Metal CO Research Articles

Routes to Bidirectional Cathodes for Reversible Aprotic Alkali Metal–CO2 Batteries

AbstractAprotic alkali metal–CO2 batteries (AAMCBs) have garnered significant interest owing to fixing CO2 and providing large energy storage capacity. The practical implementation of AAMCBs is constrained by the sluggish kinetics of the CO2 reduction reaction (CO2RR) and the CO2 evolution reaction (CO2ER). Because the CO2ER and CO2RR take place on the cathode, which connects the internal catalyst with the external environment. Building a bidirectional cathode with excellent CO2ER and CO2RR kinetics by optimizing the cathode's internal catalyst and environment has attracted most of the attention to improving the electrochemical performance of AAMCBs. However, there remains a lack of comprehensive understanding. This review aims to give a route to bidirectional cathodes for reversible AAMCBs, by systematically discussing engineering strategies of both the internal catalyst (atomic, nanoscopic, and macroscopic levels) and the external environment (photo, photo‐thermal, and force field). The CO2ER and CO2RR mechanisms and the “engineering strategies from internal catalyst to the external environment–cathode properties–CO2RR and CO2ER kinetics and mechanisms–batteries performance” relationship are elucidated by combining computational and experimental approaches. This review establishes a fundamental understanding for designing bidirectional cathodes and gives a route for developing reversible AAMCBs and similar metal–gas battery systems.

Co/SiO2 Catalyst for Methoxycarbonylation of Acetylene: On Catalytic Performance and Active Species.

Reppe carbonylation of acetylene is an atom-economic and non-petroleum approach to synthesize acrylic acid and acrylate esters, which are key intermediates in the textile, leather finishing, and polymer industries. In the present work, a noble metal-free Co@SiO2 catalyst was prepared and evaluated in the methoxycarbonylation reaction of acetylene. It was discovered that pretreatment of the catalyst by different reductants (i.e., C2H2, CO, H2, and syngas) greatly improved the catalytic activity, of which Co/SiO2-H2 demonstrated the best performance under conditions of 160 °C, 0.05 MPa C2H2, 4 MPa CO, and 1 h, affording a production rate of 4.38 gMA+MP gcat-1 h-1 for methyl acrylate (MA) and methyl propionate (MP) and 0.91 gDMS gcat-1 h-1 for dimethyl succinate (DMS), respectively. Transmission electron microscopy (TEM), X-ray diffraction (XRD), and diffuse reflectance infrared Fourier transform spectra of CO adsorption (CO-DRIFTS) measurements revealed that an H2 reduction decreased the size of the Co nanoparticles and promoted the formation of hollow architectures, leading to an increase in the metal surface area and CO adsorption on the catalyst. The hot filtration experiment confirmed that Co2(CO)8 was generated in situ during the reaction or at the pre-activation stage, which served as the genuine active species. Our work provides a facile and convenient approach to the in situ synthetization of Co2(CO)8 for a Reppe carbonylation reaction.

The nature and degree of the cooperativity of (η5-C5H5)–metal and metal–CO bonds in half-sandwich complexes of groups 5, 7, 9, and 11 transition metals

It is shown that, the cooperativity always has the same quantitative effect on the interaction energies of two cooperated chemical bonds but may have different effects on their nature.

A sustainable redox-mediated pathway for improved transition metal organic framework activation and CO2 uptake performance

A sustainable redox-mediated pathway for improved transition metal organic framework activation and CO₂ uptake performance

Photoinduced morphological transformation of a self-assembled iron(ii) coordination polymer: high-performance, non-precious metal, and self-enhancing photocatalytic CO2 reduction

Herein, uncommon self-enhancing photocatalysis has been demonstrated through photoinduced morphology transformation of a self-assembled iron coordination polymer for CO2 photoreduction.

