Superior CO2 Research Articles

Two-dimensional interfacial enhanced CO2 adsorption performance of porous organic amine solids: Structure-activity relationships and DFT calculations

The utilization of inexpensive and efficient amine-functionalized adsorbents has become a research hotspot in post-combustion capture technology. Meanwhile, the structure of the support and the selection of organic amines are the primary considerations affecting the CO2 adsorption performance. Herein, the novel solid amine adsorbent materials with amine-support interfacial effect were successfully synthesized in this study by loading four organic amines (TETA, TEPA, PEHA, and PEI) onto expanded vermiculite (EVMT) support with the layered structure. The results indicated that EVMT-50TETA exhibited superior CO2 adsorption capacity (132.5 mg/g) along with effective regeneration capability. This was attributed to the unique layered structure of EVMT that facilitates the dispersion of TETA on its surface or between layers as well as the formation of hydrogen bonds between surface functional groups (–OH) and amines to enhance the amine-support interfacial interaction. Furthermore, the minimal volume expansion of TETA during CO2 adsorption enables improved diffusion of CO2 in channels and enhanced accessibility to active sites. DFT calculations show higher binding energies and faster CO2 adsorption-diffusion rates between TETA and EVMT support. In situ DRIFTS experiments revealed that the process of CO2 adsorption followed the zwitterion mechanism, in which the zwitterion can be reversibly deprotonated to form ammonium carbamate and carbamic acid. This study provides comprehensive insights into the supports and amines interfacial effects through systematic investigation, offering both simplified synthesis strategies and profound theoretical support for studying solid amine adsorbents.

MXenes vs MBenes: Demystifying the materials of tomorrow’s carbon capture revolution

Two emerging materials, MXenes and MBenes, have garnered significant attention as promising candidates for CCS applications. Both materials possess unique properties that make them well-suited for CO2 adsorption, such as high surface area, porosity, and tunable chemical functionality. This perspective article presents a comparative evaluation of MXenes and MBenes for CO2 capture, leveraging advanced computational simulations and experimental data to elucidate their respective adsorption capacities, kinetic performance, and stability. The simulations reveal that both materials exhibit superior CO2 adsorption performance compared to conventional CCS materials, with MXenes demonstrating a slight edge in adsorption capacity and selectivity. Furthermore, the potential of MXenes and MBenes for CCS applications is discussed, including their layer thickness, selective affinity to CO2, advantages over conventional sorbents, regeneration, stability, and durability. The findings provide valuable insights into the structure–property relationships of MXenes and MBenes in the context of CO2 capture and shed light on the technology readiness of these materials for specific CCS applications. Finally, this perspective article aims to advance the fundamental understanding of these novel 2D materials for CCS, paving the way for future developments in sustainable CO2 capture technologies.Graphical abstractHighlightsMXenes and MBenes are two-dimensional layered materials with the potential to revolutionize carbon capture and storage (CCS). MXenes have several advantages over other CCS materials, such as greater porosity, higher CO2 adsorption capacity, and easier and less expensive production. MBenes are more stable in humid environments and have higher oxidation resistance and thermal conductivity than MXenes, making them a better choice for CCS applications where the CO2 stream is humid, hot, and/or corrosive. MXenes and MBenes have the potential to make CCS more efficient, cost-effective, and versatile.DiscussionWhy are MXenes and MBenes ideal for carbon capture applications?In terms of carbon capture efficiency, how do MXenes and MBenes stack up against other materials such as MOFs, zeolites, and activated carbons?Which are better, MXenes or MBenes, for carbon capture?Why do MXenes and MBenes have a selective affinity to CO2 compared to other gases such as N2 and O2?What is the optimal number of layers for MXenes/MBenes for carbon capture, and does interlayer spacing affect performance?What is the best surface termination for CO2 capture?What happens to the CO2 after it is absorbed onto MXene and MBene surfaces, and how can one remove CO2 that has been adsorbed?What are the major challenges, besides scalability, that need to be overcome for these materials to be practical?How durable and stable are MXenes and MBenes?

