First-Principles Study of Electrocatalytically Reversible CO2 Capture on Graphene-like C3 N

Multi-doped borophene catalysts with engineered defects for CO2 reduction: A DFT study

Carbon dioxide reduction reaction (CO2RR) to convert carbon dioxide (CO2) into value-added products via the electrochemical method is a conducive way to tackle the hazard of high CO2 emissions. The present DFT study reports a novel dual chromium-anchored tri-vacancy borophene (Cr2/TV-β12) electrocatalyst, which showed high selectivity and stability for CO2RR. A tri-vacancy defect was introduced in β12 borophene to create an 11-membered ring borophene sheet (TV-β12), and 28 different electrocatalysts were explored via doping various transition metals (Co, Cr, Cu, Fe, Mn, Ni, Zn). Density functional theory simulation results revealed that the Cr2/TV-β12 electrocatalyst adsorbs and activates CO2 efficiently, which was validated by the partial density of states, charge density difference, Bader charge, and crystal orbital Hamilton population analyses. The limiting potential for CO2RR was evaluated to be -0.45 V, against hydrogen evolution reaction (HER) (0.57 V), with the main product being formaldehyde. The catalyst showed selectivity towards CO2 reduction and suppressed HER. The usual problem of carbon monoxide poisoning encountered in CO2 reduction was also assessed and a high resistance against the same was established. At the outset, the research revealed that dual atom-doped tri-vacancy β12 borophene has tremendous potential to be utilized as an efficient catalyst for CO2RR.

The important role of surface charge on a new mechanism of nitrogen reduction

The electrocatalytic nitrogen reduction reaction (NRR) is a green and sustainable approach for producing ammonia. Low-cost carbon-based materials are promising catalysts for the electrochemical NRR. Among them, Cu-N₄-graphene is a unique catalytic substrate. Its catalytic performance for the NRR has remained unclear as N₂ can only be physisorbed on such a substrate. In this work, we focus on the influence of an electronic environment on the electrocatalytic NRR. DFT computations reveal that the NN bond can be effectively activated at a surface charge density of -1.88 × 10¹⁴ e cm^-2 on Cu-N₄-graphene and further the NRR proceeds via an alternating hydrogenation pathway. This work offers a new insight into the mechanism of the electrocatalytic NRR and emphasizes the importance of environmental charges in the electrocatalytic process of the NRR.

Fast light-switchable polymeric carbon nitride membranes for tunable gas separation

Switchable gas separation membranes are intriguing systems for regulating the transport properties of gases. However, existing stimuli-responsive gas separation membranes suffer from either very slow response times or require high energy input for switching to occur. Accordingly, herein, we introduced light-switchable polymeric carbon nitride (pCN) gas separation membranes with fast response times prepared from melamine precursor through in-situ formation and deposition of pCN onto a porous support using chemical vapor deposition. Our systematic analysis revealed that the gas transport behavior upon light irradiation is fully governed by the polarizability of the permeating gas and its interaction with the charged pCN surface, and can be easily tuned either by controlling the power of the light and/or the duration of irradiation. We also demonstrated that gases with higher polarizabilities such as CO2 can be separated from gases with lower polarizability like H2 and He effectively with more than 22% increase in the gas/CO2 selectivity upon light irradiation. The membranes also exhibited fast response times (<1 s) and can be turned “on” and “off” using a single light source at 550 nm.

Fast light-switchable polymeric carbon nitride membranes for tunable gas separation

Switchable gas separation membranes are intriguing systems for regulating the transport properties of gases. However, existing stimuli-responsive gas separation membranes suffer from either very slow response times or require high energy input for switching to occur. Accordingly, herein, we introduced light-switchable polymeric carbon nitride (pCN) gas separation membranes with fast response times prepared from melamine precursor through in-situ formation and deposition of pCN onto a porous support using chemical vapor deposition. Our systematic analysis revealed that the gas transport behavior upon light irradiation is fully governed by the polarizability of the permeating gas and its interaction with the charged pCN surface, and can be easily tuned either by controlling the power of the light and/or the duration of irradiation. We also demonstrated that gases with higher polarizabilities such as CO2 can be separated from gases with lower polarizability like H2 and He effectively with more than 22% increase in the gas/CO2 selectivity upon light irradiation. The membranes also exhibited fast response times (<1 s) and can be turned “on” and “off” using a single light source at 550 nm.

