A Dinuclear Cobalt Cryptate as a Homogeneous Photocatalyst for Highly Selective and Efficient Visible-Light Driven CO2 Reduction to CO in CH3CN/H2O Solution

A dinuclear cobalt complex [Co₂(OH)L¹](ClO₄)₃ ( 1 , L¹=N[(CH₂)₂NHCH₂(m-C₆H₄)CH₂NH(CH₂)₂]₃N) displays high selectivity and efficiency for the photocatalytic reduction of CO₂ to CO in CH₃CN/H₂O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm⁻². The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s⁻¹, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two Co^II ions within 1 , which is strongly supported by the results of control experiments and DFT calculations.     

氮杂穴醚双核钴配合物用于高效可见光催化二氧化碳还原

<正>能源短缺和二氧化碳排放引起的全球变暖是人类社会可持续发展所面临的主要问题。同时解决这两大问题的一条理想途径是利用催化剂和太阳能,通过人工光合作用将二氧化碳转化为有用的化学燃料或原料~1。要实现这一过程,关键在于设计合成高效、高选择性的CO2还原催化剂,并与光敏剂耦合构建高效光催化反应体系~2。目前文献报道的光催化CO_2还原生成CO催化剂的催化效率不高3-5,其催化转化数(TON)和转化频率(TOF)分     

Visible‐Light‐Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

The integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO₂ reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CN_x) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO₂ to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm^?2, λ>300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO₂ conversion.     

Eosin Y‐Functionalized Conjugated Organic Polymers for Visible‐Light‐Driven CO2 Reduction with H2O to CO with High Efficiency

Visible‐light‐driven photoreduction of CO₂ to energy‐rich chemicals in the presence of H₂O without any sacrifice reagent is of significance, but challenging. Herein, Eosin Y‐functionalized porous polymers (PEosinY‐N, N=1–3), with high surface areas up to 610 m² g^?1, are reported. They exhibit high activity for the photocatalytic reduction of CO₂ to CO in the presence of gaseous H₂O, without any photosensitizer or sacrifice reagent, and under visible‐light irradiation. Especially, PEosinY‐1 derived from coupling of Eosin Y with 1,4‐diethynylbenzene shows the best performance for the CO₂ photoreduction, affording CO as the sole carbonaceous product with a production rate of 33 μmol g^?1 h^?1 and a selectivity of 92 %. This work provides new insight for designing and fabricating photocatalytically active polymers with high efficiency for solar‐energy conversion.     

Dimension‐Matched Zinc Phthalocyanine/BiVO4 Ultrathin Nanocomposites for CO2 Reduction as Efficient Wide‐Visible‐Light‐Driven Photocatalysts via a Cascade Charge Transfer

Cascade charge transfer was realized by a H‐bond linked zinc phthalocyanine/BiVO₄ nanosheet (ZnPc/BVNS) composite, which subsequently works as an efficient wide‐visible‐light‐driven photocatalyst for converting CO₂ into CO and CH₄, as shown by product analysis and ¹³C isotopic measurement. The optimized ZnPc/BVNS nanocomposite exhibits a ca. 16‐fold enhancement in the quantum efficiency compared with the reported BiVO₄ nanoparticles at the excitation of 520 nm with an assistance of 660 nm photons. Experimental and theoretical results show the exceptional activities are attributed to the rapid charge separation by a cascade Z‐scheme charge transfer mechanism formed by the dimension‐matched ultrathin (ca. 8 nm) heterojunction nanostructure. The central Zn²⁺ in ZnPc could accept the excited electrons from the ligand and then provide a catalytic function for CO₂ reduction. This Z‐scheme is also feasible for other MPc, such as FePc and CoPc, together with BVNS.     

A Graphene‐Supported Single‐Atom FeN5 Catalytic Site for Efficient Electrochemical CO2 Reduction

Electrochemical conversion of CO₂ into valued products is one of the most important issues but remains a great challenge in chemistry. Herein, we report a novel synthetic approach involving prolonged thermal pyrolysis of hemin and melamine molecules on graphene for the fabrication of a robust and efficient single‐iron‐atom electrocatalyst for electrochemical CO₂ reduction. The single‐atom catalyst exhibits high Faradaic efficiency (ca. 97.0 %) for CO production at a low overpotential of 0.35 V, outperforming all Fe‐N‐C‐based catalysts. The remarkable performance for CO₂‐to‐CO conversion can be attributed to the presence of highly efficient singly dispersed FeN₅ active sites supported on N‐doped graphene with an additional axial ligand coordinated to FeN₄. DFT calculations revealed that the axial pyrrolic nitrogen ligand of the FeN₅ site further depletes the electron density of Fe 3d orbitals and thus reduces the Fe–CO π back‐donation, thus enabling the rapid desorption of CO and high selectivity for CO production.     