Homogeneously Distributed Cu-ZnO(-Al2O3) Nanoparticles Encapsulated with SiO2 Shells for Superior CO2 Hydrogenation Activity to Methanol

Homogeneously Distributed Cu-ZnO(-Al₂O₃) Nanoparticles Encapsulated with SiO₂ Shells for Superior CO₂ Hydrogenation Activity to Methanol

Understanding the Interplay of the Brønsted Acidity of Catalyst Ancillary Groups and the Solution Components in Iron-porphyrin-Mediated Carbon Dioxide Reduction.

The rapid and efficient conversion of carbon dioxide (CO2) to carbon monoxide (CO) is an ongoing challenge. Catalysts based on iron-porphyrin cores have emerged as excellent electrochemical mediators of the two proton + two electron reduction of CO2 to CO, and many of the design features that promote function are known. Of those design features, the incorporation of Brønsted acids in the second coordination sphere of the iron ion has a significant impact on catalyst turnover kinetics. The Brønsted acids are often in the form of hydroxyphenyl groups. Herein, we explore how the acidity of an ancillary 2-hydroxyphenyl group affects the performance of CO2 reduction electrocatalysts. A series of meso-5,10,15,20-tetraaryl porphyrins were prepared where only the functional group at the 5-meso position has an ionizable proton. A series of cyclic voltammetry (CV) experiments reveal that the complex with -OMe positioned para to the ionizable -OH shows the largest CO2 reduction rate constants in acetonitrile solvent. This is the least acidic -OH of the compounds surveyed. The turnover frequency of the -OMe derivative can be further improved with the addition of 4-trifluoromethylphenol to the solution. In contrast, the iron-porphyrin complex with -CF3 positioned opposite the ionizable -OH shows the smallest CO2 reduction rate constants, and its turnover frequency is less enhanced with the addition of phenols to the reaction solutions. The origin of this effect is rationalized based on kinetic isotope effect experiments and density functional calculations. We conclude that catalysts with weaker internal acids coupled with stronger external acid additives provide superior CO2 reduction kinetics.

Unraveling the Transformation from Type-II to Z-Scheme in Perovskite-Based Heterostructures for Enhanced Photocatalytic CO2 Reduction.

The ability to create perovskite-based heterostructures with desirable charge transfer characteristics represents an important endeavor to render a set of perovskite materials and devices with tunable optoelectronic properties. However, due to similar material selection and band alignment in type-II and Z-scheme heterostructures, it remains challenging to obtain perovskite-based heterostructures with a favorable electron transfer pathway for photocatalysis. Herein, we report a robust tailoring of effective charge transfer pathway in perovskite-based heterostructures via a type-II to Z-scheme transformation for highly efficient and selective photocatalytic CO2 reduction. Specifically, CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 heterostructures are synthesized and then investigated by ultrafast spectroscopy. Moreover, taking CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 as examples, operando experiments and theoretical calculations confirm that the type-II heterostructure could be readily transformed into a Z-scheme heterostructure through establishing a low-resistance Ohmic contact, which indicates that a fast electron transfer pathway is crucial in Z-scheme construction, as further demonstrated by CsPbBr3/Ag/TiO2 and CsPbBr3/MoS2 heterostructures. In contrast to pristine CsPbBr3 and CsPbBr3/TiO2, the CsPbBr3/Au/TiO2 heterostructure exhibits 5.4- and 3.0-fold enhancement of electron consumption rate in photocatalytic CO2 reduction. DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil that the superior CO selectivity is attributed to the lower energy of *CO desorption than that of hydrogenation to *HCO. This meticulous design sheds light on the modification of perovskite-based multifunctional materials and enlightens conscious optimization of semiconductor-based heterostructures with desirable charge transfer for catalysis and optoelectronic applications.

A layered perovskite La2Ni1-xSbxO4+δ-molten carbonate dual-phase membrane for CO2 separation

