Controlling Oxygen Reduction Reaction Activities of Ag@Pt Core–Shell Nanoparticles Via Tuning of Ag in the Surface Layer

Abstract

Herein, the effect of Pt shell thickness and Ag content in the surface layer on the oxygen reduction reaction activities of Ag@Pt core@shell nanoparticles (NPs) is discussed. Ag@Pt NPs are synthesized via the seeded‐growth method, where colloidal Ag NPs are first synthesized and used as seeds for the growth of Pt. Electrochemical activity measurements in alkaline media show a remarkable dependency between the Ag content in the shell and the oxygen reduction reaction (ORR) activity, where the overpotentials required for −1.0 mA cm−2 drop gradually, that is, 0.72, 0.77, and 0.80 V RHE for Ag@Pt‐25, Ag@Pt‐35, and Ag@Pt‐45, respectively. Tafel analysis also confirms this dependency with 73.5 mV dec−1 for Ag@Pt‐25, 71.3 mV dec−1 for Ag@Pt‐35, and 68.8 mV dec−1 for Ag@Pt‐45. A combination of the high‐resolution transmission electron microscope, X‐ray photoelectron spectroscopy, and X‐Ray diffraction analysis shows an increase of the Pt shell thickness. It is shown that the absence of Pt‐H adsorption/desorption peaks in cyclic voltammetry of Ag@Pt NPs is correlated with Ag in the surface layer, which plays an important role in the ORR activity due to the blockage of Pt(111) terrace sites. Rate‐limiting first‐electron transfer to oxygen is facilitated by decreasing Ag amount at the surface.

Nature of the Active Center for the Oxygen Reduction on Ag-Based Single-Atom Alloy Clusters

“…This outstanding performance of AgPt alloys from the experimental data suggested that in addition to the formation of M 1 O x (OH) y complexes, other unique structural config- urations in Ag-based alloys might contribute to enhanced ORR activity. 46,47 Our findings strengthen our understanding of the role and significance of these complexes formed under operational ORR conditions in dictating the catalytic behavior of these alloys during the ORR process.…”

“…This new perspective has been further explored in light of experimental findings that demonstrate superior ORR activity in AgCu and AgPd alloy nanoparticle catalysts with Cu and Pd in an oxide state, as reported in several studies. − However, it is important to note that the Ag 54 Pt 1 alloy shows activity lower than that of the Ag 54 Co 1 , Ag 54 Cu 1 , and Ag 54 Au 1 clusters. This outstanding performance of AgPt alloys from the experimental data suggested that in addition to the formation of M 1 O x (OH) y complexes, other unique structural configurations in Ag-based alloys might contribute to enhanced ORR activity. , Our findings strengthen our understanding of the role and significance of these complexes formed under operational ORR conditions in dictating the catalytic behavior of these alloys during the ORR process.…”