Heterogeneous Electrocatalysts for Metal–CO2 Batteries and CO2 Electrolysis

Heterogeneous electrocatalysis is one of the most promising ways to advance the development of metal–CO2 batteries and CO2 electrolysis technologies. Although both research areas rely upon efficient electrochemical reduction of CO2, to date the respective research has been largely carried out independently. This Focus Review introduces the latest innovative design strategies toward heterogeneous electrocatalysts applied for both metal–CO2 batteries and CO2 electrolysis. The structural design of various categories of catalysts, their synthesis methods, and electrocatalytic reactions are discussed in detail. The review also presents a discussion of the fundamental reaction mechanisms active for both applications. Finally, we will reflect on the challenges and new opportunities for each category of electrocatalysts. We hope to provide researchers a more comprehensive understanding of the design of high-performing electrocatalysts to advance both metal–CO2 batteries and CO2 electrolysis technologies.

Crown Ether- and Benzoxazine-Linked Porous Organic Polymers Displaying Enhanced Metal Ion and CO2 Capture through Solid-State Chemical Transformation

Crown Ether- and Benzoxazine-Linked Porous Organic Polymers Displaying Enhanced Metal Ion and CO₂ Capture through Solid-State Chemical Transformation

Life cycle assessment of CO2 conversion and storage in metal–CO2 electrochemical cells

AbstractResearchers have proposed a family of electrochemical technologies that incorporate CO2 as a gas cathode and alkali or alkaline earth metal anodes to exploit the high reactivity of CO2 with these metals. Such proposed cells operate by converting gaseous CO2 into solid carbonate, extracting value from CO2 in the form of electricity, and fixing the CO2 in solid form. Given the increasing number of these proof‐of‐concept studies, it is timely to critically examine the potential of such emerging technologies to reduce stationary point source emissions. Environmental life cycle assessment (LCA) during early research stages can inform important design decisions. In this study, we perform LCA on electrochemical conversion processes (ECPs) involving Li, Na, Mg, or Ca as a co‐reactant with CO2 sourced from a coal plant, evaluating differing scenarios. We find that a Na‐based primary ECP configuration that integrates capture with conversion of coal plant CO2 emissions to Na2CO3 can avoid almost 28% of emissions (and 74% under best‐case conditions) that are typically associated with conventional production of the same carbonate and electricity. This represents a net emissions decrease of 435 kg CO2‐eq per 1 MWh of electricity delivered by the ECP, from a baseline of 1,105 kg CO2‐eq emitted without any mitigation strategies. In contrast, all ECPs in a rechargeable configuration result in increased emissions compared to the conventional baseline, unless the ECP system energy requirements are provided by renewables and the conventional system is assumed to have high emissions intensity.

Insights into the Metal-CO Bond in O2M(η1-CO) (M = Cr, Mo, W, Nd, and U) Complexes.

Investigations on the structures and bonding properties of metal carbonyl compounds provide fundamental understandings on the origin of small-molecule activations. Herein, the geometry and bonding trends of a series of isovalent metal oxocarbonyl complexes O2M(η1-CO) (M = Cr, Mo, W, Nd, and U) were studied by combined matrix-isolation infrared spectroscopy and advanced quantum chemical calculations. The title complexes present red shift of C-O stretching bands in the range from 122 to 244 cm-1, indicating the difference of CO activation ability for the series of isovalent metal dioxides. Density functional theory calculations predict T-shaped structures with a C2v symmetry for all the title molecules. O2Nd(η1-CO) bears little resemblance to the other complexes in bonding characters because of the weak interactions between the NdO2 and CO moiety. For the other complexes, natural localized molecular orbital analysis reveals a gradual increase of covalent character in M-CO bonds along the metal series Cr → Mo → W→ U. Energy decomposition analysis with natural orbitals for chemical valence calculations demonstrates that the M-CO bonding patterns conform to the conventional Dewar-Chatt-Duncanson motif. The contributions from orbital interactions in total attractions increase from Cr (41.7%) to U (52.7%). The breakdown of the orbital term into pairwise interactions shows that contributions of the M ← CO σ donation decrease from Cr (59.2%) to U (28.4%), while the M → CO π* backdonation increases significantly from Cr (23.8%) to U (67.3%). The more effective overlap and the better energy matching of U 5f and U 6d valence orbitals with CO π* orbitals result in much stronger U → CO π backdonation than the other metal elements.

