Binding Energy Of CO Research Articles

Dual-bonded polyethyleneimine network with electron-withdrawing groups at α, β-sites for ultra-stable and low-energy CO2 capture in harsh environments

As an innovative approach to addressing climate change, significant efforts have been dedicated to the development of amine sorbents for CO2 capture. However, the high energy requirements and limited lifespan of these sorbents, such as oxidative and water stability, pose significant challenges to their widespread commercial adoption. Moreover, the understanding of the relationship between adsorption energy and adsorption sites is not known. In this work, a dual-bond strategy was used to create novel secondary amine structures by a polyethyleneimine (PEI) network with electron-extracted (EE) amine sites at adjacent sites, thereby weakening the CO2 binding energy while maintaining the binding ability. In-situ FT-IR and DFT demonstrated the oxygen-containing functional groups adjacent to the amino group withdraw electrons from the N atom, thereby reducing the CO2 adsorption capacity of the secondary amine, resulting in lower regeneration energy consumption of 1.39 GJ t−1-CO2. In addition, the EE sorbents demonstrated remarkable performance with retention of over 90 % of their working capacity after 100 cycles, even under harsh conditions containing 10 % O2 and 20 % H2O. DFT calculations were employed to clarify for the first time the mechanism that the oxygen functional group at the α-site hinders the formation of the urea structure, thereby being an antioxidant. These findings highlight the promising potential of such sorbents for deployment in various CO2 emission scenarios, irrespective of environmental conditions.

CO oxidation on IrO2(110) surfaces

We investigated the oxidation of CO on stoichiometric and O-rich IrO2(110) surfaces using temperature programmed reaction spectroscopy (TPRS), density functional theory (DFT) calculations and microkinetic simulations. Adsorbed CO on the s-IrO2(110) surface generates CO and CO2 peaks near 545 K during TPRS, and only about 38 % of the CO oxidized to CO2 when the initial CO layer was saturated. Pre-adsorbed O-atoms, so-called on-top oxygen (Ot), promote the oxidation of CO adsorbed on IrO2(110). On the Ot-covered surface, CO oxidation by Ot atoms produces a CO2 TPRS peak at ∼370 K, and all of the initially adsorbed CO oxidizes to CO2 when the initial Ot coverage is greater than the CO coverage. In agreement with the TPRS results, DFT calculations predict that the barrier is about 100 kJ/mol lower for CO oxidation by an Ot atom than a lattice O-atom of IrO2(110). A microkinetic model, parameterized with energy barriers computed using DFT, accurately reproduces the CO and CO2 TPRS traces only after CO binding energies are lowered to values determined using a hybrid exchange-correlation functional and the barrier for CO molecules to fill bridging O-vacancies is lowered. The simulations predict that O-vacancies play an important role in mediating the CO oxidation kinetics on s-IrO2(110), and thereby demonstrate the importance of future spectroscopic studies aimed at characterizing the nature of the surface CO and O species involved in reaction. This study provides new insights for understanding CO oxidation on IrO2(110), and provides evidence that several elementary steps can be involved in governing this chemistry.

M/BiOCl-(M=Pt, Pd, and Au) Boosted Selective Photocatalytic CO2 Reduction to C2 Hydrocarbons via *CHO Intermediate Manipulation.

Selective CO2 photoreduction to C2 hydrocarbons is significant but limited by the inadequate adsorption strength of the reaction intermediates and low efficiency of proton transfer. Herein, an ameliorative *CO adsorption and H2O activation strategy is realized via decorating bismuth oxychloride (BiOCl) nanostructures with different metal (Pt, Pd, and Au) species. Experimental and theoretical calculation results reveal that distinct *CO binding energies and *H acquisition abilities of the metal cocatalysts mediate the CO2 reduction activity and hydrocarbon selectivity. The relatively moderate *CO adsorption and *H supply over Pd/BiOCl endows it with the lowest free energy to generate *CHO, leading to its highest activity of hydrocarbon production. Specifically, the Pt cocatalyst can efficiently participate in H2O dissociation to deliver more *H for facilitating the protonation of the *CHO and *CHOH, thereby favoring CH4 production with 76.51% selectivity. A lower *H supply over Pd/BiOCl and Au/BiOCl results in a large energy barrier for *CHO or *CHOH protonation and thus a more thermodynamically favored OC─CHO coupling pathway, which endows them with vastly increased C2 hydrocarbon selectivity of 81.21% and 92.81%, respectively. The understanding of efficient C2 hydrocarbon production in this study sheds light on how materials can be engineered for photocatalytic CO2 reduction.

