HKUST-1 Derived Hollow C-Cu2−xS Nanotube/g-C3N4 Composites for Visible-Light CO2 Photoreduction with H2O Vapor

As the main component of syngas, reducing CO₂ to CO with high selectivity through photocatalysis could provide a sustainable way to alleviate energy shortage issues. Developing a photocatalytic system with low cost and high performance that is environmentally friendly is the ultimate goal towards CO₂ photoreduction. Herein, an efficient and economic three-component heterojunction photocatalyst is designed and fabricated for converting CO₂ to CO in the absence of organic sacrificial agents. The heterojunction is made of Cu_2−xS nanotubes coated with a carbon layer (C-Cu_2−xS) and g-C₃N₄. By using the classical MOF material HKUST-1 as a precursor, hollow tubular-like metal sulfides (C-Cu_2−xS) with carbon coating were synthesized and further loaded on g-C₃N₄, forming a three-component heterojunction C-Cu_2−xS@g-C₃N₄. The carbon coat in C-Cu_2−xS@g-C₃N₄ acts as an electron reservoir, which facilitates electron–hole pair separation. The optimized C-Cu_2−xS@g-C₃N₄ acted as a photocatalyst in CO₂ reduction with a high reactivity of 1062.6 μmol g⁻¹ and selectivity of 97 %. Compared with bare g-C₃N₄ (158.4 μmol g⁻¹) and C-Cu_2−xS, the reactivity is nearly 7 and 23-fold enhanced and this CO generation rate is higher than most of the reported Cu₂S or g-C₃N₄ composites under similar conditions. The prominent activity may result from enhanced light adsorption and effective charge separation. This work might open up an alternative method for the design and fabrication of high-performance and low-cost photocatalysts for efficiently and durably converting CO₂ to CO with high selectivity.     

Photosystem II Inspired NiFe-Based Electrocatalysts for Efficient Water Oxidation via Second Coordination Sphere Effect

The mismatched fast-electron-slow-proton process in the electrocatalytic oxygen evolution reaction (OER) severely restricts the catalytic efficiency. To overcome these issues, accelerating the proton transfer and elucidating the kinetic mechanism are highly sought after. Herein, inspired by photosystem II, we develop a family of OER electrocatalysts with FeO₆/NiO₆ units and carboxylate anions (TA²⁻) in the first and second coordination sphere, respectively. Benefiting from the synergistic effect of the metal units and TA²⁻, the optimized catalyst delivers superior activity with a low overpotential of 270 mV at 200 mA cm⁻² and excellent cycling stability over 300 h. A proton-transfer-promotion mechanism is proposed by in situ Raman, catalytic tests, and theoretical calculations. The TA²⁻ (proton acceptor) can mediate proton transfer pathways by preferentially accepting protons, which optimizes the O−H adsorption/activation process and reduces the kinetic barrier for O−O bond formation.     

Selective Photocatalytic Reduction of CO2 to CO Mediated by Silver Single Atoms Anchored on Tubular Carbon Nitride

Artificial photosynthesis is a promising strategy for converting carbon dioxide (CO₂) and water (H₂O) into fuels and value-added chemical products. However, photocatalysts usually suffered from low activity and product selectivity due to the sluggish dynamic transfer of photoexcited charge carriers. Herein, we describe anchoring of Ag single atoms on hollow porous polygonal C₃N₄ nanotubes (PCN) to form the photocatalyst Ag₁@PCN with Ag−N₃ coordination for CO₂ photoreduction using H₂O as the reductant. The as-synthesized Ag₁@PCN exhibits a high CO production rate of 0.32 μmol h⁻¹ (mass of catalyst: 2 mg), a high selectivity (>94 %), and an excellent stability in the long term. Experiments and density functional theory (DFT) reveal that the strong metal–support interactions (Ag−N₃) favor *CO₂ adsorption, *COOH generation and desorption, and accelerate dynamic transfer of photoexcited charge carriers between C₃N₄ and Ag single atoms, thereby accounting for the enhanced CO₂ photoreduction activity with a high CO selectivity. This work provides a deep insight into the important role of strong metal–support interactions in enhancing the photoactivity and CO selectivity of CO₂ photoreduction.     