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.

Can Charge-Modulated Metal-Organic Frameworks Achieve High-Performance CO2 Capture and Separation over H2 , N2 , and CH4 ?

CO₂ capture and separation by using charge-modulated adsorbent materials is a promising strategy to reduce CO₂ emissions. Herein, three TM-HAB (TM=Co, Ni, and Cu; HAB=hexa-aminobenzene) metal-organic frameworks (MOFs) were evaluated as charge-modulated CO₂ capture and separation materials by using density functional theory and grand canonical Monte Carlo simulations. The results showed that each TM-HAB presented a high electrical conductivity and structural stability when injecting charges. The CO₂ adsorption energy increased from 0.211 to 2.091 eV on Co-HAB, 0.262 to 2.119 eV on Ni-HAB, and 0.904 to 2.803 eV on Cu-HAB, respectively, with the increase in charge state from 0.0 to 3.0 e^- . Co-HAB and Ni-HAB were better charge-modulated CO₂ capture materials with less structure deformation based on energy decomposition analyses. The kinetic process demonstrated that considerably low energy consumptions of 0.911 and 1.589 GJ ton^-1 CO₂ were observed for a complete adsorption-desorption cycle on Co-HAB and Ni-HAB. All charged MOFs, especially Co-HAB and Ni-HAB, exhibited higher CO₂ adsorption energies and adsorption capacities than those of H₂ , N₂ , and CH₄ , thereby exhibiting high CO₂ selectivities. Interaction analysis confirmed that the injecting charges had a more pronounced enhancement in the coulombic interactions between CO₂ and MOFs. The results of this work highlight Co-HAB and Ni-HAB as promising charge-modulated CO₂ capture and separation materials with controllable CO₂ capture, high selectivity, and low energy consumption.

Sc-functionalized porphyrin-like porous fullerene for CO2 storage and separation: A first-principles evaluation

In recent years, there has been a lot of interest in capturing and storing carbon dioxide (CO₂) on porous materials as an efficient method for decreasing the adverse effects of this greenhouse gas on the environment and climate change. The current work introduces a Sc-decorated porphyrin-like porous fullerene (Sc₆@C₂₄N₂₄) as an efficient material for CO₂ capture, storage, and separation using density functional theory calculations. While CO₂ is physisorbed over pristine C₂₄N₂₄, the addition of Sc atoms on the N₄ sites of C₂₄N₂₄ greatly enhances CO₂ adsorption energy. Each Sc atom in Sc₆@C₂₄N₂₄ may adsorb up to three CO₂ molecules, resulting in a gravimetric density of 48%. Moreover, temperature may be used to modulate CO₂ adsorption/desorption over the substrate. The Sc-decorated C₂₄N₂₄ fullerene exhibits a lower affinity for adsorbing N₂, CH₄, and H₂ molecules than CO₂. As a consequence, this material might be considered for purifying CO₂ molecules from CO₂/N₂, CO₂/CH₄, and CO₂/H₂ mixtures. This study also sheds light on the nature of the Sc-CO₂ interaction as well as the underlying mechanism of selective CO₂ adsorption on Sc decorated C₂₄N₂₄.

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.

Li-doped beryllonitrene for enhanced carbon dioxide capture

In recent years, the scientific community has given more and more attention to the issue of climate change and global warming, which is largely attributed to the massive quantity of carbon dioxide emissions. Thus, the demand for a carbon dioxide capture material is massive and continuously increasing. In this study, we perform first-principle calculations based on density functional theory to investigate the carbon dioxide capture ability of pristine and doped beryllonitrene. Our results show that carbon dioxide had an adsorption energy of -0.046 eV on pristine beryllonitrene, so it appears that beryllonitrene has extremely weak carbon dioxide adsorption ability. Pristine beryllonitrene could be effectively doped with lithium atoms, and the resulting Li-doped beryllonitrene had much stronger interactions with carbon dioxide than pristine beryllonitrene. The adsorption energy for carbon dioxide on Li-doped beryllonitrene was -0.408 eV. The adsorption of carbon dioxide on Li-doped beryllonitrene greatly changed the charge density, projected density of states, and band structure of the material, demonstrating that it was strongly adsorbed. This suggests that Li-doping is a viable way to enhance the carbon dioxide capture ability of beryllonitrene and makes it a possible candidate for an effective CO2 capture material.

