Constructing abundant interfaces by decorating MoP quantum dots on CoP nanowires to induce electronic structure modulation for enhanced hydrogen evolution reaction.

Interface engineering is a method of enhancing catalytic activity while maintaining a material's surface properties. Thus, we explored the interface effect mechanism via a hierarchical structure of MoP/CoP/Cu3P/CF. Remarkably, the heterostructure MoP/CoP/Cu3P/CF demonstrates an outstanding overpotential of 64.6 mV at 10 mA cm-2 with a Tafel slope of 68.2 mV dec-1 in 1 M KOH. DFT calculations indicate that the MoP/CoP interface in the catalyst exhibited the most favorable H* adsorption characteristics (-0.08 eV) compared to the pure phases of CoP (0.55 eV) and MoP (0.22 eV). This result can be attributed to the apparent modulation of electronic structures within the interface domains. Additionally, the CoCH/Cu(OH)2/CF‖MoP/CoP/Cu3P/CF electrolyzer demonstrates excellent overall water splitting performance, achieving 10 mA cm-2 in 1 M KOH solution with a modest voltage of only 1.53 V. This electronic structure adjustment via interface effects provides a new and efficient approach to prepare high-performance hydrogen production catalysts.

Effect of yttrium content in the La2-xYxMgNi9 battery anode alloys on the structural, hydrogen storage and electrochemical properties.

The present work focuses on the studies of influence of yttrium on the crystal structure, hydrogenation properties and electrochemical behaviors of the PuNi3-type La2-xYxMgNi9 (x = 0.25; 0.50; 0.75; and 1.00) intermetallic alloys used as anodes of the Ni-MH batteries where up to 1/2 part of lanthanum was replaced by yttrium. X-ray diffraction studies revealed that all studied alloys are two-phase and contain PuNi3-type AB3 intermetallics (major phase) and Gd2Co7-type A2B7-3R compounds (secondary phase). Unit cell constants and cell volumes for the crystal structures of the AB3 intermetallics linearly decrease following an increase in Y content. Interestingly, in the LaMgNi4 Laves type structure layer yttrium occupies not only the 6c site, but also partially fills the 3a site in the LaNi5 layer. Neutron diffraction studies confirmed that the saturated La1.5Y0.5MgNi9D12.4 hydride containing approximately 1 at. H/at. Me, crystallizes with a trigonal unit cell (space group R3̄m; a = 5.3681(2) Å, c = 26.437(4) Å) and is formed via an anisotropic expansion of the original intermetallic lattice. The studied hybrid structure is composed of LaNi5D5.2 and LaMgNi4D7.2 slabs with a similar hydrogen content. Interestingly, the H-caused expansion of the AB2 and AB5 layers is slightly uneven (23.2% and 27.7%, respectively). In the whole broad substitution range of yttrium for lanthanum, La2-xYxMgNi9 alloys, independent on the content of Y, form intermetallic hydrides with a high reversible hydrogen storage capacity of ∼1.5 wt% H, while the properties of the obtained hydrides are directly related to the substitution extent Y → La. Indeed, the most rich in yttrium LaYMgNi9 alloy at 20 °C shows a more than 10 times higher equilibrium pressure of hydrogen desorption as compared to the alloy with the smallest Y content, La1.75Y0.25MgNi9. A partial substitution of Y for La increases the electrochemical discharge capacity of La2.25Y0.75MgNi9 alloy to reach ∼450 mA h g-1 at a discharge current density of 10 mA g-1. The addition of Y greatly improves the electrochemical cycling performance, with remaining electrochemical capacity of up to 60% of the initial value, after performing 500 cycles, and is much superior as compared to the Y-free La2MgNi9-type anode. Thus, tailoring yttrium content in the alloys allows improvements of the performance of the studied alloys used as hydrogen storage and battery electrode materials.

A Theoretical Study of Fe Adsorbed on Pure and Nonmetal (N, F, P, S, Cl)-Doped Ti3C2O2 for Electrocatalytic Nitrogen Reduction.

The possibility of using transition metal (TM)/MXene as a catalyst for the nitrogen reduction reaction (NRR) was studied by density functional theory, in which TM is an Fe atom, and MXene is pure Ti3C2O2 or Ti3C2O2-x doped with N/F/P/S/Cl. The adsorption energy and Gibbs free energy were calculated to describe the limiting potentials of N2 activation and reduction, respectively. N2 activation was spontaneous, and the reduction potential-limiting step may be the hydrogenation of N2 to *NNH and the desorption of *NH3 to NH3. The charge transfer of the adsorbed Fe atoms to N2 molecules weakened the interaction of N≡N, which indicates that Fe/MXene is a potential catalytic material for the NRR. In particular, doping with nonmetals F and S reduced the limiting potential of the two potential-limiting steps in the reduction reaction, compared with the undoped pure structure. Thus, Fe/MXenes doped with these nonmetals are the best candidates among these structures.

Freezing of Lennard-Jones fluid on a patterned substrate.

Using molecular dynamics simulations, we study freezing of Lennard-Jones particles at commensurate substrate with triangular pattern. Throughout the box particles freeze onto the substrate and form close-packed layers. For the moderately attractive substrates, an intermediate hexatic phase between liquid and crystal is detected in the first two layers where the hexatic-solid freezing process is continuous while, counterintuitively, the liquid-hexatic process is of first order. Moreover, we observe that liquid-hexatic and hexatic-solid transitions shift towards higher temperatures with the attraction strength increasing. By contrast, the liquid-hexatic transition shifts faster than the hexatic-solid process, significantly widening the temperature range of the hexatic phase. When this phenomenon appears, freezing in the bulk always proceeds through a first-order transition at the same temperature. In addition, changes in the average structural order (three-dimensional) of the layers indicate that freezing processes in layers near substrates seem to cost the structural order of the bulk particles in their vicinity, and an intermediate prestructural cloud of medium-ordered particles is always observed before the layering freezing.

Wall-induced phase transition controlled by layering freezing.

Molecular dynamics simulations of the Lennard-Jones model are used to study phase transitions at a smooth surface. Our motivation is the observation that the existence of an attractive wall facilitates crystallization. To investigate how this wall influences phase transitions, the strength of wall-particle interaction is varied in our studies. We find that the phase behavior depends on the strength parameter α, i.e., the ratio between wall-particle and the particle-particle attraction strength. Three critical values of the ratio, namely, αp, αw, and αc, are used to define the qualitative nature of the phase behaviors at a smooth surface. Some interesting phenomena due to the increase of α are observed. First, a set of close-packed planes, i.e., {111} planes in fcc structures or {0001} planes in hcp structures, are "rotated" from intersecting to parallel to the wall when α = αp; second, the layering phase transition close to the wall antecedes that of the bulk when α = αw. Finally, the first-order phase transition in the first two layers is supplanted by a continuous phase transition when α = αc, which to some extent can be treated as a quasi-two-dimensional process. We find that bulk freezing always discontinuously occurs through a first-order phase transition, and seems to be isolated from the freezing process occurring close to the attractive surfaces. Moreover, during the heating process, we observe minimal dependence at a strongly attractive surface.