Computational Exploration of Mechanistic Avenues in Metal-Free CO2 Reduction to CO by Disilyne Bisphosphine Adduct and Phosphonium Silaylide

Recent years have seen a growing interest in metal-free CO₂ activation by silylenes, silylones, and silanones. However, compared to mononuclear silicon species, CO₂ reduction mediated by dinuclear silicon compounds, especially disilynes, has been less explored. We have carried out extensive computational investigations to explore the mechanistic avenues in CO₂ reduction to CO by donor-stabilized disilyne bisphosphine adduct ( R1^M ) and phosphonium silaylide ( R2 ) using density functional theory calculations. Theoretical calculations suggest that R1^M exhibits donor-stabilized bis(silylene) bonding features with unusual Si−Si multiple bonding. Various modes of CO₂ coordination to R1^M have been investigated and the coordination of CO₂ by the carbon center to R1^M is found to be kinetically more facile than that by oxygen involving only one or both the silicon centers. Both the theoretically predicted reaction mechanisms of R1^M and R2 -mediated CO₂ reduction reveal the crucial role of silicon-centered lone pairs in CO₂ activations and generation of key intermediates possessing enormous strain in the Si−C−O ring, which plays the pivotal role in CO extrusion.     

Features of Protonation of the Simplest Weakly Basic Molecules,SO2, CO,N2O,CO2, and Others by Solid Carborane Superacids

An experimental study on protonation of simple weakly basic molecules (L) by the strongest solid superacid, H(CHB₁₁F₁₁), showed that basicity of SO₂ is high enough (during attachment to the acidic H atoms at partial pressure of 1 atm) to break the bridged H‐bonds of the polymeric acid and to form a mixture of solid mono‐ LH⁺⋅⋅⋅An⁻, and disolvates, L−H⁺−L. With a decrease in the basicity of L=CO (via C), N₂O, and CO (via O), only proton monosolvates are formed, which approach L−H⁺−An⁻ species with convergence of the strengths of bridged H‐bonds. The molecules with the weakest basicity, such as CO₂ and weaker, when attached to the proton, cannot break the bridged H‐bond of the polymeric superacid, and the interaction stops at stage of physical adsorption. It is shown here that under the conditions of acid monomerization, it is possible to protonate such weak bases as CO₂, N₂, and Xe.     

Back Cover: Bio-Inspired Bimetallic Cooperativity Through a Hydrogen Bonding Spacer in CO2 Reduction (Angew. Chem. Int. Ed. 8/2023)

At the core of carbon monoxide dehydrogenase (CODH) active site two metal ions together with hydrogen bonding scheme from amino acids orchestrate the interconversion between CO₂ and CO. We have designed a molecular catalyst implementing a bimetallic iron complex with an embarked second coordination sphere with multi-point hydrogen-bonding interactions. We found that, when immobilized on carbon paper electrode, the dinuclear catalyst enhances up to four fold the heterogeneous CO₂ reduction to CO in water with an improved selectivity and stability compared to the mononuclear analogue. Interestingly, quasi-identical catalytic performances are obtained when one of the two iron centers was replaced by a redox inactive Zn metal, questioning the cooperative action of the two metals. Snapshots of X-ray structures indicate that the two metalloporphyrin units tethered by a urea group is a good compromise between rigidity and flexibility to accommodate CO₂ capture, activation, and reduction.     