Ligand-Coordinated Pt Single-Atom catalyst facilitates Support-Assisted Water-Gas shift reaction

The water–gas shift (WGS) reaction (CO+H2O→CO2+H2,ΔH=-41.1kJ/mol) is an essential process in the production of hydrogen and has grown significantly in usage over time. In this study, we further explore a novel strategy that can create single-atom catalysts (SACs) from metal-ligand single-sites on high surface area oxide supports for catalyzing the WGS reaction. The metal–ligand approach results in high metal loading, exhibits an ultimate dispersion of metal species and maximizes atom efficiency. 1,10-phenanthroline-5,6-dione (PDO) was chosen as the ligand for its oxidative potential for stabilizing Pt metal cations via two different binding pockets. The single-atom nature of the Pt-ligand is characterized with extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and transmission electron microscopy (TEM) techniques. The catalytic activity is evaluated for the WGS reaction, revealing that Pt-ligand SACs supported on defective TiO2 show higher inherent catalytic activity than Pt NPs and a significantly lower activation energy. This characteristic is generally desirable for the redox mechanism. Density functional theory (DFT) calculations reveal that metal–ligand SACs allow CO interaction with oxygen atoms from the TiO2 surface. The redox mechanism of the WGS reaction demonstrates a lower effective activation barrier than the associative mechanism for Pt-ligand SAC. Moreover, the metal–ligand strategy, according to DFT results, facilitates the reaction redox mechanism by reducing the CO binding energy and promoting CO2 and H2 formation process.

Electrochemical Reduction of CO2 to Multi-Carbon Products on Sputtered Cu Nanoparticles Gas Diffusion Electrodes

