Tailoring the near‐surface composition of Pt‐based alloy can optimize the surface chemical properties of a nanocatalyst and further improve the sluggish H2 electrooxidation performance in an alkaline electrolyte. However, the construction of alloy nanomaterials with a precise near‐surface composition and smaller particle size still needs to overcome huge obstacles. Herein, ultra‐small PtRu3 binary nanoparticles (<2 nm) evenly distributed on porous carbon (PtRu3/PC), with different near‐surface atomic compositions (Pt‐increased and Ru‐increased), are successfully synthesized. XPS characterizations and electrochemical test confirm the transformation of a near‐surface atomic composition after annealing PtRu3/PC‐300 alloy; when annealing in CO atmosphere, forming the Pt‐increased near‐surface structure (500 °C), while the Ru‐increased near‐surface structure appears in an Ar heat treatment process (700 °C). Furthermore, three PtRu3/PC nanocatalysts all weaken the hydrogen binding strength relative to the Pt/PC. Remarkably, the Ru‐increased nanocatalyst exhibits up to 38.8‐fold and 9.2‐fold HOR improvement in mass activity and exchange current density, compared with the Pt/PC counterpart, respectively. CO‐stripping voltammetry tests demonstrate the anti‐CO poisoning ability of nanocatalysts, in the sequence of Ru‐increased ≥ PtRu3/PC‐300 > Pt‐increased > Pt/PC. From the perspective of engineering a near‐surface structure, this study may open up a new route for the development of high‐efficiency electrocatalysts with a strong electronic effect and oxophilic effect.
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/PCacid 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.
This paper presents a strain gauge using the mechanical-optical coupling method. The Si-based optical microring resonator was employed as the sensing element, which was embedded on the microcantilevers. The experimental results show that applying external strain triggers a clear redshift of the output resonant spectrum of the structure. The sensitivity of 93.72 pm/MPa was achieved, which also was verified using theoretical simulations. This paper provides what we believe is a new method to develop micro-opto-electromechanical system (MOEMS) sensors.
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