CNT boosted two-dimensional flaky metal-organic nanosheets for superior lithium and potassium storage

Flaky nanosheets with superior molecular structures and functions are indispensable for high-performance lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs). Herein, through a simple dispersion method, two-dimensional Co-MOF-CNT nanosheets are prepared by adding nanotubes (CNT) during the synthesis of MOF under microwave-assisted radiation conditions. The flaky dispersed sheet structure possesses more exposed surfaces and porous structures for Co-MOF-CNT, which is beneficial to offering numerous active sites and promoting the rapid transmission of Li/K-ions. Therefore, when applied as negative electrode for LIB and PIB, the Co-MOF-CNT nanosheets can provide an extremely enhanced reversible capacity (1451/286 mAh g−1 for LIBs/PIBs after 100 cycles at 100 mA g−1). In view of ex-situ XPS result, in-situ FTIR result and electrochemical detection, the excellent electrochemical performance is determined due to the activated lithium-reaction involving metal centers, CO groups and CC groups from benzene rings. The research on lithium/potassium reaction functional groups of MOF nanosheets with more activated energy-storage sites would further provide guidance for the exploration on superior-performance electrodes for future alkali metal secondary batteries.

Critical Role of Thermal Fluctuations for CO Binding on Electrocatalytic Metal Surfaces.

This work considers the evaluation of density functional theory (DFT) when comparing against experimental observations of CO binding trends on the strong binding Pt(111) and intermediate binding Cu(111) and for weak binding Ag(111) and Au(111) surfaces important in electrocatalysis. By introducing thermal fluctuations using appropriate statistical mechanical NVT and NPT ensembles, we find that the RPBE and B97M-rV DFT functionals yield qualitatively better metal surface strain trends and CO enthalpies of binding for Cu(111) and Pt(111) than found at 0 K, thereby correcting the overbinding by 0.2 to 0.3 eV to yield better agreement with the enthalpies determined from experiment. The importance of dispersion effects are manifest for the weak CO binding Ag(111) and Au(111) surfaces at finite temperatures in which the RPBE functional does not bind CO at all, while the B97M-rV functional shows that the CO–metal interactions are a mixture of chemisorbed and physisorbed species with binding enthalpies that are within ∼0.05 eV of experiment. Across all M(111) surfaces, we show that the B97M-rV functional consistently predicts the correct atop site preference for all metals due to thermally induced surface distortions that preferentially favor the undercoordinated site. This study demonstrates the need to fully account for finite temperature fluctuations to make contact with the binding enthalpies from surface science experiments and electrocatalysis applications.

Metal-CO Bonding in Mononuclear Transition Metal Carbonyl Complexes.

DFT calculations have been carried out for coordinatively saturated neutral and charged carbonyl complexes [M(CO)n]q where M is a metal atom of groups 2–10. The model compounds M(CO)2 (M = Ca, Sr, Ba) and the experimentally observed [Ba(CO)]+ were also studied. The bonding situation has been analyzed with a variety of charge and energy partitioning approaches. It is shown that the Dewar–Chatt–Duncanson model in terms of M ← CO σ-donation and M → CO π-backdonation is a valid approach to explain the M–CO bonds and the trend of the CO stretching frequencies. The carbonyl ligands of the neutral complexes carry a negative charge, and the polarity of the M–CO bonds increases for the less electronegative metals, which is particularly strong for the group 4 and group 2 atoms. The NBO method delivers an unrealistic charge distribution in the carbonyl complexes, while the AIM approach gives physically reasonable partial charges that are consistent with the EDA-NOCV calculations and with the trend of the C–O stretching frequencies. The AdNDP method provides delocalized MOs which are very useful models for the carbonyl complexes. Deep insight into the nature of the metal–CO bonds and quantitative information about the strength of the [M] ← (CO)8 σ-donation and [M(d)] → (CO)8 π-backdonation visualized by the deformation densities are provided by the EDA-NOCV method. The large polarity of the M–CO π orbitals toward the CO end in the alkaline earth octacarbonyls M(CO)8 (M = Ca, Sr, Ba) leads to small values for the delocalization indices δ(M–C) and δ(M···O) and significant overlap between adjacent CO groups, but the origin of the charge migration and the associated red-shift of the C–O stretching frequencies is the [M(d)] → (CO)8 π-backdonation. The heavier alkaline earth metals calcium, strontium and barium use their s/d valence orbitals for covalent bonding. They are therefore to be assigned to the transition metals.

