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 A1-PtZn NPs supported on PC was synthesized via one-step coreduction method at 300 °C and H2 atmosphere. Afterward, an ordered PtZn intermetallic compound (L10-PtZn/PC) was acquired at a higher annealing treatment of 600 °C for 12 h, and L10-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 L10-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 L10-PtZn/PC-acid catalyst has a mass activity of 1130 mA mgPt–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 L10-PtZn/PC-acid can provide a protection for subsurface Zn and keep the structural stability effectively. Therefore, after 2000 cycles of cyclic voltammetry, the L10-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 OHads 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.