Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems.

Recent years have seen an increasing research effort focused on nanoscaling of metal borides, a class of compounds characterized by a variety of crystal structures and bonding interactions. Despite being subject to an increasing number of studies in the application field, comprehensive studies of the size-dependent structural changes of metal borides are limited. In this work, size-dependent microstructural analysis of the VB 2 nanocrystals prepared by means of a size-controlled colloidal solution synthesis is carried out using X-ray powder diffraction. The contributions of crystallite size and strain to X-ray line broadening is separated by introducing a modified Williamson−Hall method taking into account different reflection profile shapes. For average crystallite sizes smaller than ca. 20 nm, a remarkable increase of lattice strain is observed together with a significant contraction of the hexagonal lattice decreasing primarily the cell parameter c. Exemplary density-functional theory calculations support this trend. The size-dependent lattice contraction of VB 2 nanoparticles is associated with the decrease of the interatomic boron distances along the c-axis. The larger fraction of constituent atoms at the surface is formed by boron atoms. Accordingly, lattice contraction is considered to be a surface effect. The anisotropy of the sizedependent lattice contraction in VB 2 nanocrystals is in line with the higher compressibility of its macroscopic bulk structure along the c-axis revealed by theoretical calculations of the respective elastic properties. Transmission electron microscopy indicates that the VB 2 nanocrystals are embedded in an amorphous matrix. X-ray photoelectron spectroscopy analysis reveals that this matrix is mainly composed of boric acid, boron oxides, and vanadium oxides. VB 2 nanocrystals coated with these oxygen containing amorphous species are stable up to 789°C as evidenced by thermal analysis and temperature dependent X-ray diffraction measurements carried out under Ar atmosphere. Electrokinetic measurement indicates that the aqueous suspension of VB 2 nanoparticles with hydroxyl groups on the surface region has a good stability at neutral and basic pH arising from electrostatic stabilization

We report the size-dependent structural, surface, colloidal, and thermal properties of the well-known refractory material titanium diboride prepared at the nanoscale by a sizecontrolled inorganic molten-salt technique. A combined analysis of the powder X-ray diffraction data through a modified Williamson-Hall plot, a size-strain plot, and Rietveld fitting methods indicates that TiB 2 nanocrystals with average crystallite sizes smaller than D ≈ 22 nm prefer to form defects at the titanium site rather than experience strain. The resulting composition is Ti 1-x B 2 [x = 0.03(1)-0.08 (1)]. The size-induced defect formation is accompanied by anisotropic lattice contraction that decreases primarily the cell parameter c. Transmission electron microscopy revealed that the nanocrystals are embedded [a] Physical Chemistry,

Topological aspects of the experimental electron density in TiB 2 reconstructed on base of the multipole model are obtained from high-resolution single-crystal X-ray diffraction data. The features of electron density are compared with quantum chemical calculations and analysed in terms of Quantum Theory of Atoms in Molecules for the interpretation of atomic interactions. In spite of some differences in the Laplacian, both experimental and calculated density confirmed two main bonding interactions. The B-B bond critical point suggests a * Prof. Yu. Grin