A series of Pt/C electrocatalysts with average Pt particle size of 1.8, 2.3, 3.4, 3.8, 4.7, and 5.8 nm are synthesized by reducing platinum(II) acetylacetonate with 1,2-hexadecanediol in the presence of long-chain carboxylic acid and alkylamine stabilizing agents. The prepared materials are characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray (EDX) spectrometry. The face-centered cubic structure of Pt in the materials is evident from XRD. Good spatial distribution of spherical shaped Pt nanoparticles is seen from the HRTEM images. The presence of Pt and C is observed from the EDX analysis. Linear sweep voltammetry (LSV), rotating disk electrode (RDE), and single-cell proton exchange membrane fuel cell (PEMFC) measurements are conducted to evaluate the electrocatalytic activity of Pt/C electrocatalysts. Electrochemical measurements indicate the good hydrogen oxidation and oxygen reduction activity for 1.8 and 3.4 nm size Pt particles, respectively. Kinetic analysis by RDE voltammetry reveals that the number of electrons transferred in hydrogen oxidation (HOR) and oxygen reduction (ORR) processes on 1.8 and 3.4 nm size Pt nanoparticles is 2 and 4, respectively. The high performance Pt/C anode and cathode are then used to fabricate a membrane-electrode assembly (MEA) and tested in a PEMFC. A maximum power density of 625, 760, and 1030 mW/cm 2 is observed at 333, 343, and 353 K, respectively.
Tri-n-butyl phosphate (TBP), used as the extractant in nuclear fuel reprocessing, shows superior extraction abilities for Pu(IV) over a large number of fission products including Zr(IV). We have applied density functional theory (DFT) calculations to explain this selectivity by investigating differences in electronic structures of Pu(NO3)4·2TBP and Zr(NO3)4·2TBP complexes. On the basis of our quantum chemical calculations, we have established the lowest energy electronic states for both complexes; the quintet is the ground state for the former, whereas the latter exists in the singlet spin state. The calculated structural parameters for the optimized geometry of the plutonium complex are in agreement with the experimental results. Atoms in Molecules analysis revealed a considerable amount of ionic character to M-O{TBP} and M-O{NO3} bonds. Additionally, we have also investigated the extraction behavior of TBP for metal nitrates and have estimated the extraction energies to be -73.1 and -57.6 kcal/mol for Pu(IV) and Zr(IV), respectively. The large extraction energy of Pu(IV) system is in agreement with the observed selectivity in the extraction of Pu.
A polyol reduction method is employed to prepare carbon-supported Pt and Pt-M (M ) Fe, Co, and Cr) alloy catalysts by simultaneous reduction and decomposition of metal precursors with 1,2-hexadecanediol in the presence of nonanoic acid and nonylamine protecting agents. The prepared materials are characterized by powder XRD, HRTEM, and EDX. The face-centered cubic structure of Pt in the prepared materials is evident from XRD. Good dispersion of Pt and Pt alloy nanoparticles on the carbon support is seen from the highresolution TEM images. The presence of respective elements with controlled composition is observed from EDX analysis. Electrochemical performance of the prepared materials is investigated by cyclic voltammetry and tested in a single-cell DEFC. The inhibition of formation of (hydr)oxy species on the Pt surface by the presence of alloying elements is observed. Oxygen reduction activity of the Pt-M/C (M ) Fe, Co, and Cr) is found to be ∼1.5 times higher than that of the as-synthesized and commercial Pt/C catalysts. Single-cell DEFC tests indicated the good performance of Pt-M/C (M ) Fe, Co, and Cr) compared with that of the as-synthesized and commercial Pt/C catalysts. The DEFC performance increased in the order Pt/C comm < Pt/C as-syn < Pt-Fe/C < Pt-Co/C ∼ Pt-Cr/C. Stability under DEFC operating conditions for 50 h indicated the good stability of Pt alloys compared with that of Pt catalysts.
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