Organic Donor-Acceptor-Donor Trimers Nanoparticles Stabilized by Amphiphilic Block Copolymers for Photocatalytic Generation of H2.

Photocatalytic generation of H2 via water splitting emerges as a promising avenue for the next generation of green hydrogen due to its low carbon footprint. Herein, a versatile platform is designed to the preparation of functional π-conjugated organic nanoparticles dispersed in aqueous phase via mini-emulsification. Such particles are composed of donor-acceptor-donor (DAD) trimers prepared via Stille coupling, stabilized by amphiphilic block copolymers synthesized by reversible addition-fragmentation chain transfer polymerization. The hydrophilic segment of the block copolymers will not only provide colloidal stability, but also allow for precise control over the surface functionalization. Photocatalytic tests of the resulting particles for H2 production resulted in promising photocatalytic activity (≈0.6 mmol g-1 h-1). This activity is much enhanced compared to that of DAD trimers dispersed in the water phase without stabilization by the block copolymers.

Kraft Black Liquor as a Carbonaceous Source for the Generation of Porous Monolithic Materials and Applications toward Hydrogen Adsorption and Ultrastable Supercapacitors.

High internal phase emulsions (HIPEs) have templated self-standing porous carbonaceous materials (carboHIPEs) while employing Kraft Black Liquor, a paper milling industry byproduct, as a carbon precursor source. As such, the starting emulsion has been prepared through a laboratory-made homogenizer, while native materials have been characterized at various length scales either with Raman spectrometry, X-ray diffraction (XRD), mercury intrusion porosimetry, and nitrogen absorption. After thermal carbonization, specific surface areas ranging from ∼600 m2 g-1 to 1500 m2 g-1 have been reached while maintaining a monolithic character. Despite a poor graphitization yield, the carbonaceous materials offer good electronic transport properties, reaching 31 S m-1. When tested toward energy storage applications, the native unwashed materials revealed a hydrogen storage of 0.07 wt % at 40 bar and room temperature (RT), while hydrogen retention is reaching 0.37 wt % at 40 bar and RT for the washed sample. When employed as supercapacitor electrodes, these carbonaceous foams are able to deliver high capacities of ∼140 F/g at 1 A/g, thereby matching the ones obtained from a commercial carbon reference, while additionally providing a restored remnant capacity of 120 F/g at 2 A/g over 5000 cycle numbers.

The Mg-Rich Phase NdNiMg15: Structural and Magnetic Properties.

The intermetallic NdNiMg15 is the Mg-richest phase (more than 88 atom % of Mg) discovered in the Mg-Nd-Ni system. Its structure was determined by X-ray diffraction on single crystal with the following crystal data: tetragonal system, P4/ nmm, Z = 2, a = 10.0602(1) Å, c = 7.7612(2) Å, dcalc = 2.40 g·cm-3. Its structure is made of a three-dimensional framework of magnesium atoms showing channels filled by one-dimensional chain consisting of alternating Nd and Ni atoms along the c-axis. Anti-ferromagnetic ordering was observed with TN = 9 K, which is remarkably high considering the long distances between magnetic atoms, that is, Nd atoms. The effective magnetic moment µeff is equal to 3.58 µB, which is consistent with magnetic Nd3+ ions and weakly or nonmagnetic Ni atoms. Below TN, the M( H) curves show field-induced metamagnetic transitions at critical fields increasing with decreasing temperatures. The magnetic structure of NdNiMg15 was determined from neutron powder diffraction data by considering the propagation vector k = (1/2 1/2 0). This magnetic structure consists in ferromagnetic chains along the c-axis of Nd atoms carrying moments, only separated by Ni atoms. The chains are ferromagnetically coupled within planes perpendicular to the [110] direction, and these planes are anti-ferromagnetically coupled to neighboring planes forming a checkerboard-like magnetic structure.

Hydrogen Insertion in the Intermetallic GdScGe: A Drastic Reduction of the Dimensionality of the Magnetic and Transport Properties.

Intermetallic phases have been investigated with respect to their ability to accept small atoms in interstitial sites without changing the host structure. Among those, the intermetallic compounds crystallizing in the tetragonal CeScSi-type structure are able to absorb hydrogen atoms. These compounds are of particular interest because they can show electride-like character and, therefore, can be exploited as new catalysts. Here we report the case of GdScGe which uptakes hydrogen at 623 K and under a H2 gas pressure between 0.5 and 4 MPa. The formation of the hydride GdScGeH, with H atoms entering into the [Gd4] tetrahedra, preserves the host structure but induces an anisotropic volume expansion with a strong increase of the c-parameter and a slight decrease of the a-parameter. Interestingly, we show for the first time for this family of materials that hydrogen insertion reduces the dimensionality of the magnetic and transport properties from 3D to quasi-2D which results in a vanishing of the ferromagnetic order ( TC = 350 K for GdScGe) and a change of the metallic conduction behavior to a nonmetallic one. As evidenced by density functional theory calculations, such drastic effects are accounted for through the Gd-H chemical bonding effect and the oxidizing effect of H whereas the volume expansion plays only a minor role.

NdNiMg5, a new magnesium-rich phase with an unusual structural type.

The new intermetallic NdNiMg5 was discovered during the study of the Mg-rich part of the Mg-Nd-Ni system. It was synthetized by melting of the constituent elements in a sealed tantalum tube with subsequent annealing. Its structure was determined by X-ray diffraction on a single crystal. Crystal data: orthorhombic system, Cmcm, Z = 4, a = 4.4799(2) Å, b = 9.9827(3) Å, c = 13.7854(10) Å, d(calc) = 3.49 g·cm(-3). Its structure is made of infinite layers of Mg atoms that form blocks stacked along the c axis. These blocks, with a close-packed array of Mg atoms, are separated by infinite NiNd layers and connected through short Mg-Mg bonds. In the NiNd layer, the Ni and Nd atoms form an ordered graphite-type network. Antiferromagnetic ordering is observed with T(N) = 12 K, and the effective magnetic moment µeff is equal to 3.89(1) µB.

On the strongly correlated electron hydride Ce2Ni2MgH7.7.

The intermediate valence compound Ce 2Ni 2Mg absorbs irreversibly hydrogen when exposed under 1 MPa of H 2 pressure at room temperature. The resulting hydride Ce 2Ni 2MgH 7.7 is stable in air and crystallizes as the deuteride La 2Ni 2MgD 8 in a monoclinic structure (space group P2 1 /c) with the unit cell parameters a = 11.7620(2), b = 7.7687(2), and c = 11.8969(2) A and beta = 92.75 degrees . The H-insertion in Ce 2Ni 2Mg induces a structural transition from a tetragonal to a monoclinic symmetry with an unit cell volume expansion Delta V m/ V m approximately 24.9%. The investigation of the hydride by magnetization, electrical resistivity, and specific heat measurements indicates a change from an intermediate valence behavior to a non-magnetic strongly correlated electron system. This transition results from a change of the coupling constant J cf between 4f(Ce) and conduction electrons induced by the hydrogenation.