Revealing the Potential of Ternary Medium-Entropy Alloys as Exceptional Electrocatalysts toward Nitrogen Reduction: An Example of Heusler Alloys

With less energy consumption and environmental pollution, electrochemical ammonia synthesis is regarded as the most promising way to replace the industrial Haber–Bosch process, which greatly contributes to global energy consumption and CO2 emission. At present, the best metal electrocatalyst for N2 fixation is ruthenium although its performance still suffers from a low Faradaic efficiency and a high overpotential. Alloy engineering is a promising way to discover more metal-based electrocatalysts for dinitrogen reduction reaction (N2RR), and almost all reported alloy catalysts so far are binary alloys. In this work, we proposed a large group of ternary alloy electrocatalysts (Heusler alloys) for N2RR and demonstrated their superior catalytic performance. As an example, alloying Ru with Mn and Si led to a reduced Ru–Ru distance on the surface, which facilitates an uncommon horizontal adsorption mode of N2 and results in effective activation of N2 molecules. The theoretical overpotential of N2RR on Ru2MnSi­(100-Ru) is only around 0.28 V, which ranks among the best reported results, and the usage of precious Ru is greatly reduced. Meanwhile, the adsorption of N2 on Ru2MnSi­(100-Ru) was much stronger than that of protons, and it also took less energy to drive N2RR than the hydrogen evolution reaction (HER), making HER less competitive on this catalyst. Considering the successful synthesis of numerous Heusler alloys including the six members mentioned here, our work provided a wider range of practical and excellent N2RR electrocatalysts in terms of both catalytic performance and economical cost

Computational Screening of Transition Metal–Phthalocyanines for the Electrochemical Reduction of Carbon Dioxide

Molecular complexes containing low-cost transition-metal (TM) centers have been extensively studied for the electrochemical reduction of carbon dioxide. Of all the molecular catalysts reported so far, only a few of them are selective for CO2 reduction, and moreover, these catalysts mainly produce carbon monoxide or formic acid. However, molecular catalysts generating highly reduced products such as hydrocarbons are very rare. Herein, we explore the electrocatalytic activity of TM–Phthalocyanine (TM-Pc) by placing different transition metals into the vacant N4 cavity toward the reduction of CO2. By using first-principles calculations, we demonstrate that among all the 3d transition metals used, Chromium−Phthalocyanine (Cr-Pc)–Pc shows excellent performance for converting CO2 to methane with a limiting potential of −0.34 V. In comparison, the limiting potentials for the CO2 reduction reaction (CO2RR) to CH4 for the best catalyst considered so far such as Cu(111) and Cu(211) are −0.93 V and −0.74 V, respectively. Chromium, being a non-noble metal, presents as a promising TM for catalyzing CO2RR. Co-Pc however converts CO2 to methanol with a limiting potential of −0.69 V. This report shows that Pc with different TMs can provide an effective pathway for tuning the catalytic performance of electrocatalysts, which could help in the design of molecular catalysts in the future that will expectantly soon emerge at an industrial scale

Two-Dimensional Janus Antimony Selenium Telluride with Large Rashba Spin Splitting and High Electron Mobility

Janus two-dimensional materials with large Rashba spin splitting and high electron mobility are rarely reported but highly desired for nanoscale spintronics. Herein, using density functional theory calculations, we predicated Janus Sb2SexTe3–x (x = 1 or 2) monolayers simultaneously harboring these fascinating properties. The predicated monolayers are indirect semiconductors with great dynamical, thermal, and mechanical stability. The spin–orbital coupling (SOC) and the out-of-plane asymmetry lead to Rashba spin splitting at the conduction band minimum (CBM), which can be effectively tuned by the small uniaxial strain. The strong band dispersion at the CBM leads to small electron effective mass, consequently enabling a high electron mobility that reaches up to 6816.63 cm2 V–1 s–1. Moreover, Janus Sb2SexTe3–x monolayers possess great light absorption capability within the visible and infrared regions of solar light. Our findings highlight promising candidates for high-speed spintronic devices and may motivate more research efforts on carrier transport and SOC effects in Janus group V and VI monolayers

Multifunctional Porous Graphene for Nanoelectronics and Hydrogen Storage: New Properties Revealed by First Principle Calculations

Multifunctional Porous Graphene for Nanoelectronics and Hydrogen Storage: New Properties Revealed by First Principle Calculation

N/P-Doped MoS₂ Monolayers as Promising Materials for Controllable CO₂ Capture and Separation under Reduced Electric Fields: A Theoretical Modeling

Reversible CO2 capture with applied external electric fields on solid adsorbents is a promising approach to reduce CO2 emissions. However, the strengths of the applied electric fields are too high to be performed in practice. So, it is vital to develop new strategies to reduce the strengths of the electric fields. Through the investigation of CO2 capture on N/P-doped MoS2 on the density functional theory (DFT) level, we find that the strengths of the electric fields on N/P-doped MoS2 can be reduced significantly compared with the system without doping. Moreover, the reversible CO2 capture on them can be controlled by turning on/off the electric field, which is an exothermic reaction without an energy barrier. Especially for N-doped MoS2 with a larger partial charge distribution difference, the required external electric field for efficient reversible CO2 capture is 3–64% of the synthesized two-dimensional (2D) materials such as BN, C2N, C3N, MoS2, and N-doped pentagraphene. Additionally, the materials with an applied electric field can separate CO2 from pre- and postcombustion gas mixtures (CO2, N2, CH4, and H2). In all, the study provides useful insights that chemical doping on adsorbents is an effective strategy to reduce the required electric field for reversible CO2 capture and gas separation

Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide

Reducing carbon dioxide to hydrocarbon fuel with solar energy is significant for high-density solar energy storage and carbon balance. In this work, single atoms of palladium and platinum supported on graphitic carbon nitride (g-C3N4), i.e., Pd/g-C3N4 and Pt/g-C3N4, respectively, acting as photocatalysts for CO2 reduction were investigated by density functional theory calculations for the first time. During CO2 reduction, the individual metal atoms function as the active sites, while g-C3N4 provides the source of hydrogen (H*) from the hydrogen evolution reaction. The complete, as-designed photocatalysts exhibit excellent activity in CO2 reduction. HCOOH is the preferred product of CO2 reduction on the Pd/g-C3N4 catalyst with a rate-determining barrier of 0.66 eV, while the Pt/g-C3N4 catalyst prefers to reduce CO2 to CH4 with a rate-determining barrier of 1.16 eV. In addition, deposition of atom catalysts on g-C3N4 significantly enhances the visible-light absorption, rendering them ideal for visible-light reduction of CO2. Our findings open a new avenue of CO2 reduction for renewable energy supply

Porous Polyethersulfone-Supported Zeolitic Imidazolate Framework Membranes for Hydrogen Separation

ZIF-8 thin layer has been synthesized on the asymmetric porous polyethersulfone (PES) substrate via secondary seeded growth. Continuous and dense ZIF-8 layer, containing microcavities, has good affinity with the PES support. Single gas permeance was measured for H₂, N₂, CH₄, O₂, and Ar at different pressure gradients and temperatures. Molecular sieving separation has been achieved for selectively separating hydrogen from larger gases. At 333 K, the H₂ permeance can reach ∼4 × 10^–7 mol m^–2 s^–1 Pa^–1, and the ideal separation factors of H₂ from Ar, O₂, N₂, and CH₄ are 9.7, 10.8, 9.9, and 10.7, respectively. Long-term hydrogen permeance and H₂/N₂ separation performance show the stable permeability of the derived membranes

Graphyne and Graphdiyne: Versatile Catalysts for Dehydrogenation of Light Metal Complex Hydrides

The interaction between new two-dimensional carbon allotropes, i.e., graphyne (GP) and graphdiyne (GD), and light metal complex hydrides LiAlH₄, LiBH₄, and NaAlH₄ was studied using density functional theory (DFT) incorporating long-range van der Waals dispersion correction. The interaction of light metal complex hydrides with GP and GD is much stronger than that with fullerene because of the well-defined pore structure of GP and GD. Such strong interactions greatly affect the degree of charge donation from the alkali metal atom to AlH₄ or BH₄, consequently destabilizing the Al–H or B–H bonds. Compared to the isolated light metal complex hydride, the presence of GP or GD can lead to a significant reduction of the hydrogen removal energy. Most interestingly, the hydrogen removal energies for LiBH_<i>x</i> on GP and with GD are found to be lowered at all the stages (<i>x</i> from 4 to 1), whereas the H-removal energy in the third stage is increased for LiBH₄ on fullerene. In addition, the presence of uniformly distributed pores on GP and GD is expected to facilitate the dehydrogenation of light metal complex hydrides. The present results highlight new interesting materials to catalyze light metal complex hydrides for potential application as media for hydrogen storage. Because GD has been successfully synthesized in a recent experiment, we hope the present work will stimulate further experimental investigations in this direction

Enabling Room-Temperature Triferroic Coupling in Dual Transition-Metal Dichalcogenide Monolayers Via Electronic Asymmetry

Triferroic compounds are the ideal platform for multistate information devices but are rare in the two-dimensional (2D) form, and none of them can maintain macroscopic order at room temperature. Herein, we propose a general strategy for achieving 2D triferroicity by imposing electric polarization into a ferroelastic magnet. Accordingly, dual transition-metal dichalcogenides, for example, 1T′-CrCoS4, are demonstrated to display room-temperature triferroicity. The magnetic order of 1T′-CrCoS4 undergoes a magnetic transition during the ferroic switching, indicating robust triferroic magnetoelectric coupling. In addition, the negative out-of-plane piezoelectricity and strain-tunable magnetic anisotropy make the 1T′-CrCoS4 monolayer a strong candidate for practical applications. Following the proposed scheme, a new class of 2D room-temperature triferroic materials is introduced, providing a promising platform for advanced spintronics

Metal-Free Single Atom Catalyst for N₂ Fixation Driven by Visible Light

Solar nitrogen (N2) fixation is the most attractive way for the sustainable production of ammonia (NH3), but the development of a highly active, long-term stable and low-cost catalyst remains a great challenge. Current research efforts for N2 reduction mainly focus on the metal-based catalysts using the electrochemical approach, while metal-free or solar-driven catalysts have been rarely explored. Herein, on the basis of a concept of electron “acceptance-donation”, a metal-free photocatalyst, namely, boron (B) atom, decorated on the optically active graphitic-carbon nitride (B/g-C3N4), for the reduction of N2 is proposed by using extensive first-principles calculations. Our results reveal that gas phase N2 can be efficiently reduced into NH3 on B/g-C3N4 through the enzymatic mechanism with a record low onset potential (0.20 V). Moreover, the B-decorated g-C3N4 can significantly enhance the visible light absorption, rendering them ideal for solar-driven reduction of N2. Importantly, the as-designed catalyst is further demonstrated to hold great promise for synthesis due to its extremely high stability. Our work is the first report of metal-free single atom photocatalyst for N2 reduction, offering cost-effective opportunities for advancing sustainable NH3 production