The electrochemical reduction of CO2 is a technology of great environmental and economic interest as it provides a promising solution for reducing the concentration of CO2 with producing valuable chemical compounds. Cu and its alloys have attracted much attention because of their moderate CO binding energy for reducing CO2 to multi-carbon (C2+) products[1]. The reactivity and product selectivity of the CO2 reduction reaction (CO2RR) depend on the interfacial structure and the nano-scale morphology of the catalyst as well as on the catalyst material composition. Especially for the gas diffusion electrodes (GDEs), the catalyst morphology has a significant influence on the formation of triple-phase boundary that increases CO2 reactivity and product selectivity[2,3]. However, the influence of catalyst morphology including catalyst thickness, porosity, particle size on CO2RR has not been fully understood yet because of the complex CO2RR mechanism and catalyst structure in GDEs. In this study, we investigated the relationship between product selectivity and the thickness of the Cu controlled by sputtering techniques and characterized nanostructure of the Cu-GDEs.The Cu catalyst layer (CL) was deposited on a commercial carbon-based gas diffusion layer (GDL) with a micro porous layer (MPL) by magnetron sputtering from a pure Cu target at room temperature. The geometric area of the deposited Cu was 0.5 cm2. The nanostructures of GDEs were evaluated using scanning transmission electron microscopy equipped with energy dispersive X-ray analyzer (STEM-EDX). Electrochemical experiments were carried out in a three-electrode setup using a Biologic-VSP instrument. A home-made three-compartment flow cell was used with the Cu-GDE as the working electrode between the gas and cathode compartments. An Ag/AgCl electrode was placed in the cathode compartment as the reference electrode and a Pt mesh as the counter electrode in the anode compartment. 1 M KCl was used as the catholyte, saturated KHCO3 was used as the anolyte and a proton exchange membrane (Nafion 117) was used to separate the anode and cathode compartments. The CO2 gas flow to a gas compartment was kept at 30 sccm. Electrochemical CO2RR was performed by chronopotentiometry. The gas products were quantified using a gas chromatography with thermal conductivity detector. As for the liquid products, alcohols were evaluated using a gas chromatography with flame ionization detector and organic acids were detected by high performance liquid chromatography with conductivity detector, respectively.The faradaic efficiencies (FEs) of CO2RR products using GDEs with various CL thickness of 70, 300, 1000, 2000 nm were measured under current density of 400 mA cm-2. The GDE with CL thickness of x nm is written as CLxGDE. The major gas and liquid products for all the GDEs were ethylene and ethanol with the FE of around 37-42% and 26-31%, respectively. As decreasing CL thickness from 2000 nm, FEs for C2+ products (FEC2+), such as ethylene, ethanol, n-propanol etc., were increased from that of CL2000GDE of 69%. The maximum FEC2+ reaching 81% was achieved for CL300GDE. The FEC2+ for CL70GDE was slightly decreased down to 76%. In comparison with the FEs for CL2000GDE, the FEs of ethylene, ethanol, and n-propanol were each increased by 2-5%, while FE of H2 was decreased for CL300GDE.To clarify the details of CL morphology, the surface structure of CL300GDEs was observed before and after the CO2RR measurement using STEM-EDX. Figures (a) and (b) show cross-sectional images of nano-scale annular dark field (ADF)-STEM and EDX mapping (purple color show Cu and cyan blue color show C) before the CO2RR measurement. The Cu layer was uniformly stacked on MPL with the designed thickness of 300 nm. Figures (c) and (d) show cross-sectional images of ADF-STEM and EDX mapping after the CO2RR measurement. Cu nanoparticles less than 50 nm were distributed on the surface and inside of the MPL. The stacked Cu layer as observed before the CO2RR measurement was not observed after the CO2RR. These results indicate that Cu atoms migrate during the CO2RR and distributed Cu nanoparticles exhibit the high FEC2+. We will discuss the influence of Cu migration during the CO2RR on product selectivity from the results of synchrotron-based analysis and nanostructure observation in the presentation.[1] A. Bagger et al., ChemPhysChem. 2017, 18, 3266-3273.[2] N. T. Nesbitt et al., ACS Catal. 2020, 10, 14093-14106.[3] A. Inoue et al., EES Catal. 2023, 1, 9–16.Fig. Cross-sectional images of (a), (c) ADF-STEM and (b), (d) EDX mapping before and after CO2RR for CL300GDEs, respectively. Purple color show Cu and cyan blue color show C. Figure 1

In-situ electrochemical interface of Cu@Ag/C towards the ethylene electrosynthesis with adequate *CO supply

The conversion of carbon dioxide to ethylene by electrochemical reduction (CO2RR) provides a new strategy for achieving carbon dioxide conversion. However, copper-based catalysts have the disadvantages of unsatisfactory selectivity and low current density, which limit the potential CO2RR industrial expansion. Researches have verified that the real reaction sites at the catalyst surface often undergo reconstruction during the reaction, therefore, understanding and utilizing this phenomenon is crucial for improving catalytic performance. In this work, we introduced additional Ag component into Cu@Ag/C tandem catalyst by in-situ electrochemical reconstruction of Cu2CO3(OH)2/AgCl/C precursor. This electro-reduced catalyst exhibits a C2H4 Faradaic efficiency of 50.41% in H-cell, and 58.03% in the flow cell, surpassing the counterparts of pure Cu and Ag, as well as the Cu-Ag homolog with separated interface. Moreover, it also provides a long-term stability of 21 h with the ethylene Faraday efficiency (FE) over 50%. The appropriate amount of Ag dopant into the Cu catalyst changes the electronic structure of Cu surface by the electron transfer from Cu to Ag, which distinctly enhances the binding energy of CO2 on the catalyst. Meanwhile, in-situ Raman results and theoretical calculation reveal that the introduction of silver increases the number of active sites and improves the coverage of *CO intermediate, thereby accelerating the kinetics of C–C coupling and reducing its energy barrier. The combination of cascade catalytic strategy and in-situ electroreduction interface provides potential applications for future artificial carbon balance.