A new series of layered perovskite K2NiF4 structure La2Ni1-xSbxO4+δ (LNSx, x = 0, 0.025, 0.05) were used to prepare the LNSx-molten carbonate (MC) dual-phase membrane for CO2 separation. Sb doping at the Ni site is expected to enhance CO2 permeability and improve the resistance towards CO2/carbonate corrosion. In this work, the CO2 permeability of the LNSx- MC membrane was investigated for CO2-containing atmospheres with and without oxygen, and correlated with the lattice characteristics, microstructure, chemical bond, and conductivity of LNSx support. The result shows that the introduction of Sb improves the structure symmetry and increases the interstitial oxygen concentration, which is beneficial for oxygen ion transport. The superior CO2 permeability of Sb-doped sample is confirmed by the higher permeation fluxes with value of 0.15 mL min−1 cm−2 at 800 °C of LNS0.025-MC dual-phase membrane in 50% CO2 + 50% N2. In addition, the LNS0.025-MC dual-phase membrane achieves a great enhancement in chemical and structural stability compared to the LNS0. In the simulated flue gas 15% CO2 + 10% O2 + 75% N2, the LNS0.05-based dual phase membrane shows a high permeation flux of 1.07 mL min−1 cm−2 at 800 °C, which is 2 times higher than that of LNS0-based dual-phase membrane.

Dual synergistic effect of the amine-functionalized MIL-101@cellulose sorbents for enhanced CO2 capture at ambient temperature

The development of high carbon dioxide (CO2) sorption capacity materials is necessary for the deployment of the CO2 capture and storage strategy. Metal-organic frameworks (MOFs) have emerged as promising substitutes for traditional liquid and solid CO2 capture sorbents due to their high surface area, tunable pore size, diverse composition, and various physical and chemical properties. However, MOFs feature the intrinsic limitations of powder agglomeration, weak binding affinity, and sluggish diffusion kinetics, thus hindering their industrial application in CO2 capture. Herein, we design an amine-functionalized MIL-101@cellulose (NH2-MIL-101@BM) composite sorbent by anchoring NH2-MIL-101 nanoparticles onto the BM matrix through hydrogen bonding interaction. The dual synergistic effect, origin from the physical sorption synergistic effect and chemisorption synergistic effect proposed between NH2-MIL-101 and BM, not only facilitates the mass transfer of CO2 by reducing the diffusion resistance through hierarchical-pore structure but also offers stronger sorption sites with CO2 by increasing the adsorption energy of metal-CO2 or amine-CO2, which are confirmed by series of characterizations and theory functional calculations. Benefiting from the above merits, the NH2-MIL-101@20 %BM sorbent delivers a superior initial CO2 sorption capacity of 13.4 mmol/g when the BM doping amount is 20 wt% at 25 °C, and also shows good recycle stability even after 15 runs with maintainable structure. This work displays the in-depth mechanism understanding for enhanced CO2 capture, providing value inspiration for future MOF-based composite sorbent construction for CO2 capture at ambient temperatures.

Unveiling the mechanisms behind high CO2 adsorption by the selection of suitable ionic liquids incorporated into a ZIF-8 metal organic framework: A computational approach

There is growing focus on the crucial task of effectively capturing carbon dioxide (CO2) from the atmosphere to mitigate environmental consequences. Metal-organic frameworks (MOFs) have been used to replace many conventional materials in gas separation, and the incorporation of ionic liquids (ILs) into porous MOFs has shown promise as a new technique for improving CO2 capture and separation. However, the driving force underlying the electronic modulation of MOF nanostructures and the mechanisms behind their high CO2 adsorption remain unclear. This study reports the effect of encapsulating different imidazolium ILs in porous ZIF-8, to clarify the adsorption mechanism of CO2 using density functional theory (DFT)-based approaches. For this purpose, a range of anions, including bis(trifluoromethylsulfonyl)imide [NTf2], methanesulfonate [MeSO3], and acetate [AC], were combined with the 1-ethyl-3-methylimidazolium [EMIM]+ cation. [EMIM]+-based ILs@ZIF-8 composites were computationally investigated to identify suitable materials for CO2 capture. First, the intermolecular and intramolecular interactions between [EMIM]+ and different anions were examined in detail, and their effects on CO2 adsorption were explored. Subsequently, the integration of these ILs into the ZIF-8 solid structure was studied to reveal how their interactions influenced the CO2 adsorption behavior. Our results demonstrate that the incorporation of ILs strongly affects the adsorption capability of CO2, which is highly dependent on the nature of the ILs inside the ZIF-8 framework. DFT simulations further confirmed that the incorporation of ILs into ZIF-8 led to superior CO2 capture compared to isolated ILs and pristine ZIF-8. This improvement was attributed to the mutual interactions between the ILs and ZIF-8, which effectively fine-tuned CO2 adsorption within the composite structure. This understanding may act as a general guide for gaining more insight into the interfacial interactions between ILs and ZIFs structures and how these molecular-level interactions can help predict the selection of ILs for CO2 adsorption and separation, thereby addressing environmental challenges with greater precision and effectiveness.

