Enhanced Electrocatalytic Activity toward the Oxygen Reduction Reaction through Alloy Formation: Platinum-Silver Alloy Nanocages

Platinum-silver nanocage catalysts with a precisely defined shape and composition were synthesized using the galvanic replacement reaction (GRR) and utilized as electrocatalysts for the oxygen reduction reaction (ORR). The electrocatalytic activity of these platinum-silver nanocages was determined as a function of platinum-content. The specific current density of all platinum-silver nanocages was found to be 2-3 times greater than the specific current densities previously reported for solid platinum catalysts under similar conditions. The highest specific current densities were observed for the platinum-silver nanocages with the lowest platinum content. After a thorough structural and electronic investigation by TEM, XRD, and XPS, it was determined that all platinum-silver nanocage catalysts exibit an expanded lattice compared to pure platinum materials. This resulted in a negative shift in the onset potential of the oxygen reduction reaction. However, despite this negative shift, the catalyst with a low platinum content exhibited an enhanced catalytic activity due to an increased Pt 4f binding energy. This is an indication of a downshifted d-band position and advantageous shift in the adsorption energy of oxygen-containing intermediates on the surface of the catalyst.