Quantum Dot Assembly for Light‐Driven Multielectron Redox Reactions,such as Hydrogen Evolution and CO2 Reduction

Light‐driven multielectron redox reactions (e.g., hydrogen (H₂) evolution, CO₂ reduction) have recently appeared at the front of solar‐to‐fuel conversion. In this Minireview, we focus on the recent advances in establishing semiconductor quantum dot (QD) assemblies to enhance the efficiencies of these light‐driven multielectron reduction reactions. Four models of QD assembly are established to promote the sluggish kinetics of multielectron transfer from QDs to cocatalysts, thus leading to an enhanced activity of solar H₂ evolution or CO₂ reduction. We also forecast the potential applications of QD assemblies in other multielectron redox reactions, such as nitrogen (N₂) fixation and oxygen (O₂) evolution from H₂O.     

Highly Efficient Porous Carbon Electrocatalyst with Controllable N-Species Content for Selective CO2 Reduction

We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO₂ reduction reaction (CO₂RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen-rich metal–organic framework (Zn-MOF-74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO₂RR. The NPC exhibits superior CO₂RR activity with a small onset potential of −0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at −0.55 V vs. RHE, one of the highest values among NPC-based CO₂RR electrocatalysts. This work advances an effective and facile way towards highly active and cost-effective alternatives to noble-metal CO₂RR electrocatalysts for practical applications.     

Visible‐Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation

Research on the photochemical reduction of CO₂, initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high‐volume chemicals whose dehydrogenation is of interest, so the coupling of a CO₂ photoreduction to a hydrocarbon‐photodehydrogenation reaction seems a worthwhile concept to explore. A three‐component construct was prepared including graphitic carbon nitride (g‐CN) as a visible‐light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole–electron charge separation, and an electron donor to a rhenium‐based CO₂ reduction catalyst. Upon photoactivation of g‐CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible‐light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium‐based catalyst active for the selective reduction of CO₂ to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS). An experimental Z‐scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.     

Lattice Distortion in Hollow Multi‐Shelled Structures for Efficient Visible‐Light CO2 Reduction with a SnS2/SnO2 Junction

Precise control of the micro‐/nanostructures of nanomaterials, such as hollow multi‐shelled structures (HoMSs), has shown its great advantages in various applications. Now, the crystal structure of building blocks of HoMSs are controlled by introducing the lattice distortion in HoMSs, for the first time. The lattice distortion located at the nanoscale interface of SnS₂/SnO₂ can provide additional active sites, which not only provide the catalytic activity under visible light but also improve the separation of photoexcited electron–hole pairs. Combined with the efficient light utilization, the natural advantage of HoMSs, a record catalytic activity was achieved in solid–gas system for CO₂ reduction, with an excellent stability and 100 % CO selectivity without using any sensitizers or noble metals.     

Efficient Electrocatalytic Reduction of CO2 by Nitrogen‐Doped Nanoporous Carbon/Carbon Nanotube Membranes: A Step Towards the Electrochemical CO2 Refinery

Herein we introduce a straightforward, low cost, scalable, and technologically relevant method to manufacture an all‐carbon, electroactive, nitrogen‐doped nanoporous‐carbon/carbon‐nanotube composite membrane, dubbed “HNCM/CNT”. The membrane is demonstrated to function as a binder‐free, high‐performance gas diffusion electrode for the electrocatalytic reduction of CO₂ to formate. The Faradaic efficiency (FE) for the production of formate is 81 %. Furthermore, the robust structural and electrochemical properties of the membrane endow it with excellent long‐term stability.     

In Situ Generation of an N‐Heterocyclic Carbene Functionalized Metal–Organic Framework by Postsynthetic Ligand Exchange: Efficient and Selective Hydrosilylation of CO2

The reported metal–organic framework (MOF) catalyst realizes CO₂ to methanol transformation under ambient conditions. The MOF is one rare example containing metal‐free N‐heterocyclic carbene (NHC) moieties, which are installed using an in situ generation strategy involving the incorporation of an imidazolium bromide based linker into the MOF by postsynthetic ligand exchange. Importantly, the resultant NHC‐functionalized MOF is the first catalyst capable of performing quantitative hydrogen transfer from silanes to CO₂, thus achieving quantitative (>99 %) methanol yield. Density‐functional theory calculations indicate the high catalytic activity of the NHC sites in MOFs are attributed to the decreased reaction barrier of a reaction route involving the formation of an NHC‐silane adduct. In addition, the MOF‐immobilized NHC catalyst shows enhanced stability for up to eight cycles without base activation, as well as high selectivity towards the desired silyl methoxide product.     