Combined experimental and theoretical studies on adsorption characteristics of graphitic carbon nitride for flue gas molecules

Graphitic carbon nitride (g-C3N4) is a novel selective adsorbent for separation of Hg0 and Hg2+, which plays a pivotal role in mercury continuous emission monitoring systems (Hg-CEMS). However, some of the flue gas components may interfere with their binding characteristics with g-C3N4. This study employs the density functional theory (DFT) and experimental method to investigate the adsorption behavior of gas components on g-C3N4 and elucidates the intrinsic driving forces behind these interactions and assesses their impact on separation of Hg0 and HgCl2. The binding energies of H2O, SO2, CO2, NO, and O2 molecules on g-C3N4 are −0.575 eV, −0.530 eV, −0.309 eV, −0.246 eV, and −0.238 eV, respectively. The electronic structure and weak interaction analyses indicate that these interactions are primarily van der Waals forces caused by multi-atomic interactions. In contrast, the binding energy between HCl and g-C3N4 is −0.557 eV, primarily controlled by weak H-N covalent bonds. The co-adsorption results indicate that flue gas molecules exert negligible effects on the binding of HgCl2 to g-C3N4 because the changes in binding energy are within 0.15 eV. The experimental results verify that under practical operating conditions, the adsorption of H2O, HCl, SO2, CO2, NO, and O2 on g-C3N4 is below 0.1 %, demonstrating those components do not interfere with the separation of Hg0 and HgCl2 by g-C3N4, nor do they affect the regeneration performance of g-C3N4. This study provides new insights into the development and practical application of separation and conversion modules in Hg-CEMS technologies.

Cu Based Dilute Alloys for Tuning the C2+ Selectivity of Electrochemical CO2 Reduction.

Electrochemical CO2 reduction is a promising technology for replacing fossil fuel feedstocks in the chemical industry but further improvements in catalyst selectivity need to be made. So far, only copper-based catalysts have shown efficient conversion of CO2 into the desired multi-carbon (C2+) products. This work explores Cu-based dilute alloys to systematically tune the energy landscape of CO2 electrolysis toward C2+ products. Selection of the dilute alloy components is guided by grand canonical density functional theory simulations using the calculated binding energies of the reaction intermediates CO*, CHO*, and OCCO* dimer as descriptors for the selectivity toward C2+ products. A physical vapor deposition catalyst testing platform is employed to isolate the effect of alloy composition on the C2+/C1 product branching ratio without interference from catalyst morphology or catalyst integration. Six dilute alloy catalysts are prepared and tested with respect to their C2+/C1 product ratio using different electrolyzer environments including selected tests in a 100-cm2 electrolyzer. Consistent with theory, CuAl, CuB, CuGa and especially CuSc show increased selectivity toward C2+ products by making CO dimerization energetically more favorable on the dominant Cu facets, demonstrating the power of using the dilute alloy approach to tune the selectivity of CO2 electrolysis.

A comparative DFT study of CO and NO capture by copper- and titanium-functionalized SiC and GeC monolayers

In this work, the interactions of NO and CO molecules with silicon carbide (SiC) and germanium carbide (GeC) graphene-like nanosheets, functionalized with titanium and copper atoms, are comparatively studied through density-functional calculations. The results indicate that NO and CO molecules are only slightly adsorbed on the pristine carbide nanosheets. Also, the copper and titanium adatoms are chemisorbed on the monolayers, leading to stable functionalized carbide nanosheets. These adatoms greatly enhance the binding energies of CO and NO. In particular, the titanium-functionalized GeC monolayers display the highest adsorption energies for CO and NO and also the largest changes in their work functions upon molecule adsorption, indicating that they could be useful for trapping or detecting these molecules.

