Converting bimetallic M (M = Ni, Co, or Fe)-Sn nanoparticles into phosphides: a general strategy for the synthesis of ternary metal phosphide nanocrystals.

Ternary metal tin phosphides are promising candidates for electrochemical or catalytic applications. Nevertheless, their synthesis, neither as bulk nor nanomaterials is well investigated in the literature. Here, we describe a general synthetic strategy to convert bimetallic M-Sn (M = Ni, Co, and Fe) nanoparticles to ternary metal phosphides by decomposition of tributylphosphine at 300 °C. At high phosphorus concentrations, Ni3Sn4 nanoparticles convert to hybrid structured Ni2SnP and ß-Sn. The CoSn2 and FeSn2 nanoparticles undergo a phosphorization, too and form hybrid nanocrystals reported here for the first time, containing ternary or binary phosphides. We identified the crystal structure of the nanoparticles via XRD and HRTEM measurements using the diffraction data given for Ni2SnP in literature. We were able to locate the Ni2SnP and ß-Sn crystal structure within the nanoparticles to demonstrate the phase composition of the nanoparticles. By transferring the synthesis to cobalt and iron, we obtained nanoparticles exhibiting similar hybrid structures and ternary element compositions for Co-Sn-P and binary Fe-P and FeSn2 compositions. In the last step, we used the given information to propose a conversion mechanism from the binary M-Sn nanoparticles through phosphorization.

Microstructure degradation of Ni/CGO anodes for solid oxide fuel cells after long operation time using 3D reconstructions by FIB tomography.

Solid oxide fuel cells (SOFCs) are electrochemical conversion devices, which essentially consist of two porous electrodes separated by a dense, oxide ion conducting electrolyte. The performance and the durability of SOFCs strongly depend on the electrode microstructure. In this paper, the impact of a relatively long exposure time (up to 20 000 h) under realistic operation terms (temperature (T) = 850 °C, current density (J) = 190-250 mA cm-2) in the kinetics of microstructural degradation are investigated for porous nickel (Ni)/ceria gadolinium oxide (CGO) anodes, to understand the microstructural evolution in SOFC cermet anodes. A combined system of Focused Ion Beam (FIB) and Scanning Electron Microscope (SEM) tomography was used to analyze various anode microstructures aged during different operating times (2500 h, 15 000 h and 20 000 h). The methodologies of image acquisition as well as the segmentation and the object recognition were improved, offering a reliable quantification of Ni-grain growth, connectivity, tortuosity factor and triple phase boundary length (TPBL). The representative volume element (RVE) was also studied, and its dependence on aging time was confirmed. To construct a volume that can be accurate and representative for the whole sample, the necessary corresponding 3D reconstruction size was adjusted by increasing operating time, in order to suppress the influence of microstructure variation caused by Ni and CGO agglomeration. Statistically significant 3D microstructural changes were observed in the anode by increasing the operating time, including nickel particle size distribution, changes in connectivity of the ceramic part (CGO) and a significant decrease of contiguous triple phase boundary densities. Additional qualitative observations were done in order to gain a complete insight of the degradation phenomena in nickel based cermet anodes.

Manganese oxide phases and morphologies: A study on calcination temperature and atmospheric dependence.

Manganese oxides are one of the most important groups of materials in energy storage science. In order to fully leverage their application potential, precise control of their properties such as particle size, surface area and Mn (x) (+) oxidation state is required. Here, Mn3O4 and Mn5O8 nanoparticles as well as mesoporous α-Mn2O3 particles were synthesized by calcination of Mn(II) glycolate nanoparticles obtained through an economical route based on a polyol synthesis. The preparation of the different manganese oxides via one route facilitates assigning actual structure-property relationships. The oxidation process related to the different MnO x species was observed by in situ X-ray diffraction (XRD) measurements showing time- and temperature-dependent phase transformations occurring during oxidation of the Mn(II) glycolate precursor to α-Mn2O3 via Mn3O4 and Mn5O8 in O2 atmosphere. Detailed structural and morphological investigations using transmission electron microscopy (TEM) and powder XRD revealed the dependence of the lattice constants and particle sizes of the MnO x species on the calcination temperature and the presence of an oxidizing or neutral atmosphere. Furthermore, to demonstrate the application potential of the synthesized MnO x species, we studied their catalytic activity for the oxygen reduction reaction in aprotic media. Linear sweep voltammetry revealed the best performance for the mesoporous α-Mn2O3 species.

Synthesis and electrochemical performance of surface-modified nano-sized core/shell tin particles for lithium ion batteries.

Tin is able to lithiate and delithiate reversibly with a high theoretical specific capacity, which makes it a promising candidate to supersede graphite as the state-of-the-art negative electrode material in lithium ion battery technology. Nevertheless, it still suffers from poor cycling stability and high irreversible capacities. In this contribution, we show the synthesis of three different nano-sized core/shell-type particles with crystalline tin cores and different amorphous surface shells consisting of SnOx and organic polymers. The spherical size and the surface shell can be tailored by adjusting the synthesis temperature and the polymer reagents in the synthesis, respectively. We determine the influence of the surface modifications with respect to the electrochemical performance and characterize the morphology, structure, and thermal properties of the nano-sized tin particles by means of high-resolution transmission electron microscopy, x-ray diffraction, and thermogravimetric analysis. The electrochemical performance is investigated by constant current charge/discharge cycling as well as cyclic voltammetry.