Charge controlled capture/release of CH4 on Nb2CTx MXene: A first-principles calculation

Methane is not only the main cause of coal mine accidents but also a contributor to global warming, meanwhile, it is clean energy. It is necessary to find an advanced material which can capture methane efficiently for its utilization. In this paper, the adsorption of CH₄ gas molecules on Nb₂CT_x(T = O, F, Cl, OH) is studied by first-principles calculation. The results indicate that the adsorption of CH₄ on Nb₂CT_x(T = O, F, Cl, OH) is weak, and the adsorption of CH₄ on Nb₂C(OH)₂ is the best. The calculation results of binding energy and cohesive energy show that Nb₂CO₂ has the best stability. The adsorption behavior of CH₄ on Nb₂CO₂ under charge control is further studied. With the increase of negative charge state in the system, the adsorption of CH₄ on Nb₂CO₂ is significantly enhanced, from physical adsorption to chemical adsorption; when the charge state of the system is greater than or equal to -2, Nb₂CO₂ can capture CH₄ effectively, and the charges transferred from Nb₂CO₂ to CH₄ mainly come from Nb atom. After the removal of the extra charge, the adsorption of CH₄ on Nb₂CO₂ becomes weak and returns to physical adsorption state; CH₄ gas molecules are easy to desorb. Therefore, Nb₂CO₂ can capture and release CH₄ molecules by regulating the charge state of Nb₂CO₂, and Nb₂CO₂ is expected to become an excellent candidate material for CH₄ capture/release.

Reversible CO2 storage and efficient separation using Ca decorated porphyrin-like porous C24N24 fullerene: a DFT study

The search for novel materials for effective storage and separation of CO₂ molecules is a critical issue for eliminating or lowering this harmful greenhouse gas. In this paper, we investigate the potential application of a porphyrin-like porous fullerene (C₂₄N₂₄) as a promising material for CO₂ storage and separation using thorough density functional theory calculations. The results show that CO₂ is physisorbed on bare C₂₄N₂₄, implying that this material cannot be used for efficient CO₂ storage. Coating C₂₄N₂₄ with Ca atoms, on the other hand, can greatly improve the adsorption strength of CO₂ molecules due to polarization and charge-transfer effects. Furthermore, the average adsorption energy for each of the maximum 24 absorbed CO₂ molecules on the fully decorated Ca₆C₂₄N₂₄ fullerene is −0.40 eV, which fulfills the requirement needed for efficient CO₂ storage (−0.40 to −0.80 eV). The Ca coated C₂₄N₂₄ fullerene also have a strong potential for CO₂ separation from CO₂/H₂, CO₂/CH₄, and CO₂/N₂ mixtures.

Using dispersion-corrected DFT calculations, the potential application of a porphyrin-like porous fullerene (C₂₄N₂₄) as an efficient material for CO₂ storage and separation was investigated.

Interface-enhanced CO2 capture via the synthetic effects of a nanomaterial-supported ionic liquid thin film

Ionic liquids (ILs) are effective CO2 capture media and recent experimental evidence has demonstrated that the addition of two-dimensional (2D) nanomaterials into ILs can effectively improve their CO2 capturing capability. However, an in-depth mechanism on how 2D nanomaterials enhance CO2 absorption is poorly documented. In this study, the adsorption of CO2 by a representative IL, namely 1-ethyl-3-methyl-imidazole-tetrafluoroborate ([EMIM][BF4]), coated on graphene (GRA, the prototype 2D nanomaterial) and nitrogenized graphene (C3N) was investigated by molecular dynamics simulations. The influence of the IL film thickness on the amount of CO2 adsorption was systematically analyzed. Our data clearly indicate that at the IL-gas interface the CO2 accumulation is significantly enhanced. In contrast, at the IL-GRA and IL-C3N interfaces, only slight enhancement was observed for CO2 accumulation. Quantitative calculations of the adsorption-free energy for CO2 inside the IL film further support the simulation results. Our present results also reveal that the sub-nanometer IL film possesses a considerably high CO2 capture efficiency because of the formation of the reduced bulk IL region. Moreover, the nanomaterial substrate surfaces can effectively accelerate the diffusion of CO2, which is beneficial for the CO2 mass transfer. In general, our theoretical study provides a deep microscopic understanding of the CO2 capture by nanomaterials and IL composites. These results could benefit the design and fabrication of a high-performance CO2 capture and storage medium through the synthetic effects of ILs and nanomaterials.