Performance of Transition Metals in Imidazolium‐Assisted CO2 Reduction in Acetonitrile

AbstractThis study explores the electrochemical reduction of CO2 in dry acetonitrile containing 1,3‐dimethyl imidazolium cations, utilizing late‐transition metals (Au, Ag, Zn, Cu, and Ni). All metals exhibit remarkable selectivity, nearing 100 %, for CO formation. Particularly noteworthy is Au, which manifests the lowest (−2.37 V vs. Ag/Ag+) overpotential in chronopotentiometry experiments. We propose that, for metals with lower CO binding energies compared to Au (Ag and Zn electrodes) – calculated by DFT, the rate‐determining step is the adsorption of CO2. This distinction in CO2 adsorption is reinforced by the examination of partial charge transfer from negatively charged slabs to CO2 (−0.241 a.u with the Au electrode and +0.002 a.u with the Zn electrode). Conversely, the greater CO binding energy calculated for Cu and Ni likely diminishes electrocatalytic activity relative to the Au electrode. Our results unveil a volcano trend in catalyst activity, albeit with smaller performance disparities between the late‐transition metals and Au than previously observed in aqueous conditions, possibly due to the co‐catalytic influence of imidazolium cations. This study suggests that metals unsuitable for aqueous environments hold promise for cost‐effective and viable electrochemical conversion of CO2 to CO in non‐aqueous media containing imidazolium compounds.

Synergistic Effects of Amine Functional Groups and Enriched-Atomic-Iron Sites in Carbon Dots for Industrial-Current-Density CO2 Electroreduction.

Metal phthalocyanine molecules with Me-N4 centers have shown promise in electrocatalytic CO2 reduction (eCO2R) for CO generation. However, iron phthalocyanine (FePc) is an exception, exhibiting negligible eCO2R activity due to a higher CO2 to *COOH conversion barrier and stronger *CO binding energy. Here, amine functional groups onto atomic-Fe-rich carbon dots (Af-Fe-CDs) are introduced via a one-step solvothermal molecule fusion approach. Af-Fe-CDs feature well-defined Fe-N4 active sites and an impressive Fe loading (up to 8.5wt%). The synergistic effect between Fe-N4 active centers and electron-donating amine functional groups in Af-Fe-CDs yielded outstanding CO2-to-CO conversion performance. At industrial-relevant current densities exceeding 400mA cm-2 in a flow cell, Af-Fe-CDs achieved >92% selectivity, surpassing state-of-the-art CO2-to-CO electrocatalysts. The in situ electrochemical FTIR characterization combined with theoretical calculations elucidated that Fe-N4 integration with amine functional groups in Af-Fe-CDs significantly reduced energy barriers for *COOH intermediate formation and *CO desorption, enhancing eCO2R efficiency. The proposed synergistic effect offers a promising avenue for high-efficiency catalysts with elevated atomic-metal loadings.

Adsorption and Diffusion Properties of Functionalized MOFs for CO2 Capture: A Combination of Molecular Dynamics Simulation and Density Functional Theory Calculation.

The capture of carbon dioxide (CO2) from fuel gases is a significant method to solve the global warming problem. Metal-organic frameworks (MOFs) are considered to be promising porous materials and have shown great potential for CO2 adsorption and separation applications. However, the adsorption and diffusion mechanisms of CO2 in functionalized MOFs from the perspective of binding energies are still not clear. Actually, the adsorption and diffusion mechanisms can be revealed more intuitively by the binding energies of CO2 with the functionalized MOFs. In this work, a combination of molecular dynamics simulation and density functional theory calculation was performed to study CO2 adsorption and diffusion mechanisms in five different functionalized isoreticular MOFs (IRMOF-1 through -5), considering the influence of functionalized linkers on the adsorption capacity of functionalized MOFs. The results show that the CO2 uptake is determined by two elements: the binding energy and porosity of MOFs. The porosity of the MOFs plays a dominant role in IRMOF-5, resulting in the lowest level of CO2 uptake. The potential of mean force (PMF) of CO2 is strongest at the CO2/functionalized MOFs interface, which is consistent with the maximum CO2 density distribution at the interface. IRMOF-3 with the functionalized linker -NH2 shows the highest CO2 uptake due to the higher porosity and binding energy. Although IRMOF-5 with the functionalized linker -OC5H11 exhibits the lowest diffusivity of CO2 and the highest binding energy, it shows the lowest CO2 uptake. Accordingly, among the five simulated functionalized MOFs, IRMOF-3 is an excellent CO2 adsorbent and IRMOF-5 can be used to separate CO2 from other gases, which will be helpful for the designing of CO2 capture devices. This work will contribute to the design and screening of materials for CO2 adsorption and separation in practical applications.

