Theoretical study of adsorption properties and CO oxidation reaction on surfaces of higher tungsten boride

Most modern catalysts are based on precious metals and rear-earth elements, making some of organic synthesis reactions economically insolvent. Density functional theory calculations are used here to describe several differently oriented surfaces of the higher tungsten boride WB5-x, together with their catalytic activity for the CO oxidation reaction. Based on our findings, WB5-x appears to be an efficient alternative catalyst for CO oxidation. Calculated surface energies allow the use of the Wulff construction to determine the equilibrium shape of WB5-x particles. It is found that the (010) and (101) facets terminated by boron and tungsten, respectively, are the most exposed surfaces for which the adsorption of different gaseous agents (CO, CO2, H2, N2, O2, NO, NO2, H2O, NH3, SO2) is evaluated to reveal promising prospects for applications. CO oxidation on B-rich (010) and W-rich (101) surfaces is further investigated by analyzing the charge redistribution during the adsorption of CO and O2 molecules. It is found that CO oxidation has relatively low energy barriers. The implications of the present results, the effects of WB5-x on CO oxidation and potential application in the automotive, chemical, and mining industries are discussed.

Two-Dimensional Transition Metal-Hexaaminobenzene Monolayer Single-Atom Catalyst for Electrocatalytic Carbon Dioxide Reduction

Electrocatalytic reduction of CO₂ to valuable fuels and chemicals can not only alleviate the energy crisis but also improve the atmospheric environment. The key is to develop electrocatalysts that are extremely stable, efficient, selective, and reasonably priced. In this study, spin-polarized density function theory (DFT) calculations were used to comprehensively examine the catalytic efficacy of transition metal-hexaaminobenzene (TM-HAB) monolayers as single-atom catalysts for the electroreduction of CO₂. In the modified two-dimensional TM-HAB monolayer, our findings demonstrate that the binding of individual metal atoms to HAB can be strong enough for the atoms to be evenly disseminated and immobilized. In light of the conflicting hydrogen evolution processes, TM-HAB effectively inhibits hydrogen evolution. CH₄ dominates the reduction byproducts of Sc, Ti, V, Cr, and Cu. HCOOH makes up the majority of Zn's reduction products. Co's primary reduction products are CH₃OH and CH₄, whereas Mn and Fe's primary reduction products are HCHO, CH₃OH, and CH₄. Among these, the Ti-HAB reduction products have a 1.14 eV limiting potential and a 1.31 V overpotential. The other monolayers have relatively low overpotentials between 0.01 V and 0.7 V; therefore, we predict that TM-HAB monolayers will exhibit strong catalytic activity in the electrocatalytic reduction of CO₂, making them promising electrocatalysts for CO₂ reduction.

Carbon dioxide adsorption and conversion to methane and ethane on hydrogen boride sheets

Hydrogen boride (HB) sheets are metal-free two-dimensional materials comprising boron and hydrogen in a 1:1 stoichiometric ratio. In spite of the several advancements, the fundamental interactions between HB sheets and discrete molecules remain unclear. Here, we report the adsorption of CO2 and its conversion to CH4 and C2H6 using hydrogen-deficient HB sheets. Although fresh HB sheets did not adsorb CO2, hydrogen-deficient HB sheets reproducibly physisorbed CO2 at 297 K. The adsorption followed the Langmuir model with a saturation coverage of 2.4 × 10-4 mol g-1 and a heat of adsorption of approximately 20 kJ mol-1, which was supported by density functional theory calculations. When heated in a CO2 atmosphere, hydrogen-deficient HB began reacting with CO2 at 423 K. The detection of CH4 and C2H6 as CO2 reaction products in a moist atmosphere indicated that hydrogen-deficient HB promotes C-C coupling and CO2 conversion reactions. Our findings highlight the application potential of HB sheets as catalysts for CO2 conversion.

CO2 Capture, Separation and Reduction on Boron-Doped MoS2 , MoSe2 and Heterostructures with Different Doping Densities: A Theoretical Study

Designing high-performance materials for CO₂ capture and conversion is of great significance to reduce the greenhouse effect and alleviate the energy crisis. The strategy of doping is widely used to improve activity and selectivity of the materials. However, it is unclear how the doping densities influence the materials' properties. Herein, we investigated the mechanism of CO₂ capture, separation and conversion on MoS₂ , MoSe₂ and Janus MoSSe monolayers with different boron doping levels using density functional theory (DFT) simulations. The results indicate that CO₂ , H₂ and CH₄ bind weakly to the monolayers without and with single-atom boron doping, rendering these materials unsuitable for CO₂ capture from gas mixtures. In contrast, CO₂ binds strongly to monolayers doped with diatomic boron, whereas H₂ and CH₄ can only form weak interactions with these surfaces. Thus, the monolayers doped with diatomic boron can efficiently capture and separate CO₂ from such gas mixtures. The electronic structure analysis demonstrates that monolayers doped with diatomic doped are more prone to donating electrons to CO₂ than those with single-atom boron doped, leading to activation of CO₂ . The results further indicate that CO₂ can be converted to CH₄ on diatomic boron doped catalysts, and MoSSe is the most efficient of the surfaces studied for CO₂ capture, separation and conversion. In summary, the study provides evidence for the doping density is vital to design materials with particular functions.