B3O3 monolayer: an emerging 2D material for CO2 capture

The calculated CO2 capture capacity of the desired B3O3 monolayer in the present study is high that it can be recognized as an emerging material for efficient CO2 capture.

Selective adsorption of CO2 from gas mixture by P-decorated C24N24 fullerene assisted by an electric field: A DFT approach

Selective, reversible and tailored adsorption of CO₂ from gas mixture is always demanded to control global warming. We for the first time used P-decorated C₂₄N₂₄ fullerene for selective separation of CO₂ from N₂/CO₂ mixture in the presence of an electric field by using density functional theory methods. The computed geometrical parameters evince that the binding distances and bond angles (OCO) are remarkably reduced in electric field and that transformed the physisorption to chemisorption by increasing the field from 0.012 to 0.013 au. The adsorption/desorption of CO₂ over the substrate can be easily controlled by switching on and off the electric field. This study reveals that P@C₂₄N₂₄ is a selective adsorbent of CO₂ from N₂/CO₂ mixture and will help the future synthesis of selective, controllable and regenerable adsorbent for the CO₂ separation from gas mixture in presence of electric field.

Half-metallic two-dimensional polyaniline with 3d-transition-metal decoration

Possible half-metallic behavior was explored in 3d-transition-metal (Fe, Co, and Ni) decorated two-dimensional polyaniline (C₃N) on the basis of density-functional theory. 3d-transition-metal atoms would prefer to adsorb on top of the carbon hexagonal ring. The calculated electronic structures suggest the Fe and Co decorated polyanilines ([Formula: see text]Fe and [Formula: see text]Co) are magnetic half-metals, while the Ni-decorated polyaniline ([Formula: see text]Ni) is a nonmagnetic semiconductor with an enlarged band gap. In [Formula: see text]Fe, the half-metallic energy window can be as large as 0.7 eV. Interestingly, there are two half-metallic energy windows with opposite spins near Fermi level in [Formula: see text]Co. The energy windows and band gaps can be modulated by the distance between 3d-transition-metal atoms and C₃N. Due to the large half-metallic energy window and the appropriate band gap, 3d-transition-metal decorated C₃N may be used in nanoscale spintronic devices.

Design of a Graphene Nitrene Two-Dimensional Catalyst Heterostructure Providing a Well-Defined Site Accommodating One to Three Metals, with Application to CO2 Reduction Electrocatalysis for the Two-Metal Case

Recently, the reduction of CO₂ to fuels has been the subject of numerous studies, but the selectivity and activity remain inadequate. Progress has been made on single-site two-dimensional catalysts based on graphene coupled to a metal and nitrogen for the CO₂ reduction reaction (CO₂RR); however, the product is usually CO, and the metal-N environment remains ambiguous. We report a novel two-dimensional graphene nitrene heterostructure (grafiN₆) providing well-defined active sites (N₆) that can bind one to three metals for the CO₂RR. We find that homobimetallic FeFe-grafiN₆ could reduce CO₂ to CH₄ at -0.61 V and to CH₃CH₂OH at -0.68 V versus reversible hydrogen electrode, with high product selectivity. Moreover, the heteronuclear FeCu-grafiN₆ system may be significantly less affected by hydrogen evolution reaction, while maintaining a low limiting potential (-0.68 V) for C1 and C2 mechanisms. Binding metals to one N₆ site but not the other could promote efficient electron transport facilitating some reaction steps. This framework for single or multiple metal sites might also provide unique catalytic sites for other catalytic processes.

Molecular design and experimental study on synergistic catalysts for the synthesis of cyclocarbonate from styrene oxide and CO2

Taking the reaction between styrene oxide and CO₂ to yield cyclocarbonate as the target, the activities of synergistic catalysts, which are composed of Br⁻ and alcohol compounds serving as hydrogen bond donors (HBDs), were predicted by DFT calculations and confirmed by subsequent experiments.