Advanced Catalyst for CO2 Photo-Reduction: From Controllable Product Selectivity by Architecture Engineering to Improving Charge Transfer Using Stabilized Au Clusters

Despite enormous progress and improvement in photocatalytic CO₂ reduction reaction (CO₂RR), the development of photocatalysts that suppress H₂ evolution reaction (HER), during CO₂RR, remains still a challenge. Here, new insight is presented for controllable CO₂RR selectivity by tuning the architecture of the photocatalyst. Au/carbon nitride with planar structure (p Au/CN) showed high activity for HER with 87% selectivity. In contrast, the same composition with a yolk@shell structure (Y@S Au@CN) exhibited high selectivity of carbon products by suppressing the HER to 26% under visible light irradiation. Further improvement for CO₂RR activity was achieved by a surface decoration of the yolk@shell structure with Au₂₅(PET)₁₈ clusters as favorable electron acceptors, resulting in longer charge separation in Au@CN/Au_c Y@S structure. Finally, by covering the structure with graphene layers, the designed catalyst maintained high photostability during light illumination and showed high photocatalytic efficiency. The optimized Au@CN/Au_c/G Y@S structure displays high photocatalytic CO₂RR selectivity of 88%, where the CO and CH₄ generations during 8 h are 494 and 198 µmol/gcat., respectively. This approach combining architecture engineering and composition modification provides a new strategy with improved activity and controllable selectivity toward targeting applications in energy conversion catalysis.     

Single-atom catalysts with bimetallic centers for high-performance electrochemical CO2 reduction

The electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach to alleviating global warming while concomitantly producing synthesis gas. Simultaneously achieving high current densities and tunable CO/H₂ (syngas) ratios remains a highly desired yet difficult challenge. Herein, we developed a 3D carbon-based material exhibiting bimetallic centers (NiNC and FeNC) with synergistic effects for the CO₂RR. The molar CO/H₂ ratio (∼1:3 to ∼4:1) was altered by varying the configuration structures of the metal-N sites and tuning the applied potential for industrial applications of syngas. Density functional theory calculations verified these experimental results. Additionally, varying the configuration structures of bimetallic centers changed the rate-limiting steps of FePc@NiNC(+0.95 eV), NiNC/FeNC (+1.25 eV) and NiPc@FeNC (+1.37 eV) for CO₂RR, while maintaining high catalytic activity with tunable syngas production. The reported materials system in this work represents a significant advancement of the CO₂RR towards practical applications.     

Single-Atom Catalysts and Dual-Atom Catalysts for CO2 Electroreduction: Competition or Cooperation?

Developing highly active and selective electrocatalysts for electrochemical reduction of CO₂ can reduce environmental pollution and mitigation of greenhouse gas emission. Owing to maximal atomic utilization, the atomically dispersed catalysts are broadly adopted in CO₂ reduction reaction (CO₂RR). Dual-atom catalysts (DACs), with more flexible active sites, distinct electronic structures, and synergetic interatomic interactions compared to single-atom catalysts (SACs), may have great potential to enhance catalytic performance. Nevertheless, most of the existing electrocatalysts have low activity and selectivity due to their high energy barrier. Herein, 15 electrocatalysts are explored with noble metallic (Cu, Ag, and Au) active sites embedded in metal–organic hybrids (MOHs) for high-performance CO₂RR and studied the relationship between SACs and DACs by first-principles calculation. The results indicated that the DACs have excellent electrocatalytic performance, and the moderate interaction between the single- and dual-atomic center can improve catalytic activity in CO₂RR. Four among the 15 catalysts, including (CuAu), (CuCu), Cu(CuCu), and Cu(CuAu) MOHs inherited a capability of suppressing the competitive hydrogen evolution reaction with favorable CO overpotential. This work not only reveals outstanding candidates for MOHs-based dual-atom CO₂RR electrocatalysts but also provides new theoretical insights into rationally designing 2D metallic electrocatalysts.     

