluated through two different combinatorial high-throughput screening methods to gain validity: (1) multielectrode half-cell method and (2) optical screening method. From the combinatorial results, the spot at 79:12:9 for Pd-Ir-Ce (at. %) in the array showed the highest ORR activity. The electrochemical characterizations of the single catalyst demonstrates that the optimized Pd79Ir12Ce9/C catalyst shows 1.5 times the ORR activity compared to that of Pd/C catalyst at 0.85 V (vs. RHE). In the Pd-Ir-Ce based catalysts, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results reveal that Ir and Ce are present in the form of IrO2 and CeO2, respectively, and the electron configuration of Pd is effectively modified through the decoration with IrO2 and CeO2. From the results, we suggest that the electro-modification of Pd through strong metal-metal oxide interaction with IrO2-CeO2 was a reason for the enhanced ORR activity.