Synthesis, characterisation and Electrochemical studies of transition metal CO(II) complexes of Mannich bases from newly synthesised Schiff bases ligand

Synthesis, characterisation and Electrochemical studies of transition metal CO(II) complexes of Mannich bases from newly synthesised Schiff bases ligand

Giant Effect of Negative Compressibility in a Water-Porous Metal-CO2 System for Sensing Applications.

When compressed, the size of ordinary materials reduces. The opposite effect, when a material or system increases (decreases) its volume upon compression (decompression), is called Negative Compressibility (NC). NC is extremely rare, while being attractive for a wide range of applications. Here we demonstrate, by both experiments and MD simulations, a pronounced effect of volumetric NC in a system consisting of water, porous metal and CO2. This effect is achieved due to a new extrusion-adsorption cycle of water from-into a porous metal driven by a wetting-nonwetting transition due to the increase-decrease of CO2 pressure. The heterogeneous nature of such a system leads to unprecedented NC of up to ∼ 90% in a narrow pressure range, meaning that almost a double volume increase (decrease) upon compression (decompression) is achieved. As long as the wetting-nonwetting transition is achieved, the proposed approach is not limited to water and a specific porous metal. An example of the application of this phenomenon is miniature sensors, particularly for threshold CO2 pressure detection.

Metalloenzyme mimic: diironhexacarbonyl cluster coupled to redox-active 4-mercapto-1,8-naphthalic anhydride ligands

The non-innocent redox-active ligand, 4-mercapto-1,8-naphthalic anhydride (HS-NAH), has been used in the design and synthesis of a diironhexacarbonyl complex, [μ-(S-NAH)2Fe2(CO)6]. [μ-(S-NAH)2Fe2(CO)6] has been characterized by spectroscopic methods and cyclic voltammetry. Infrared spectrum of [μ-(S-NAH)2Fe2(CO)6] displays peaks corresponding to terminal metal CO groups (2081, 2044, 2006 cm−1) and peaks assigned to C=O of the naphthalic anhydrides (1780, 1740 cm−1). Electrochemical measurements of [μ-(S-NAH)2Fe2(CO)6] feature redox events that are metal-based (irreversible, Epc: − 1.13 V, − 1.60 V vs Fc/Fc+) and naphthalic anhydride centered (partially chemically reversible, Epc: − 1.99 V; Epa: − 1.90 V vs Fc/Fc+). Cyclic voltammetric analysis of [μ-(S-NAH)2Fe2(CO)6] in the presence of acetic acid show that the complex mimics the active site of [Fe–Fe]-hydrogenase by catalyzing the electrochemical reduction of protons to hydrogen with an overpotential of − 0.67 V. The bi-functional model, [μ-(S-NAH)2Fe2(CO)6], exhibits electronic coupling with synergistic metal–ligand interactions leading to transformation of protons to molecular hydrogen.

CO oxidation on Pt based binary and ternary alloy nanocatalysts: Reaction pathways and electronic descriptor

The design of stable, highly active heterogeneous nanocatalyst with no CO poisoning is a challenge for the catalytic converter industry. This can be achieved by defining electronic descriptor and by understanding the bonding mechanism. We present results using density functional theory to design optimal metal nanoalloy catalysts for CO oxidation. The adsorption configuration of O2 and O on different active sites is studied in detail to find the efficient reaction pathway for CO oxidation. The varying extent of back-donation of charge is found to be the factor deciding the CO tolerance. The trade-off between the activity and CO tolerance signifies that there is an upper limit for alloying Pt with Ni and Co. An electronic descriptor based on the occupancy of the d orbital and d band center of the host atom is defined to explain the site dependent activity of nanocatalysts. The role of underneath carbon surface on the CO oxidation activity of metal sites and CO poisoning is described.

