(617ep) Mn@Ptn (n = 1, 2, and 3) Core-Shell Nanoparticles: Synthesis, Characterization and Electrocatalysis

We report the synthesis of Mn@Ptn (n = 1, 2, 3) core-shell nanoparticles (NPs) and their electrocatalytic properties. The syntheses are achieved by one-pot sonochemical reactions between Pt(acac)2 and Mn(acac)2 in ethylene glycol. The shell-thickness of the NPs can be controlled from 1 monolayer (ML) to 2 ML through variation of the composition of reacting solution. X-ray diffractometry, transmission electron microscope (TEM), and energy dispersive X-ray spectroscopy (EDS), and inductively couple plasma-absorption emission spectroscopy are used for the analyses of the crystal structure, particle size, morphology, and composition, respectively. The formation of core-shell NPs is confirmed by EDS line profiles coupled with scanning TEM and the electronic states of Pt are analyzed by X-ray photoelectron spectroscopy. The NPs are investigated as electrocatalysts in oxygen reduction reaction (ORR). The linear sweep voltammograms of Mn@Ptn catalysts show unprecedentedly high activity in ORR with the mass activity 14-16 times larger than that of pure Pt NP. Within the Mn@Ptn series, the activity increases as the Pt shell thickness increases. This trend and theoretical calculations on the binding energies of H or O atom on Pt/Mn model structures suggest that the ORR on Mn@Ptn electrocatalysts follows the associative mechanism. The durability test data, measured by ORR activity after electrochemical cycling, show that Mn@Ptn samples have improved retention of kinetics from that of Pt. Especially, the Mn@Pt3 sample with 2 ML thick Pt-shells shows remarkably high stability compared with the other two Mn@Ptn samples as well as pure Pt  catalyst