Synthesis,crystal structure and characterization of a three‐dimensional CdII coordination polymer constructed from 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalate

Bifunctional organic ligands are very popular for the design of coordination polymers because they allow the formation of a great diversity of structures. In the title coordination polymer, the new bifunctional inversion‐symmetric ligand 2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalic acid (abbreviated as H₂bttpa) links Cd^II cations, giving rise to the three‐dimensional Cd^II coordination polymer catena‐poly[diaqua[μ₄‐2,5‐bis(1H‐1,2,4‐triazol‐1‐yl)terephthalato‐κ⁴O¹:O⁴:N⁴:N^4′]cadmium(II)], [Cd(C₁₂H₆N₆O₄)(H₂O)₂]_n or [Cd(bttpa)(H₂O)₂]_n. The asymmetric unit consists of half a Cd^II cation, half a bttpa²⁻ ligand and one coordinated water molecule. The Cd^II cation is located on a twofold axis and is hexacoordinated in a distorted octahedral environment of four O and two N atoms. Four different bttpa²⁻ ligands contribute to this coordination, with two carboxylate O atoms in trans positions and two triazole N atoms in cis positions. Two aqua ligands in cis positions complete the coordination sphere. The fully deprotonated bttpa²⁻ ligand sits about a crystallographic centre of inversion and links two Cd^II cations to form a chain in a μ₂‐terephthalato‐κ²O¹:O⁴ bridge. This chain extends in the other two directions via the triazole heterocycles, producing a three‐dimensional framework. O—H…O hydrogen bonds and weak C—H…N interactions stabilize the three‐dimensional crystal structure. The FT–IR spectrum, X‐ray powder pattern, thermogravimetric behaviour and solid‐state photoluminescence of the title polymer have been investigated. The photoluminescence is enhanced and red‐shifted with respect to the uncoordinated ligand.     

Selective Carbanion–Pyridine Coordination of a Reactive P,N Ligand to RhI

Ligands with reactive carbon sites in the periphery of a metal center have emerged as a powerful approach for metal–ligand bond activation. These reactive carbon sites are commonly generated by deprotonation strategies. Carbon–silicon bond cleavage is a potential alternative to access such constructs. Herein, the monodesilylation of bis-silyl-substituted P,N scaffold PN^Si2 in the coordination sphere of [Rh^I(Cl)(CO)( PN^Si2 )] ( 1 ) with sodium azide is disclosed. This affords a unique dinucleating anionic κ²-C,N-κ¹-P ligand with a carbanionic methine carbon atom directly bound to rhodium as part of a four-membered Rh-N-C-C rhodacycle. This dimer undergoes meta-pyridine C−H activation facilitated by weak bases, which leads to a desymmetrization of the system and provides a σ,π-bridging 3-pyridyl fragment bound to Rh^I. The facile Si−C cleavage strategy may pave the way to studying the reactivity and functionalization of a variety of κ²-C,N-coordinated pyridine scaffolds for selective transformations.     

Urea Production on Metal-Free Dual Silicon Doped C9N4 Nanosheet Under Ambient Conditions by Electrocatalysis: A First Principles Study

The development of cheap, eco-friendly electrocatalysts for urea synthesis which avoids the traditional nitrogen reduction to form ammonia, is very important to meet our growing demand for urea. Herein, based on density functional theory, we propose a novel electrocatalyst (dual Si doped C₉N₄ nanosheet) composed of totally environmentally benign non-metal earth abundant elements, which is able to adsorb N₂ and CO₂ together. Reduction of CO₂ to CO happens, which is then inserted into activated N−N bond, and it produces *N(CO)N intermediate, which is the crucial step for urea formation. Eventually following several proton coupled electron transfer processes, urea is formed under ambient conditions. The limiting potential value for urea formation is found to be lower than that of NH₃ formation and HER (hydrogen evolution reaction). Moreover, the faradaic efficiency of our proposed catalyst system is 100 % for urea formation, which suggests greater selectivity of urea formation over other competitive reactions.     