Three‐in‐One Oxygen Vacancies: Whole Visible‐Spectrum Absorption,Efficient Charge Separation,and Surface Site Activation for Robust CO2 Photoreduction

A facile and controllable in situ reduction strategy is used to create surface oxygen vacancies (OVs) on Aurivillius‐phase Sr₂Bi₂Nb₂TiO₁₂ nanosheets, which were prepared by a mineralizer‐assisted soft‐chemical method. Introduction of OVs on the surface of Sr₂Bi₂Nb₂TiO₁₂ extends photoresponse to cover the whole visible region and also tremendously promotes separation of photoinduced charge carriers. Adsorption and activation of CO₂ molecules on the surface of the catalyst are greatly enhanced. In the gas‐solid reaction system without co‐catalysts or sacrificial agents, OVs‐abundant Sr₂Bi₂Nb₂TiO₁₂ nanosheets show outstanding CO₂ photoreduction activity, producing CO with a rate of 17.11 μmol g^?1 h^?1, about 58 times higher than that of the bulk counterpart, surpassing most previously reported state‐of‐the‐art photocatalysts. Our study provides a three‐in‐one integrated solution to advance the performance of photocatalysts for solar‐energy conversion and generation of renewable energy.     

Nanocrystal/Metal–Organic Framework Hybrids as Electrocatalytic Platforms for CO2 Conversion

The tunable chemistry linked to the organic/inorganic components in colloidal nanocrystals (NCs) and metal–organic frameworks (MOFs) offers a rich playground to advance the fundamental understanding of materials design for various applications. Herein, we combine these two classes of materials by synthesizing NC/MOF hybrids comprising Ag NCs that are in intimate contact with Al‐PMOF ([Al₂(OH)₂(TCPP)]) (tetrakis(4‐carboxyphenyl)porphyrin (TCPP)), to form Ag@Al‐PMOF. In our hybrids, the NCs are embedded in the MOF while still preserving electrical contact with a conductive substrate. This key feature allows the investigation of the Ag@Al‐PMOFs as electrocatalysts for the CO₂ reduction reaction (CO₂RR). We show that the pristine interface between the NCs and the MOFs accounts for electronic changes in the Ag, which suppress the hydrogen evolution reaction (HER) and promote the CO₂RR. We also demonstrate a minor contribution of mass‐transfer effects imposed by the porous MOF layer under the chosen testing conditions. Furthermore, we find an increased morphological stability of the Ag NCs when combined with the Al‐PMOF. The synthesis method is general and applicable to other metal NCs, thus revealing a new way to think about rationally tailored electrocatalytic materials to steer selectivity and improve stability.     

Highly Efficient Porous Carbon Electrocatalyst with Controllable N‐Species Content for Selective CO2 Reduction

We report a straightforward strategy to design efficient N doped porous carbon (NPC) electrocatalyst that has a high concentration of easily accessible active sites for the CO₂ reduction reaction (CO₂RR). The NPC with large amounts of active N (pyridinic and graphitic N) and highly porous structure is prepared by using an oxygen‐rich metal–organic framework (Zn‐MOF‐74) precursor. The amount of active N species can be tuned by optimizing the calcination temperature and time. Owing to the large pore sizes, the active sites are well exposed to electrolyte for CO₂RR. The NPC exhibits superior CO₂RR activity with a small onset potential of ?0.35 V and a high faradaic efficiency (FE) of 98.4 % towards CO at ?0.55 V vs. RHE, one of the highest values among NPC‐based CO₂RR electrocatalysts. This work advances an effective and facile way towards highly active and cost‐effective alternatives to noble‐metal CO₂RR electrocatalysts for practical applications.     

Reduced SnO2 Porous Nanowires with a High Density of Grain Boundaries as Catalysts for Efficient Electrochemical CO2‐into‐HCOOH Conversion

Electrochemical conversion of CO₂ into energy‐dense liquids, such as formic acid, is desirable as a hydrogen carrier and a chemical feedstock. SnO_x is one of the few catalysts that reduce CO₂ into formic acid with high selectivity but at high overpotential and low current density. We show that an electrochemically reduced SnO₂ porous nanowire catalyst (Sn‐pNWs) with a high density of grain boundaries (GBs) exhibits an energy conversion efficiency of CO₂‐into‐HCOOH higher than analogous catalysts. HCOOH formation begins at lower overpotential (350 mV) and reaches a steady Faradaic efficiency of ca. 80 % at only −0.8 V vs. RHE. A comparison with commercial SnO₂ nanoparticles confirms that the improved CO₂ reduction performance of Sn‐pNWs is due to the density of GBs within the porous structure, which introduce new catalytically active sites. Produced with a scalable plasma synthesis technology, the catalysts have potential for application in the CO₂ conversion industry.