Alumina Incorporation in Self-Supported Poly(ethylenimine) Sorbents for Direct Air Capture.

Self-supported branched poly(ethylenimine) scaffolds with ordered macropores are synthesized with and without Al2O3 powder additive by cross-linking poly(ethylenimine) (PEI) with poly(ethylene glycol) diglycidyl ether (PEGDGE) at -196 °C. The scaffolds' CO2 uptake performance is compared with a conventional sorbent, i.e., PEI impregnated on an Al2O3 support. PEI scaffolds with Al2O3 additive show narrow pore size distribution and thinner pore walls than alumina-free materials, facilitating higher CO2 uptake at conditions relevant to direct air capture. The PEI scaffold containing 6.5 wt % Al2O3 had the highest CO2 uptake of 1.23 mmol/g of sorbent under 50% RH 400 ppm of CO2 conditions. In situ DRIFT spectroscopy and temperature-programmed desorption experiments show a significant CO2 uptake contribution via physisorption as well as carbamic acid formation, with lower CO2 binding energies in PEI scaffolds relative to conventional PEI sorbents, likely a result of a lower population of primary amines due to the amine cross-linking reactions during scaffold synthesis. The PEI scaffold containing 6.5 wt % Al2O3 is estimated to have the lowest desorption energy penalty under humid conditions, 4.6 GJ/tCO2, among the sorbents studied.

Insight into the ordering process and ethanol oxidation performance of Au-Pt-Cu ternary alloys.

Direct ethanol fuel cells (DEFCs), which have been widely recognized as nontoxic and green energy conversion devices, show attractive application prospects for liquid hydrogen-carriers, due to the higher specific energy and lower toxicity of ethanol. Pt-based catalysts are widely used in DEFCs, while their poor poisoning resistance highlights the importance of composition and structure optimization. Herein, we synthesized a series of reduced graphene oxide supported ternary alloy AuxPt1-xCu3/rGO (x = 0-1) catalysts with excellent ethanol oxidation performance and a composition-dependent volcano plot trend of the ordering degree was observed and rationalized. The highest Pt-normalized mass activity of Au0.8Pt0.2Cu3/rGO is attributed to the optimized CO binding energy according to DFT calculations. This work not only provides an efficient EOR catalyst based on ordered alloys AuxPt1-xCu3 (x = 0-1), but also offers valuable insight into the role of a third metal in tuning the structure and function of alloys.

Efficient mapping of CO adsorption on Cu1−xMx bimetallic alloys via machine learning

A two-step machine learning model to predict CO binding energies on CuM(111)/(100) bimetallic surfaces and enhance the CO2RR selectivity towards C2 products.

Spectroscopic investigation of size-dependent CO2 binding on cationic copper clusters: analysis of the CO2 asymmetric stretch.

Photofragmentation spectroscopy, combined with quantum chemical computations, was employed to investigate the position of the asymmetric CO2 stretch in cold, He-tagged Cun[CO2]+ (n = 1-10) and Cun[CO2][H2O]+ (n = 1-7) complexes. A blue shift in the band position was observed compared to the free CO2 molecule for Cun[CO2]+ complexes. Furthermore, this shift was found to exhibit a notable dependence on cluster size, progressively redshifting with increasing cluster size. The computations revealed that the CO2 binding energy is the highest for Cu+ and continuously decreases with increasing cluster size. This dependency could be explained by highlighting the role of polarization in electronic structure, according to energy decomposition analysis. The introduction of water to this complex amplified the redshift of the asymmetric stretch, showing a similar dependency on the cluster size as observed for Cun[CO2]+ complexes.