Realization of selective CO detection by Ni-incorporated metal-organic frameworks

In this study, two different kinds of MOFs such as Ni-VNU-74-I and -II were examined for CO gas sensing. The Ni-VNU-74-I and -II showed different pore sizes and surface areas. The as-synthesized iso-reticular type Ni-VNU-74-I and -II sensors showed well crystallin chrysanthemums like morphology with great thermal stability, and surface areas (up to 2350 m2/g). Gas-sensing studies were performed systematically at different temperatures and towards different gases. The Ni-VNU-74-II gas sensor showed a stronger gas response (Ra/Rg = 1.7) to 50 ppm CO gas than to other gases at 200 °C because of the higher quadrupole moment of the CO gas molecules, leading to a strong interaction with a partial charge in the open metal Ni sites. In addition, the better performance of the Ni-VNU-74-II gas sensor compared to the Ni-VNU-74-I gas sensor (Ra/Rg for 50 ppm CO gas = 1.2) was related to the better interaction between the open metal sites (Ni) and CO molecules through a special structure of the Ni-VNU-74-II gas sensor with smaller pore sizes, higher surface area, and higher concentration of open metal Ni2+ sites. The sensing performance in this work indicates Ni-MOFs as the potential gas sensors for the detection of harmful gases in practical applications.

Theoretical Analysis of Fe K-Edge XANES on Iron Pentacarbonyl.

Iron pentacarbonyl (Fe(CO)5) is a versatile material that is utilized as an inhibitor of flame, shows soot suppressibility, and is used as a precursor for focused electron-beam-induced deposition (FEBID). X-ray absorption near-edge structure (XANES) of the K edge, which is a powerful technique for monitoring the oxidation states and coordination environment of metal sites, can be used to gain insight into Fe(CO)5-related reaction mechanisms in in situ experiments. We use a finite difference method (FDM) and molecular-orbital-based time-dependent density functional theory (TDDFT) calculations to clarify the Fe K-edge XANES features of Fe(CO)5. The two pre-edge peaks P1 and P2 are mainly the Fe(1s) → Fe–C(σ*) and Fe(1s) → Fe–C(π*) transitions, respectively. When the geometry transformed from D3h to C4v symmetry, a ∼30% decrease of the pre-edge P2 intensity was observed in the simulated spectra. This implies that the π bonding of Fe and CO is sensitive to changes in geometry. The following rising edge and white line regions are assigned to the Fe(1s) → Fe(4p)(mixing C(2p)) transitions. Our results may provide useful information to interpret XANES spectra variations of in situ reactions of metal–CO or similar compounds with π acceptor ligandlike metal–CN complexes.

Reply to the 'Comment on "Revisiting π backbonding: the influence of d orbitals on metal-CO bonds and ligand red shifts"' by G. Frenking and S. Pan, Phys. Chem. Chem. Phys., 2019, 22, DOI: 10.1039/C9CP05951B.

We respond to the comment by Pan and Frenking with regard to our investigation on transition and alkaline earth metal d orbital influence on their bonding to carbonyl ligands to clarify misconceptions. We do not consider the points raised in the comment as affecting our conclusions.

Metal–CO2 Batteries at the Crossroad to Practical Energy Storage and CO2 Recycle

AbstractMetal–CO2 batteries show great promise in meeting the growing energy, chemical, and environmental demands of daily life and industry, because of their advantages of high flexibility and efficiency in both energy storage and CO2 recycle applications. It has been a trend that Li/Na‐CO2 and Zn/Al‐CO2 systems show different developments to achieve practical energy storage (e.g., high electricity supply) and CO2 recycling (e.g., flexible chemical production), respectively, which is often neglected. This inhibits the application of metal–CO2 batteries in maximizing energy supply and value‐added CO2 conversion. This progress report presents a critically selected overview of the individual developments of metal–CO2 batteries with emphasis on diverse fundamental origins, performance advantages, and the future of these two systems. Furthermore, the reaction pathways, particularly for catalytic materials, for the Li/Na‐CO2 and Zn/Al‐CO2 systems are discussed. Finally, the challenges of these two systems along with a hybrid Li/Na‐CO2 battery design that may simultaneously provide high operating voltages and flexible chemicals are outlined.