Heterostructure construction of covalent organic frameworks/Ti3C2-MXene for high-efficiency electrocatalytic CO2 reduction

The in situ fabrication of imine-bonded porphyrin COFs and an MXene heterostructure can accelerate the electron transfer at interfaces, exhibiting superior electrocatalytic CO2 reduction selectivity with 97.28% TOF value (CO2-to-CO) at a bias of −0.6 V vs. RHE.

Revealing the role of a bridging oxygen in a carbon shell coated Ni interface for enhanced alkaline hydrogen oxidation reaction.

Encapsulating metal nanoparticles inside carbon layers is a promising approach to simultaneously improving the activity and stability of electrocatalysts. The role of carbon layer shells, however, is not fully understood. Herein, we report a study of boron doped carbon layers coated on nickel nanoparticles (Ni@BC), which were used as a model catalyst to understand the role of a bridging oxygen in a carbon shell coated Ni interface for the improvement of the hydrogen oxidation reaction (HOR) activity using an alkaline electrolyte. Combining experimental results and density functional theory (DFT) calculations, we find that the electronic structure of Ni can be precisely tailored by Ni-O-C and Ni-O-B coordinated environments, leading to a volcano type correlation between the binding ability of the OH* adsorbate and HOR activity. The obtained Ni@BC with a optimized d-band center displays a remarkable HOR performance with a mass activity of 34.91 mA mgNi-1, as well as superior stability and CO tolerance. The findings reported in this work not only highlight the role of the OH* binding strength in alkaline HOR but also provide guidelines for the rational design of advanced carbon layers used to coat metal electrocatalysts.

A unique one-pot strategy for PdH0.706 nanoparticles with enhanced stability and activity towards the ethanol oxidation reaction.

We present a novel and universal solvothermal method for fabricating high-hydrogen-content PdH0.706 nanoparticles, which demonstrate 1.53 A mg-1 ethanol oxidation activity, 1.39 and 1.76 times higher than hydrogen-free Pd and commercial Pd black, respectively, along with superior stability and CO tolerance under alkaline conditions.

Nanosilica polyamidoamine dendrimers for enhanced direct air CO2 capture.

Exploring efficient systems to recover CO2 from the atmosphere could be a way to address the global carbon emissions issue. Herein, we report the synthesis of nanosilica (NS) functionalized with polyamidoamine (PAMAM) dendrimers (NS-PAMAM) as efficient adsorbents for CO2 capture under simulated direct air capture (DAC) (400 ppm CO2 in helium at 30 °C) and indoor air (≥400 ppm, 50 ± 3% RH at 30 °C) conditions. The results inferred that the 1st (NS-G1.0), 2nd (NS-G2.0), 3rd (NS-G3.0), and 4th (NS-G4.0) generations of the NS-PAMAM dendrimers exhibited excellent performance for CO2 capture. Compared to the other generations, NS-G3.0 demonstrated superior CO2 adsorption capacities of 0.50 mmol g-1 under simulated dry CO2 conditions (400 ppm in He), 1.02 mmol g-1 under indoor air (dry) CO2 conditions (≥400 ppm, 26 ± 3% RH), and 1.54 mmol g-1 under indoor air (humid) CO2 conditions (≥400 ppm, 50 ± 3% RH). The study included the evaluation of CO2 adsorption-desorption performance of the NS-PAMAM dendrimers under varying structural and chemical parameters, kinetics, regeneration at low temperature (80 °C), as well as CO2 adsorption under humid conditions. Additionally, NS-G3.0 displayed a substantially superior performance with stable CO2 capture displayed during ten short temperature swing adsorption (TSA) cycles, making it a promising candidate for CO2 capture from ambient air. Finally, we demonstrated the recovery and reutilization of the captured CO2 for both the synthesis of formate via carbonate hydrogenation and for the production of calcium carbonate pellets.