Two-Dimensional Carbon Nitride as a Support of Single Metal Atom for Carbon Dioxide Reduction Reaction

Electrochemical conversion of CO2 into added-value chemicals is an important approach to recycle CO2. Heterogeneous catalysis is widely used in industrial applications because of the possibility of facile separation, which reduces the operating costs, although heterogeneous catalysts often have limited selectivity. In contrast, homogeneous catalysts are very selective although they have limited industrial applications due to their cost, the use of precious metals, and the difficulty in separating and recovering the catalysts. Currently, the research community is trying to combine the properties of homogeneous and heterogeneous catalysts. From the heterogeneous catalyst perspective, research has been focused on creating smaller and dispersed catalyst particles. Single-atom catalysts (SACs), which comprise atoms of metal species dispersed on a solid support, are expected to bridge the homogeneous and heterogeneous catalyst properties.The work described herein explores, by means of density functional simulations, the electrocatalytic CO2 reduction reaction (CO2RR) using several single transition metal atoms anchored in 2D graphitic carbon nitride (g-C3N4),1 focusing on the group XI transition metals since they include Cu, the only transition metal capable of reducing CO2 to hydrocarbons and alcohols with acceptable faradaic efficiencies. Moreover, the Cu1/g-C3N4 system has been experimentally evaluated as CO2RR electrocatalysts. 2D g-C3N4 has been demonstrated to be a competitive candidate for electrocatalytic CO2 reduction since it can act as an active support for single metal-atom catalysts, mainly Cu, Pd, and Pt, and the deposition of Au single atom was experimentally characterized.The computational hydrogen electrode model has been used to explore the suitability of several transition metals atoms anchored to C3N4, showing that single atoms enhance the catalytic activity of the system as the first proton–electron transfer is thermodynamically favored in comparison to bare carbon nitride support. Our theoretical interpretations are consistent with the experimental results using Cu1/g-C3N4,2 revealing that the competitive H2 generation is favored due to the strong CO binding energies. This fact reinforced the capability of our computational models to predict the behavior of several single metal atom electrocatalysts to reduce CO2, for instance, predicting that Au can promote the methane formation after eight electron-proton transfer processes. Our computational study paves the road to finding suitable metals that catalyze the first proton–electron transfer in the carbon dioxide reduction reaction. Posada-Pérez, A. Vidal-López, M. Solà, and A. Poater, 2023, Phys. Chem. Chem. Phys, 25, 8574.Cometto, A. Ugolotti, E. Grazietti, A. Moretto, G. Bottaro, L. Armelao, C. Di Valentin, L. Calvillo and G. A. Granozzi, npj 2D Mater. Appl., 2021, 5, 63. Figure 1

In Situ STM Investigations of Cu(100) and Bimetallic Ag/Cu(100) Model Catalysts for CO2 Electroreduction in Bicarbonate Solution