Partially Oxidized Palladium Nanodots for Enhanced Electrocatalytic Carbon Dioxide Reduction

Here we report a partially oxidized palladium nanodot (Pd/PdO_x) catalyst with a diameter of around 4.5 nm. In aqueous CO₂‐saturated 0.5 m KHCO₃, the catalyst displays a Faradaic efficiency (FE) of 90 % at −0.55 V vs. reversible hydrogen electrode (RHE) for carbon monoxide (CO) production, and the activity can be retained for at least 24 h. The improved catalytic activity can be attributed to the strong adsorption of CO₂^.− intermediate on the Pd/PdO_x electrode, wherein the presence of Pd²⁺ during the electroreduction reaction of CO₂ may play an important role in accelerating the carbon dioxide reduction reaction (CO₂RR). This study explores the catalytic mechanism of a partially oxidized nanostructured Pd electrocatalyst and provides new opportunities for improving the CO₂RR performance of metal systems.     

Are Two Metal Ions Better than One? Mono- and Binuclear α-Diimine-Re(CO)3 Complexes with Proton-Responsive Ligands in CO2 Reduction Catalysis

Here, the reduction chemistry of mono- and binuclear α-diimine-Re(CO)₃ complexes with proton responsive ligands and their application in the electrochemically-driven CO₂ reduction catalysis are presented. The work was aimed to investigate the impact of 1) two metal ions in close proximity and 2) an internal proton source on catalysis. Therefore, three different Re complexes, a binuclear one with a central phenol unit, 3 , and two mononuclear, one having a central phenol unit, 1 , and one with a methoxy unit, 2 , were utilised. All complexes are active in the CO₂-to-CO conversion and CO is always the major product. The catalytic rate constant k_cat for all three complexes is much higher and the overpotential is lower in DMF/water mixtures than in pure DMF (DMF=N,N-dimethylformamide). Cyclic voltammetry (CV) studies in the absence of substrate revealed that this is due to an accelerated chloride ion loss after initial reduction in DMF/water mixtures in comparison to pure DMF. Chloride ion loss is necessary for subsequent CO₂ binding and this step is around ten times faster in the presence of water [ 2 : k^Cl(DMF)≈1.7 s⁻¹; k^Cl(DMF/H₂O)≈20 s⁻¹]. The binuclear complex 3 with a proton responsive phenol unit is more active than the mononuclear complexes. In the presence of water, the observed rate constant k_obs for 3 is four times higher than of 2 , in the absence of water even ten times. Thus, the two metal centres are beneficial for catalysis. Lastly, the investigation showed that the phenol unit has no impact on the rate of the catalysis, it even slows down the CO₂-to-CO conversion. This is due to an unproductive, competitive side reaction: After initial reduction, 1 and 3 loose either Cl⁻ or undergo a reductive OH deprotonation forming a phenolate unit. The phenolate could bind to the metal centre blocking the sixth coordination site for CO₂ activation. In DMF, O−H bond breaking and Cl⁻ ion loss have similar rate constants [ 1 : k^Cl(DMF)≈2 s⁻¹, k^OH≈1.5 s⁻¹], in water/DMF Cl⁻ loss is much faster. Thus, the effect on the catalytic rate is more pronounced in DMF. However, the acidic protons lower the overpotential of the catalysis by about 150 mV.     

Shielding of Electron Acceptors Coordinated to Rhenium(I) by Carboxylato Groups. Intraligand and Charge‐Transfer Excited‐State Properties of fac‐(‘Anthraquinone‐2‐carboxylato')(2,2′‐bipyridine)tricarbonylrhenium (fac‐[ReI(aq‐2‐CO2)(2,2′‐bipy)(CO)3])

