Adjusting the Near-Surface Composition of Pt–Zn Intermetallic Nanoparticles to Enhance Methanol Oxidation Activity and Stability

Abstract

Platinum-based materials are promising catalysts for methanol oxidation reaction (MOR) in direct methanol fuel cells (DMFCs), but it is challenging to balance activity and stability in actual application. Thus, in our work, the graphitized porous carbon (PC) with a high specific surface area and hierarchical porous structure was successfully prepared as the supported material. Disordered A 1 -PtZn NPs supported on PC was synthesized via one-step coreduction method at 300 °C and H 2 atmosphere. Afterward, an ordered PtZn intermetallic compound (L 10 -PtZn/PC) was acquired at a higher annealing treatment of 600 °C for 12 h, and L 10 -PtZn/PC-acid with Pt-skin was also obtained via acid etching. The smaller PtZn nanoparticles (ca. < 5 nm) can be synthesized and distributed on the PC homogeneously. The L 10 -PtZn/PC-acid catalysts display a high order degree and stronger electronic interaction between Pt and Zn atoms, which is favorable for withstanding CO poisoning in MOR. Thus, the L 10 -PtZn/PC-acid catalyst has a mass activity of 1130 mA mg Pt –1 and a specific activity of 2.23 mA cm –2, which are 3.0 and 2.2 times higher than commercial Pt/C. Additionally, the Pt-skin of L 10 -PtZn/PC-acid can provide a protection for subsurface Zn and keep the structural stability effectively. Therefore, after 2000 cycles of cyclic voltammetry, the L 10 -PtZn/PC-acid sample remains 86.62% of the initial peak current density, while commercial Pt/C only retains 47.65%. In situ FTIR studies have demonstrated that the OH ads species easily absorbed on the Zn atoms and facilitates a direct pathway without CO in the MOR on the intermetallic PtZn. This work provides a novel strategy to develop an ideal near-surface composition Pt-based nanocatalyst with high activity and stability for direct methanol fuel cells.

Topics & Concepts