The electrochemical conversion of carbon dioxide (CO2RR) to valuable chemicals and fuels plays a crucial role in the sustainable energy economy as it represents a promising potential for the renewable energy storage as well as closing the carbon loop.[1,2] Thus, the design and development of a highly efficient and selective electrocatalyst for CO2RR has become a topic of great importance in recent years. Among elemental metals, copper exhibits unique catalytic behaviour to reduce CO2 towards multi-carbon products with reasonable Faradaic efficiency due to its moderate CO-binding energy.[3,4] However, the selectivity and activity of pure copper is still far away for a practical application. The integration of a secondary metal species provides a promising strategy to improve the catalytical performance of the copper catalyst. Combination with silver is particularly interesting for such bimetallic catalysts, since Ag is a highly efficient catalyst for CO2RR to CO, probably the most important intermediate in the CO2RR, and has been shown to promote the formation of multi-carbon products.[5]Here, we present in situ scanning tunnelling microscopy studies of well-defined Cu and AgCu electrodes in CO2-satured 0.1 M KHCO3, which is one of the most common electrolytes for CO2 electroreduction. For Cu(100) in the double layer potential range, coexistence of two ordered (bi)carbonate adlayer phases was observed (Fig. 1a,b, published in [6]). These adlayer phases have a highly complex structure, exhibit dynamic fluctuations, and undergo a potential dependent order-disorder transition at about 0 V vs. the reversible hydrogen electrode. Detailed density functional calculations reveal that the observed layer is composed of carbonate and water that coadsorb on the electrode surface, underlining the key role of water in the stabilization of the (bi)carbonate adlayers.[6]Upon decreasing the potential to the onset of CO2RR, the formation of Cu nanoclusters is observed on the Cu(100) surfaces by in situ STM. This surface restructuring can be assigned to the influence of CO intermediates formed in the CO2RR. Upon subsequent increase of the potential back into the double layer range, the clusters disperse, resulting in a highly disordered interface structure that contains Cu adatoms, (bi)carbonates, and further molecular adsorbates. This irreversible change of the molecular-scale electrode surface is supported by spectroscopic results.AgCu bimetallic model catalysts were prepared by electrodeposition of submonolayer Ag coverage on Cu(100) in 0.1 M H2SO4. Silver forms islands on Cu(100) with a hexagonal quasi-Ag(111) atomic lattice. After the preparation and characterization of the Ag-decorated Cu(100), the electrolyte was exchanged under potential control to 0.1 M KHCO3. The electrolyte exchange results in the distinct restructuring on the surface in the double layer potential range, in which the islands develop a strongly anisotropic shape. In addition, appearance of new islands and a reduced surface mobility are observed. Furthermore, in contrast to the Ag-free Cu(100), high-resolution STM images show a disordered molecular adlayer.Our results demonstrate the pronounced role of adsorbed (bi)carbonate at the catalyst/electrolyte interface and its impact on the surface morphology and dynamics already at potentials in the double layer regime. These adsorbate-induced structural changes need to be considered for a fundamental understanding and rational design of electrocatalysts for CO2RR.The Authors gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) via SPP 2080, project no. 327886311.

CO2 capture and storage by metal and non-metal decorated silicon carbide nanotubes: a DFT study

This study addressed the nano-mechanism of CO2 capture by Al-doped, B-doped and N-doped single-walled silicon carbide nanotubes (SWSiCNTs) using the prominent density functional theory. The results showed absolute interactions between CO2 and B- and N- impurity atoms of the SWSiCNT surface with the highest adsorption energy of −1.85 eV and −1.83 eV respectively. Analysis of the binding energy of CO2 to Al-doped SWSiCNT revealed that chemisorption between them is stronger than B-doped and N-doped SWSiCNTs. Results from optical adsorption spectra revealed that both B-and N-doped systems adsorb CO2 in the visible region of the electromagnetic spectrum while B-doped SiCNT shows the highest adsorption. This study recommends B- and N-doped SiCNTs as candidates for CO2 capture and storage with higher efficiency by B-doped SiCNT, while the performance of the Al-doped system was underscored.

CO Binding Energy is an Incomplete Descriptor of Cu-Based Catalysts for the Electrochemical CO2 Reduction Reaction.

CO binding energy has been employed as a descriptor in the catalyst design for the electrochemical CO2 reduction reactions (CO2 RR). The reliability of the descriptor has yet been experimentally verified due to the lack of suitable methods to determine CO binding energies. In this work, we determined the standard CO adsorption enthalpies ( ) of undoped and doped oxide-derived Cu (OD-Cu) samples, and for the first time established the correlation of with the Faradaic efficiencies (FE) for C2+ products. A clear volcano shaped dependence of the FE for C2+ products on is observed on OD-Cu catalysts prepared with the same hydrothermal durations, however, the trend becomes less clear when all catalysts investigated are taken into account. The relative abundance of Cu sites active for the CO2 -to-CO conversion and the further reduction of CO is identified as another key descriptor.