The photophysical and photochemical properties of (OC‐6‐33)‐(2,2′‐bipyridine‐κN¹,κN¹′)tricarbonyl(9,10‐dihydro‐9,10‐dioxoanthracene‐2‐carboxylato‐κO)rhenium (fac‐[Re^I(aq‐2‐CO₂)(2,2′‐bipy)(CO)₃]) were investigated and compared to those of the free ligand 9,10‐dihydro‐9,10‐dioxoanthracene‐2‐carboxylate (=anthraquinone‐2‐carboxylate) and other carboxylato complexes containing the (2,2′‐bipyridine)tricarbonylrhenium ([Re(2,2′‐bipy)(CO)₃]) moiety. Flash and steady‐state irradiations of the anthraquinone‐derived ligand (λ_exc 337 or 351 nm) and of its complex reveal that the photophysics of the latter is dominated by processes initiated in the Re‐to‐(2,2′‐bipyridine) charge‐transfer excited state and 2,2′‐bipyridine‐ and (anthraquinone‐2‐carboxylato)‐centered intraligand excited states. In the reductive quenching by N,N‐diethylethanamine (TEA) or 2,2′,2″‐nitrilotris[ethanol] TEOA, the reactive states are the 2,2′‐bipyridine‐centered and/or the charge‐transfer excited states. The species with a reduced anthraquinone moiety is formed by the following intramolecular electron transfer, after the redox quenching of the excited state: [Re^I(aq−2−CO₂)(2,2′‐bipy^.)(CO)₃]⁻⇌[Re^I(aq−2−CO₂^.)(2,2′‐bipy)(CO)₃]⁻ The photophysics, particularly the absence of a Re^I‐to‐anthraquinone charge‐transfer excited state photochemistry, is discussed in terms of the electrochemical and photochemical results.     

Molecular Engineering of Cation Solvation Structure for Highly Selective Carbon Dioxide Electroreduction

Balancing the activation of H₂O is crucial for highly selective CO₂ electroreduction (CO₂RR), as the protonation steps of CO₂RR require fast H₂O dissociation kinetics, while suppressing hydrogen evolution (HER) demands slow H₂O reduction. We herein proposed one molecular engineering strategy to regulate the H₂O activation using aprotic organic small molecules with high Gutmann donor number as a solvation shell regulator. These organic molecules occupy the first solvation shell of K⁺ and accumulate in the electrical double layer, decreasing the H₂O density at the interface and the relative content of proton suppliers (free and coordinated H₂O), suppressing the HER. The adsorbed H₂O was stabilized via the second sphere effect and its dissociation was promoted by weakening the O−H bond, which accelerates the subsequent *CO₂ protonation kinetics and reduces the energy barrier. In the model electrolyte containing 5 M dimethyl sulfoxide (DMSO) as an additive (KCl-DMSO-5), the highest CO selectivity over Ag foil increased to 99.2 %, with FE_CO higher than 90.0 % within −0.75 to −1.15 V (vs. RHE). This molecular engineering strategy for cation solvation shell can be extended to other metal electrodes, such as Zn and Sn, and organic molecules like N,N-dimethylformamide.     

Tailoring the Pore Size,Basicity, and Binding Energy of Mesoporous C3N5 for CO2 Capture and Conversion

We investigated the CO₂ adsorption and electrochemical conversion behavior of triazole-based C₃N₅ nanorods as a single matrix for consecutive CO₂ capture and conversion. The pore size, basicity, and binding energy were tailored to identify critical factors for consecutive CO₂ capture and conversion over carbon nitrides. Temperature-programmed desorption (TPD) analysis of CO₂ demonstrates that triazole-based C₃N₅ shows higher basicity and stronger CO₂ binding energy than g-C₃N₄. Triazole-based C₃N₅ nanorods with 6.1 nm mesopore channels exhibit better CO₂ adsorption than nanorods with 3.5 and 5.4 nm mesopore channels. C₃N₅ nanorods with wider mesopore channels are effective in increasing the current density as an electrocatalyst during the CO₂ reduction reaction. Triazole-based C₃N₅ nanorods with tailored pore sizes exhibit CO₂ adsorption abilities of 5.6–9.1 mmol/g at 0 °C and 30 bar. Their Faraday efficiencies for reducing CO₂ to CO are 14–38% at a potential of −0.8 V vs. RHE.     

