Zhijian Wu

MXenes are two‐dimensional carbides and nitrides with the formula of M _{n +1} X _n and have attracted increasing interest in diverse fields. In this study, the structural, electronic, and mechanical properties of M ₂ X (M = Zr, Hf; X = C, N) have been studied by using the first principles method. The ideal strain–stress curves in response to the tensile strain under uniaxial and biaxial tension have been evaluated. The results indicated that all the studied structures are metallic and stable both mechanically and dynamically. The hybridization between Zr 4 d (Hf 5 d ) and N 2 p orbitals lies lower in energy than that between Zr 4 d (Hf 5 d ) and C 2 p orbitals. M ₂ N is relatively stiffer than M ₂ C due to the large Young's modulus and shear modulus, in which Hf ₂ N has the best mechanical performance. This is also confirmed by the strain–stress curves, where Hf ₂ N has the highest ideal strength (41.9 GPa) and extended critical strain (13%). In addition, the shear modulus and Young's modulus are also the largest for Hf ₂ N. Therefore, the improved elastic properties and high critical strain make Hf ₂ N suited for applications in such as flexible devices.

Sustainable hydrogen production via durable direct seawater electrolysis enabled by the synergistic effect between p-block M and active site Ru.

The electrochemical nitrate reduction reaction (NO₃RR) offers a sustainable route for ambient ammonia synthesis. While metal-nitrogen-carbon (M-N-C) single-atom catalysts have emerged as promising candidates for the NO₃RR, the structure-activity relations underlying their catalytic behavior remain to be elucidated. Through systematic analysis of reported experimental data and pH-field coupled microkinetic modeling on a reversible hydrogen electrode (RHE) scale, we reveal that the coordination-dependent activity originates from distinct scaling relations governed by metal-intermediate interactions. M-N-Pyrrolic catalysts generally demonstrate higher turnover frequencies for ammonia production than M-N-Pyridinic catalysts. Meanwhile, the adsorption and protonation of nitrate, which is a step often dismissed and/or assumed to be simultaneous in many previous reports, are identified to be the rate-determining step (RDS) in the NO₃RR. Remarkably, our subsequent experimental validation confirms the theoretical predictions under both neutral and alkaline conditions. This study offers a comprehensive mechanistic framework for interpreting the electrocatalytic activity of M-N-C catalysts in the NO₃RR, showing that a classical thermodynamic "limiting-potential model" is not sufficiently accurate to capture the RDS and the catalytic performance trends of different materials (even on M-N-Pyrrolic and M-N-Pyridinic catalysts). These findings provide brand new insights into the reaction mechanism of the NO₃RR and establish fundamental design principles for electrocatalytic ammonia synthesis.

The adsorption separation and extraction of low-concentration boron from salt-lake brine have great significance. Magnetic separation avoids the problem of adsorbent granulation and improves the usage efficiency. The silicon-based adsorbents have attracted interest due to their superior acid and alkali resistance, in which polyhydroxy graphene enhances the adsorption of boron ions. Herein different boron adsorbents, derived by magnetic separation, were developed and characterized by SEM, TEM, XPS, VSM, FT-IR, and XRD analysis. The adsorption-desorption performance of boron adsorbents with different compositions was evaluated. The isotherms and kinetics parameters of the boron extraction were evaluated based on adsorption-desorption tests. The graphene-based magnetic adsorbent (Go-Fe₃O₄@SiO₂@mSiO₂-Glu) registered a high boron adsorption capacity of 23.90 mg/g at pH = 9 in the boron solution and 24.84 mg/g for East Taigener salt-lake brine. The Na⁺, Mg²⁺, Ca²⁺, and Cl⁻ ions have little interference with the boron adsorption. The adsorbents exhibit magnetic separation performance and good cycle life. The results showed that acid-alkali desorption solution has little effect on the adsorbents, and the composite of graphene enhances the adsorption of boron ions. The adsorbents developed in this study are promising to recover boron from low-concentration boron-containing salt-lake brines.