Ptfe Lab Report

The carbon supported PtFeS catalysts were prepared by a modified polyol method. In brief, 0.3 g carbon (Ketjen-black heat-treated at 2250 °C, SE = 160 m2 g-1) was dispersed in 135 g ethylene glycol. 5.993 g of 8 wt% H2PtCl6 (Umicore; Pt content, 39.8 wt%), 1.874 g of 8 wt% FeCl3. 6H2O (Sigma-Aldrich), and 0.352 g of 8 wt% (NH2)2SC (Sigma-Aldrich) previously mixed in ethylene glycol were added to the dispersion. The pH of the stirred reaction mixture was adjusted to ∼11 using 1 M NaOH dissolved in ethylene glycol. Then, 2.095 g of 50 wt% H2NaPO2.H2O and 1.57 g of 20 wt% hydrazine were added to the reaction mixture. The resulting mixtures were reduced in a microwave reactor at 250 °C for ∼1 h. The reduced resulting product was washed with deionized water 4 times and dried in a freeze dryer. The as-prepared sample was treated with 1 M nitric acid solution to dissolve Fe and S atom on the surface of PtFeS catalyst at room temperature (RT) for 1 h and then washed 4 times with deionized water and dried in a freeze dryer again, thereby obtaining a 38 wt% PtFeS/C catalyst. For the comparison, 37 wt% Pt/C was prepared following the literature procedure [22]. 2.2 Characterization X-ray diffraction (XRD) patterns were obtained using a Philips X’pert Pro X-ray diffractometer equipped with a Cu-Kα source at 40 kV and 40 mA. The crystalline sizes of Pt alloy particles on the carbon supports were calculated from the XRD patterns by using Scherrer’s equation [23]. TEM images and the two-dimensional mapping of each element by scanning transmission electron microscopy (STEM) were obtained using a G2 FE-TEM Tecnai microscope at an accelerating voltage of 200 kV. The content of Pt alloy catalyst in the supported catalysts was obtained by ICP-AES (RF source: Jobin Yvon 2301, 40.68 MHz). X-ray photoelectron spectroscopy (XPS) was performed using an AXIS (Q2000) photoelectron spectrometer equipped with mono-Al-Ka X-ray source operating at 1486.6 eV. Electrochemical performances were obtained by the thin active layer rotating disk electrode method using Nafion® as a binder using a three-electrode electrochemical cell. Cyclic voltammogram (CV) for the ECSA was recorded in the potential range 0.05–1.2 V (vs. normal hydrogen electrode (NHE), a scan rate of 20 mV s-1) at RT in 0.1 M HClO4 solution, saturated with nitrogen by bubbling the N2 gas for 30 min [24]. The ECSA of Pt alloy in the supported catalyst was estimated from the integrated area of the hydrogen desorption region of the CV in the potential range 0.05–0.4 V reported in the literature [25]. The linear scan voltammograms (LSV) for ORR was obtained at RT at a scan rate of 5 mV s-1 in 0.1 M HClO4 solution, saturated with oxygen by bubbling pure oxygen gas for 30 min. In order to evaluate the electrochemical stabilities of the Pt and PtFeS catalysts, the accelerated durability test (ADT) was performed by cycling cathode potential between 0.6 and 1.0 V vs. RHE at a sweep rate 50 mV/s for 3,000 cycles during the CV measurement. LSV for the ORR and CV were recorded at before and after 3,000 cycles. 2.3 …show more content…
3a–b. All the catalyst nanoparticles are uniformly distributed on the carbon support with a graphitic layer. Although the average particle size of Pt and PtFeS catalysts, obtained from more than 20 nanoparticles in their corresponding TEM images, is 3.12 and 3.37 nm, respectively, a clear difference in the morphology was observed. The TEM image of Pt catalyst shows spherical shaped Pt nanoparticles, in contrast to PtFeS catalyst exhibiting a mixture of spherical and rod-like morphology. The rod-typed morphology observed in the PtFeS catalyst indicates that nanoparticles are horizontally overgrown at the edge of preformed nanoparticles by the decomposition of thiol compound. The mapping of the electron energy-loss spectroscopy (EELS) using a scanning transmission electron microscope (STEM) was performed to reveal the distribution of Pt, Fe, and S elements in a representative single nanoparticle of the PtFeS catalyst as shown in Fig. 3c. Overlapping the mapping of Pt, Fe, and S EEL signals from a single nanoparticle validates the core–shell structure, indicating the formation of sulfur and iron atom-rich core and Pt-rich shell. Those structures could form more favorable compressive strain on Pt because of the contraction by binary alloy of Fe and S in the core. The apparent positive effect of PtFeS core–shell structure enables convenient tuning of the geometric properties of Pt in the alloy