Halide-guided carbon-affinity active sites in BimOnBrp-derived Bi2O2CO3 for efficient electrocatalytic CO2 reduction to formate

Br introduces a bismuth-rich phase (Bi24O31Br10), promoting external Bi–O structural characteristics and superior CO2 electroreduction reaction (CO2RR) performance.

Synthesis of “all-in-one” hypercrosslinked organic polymers: experimental and kinetic models for CO2 chemical fixation and iodine adsorption

A series of “all-in-one” hypercrosslinked polymers have been constructed by Friedel–Crafts alkylation and quaternization reactions, which exhibit superior CO2 conversion performance and effective iodine adsorption capacity.

Enhanced performance of proton exchange membrane fuel cells by Pt/carbon/antimony-doped tin dioxide triple-junction catalyst

A composite material comprising carbon black and Sb-doped SnO2 (ATO) is employed as a support for a Pt catalyst in a membrane electrode assembly (MEA) to improve the performance of a proton-exchange membrane fuel cell under low-humidity conditions. The effects of Sb-doping on the crystal, structural, and electrochemical characteristics of ATO particles are being examined. In a single cell test, the ratio of Sb in ATO is systematically optimized to improve performance. The distribution of Pt nanoparticles is uniform on carbon black and ATO carrier, forming notable triple-junction points at the interface of carbon black and ATO carrier. This structure thus induces a strong interaction between Pt and ATO, promoting the content of metallic Pt. Compared with a Pt/C catalyst, the best-performing Pt/C–ATO catalyst exhibits superior electrochemical activity, stability, and CO tolerance. The power density of MEA with the Pt/C–ATO catalyst is 15% higher than that of the MEA with the Pt/C catalyst

Investigation of barium iron oxides for CO2 capture and chemical looping oxygen uncoupling

The performance of two underexploited ternary oxides – Ba3Fe2O6 and Ba5Fe2O8 are investigated for carbon dioxide capture and chemical looping oxygen uncoupling. The ternary compound Ba3Fe2O6 was found to have a structure characterised by space group Pa3¯. Experimental results have shown that both Ba3Fe2O6 and Ba5Fe2O8 are capable of cyclically capturing CO2 at temperatures above 800 °C. Ba5Fe2O8 demonstrated superior CO2 capture performance compared to Ba3Fe2O6, with consistent gravimetric CO2 uptake capacities of 4.35 wt% and 13.39 wt% at 900 °C and 1000 °C, respectively, over 20 cycles. In comparison, Ba3Fe2O6 demonstrated high initial CO2 uptake capacities which deteriorated cyclically, with 20 cycle average capacities of 7.73 wt% and 11.99 wt% at 900 °C and 1000 °C, respectively. Ba3Fe2O6 also exhibits excellent recyclability and satisfactory chemical looping oxygen uncoupling (CLOU) activity over temperature swing cycles between 550 °C and 950 °C. In contrast, the strong affinity with CO2 makes Ba5Fe2O8 unsuitable for application in chemical looping oxygen uncoupling or chemical looping air separation, especially in the presence of substantial partial pressures of CO2.

Molecular simulation combined with DFT calculation guided heteroatom-doped biochar rational design for highly selective and efficient CO2 capture

Using solid sorbents for post-combustion CO2 capture from flue gas have shown many potential advantages. The heteroatom doping technique can significantly enhance the CO2 adsorption performance of biochar. However, the diverse forms of heteroatom doping make the development process complex and expensive. To address this, this work firstly used density functional theory (DFT) calculations to screen out three kinds of doping forms (BCO2, P-C, and C-S-C) on biochar, which can improve the CO2 adsorption energy and the theoretical selectivity. Subsequently, the adsorption isotherms simulated by grand canonical Monte Carlo (GCMC) showed the CO2 adsorption capacity on heteroatom-doped biochar at low pressure (≤1 bar) was higher than that of the pristine biochar, which can show excellent performance in flue gas CO2 trapping. Then, three types of heteroatom-doped biochar were synthesized based on theoretical calculations. Among them, P-doped biochar exhibited superior CO2 adsorption capacity (1.34 mmol/g) at 72 °C and 1 bar, which was 10.7 % higher than the pristine biochar. Through adsorption isotherm experiments, it was found that the performance of materials under low pressure is dominated by heteroatom doping, while under high pressure, it is dominated by pore structure, which is consistent with the conclusion obtained from GCMC simulation. And adsorption kinetics experiments revealed that the impact of heteroatom doping becomes more pronounced as the temperature increases, and heteroatom doping can optimize CO2 adsorption kinetics. Furthermore, the heteroatom-doped biochar exhibits exceptional thermal, chemical, and cyclic stability.

