Beyond Strain and Ligand Effects: Microstrain-Induced Enhancement of the Oxygen Reduction Reaction Kinetics on Various PtNi/C Nanostructures
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- 作者：Raphaël Chattot ; Tristan Asset ; Pierre Bordet ; Jakub Drnec ; Laetitia Dubau ; Frédéric Maillard
- 刊名：ACS Catalysis
- 出版年：2017
- 出版时间：January 6, 2017
- 年：2017
- 卷：7
- 期：1
- 页码：398-408
- 全文大小：715K
- ISSN：2155-5435
文摘
The electrical performance of a proton exchange membrane fuel cell is limited by the slow oxygen reduction reaction (ORR) kinetics. Catalytic improvements for the ORR have been obtained on alloyed PtM/C or M-rich-core@Pt-rich-shell/C catalysts (where M is an early or late transition metal) in comparison to pure Pt/C, due to a combination of strain and ligand effects. However, the effect of the fine nanostructure of the nanomaterials on the ORR kinetics remains underinvestigated. Here, nanometer-sized PtNi/C electrocatalysts with low Ni content (∼15 atom %) but different nanostructures and different densities of grain boundary were synthesized: solid, hollow, or “sea sponge” PtNi/C nanoalloys, and solid Ni-core@Pt-shell/C nanoparticles. These nanostructures were characterized by transmission and scanning transmission electron microscopy, X-ray energy dispersive spectroscopy, synchrotron wide-angle X-ray scattering (WAXS), atomic absorption spectroscopy, and electrochemical techniques. Their electrocatalytic activities for the ORR were determined and structure–activity relationships established. The results showed the following: (i) The compression of the Pt lattice by ca. 15 atom % Ni provides mild ORR activity enhancement in comparison to pure Pt/C. (ii) Highly defective PtNi/C nanostructures feature up to 9.3-fold enhancement of the ORR specific activity over a commercial Pt/C material with similar crystallite size. (iii) The enhancement of the ORR kinetics can be ascribed to the presence of structural defects, as shown by two independent parameters: the microstrain determined from WAXS and the average COads electrooxidation potential (μ1p>CO p>) determined from COads stripping measurements. This work indicates that, at fixed Ni content, ORR activity can be tuned by nanostructuring and suggests that targeting structural disorder is a promising approach to improve the electrocatalytic properties of mono- or bimetallic nanocatalysts.