Gelatin-Derived 1D Carbon Nanofiber Architecture with Simultaneous Decoration of Single Fe−Nx Sites and Fe/Fe3C Nanoparticles for Efficient Oxygen Reduction

Exploring high-performance non-precious-metal electrocatalysts for the oxygen reduction reaction (ORR) is critical. Herein, a scalable and cost-effective strategy is reported for the construction of one-dimensional carbon nanofiber architectures with simultaneous decoration of single Fe−N_x sites and highly dispersed Fe/Fe₃C nanoparticles for efficient ORR, through the Fe^III-complex-assisted electrospinning of gelatin nanofibers with subsequent pre-oxidation and carbonization. Results show that the presence of a Fe^III complex enables the 1D gelatin nanofibers to be well retained during the pre-oxidation process. Owing to the distinct 1D nanofiber structure and the synergistic effect of Fe/Fe₃C and Fe−N_x sites, the resulting electrocatalyst is highly active for ORR with a half-wave potential of 0.885 V (outperforming commercial Pt/C) and a superior electrochemical stability in alkaline electrolytes. Similarly, it also shows a high power density (144.7 mW cm⁻²) and a superior stability in Zn-air batteries. This work opens a path for the design and synthesis of 1D carbon electrocatalyst for efficient ORR catalysis.     

A Biomass-Derived Carbon-Based Electrocatalyst for Efficient N2 Fixation to NH3 under Ambient Conditions

Currently, NH₃ production primarily depends on the Haber–Bosch process, which operates at elevated temperatures and pressures and leads to serious CO₂ emissions. Electrocatalytic N₂ reduction offers an environmentally benign approach for the sustainable synthesis of NH₃ under ambient conditions. This work reports the development of biomass-derived amorphous oxygen-doped carbon nanosheet (O−CN) using tannin as the precursor. As a metal-free electrocatalyst for N₂-to-NH₃ conversion, such O−CN shows high catalytic performances, achieving a large NH₃ yield of 20.15 μg h⁻¹ mg⁻¹_cat. and a high Faradic efficiency of 4.97 % at −0.6 V vs. reversible hydrogen electrode (RHE) in 0.1 m HCl at ambient conditions. Remarkably, it also exhibits high electrochemical selectivity and durability.     

Electrocatalysts Derived from Copper Complexes Transform CO into C2+ Products Effectively in a Flow Cell

Electrochemical reactors that electrolytically convert CO₂ into higher-value chemicals and fuels often pass a concentrated hydroxide electrolyte across the cathode. This strongly alkaline medium converts the majority of CO₂ into unreactive HCO₃⁻ and CO₃²⁻ byproducts rather than into CO₂ reduction reaction (CO2RR) products. The electrolysis of CO (instead of CO₂) does not suffer from this undesirable reaction chemistry because CO does not react with OH⁻. Moreover, CO can be more readily reduced into products containing two or more carbon atoms (i. e., C₂₊ products) compared to CO₂. We demonstrate here that an electrocatalyst layer derived from copper phthalocyanine ( CuPc ) mediates this conversion effectively in a flow cell. This catalyst achieved a 25 % higher selectivity for acetate formation at 200 mA/cm² than a known state-of-art oxide-derived Cu catalyst tested in the same flow cell. A gas diffusion electrode coated with CuPc electrolyzed CO into C₂₊ products at high rates of product formation (i. e., current densities ≥200 mA/cm²), and at high faradaic efficiencies for C₂₊ production (FE_C2+; >70 % at 200 mA/cm²). While operando Raman spectroscopy did not reveal evidence of structural changes to the copper molecular complex, X-ray photoelectron spectroscopy suggests that the catalyst undergoes conversion to a metallic copper species during catalysis. Notwithstanding, the ligand environment about the metal still impacts catalysis, which we demonstrated through the study of a homologous CuPc bearing ethoxy substituents. These findings reveal new strategies for using metal complexes for the formation of carbon-neutral chemicals and fuels at industrially relevant conditions.     

