Bottom-Up Assembly of Ni₂P Nanoparticles into Three-Dimensional Architectures: An Alternative Mechanism for Phosphide Gelation

The synthesis of Ni₂P nanoparticle three-dimensional architectures using two different approaches is reported. The oxidation-induced sol–gel method involves chemical oxidation of surface phosphorus to form P–O–P linkages between particles in the gel network, similar to the mechanism originally reported for InP nanoparticles. The second method, metal-assisted gelation, occurs by cross-linking of pendant carboxylate functionalities on surface-bound thiolate ligands via metal ions to yield an interconnected particle network. The method of gel network formation can be tuned by changing the surface ligand terminal functionalities and the nature (oxygen-transferring or non-oxygen-transferring) of the oxidant. Both methods produce porous, high surface area materials with thermal stabilities above 400 °C

A New Crystalline LiPON Electrolyte: Synthesis, Properties, and Electronic Structure

The new crystalline compound, Li2PO2N, was synthesized using high temperature solid state methods starting with a stoichiometric mixture of Li2O, P2O5, and P3N5. Its crystal structure was determined ab initio from powder X-ray diffraction. The compound crystallizes in the orthorhombic space group Cmc2(1) (# 36) with lattice constants a = 9.0692(4) angstrom, b = 53999(2) angstrom, and c = 4.6856(2) angstrom. The crystal structure of SD-Li2PO2N consists of parallel arrangements of anionic chains formed of corner sharing (PO2N2) tetrahedra. The chains are held together by Li+ cations. The structure of the synthesized material is similar to that predicted by Du and Holzwarth on the basis of first principles calculations (Phys. Rev. B 81,184106 (2010)). The compound is chemically and structurally stable in air up to 600 degrees C and in vacuum up to 1050 degrees C. The Arrhenius activation energy of SD-Li2PO2N in pressed pellet form was determined from electrochemical impedance spectroscopy measurements to be 0.6 eV, comparable to that of the glassy electrolyte LiPON developed at Oak Ridge National Laboratory. The minimum activation energies for Li ion vacancy and interstitial migrations are computed to be 0.4 eV and 0.8 eV, respectively. First principles calculations estimate the band gap of SD-Li2PO2N to be larger than 6 eV. (C) 2013 Elsevier B.V. All rights reserved

Effect of Synthetic Levers on Nickel Phosphide Nanoparticle Formation: Ni₅P₄ and NiP₂

Due to their unique catalytic, electronic, and redox processes, Ni₅P₄ and NiP₂ nanoparticles are of interest for a wide-range of applications from the hydrogen evolution reaction to energy storage (batteries); yet synthetic approaches to these materials are limited. In the present work, a phase-control strategy enabling the arrested-precipitation synthesis of nanoparticles of Ni₅P₄ and NiP₂ as phase-pure samples using different Ni organometallic precursors and trioctylphosphine (TOP) is described. The composition and purity of the product can be tuned by changing key synthetic levers, including the Ni precursor, the oleylamine (OAm) coordinating solvent and TOP concentrations, temperature, time, and the presence or absence of a moderate temperature soak step to facilitate formation of Ni and/or Ni–P amorphous nanoparticle intermediates. Notably, the 230 °C intermediate step favors the ultimate formation of Ni₂P and hinders further phosphidation to form Ni₅P₄ or NiP₂ as phase-pure products. In the absence of this step, increasing the P/Ni ratio (13–20), reaction temperature (350–385 °C), and time (10–48 h) favors more P-rich phases, and these parameters can be adjusted to generate either Ni₅P₄ or NiP₂. The phase of the obtained particles can also be tuned between pure Ni₂P to Ni₅P₄ and NiP₂ by simply decreasing the OAm/TOP ratio and/or changing the nickel precursor (nickel­(II)­acetylacetonate, nickel­(II)­acetate tetrahydrate, or bis­(cyclooctadiene)­nickel(0)). However, at high concentrations of OAm, the product formed is the same regardless of Ni precursor, suggesting the formation of a uniform Ni intermediate (an Ni-oleylamine complex) under these conditions that is responsible for product distribution. Intriguingly, under the extreme phosphidation conditions required to favor Ni₅P₄ and NiP₂ over Ni₂P (large excess of TOP), the 20–30 nm crystallites assemble into supraparticles with diameters of 100–500 nm. These factors are discussed in light of a comprehensive synthetic scheme utilized to control P incorporation in nickel phosphides

Nb-doped TiO2/carbon composite supports synthesized by ultrasonic spray pyrolysis for proton exchange membrane (PEM) fuel cell catalysts

In this paper we report the use of both ultrasonic spray pyrolysis and microwave-assisted polyol reduction methods to synthesize Nb-doped TiO2/carbon (25 wt% Nb0.07Ti0.93O2/75 wt% carbon) composite supports and Pt0.62Pd0.38 alloy catalysts, respectively. The physicochemical properties of the synthesized supports and their Pt0.62Pd0.38 supported catalysts are evaluated using several methods including XRD, TEM, BET surface area analysis, TGA, as well as ICP-MS elemental analysis. The electronic conductivities and thermal/chemical stabilities of the supports are also evaluated with respect to their possible use as catalyst supports. Electrochemical measurements for oxygen reduction activity of the Pt0.62Pd0.38 alloy catalysts supported on oxide/carbon composites are also carried out in order to check their suitability for possible PEM fuel cell applications. The results show that 20wt%Pt0.62Pd0.38/25 wt%(Nb0.07Ti0.93O2)-75 wt%C catalysts exhibit enhanced mass activities compared to those of commercially available 48wt% Pt/C and home-made 20wt% Pt62Pd38/C catalysts.Peer reviewed: YesNRC publication: Ye