Compressive Strain in Platinum-Iridium-Nickel Zigzag-Like Nanowire Boosts Hydrogen Catalysis.

Strain effect in the structurally defective materials can contribute to the catalysis optimization. However, it is challenging to achieve the performance improvement by strain modulation with the help of geometrical structure because strain is spatially dependent. Here, a new class of compressively strained platinum-iridium-metal zigzag-like nanowires (PtIrM ZNWs, M=nickel (Ni), cobalt (Co), iron (Fe), zinc (Zn) and gallium (Ga)) is reported as the efficient alkaline hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) catalysts. Particularly, the optimized PtIrNi ZNWs with 3% compressive strain (cs-PtIrNi ZNWs) can achieve the highest HER/HOR performances among all the catalysts investigate. Their HOR mass and specific activities are 3.2/14.4 and 2.6/32.7 times larger than those of PtIrNi NWs and commercial Pt/C, respectively. Simultaneously, they can exhibit the superior stability and high CO resistance for HOR. Further, experimental and theoretical studies collectively reveal that the compressive strain in cs-PtIrNi ZNWs effectively weakens the adsorption of hydroxyl intermediate and modulates the electronic structure, resulting in the weakened hydrogen binding energy (HBE) and moderate hydroxide binding energy (OHBE), beneficial for the improvement of HOR performance. This work highlights the importance of strain tuning in enhancing Pt-based nanomaterials for hydrogen catalysis and beyond.

Tuning CO2 photoreduction: CoN/KPCN catalysts for High CH4 selectivity through an efficient microwave molten salt heating synthesis

Photocatalytic reduction of CO2 to CH4 holds promise for sustainable energy and CO2 mitigation. In this study, we present the rapid synthesis of efficient composite photocatalysts via a one-step microwave molten salt heating method. Typically, potassium ions (K+) are directionally doped into polymeric carbon nitride (PCN) interlayer cavities, while CoN nanoparticles selectively form on K-doped PCN (KPCN). CoN/KPCN catalysts exhibit exceptional photocatalytic performance, yielding 45.71 μmol g−1 h−1 CH4 with 98.18% selectivity under visible light illumination. This mainly results from the synergistic effect of the enhanced crystallinity, expanded light absorption, efficient charge transfer, superior CO2 adsorption, and enhanced carrier dynamics. More importantly, the introduction of K+ is in favor of the high CH4 photoreduction selectivity both in view of kinetically and thermodynamically. This study informs carbon nitride-based photocatalyst development and underscores the potential of CoN/KPCN as a catalyst for high CH4 selectivity in CO2 photoreduction, contributing to sustainable energy and environmental conservation.

Hydrogen Spillover Induced PtCo/CoOx Interfaces with Enhanced Catalytic Activity for CO Oxidation at Low Temperatures in Humid Conditions.

The development of catalysts with abundant active interfaces for superior low-temperature catalytic CO oxidation is critical to meet increasingly rigorous emission requirements, yet still challenging. Herein, this work reports a PtCo/CoOx/Al2O3 catalyst with PtCo clusters and enriched Pt─O─Co interfaces induced by hydrogen spillover from the Pt sites and self-oxidation process in air, exhibiting excellent performance for CO oxidation at low temperatures and humid conditions. The combination of structural characterizations and in situ Fourier transform infrared spectroscopy reveals that the PtCo cluster effectively prevents CO saturation/poisoning on the Pt surface. Additionally, the presence of Pt─O─Co interfaces in the PtCo/CoOx/Al2O3 catalyst provides a significant number of active sites for oxygen activation and ─OH formation. This facilitates efficient generation of CO2 at ambient temperature by coupling with nearby adsorbed CO molecules, resulting in superior low-temperature activity and long-term stability for CO oxidation under humid conditions. This work provides a facile route toward rationalizing the design of catalysts with more active interfaces for superior low-temperature CO oxidation under humid conditions for practical applications.