Atomically Precise Copper Nanoclusters for Highly Efficient Electroreduction of CO2 towards Hydrocarbons via Breaking the Coordination Symmetry of Cu Site

We propose an effective highest occupied d-orbital modulation strategy engendered by breaking the coordination symmetry of sites in the atomically precise Cu nanocluster (NC) to switch the product of CO₂ electroreduction from HCOOH/CO to higher-valued hydrocarbons. An atomically well-defined Cu₆ NC with symmetry-broken Cu−S₂N₁ active sites (named Cu₆(MBD)₆, MBD=2-mercaptobenzimidazole) was designed and synthesized by a judicious choice of ligand containing both S and N coordination atoms. Different from the previously reported high HCOOH selectivity of Cu NCs with Cu−S₃ sites, the Cu₆(MBD)₆ with Cu−S₂N₁ coordination structure shows a high Faradaic efficiency toward hydrocarbons of 65.5 % at −1.4 V versus the reversible hydrogen electrode (including 42.5 % CH₄ and 23 % C₂H₄), with the hydrocarbons partial current density of −183.4 mA cm⁻². Theoretical calculations reveal that the symmetry-broken Cu−S₂N₁ sites can rearrange the Cu 3d orbitals with as the highest occupied d-orbital, thus favoring the generation of key intermediate *COOH instead of *OCHO to favor *CO formation, followed by hydrogenation and/or C−C coupling to produce hydrocarbons. This is the first attempt to regulate the coordination mode of Cu atom in Cu NCs for hydrocarbons generation, and provides new inspiration for designing atomically precise NCs for efficient CO₂RR towards highly-valued products.     

Molecular Modification of Single Cobalt Sites Boosts the Catalytic Activity of CO2 Electroreduction into CO

Electroreduction of CO₂ into carbonaceous fuels or industrial chemicals using renewable energy sources is an ideal way to promote global carbon recycling. Thus, it is of great importance to develop highly selective, efficient, and stable catalysts. Herein, we prepared cobalt single atoms (Co SAs) coordinated with phthalocyanine (Co SAs-Pc). The anchoring of phthalocyanine with Co sites enabled electron transfer from Co sites to CO₂ effectively via the π-conjugated system, resulting in high catalytic performance of CO₂ electroreduction into CO. During the process of CO₂ electroreduction, the Faradaic efficiency (FE) of Co SAs-Pc for CO was as high as 94.8 %. Meanwhile, the partial current density of Co SAs-Pc for CO was −11.3 mA cm⁻² at −0.8 V versus the reversible hydrogen electrode (vs RHE), 18.83 and 2.86 times greater than those of Co SAs (−0.60 mA cm⁻²) and commercial Co phthalocyanine (−3.95 mA cm⁻²), respectively. In an H-cell system operating at −0.8 V vs RHE over 10 h, the current density and FE for CO of Co SAs-Pc dropped by 3.2 % and 2.5 %. A mechanistic study revealed that the promoted catalytic performance of Co SAs-Pc could be attributed to the accelerated reaction kinetics and facilitated CO₂ activation.     

Theoretical study of the relative stabilities of H+(X)2 and H+(X)3 conformers and their clustering energies: X  CO and N2

Third-order Møller–Plesset perturbation theory (MP 3) with a 6-31G** basis set was applied to study the relative stabilities of H⁺(X)₂ conformations (X ? CO and N₂) and their clustering energies. The effect of both basis set extensions and electron correlation is not negligible on the relative stabilities of the H⁺(CO)₂ clusters. The most stable conformation of H⁺(CO)₂ is found to be a C_∞v structure in which a carbon atom of CO bonds to the proton of H⁺(CO), whereas that of H⁺(N₂)₂ is a symmetry D_∞h structure. The second lowest energy conformations of H⁺(CO)₂ and H⁺(N₂)₂ lie within 2 kcal/mol above the energies of the most stable structures. Clustering energies computed using MP 3 method with the 6-31G** basis set are in good agreement with the experimental findings of Hiraoka, Saluja, and Kebarle. The low-lying singlet conformations of H⁺(X)₃ (X ? CO and N₂) have been studied by the use of the Hartree–Fock MO method with the 6-31G** basis set and second-order Møller–Plesset perturbation theory with a 4-31G basis set. The most stable structure is a T-shaped structure in which a carbon atom of CO (or a nitrogen atom of N₂) attacks the proton of the most stable conformation of H⁺(X)₂ clusters.