Discovery of Self-Assembled 2D Ru/Si Superlattices Boosting Hydrogen Evolution.

2D heterostructuring is a versatile methodology for designing nanoarchitecture catalytic systems that allow for reconstruction and modulation of interfaces and electronic structures. However, catalysts with such structures are extremely scarce due to limited synthetic strategies. Here, a highly ordered 2D Ru/Si/Ru/Si… nano-heterostructures (RSHS) is reported by acid etching of the LaRuSi electride. RSHS shows a superior electrocatalytic activity for hydrogen evolution with an overpotential of 14 mV at 10 mA cm-2 in alkaline media. Both experimental analysis and first-principles calculations demonstrate that the electronic states of Ru can be tuned by strong interactions of the interfacial Ru-Si, leading to an optimized hydrogen adsorption energy. Moreover, due to the synergistic effect of Ru and Si, the energy barrier of water dissociation is significantly reduced. The well-organized superlattice structure will provide a paradigm for construction of efficient catalysts with tunable electronic states and dual active sites.

Dipole Coupling Accelerated H2 O Dissociation by Magnesium-Based Intermetallic Catalysts.

The water (H2 O) dissociation is critical for various H2 O-associated reactions, including water gas shift, hydrogen evolution reaction and hydrolysis corrosion. While the d-band center concept offers a catalyst design guideline for H2 O activation, it cannot be applied to intermetallic or main group elements-based systems because Coulomb interaction was not considered. Herein, using hydrolysis corrosion of Mg as an example, we illustrate the critical role of the dipole of the intermetallic catalysts for H2 O dissociation. The H2 O dissociation kinetics can be enhanced using Mgx Mey (Me=Co, Ni, Cu, Si and Al) as catalysts, and the hydrogen generation rate of Mg2 Ni-loaded Mg reached 80 times as high as Ni-loaded Mg. The adsorbed H2 O molecules strongly couple with the Mg-Me dipole of Mgx Mey , lowering the H2 O dissociation barrier. The dipole-based H2 O dissociation mechanism is applicable to non-transition metal-based systems, such as Mg2 Si and Mg17 Al12 , offering a flexible catalyst design strategy for controllable H2 O dissociation.

Antisite-Defects Control of Magnetic Properties in MnSb2Te4.

The intrinsic magnetic topological materials Mn(Sb/Bi)2n+2Te3n+4 have attracted extensive attention due to their topological quantum properties. Although, the Mn-Sb/Bi antisite defects have been frequently reported to exert significant influences on both magnetism and band topology, their formation mechanism and the methods to manipulate their distribution and concentration remain elusive. Here, we present MnSb2Te4 as a typical example and demonstrate that Mn-Sb antisite defects and magnetism can be tuned by controlling the crystal growth conditions. The cooling rate is identified as the primary key parameter. Magnetization and chemical analysis demonstrate that a slower cooling rate would lead to a higher Mn concentration, a higher magnetic transition temperature, and a higher saturation moment. Further analysis indicates that the Mn content at the original Mn site (MnMn, 3a site) varies more significantly with the cooling rate than the Mn content at the Sb site (MnSb, 6c site). Based on experimental observations, magnetic phase diagrams regarding MnMn and MnSb concentrations are constructed. With the assistance of first-principles calculations, it is demonstrated that the Mn-Sb mixing states primarily result from the mixing entropy and the growth kinetics. The present findings offer valuable insights into defects engineering for preparation of two-dimensional quantum materials.

Application of Raman imaging and scanning electron microscopy techniques for the advanced characterization of geological samples.

Raman is an important tool for diagnosing minerals in geoscience. However, smaller magnification of optical microscope assembled in conventional Raman spectroscopy limits the application of Raman in sub-micro and nano scale. Raman imaging and scanning electron microscopy (RISE) combine the advantage of scanning electron microscope and Raman spectroscopy, which can collect the morphology, composition, and structure information in the same micro region of the geological sample in situ. In this paper, we introduce the development and working mechanism of RISE, and carried out some typical applications in different research of geoscience. The purpose of this review is to allow readers to understand the basic principles and application potential of RISE in geoscience. Finally, we briefly point out current challenges faced by this technology and some research directions in the future. HIGHLIGHTS: Raman imaging and scanning electron microscopy as potential method was proposed for the research on geosciences. Common polymorphism and isomorphism were distinguished clearly in situ. A new research route for tiny inclusion and organic matter in situ was developed.

Facile Synthesis of Ti2AC (A = Zn, Al, In, and Ga) MAX Phases by Hydrogen Incorporation into Crystallographic Voids.

While using hydride precursors, such as TiH2, can promote the formation of some MAX phases, the mechanism for this stabilization effect by hydrogen has been unsolved. Herein, we report a facile synthesis method of Ti2AC (A = Zn, Al, In, and Ga) MAX phases using hydrogen as the phase stabilizer at their crystallographic voids. DFT calculations revealed that hydrogen could be incorporated in the center of the Ti3A (A = Zn, Al, Ga, and In) cages of Ti2AC MAX phases. The hydrogen is accommodated as an anion as a result of electron transfer from the surrounding Ti and A to H, leading to the stabilized state through Coulomb interaction between (Ti3A)δ+ and H-. Consequently, high-purity Ti2AC (A = Zn, Al, Ga, and In) was directly synthesized under pressure-less and milder temperature conditions by simply employing TiH2 as the precursor. These findings indicate that utilizing hydrogen could be one of the experimental parameters to facilitate the formation of materials having crystallographic voids.