A new transition metal diphosphide α-MoP2 synthesized by a high-temperature and high-pressure technique

Monoclinic $\alpha $-MoP$_{2}$, with the OsGe$_{2}$-type structure (space group $C2/m$, $Z = 4$) and lattice parameters $a = 8.7248(11) $ Å, $b = 3.2322(4) $ Å, $c = 7.4724(9) $ Å, and $\beta =119.263^\circ $, was synthesized under a pressure of 4 GPa at a temperature between 1100 ${^\circ}$C and 1200 ${^\circ}$C. The structure of $\alpha $-MoP$_{2}$ and its relationship to other transition metal diphosphides are discussed. Surprisingly, the ambient pressure phase orthorhombic $\beta $-MoP$_{2}$ (space group Cmc2$_{1}$) is denser in structure than $\alpha $-MoP$_{2}$. Room-temperature high-pressure x-ray diffraction studies exclude the possibility of phase transition from $\beta $-MoP$_{2}$ to $\alpha $-MoP$_{2}$, suggesting that $\alpha $-MoP$_{2}$ is a stable phase at ambient conditions; this is also supported by the total energy and phonon calculations.     

MoP在高压下的电子,声子和电声耦合性质的第一性原理计算

使用第一性原理方法,研究了拓扑材料MoP在高压下的电子结构和晶格动力学行为.高压下MoP的晶体结构和费米面附近的电子能带相对稳定,但是声子能谱以及电声子耦合参数随着压强的增大有明显的变化.声子谱中高频光学支逐渐硬化,低频声学支中也有部分出现明显软化,体系的电声子耦合随压强的增大而逐步变强,导致超导转变温度从常压下的零提高到30 GPa时的0.16 K,最后在50 GPa时提高到1.21 K,与实验的变化趋势基本一致.研究揭示了高压下MoP中出现的超导现象主要是电声子耦合造成的,为理解实验观测到的拓扑超导共存现象提供了一定的理论支持.     

A novel route to the synthesis of H-ZSM-5-supported MoP and Ni2P phosphides

Abstract

In this work, we report a novel synthesis of H-ZSM-5-supported MoP and Ni₂P phosphides. The current approach uses a cinnamic strong alkali anion exchange resin (D201) as a reductant instead of H₂ and employs an inert gas as a feed gas. The formation mechanism was proposed by thermogravimetry-mass spectrometry (TG-MS) and X-ray diffraction (XRD). D201 resin is carbonized to produce C and H₂, and a small portion of Mo/Ni and PO_x species are firstly reduced by H₂ and then the rest of the metal and PO_x species are reduced by C, to produce MoP/Ni₂P on the H-ZSM-5, with the release of H₂O, CO and CO₂.     

Synergistically Interactive Pyridinic‐N–MoP Sites: Identified Active Centers for Enhanced Hydrogen Evolution in Alkaline Solution

For electrocatalysts for the hydrogen evolution reaction (HER), encapsulating transition metal phosphides (TMPs) into nitrogen‐doped carbon materials has been known as an effective strategy to elevate the activity and stability. Yet still, it remains unclear how the TMPs work synergistically with the N‐doped support, and which N configuration (pyridinic N, pyrrolic N, or graphitic N) contributes predominantly to the synergy. Here we present a HER electrocatalyst (denoted as MoP@NCHSs) comprising MoP nanoparticles encapsulated in N‐doped carbon hollow spheres, which displays excellent activity and stability for HER in alkaline media. Results of experimental investigations and theoretical calculations indicate that the synergy between MoP and the pyridinic N can most effectively promote the HER in alkaline media.