Strong chemisorption of CO2 on B10-B13 planar-type clusters

An ab initio density functional study was performed investigating the adsorption of CO₂ on neutral boron B _n (n  =  10-13) clusters that are characterized by planar and quasiplanar ground-state atomic structures. For all four clusters, we found large chemisorption binding energies, reaching 1.6 eV between CO₂ and B₁₂, with the adsorbed molecule oriented in the plane of the cluster and adsorbed along the cluster edge. A configuration with chemisorbed dissociated CO₂ molecule also exists for B₁₁ and B₁₃ clusters. The strong adsorption is due to the bending of the CO₂ molecule, which provides energetically accessible fully in-plane frontier molecular orbitals matching the edge states of the clusters. At the same time, the intrinsic dipole moment of a bent CO₂ molecule facilitates the transfer of excess electronic charge from the cluster edges to the molecule.

Recyclable and superior selective CO2 adsorption of C4B32 and Ca@C4B32: a new category of perfect cubic heteroborospherenes

A new category of the perfect cubic heteroborospherenes C₄B₃₂ and Ca@C₄B₃₂ shows superior CO₂-capture and -separation abilities.

Boosting water oxidation electrocatalysts with surface engineered amorphous cobalt hydroxide nanoflakes

Enriching dominant active intermediates is most pivotal in developing efficient non-noble oxygen evolution reaction (OER) electrocatalysts for water oxidation. Herein, we report surface-engineered amorphous cobalt hydroxide nanoflakes on nickel foam as highly active electrocatalysts for boosting water oxidation by a new repeatedly switching current-polarity strategy. It is discovered that sulfur introduction can simultaneously increase the Co3+/Co2+ ratio to generate more targeted OOH* intermediates and regulate the surface electronic structure to greatly boost its intrinsic activity. The density functional theory (DFT) calculations further confirm the reduction of the free energy of the OOH* intermediates. Consequently, our Co(OH)xS electrocatalyst exhibits an ultralow overpotential of 283 and 365 mV at 100 and 1000 mA cm-2 in alkaline media, respectively, and its turnover frequency (TOF) is more than 4 times higher than the corresponding Co(OH)x catalysts. This heteroatom triggered surface engineering may open up avenues to explore other efficient non-noble metal electrocatalysts for water oxidation.

A theoretical insight into a feasible strategy for the fabrication of borophane

This theoretical study demonstrates a feasible strategy for the fabrication of borophane through the mechanism of hydrogen decomposition on charged borophene.

Electric field controlled CO2 capture and CO2/N2 separation on MoS2 monolayers

Developing new materials and technologies for efficient CO₂ capture, particularly for separation of CO₂ post-combustion, will significantly reduce the CO₂ concentration and its impacts on the environment. A challenge for CO₂ capture is to obtain high performance adsorbents with both high selectivity and easy regeneration. Here, CO₂ capture/regeneration on MoS₂ monolayers controlled by turning on/off external electric fields is comprehensively investigated through a density functional theory calculation. The calculated results indicate that CO₂ forms a weak interaction with MoS₂ monolayers in the absence of an electric field, but strongly interacts with MoS₂ monolayers when an electric field of 0.004 a.u. is applied. Moreover, the adsorbed CO₂ can be released from the surface of MoS₂ without any energy barrier once the electric field is turned off. Compared with the adsorption of CO₂, the interactions between N₂ and MoS₂ are not affected significantly by the external electric fields, which indicates that MoS₂ monolayers can be used as a robust absorbent for controllable capture of CO₂ by applying an electric field, especially to separate CO₂ from the post-combustion gas mixture where CO₂ and N₂ are the main components.

High-mobility anisotropic transport in few-layer γ-B28 films

Recent reports of successful synthesis of atomically thin boron films have raised great prospects of discovering novel electronic and transport properties in a new type of 2D materials. Here we show by first-principles calculations that monolayer and bilayer γ-B₂₈ films are intrinsically metallic while the thicker films possess intriguing electronic states that exhibit moderate to large bandgaps in all the interior layers but are nearly gapless at the surface. Remarkably, these surface electronic states are tunable by strain, allowing the outermost layer to transition between a semimetal and a narrow-gap semiconductor. Moreover, these surface states almost exclusively occupy a wide energy range around the Fermi level, thus dominating the electronic transport in γ-B₂₈ films. The dispersions of the surface electronic bands are direction sensitive, and with hole injection producing anisotropic and very high carrier mobility up to 104 cm² V^-1 s^-1. Surprisingly, surface passivation can open a sizable bandgap, which offers an additional avenue for effective band engineering and explains the experimental observation of a large bandgap in the synthesized film. These results make few-layer γ-B₂₈ films desirable candidate materials for catalysis and electronics applications.

In-plane graphene/boron-nitride heterostructures as an efficient metal-free electrocatalyst for the oxygen reduction reaction

Exploiting metal-free catalysts for the oxygen reduction reaction (ORR) and understanding their catalytic mechanisms are vital for the development of fuel cells (FCs). Our study has demonstrated that in-plane heterostructures of graphene and boron nitride (G/BN) can serve as an efficient metal-free catalyst for the ORR, in which the C-N interfaces of G/BN heterostructures act as reactive sites. The formation of water at the heterointerface is both energetically and kinetically favorable via a four-electron pathway. Moreover, the water formed can be easily released from the heterointerface, and the catalytically active sites can be regenerated for the next cycle. Since G/BN heterostructures with controlled domain sizes have been successfully synthesized in recent reports (e.g. Nat. Nanotechnol., 2013, 8, 119), our results highlight the great potential of such heterostructures as a promising metal-free catalyst for the ORR in FCs.

Strong chemisorption of CO on M@Bn− (M = Co, Ir, Rh, Ru, Ta, Nb, n = 8–10) clusters: an implication for wheel boron clusters as CO gas detectors

The potential applications of wheel M@B_n⁻ clusters in CO detection have been proposed theoretically.