Achieving Tunable Selectivity and Activity of CO2 Electroreduction to CO via Bimetallic Silver–Copper Electronic Engineering

Limited comprehension of the reaction mechanism has hindered the development of catalysts for CO₂ reduction reactions (CO₂RR). Here, the bimetallic AgCu nanocatalyst platform is employed to understand the effect of the electronic structure of catalysts on the selectivity and activity for CO₂ electroreduction to CO. The atomic arrangement and electronic state structure vary with the atomic ratio of Ag and Cu, enabling tunable d-band centers to optimize the binding strength of key intermediates. Density functional theory calculations confirm that the variation of Cu content greatly affects the free energy of *COOH, *CO (intermediate of CO), and *H (intermediates of H₂), which leads to the change of the rate-determining step. Specifically, Ag₉₆Cu₄ reduces the free energy of the formation of *COOH while maintaining a relatively high theoretical overpotential for hydrogen evolution reaction(HER), thus achieving the best CO selectivity. While Ag₇₀Cu₃₀ shows relatively low formation energy of both *COOH and *H, the compromised thermodynamic barrier and product selectivity allows Ag₇₀Cu₃₀ the best CO partial current density. This study realizes the regulation of the selectivity and activity of electrocatalytic CO₂ to CO, which provides a promising way to improve the intrinsic performance of CO₂RR on bimetallic AgCu.     

Synthesis of dual Z-scheme photocatalyst ZnFe2O4/PANI/Ag2CO3 with enhanced visible light photocatalytic activity and degradation of pollutants

The ZnFe₂O₄/PANI/Ag₂CO₃ photocatalyst was synthesized by the co-precipitation method. The composition, morphology and optical properties of the synthesized photocatalyst were characterized. Compared with pure Ag₂CO₃, ZnFe₂O₄, PANI/Ag₂CO₃ and ZnFe₂O₄/Ag₂CO₃, ZnFe₂O₄/PANI/Ag₂CO₃ has the best photocatalytic ability of bisphenol A can reach 86.36% under 40 min of light, and it has a certain ability to be reused. At the same time, after 1 h of light, the degradation rate of Nitrobenzene can reach 90%. The reason for the increased catalytic ability of ZnFe₂O₄/PANI/Ag₂CO₃ can be attributed to the extended absorption capacity of the visible light region and the efficient separation of electron-hole pairs.     

Metal‐Cluster‐Decorated TiO2 Nanotube Arrays: A Composite Heterostructure toward Versatile Photocatalytic and Photoelectrochemical Applications

Recent years have witnessed increasing interest in the solution‐phase synthesis of atomically precise thiolate‐protected gold clusters (Au_x); nonetheless, research on the photocatalytic properties of Au_x–semiconductor nanocomposites is still in its infancy. In this work, recently developed glutathione‐capped gold clusters and highly ordered nanoporous layer‐covered TiO₂ nanotube arrays (NP‐TNTAs) are employed as nanobuilding blocks for the construction of a well‐defined Au_x/NP‐TNTA heterostructure via a facile electrostatic self‐assembly strategy. Versatile photocatalytic performances of the Au_x/NP‐TNTA heterostructure which acts as a model catalyst, including photocatalytic oxidation of organic pollutant, photocatalytic reduction of aromatic nitro compounds and photoelectrochemical (PEC) water splitting under simulated solar light irradiation, are systematically exploited. It is found that synergistic interaction stemming from monodisperse coverage of Au_x clusters on NP‐TNTAs in combination with hierarchical nanostructure of NP‐TNTAs reinforce light absorption of Au_x/NP‐TNTA heterostructure especially within visible region, hence contributing to the significantly enhanced photocatalytic and PEC water splitting performances. Moreover, photocatalytic and PEC mechanisms over Au_x/NP‐TNTA heterostructure are elucidated and corresponding reaction models were presented. It is anticipated that this work could boost new insight for photocatalytic properties of metal‐cluster‐sensitized semiconductor nanocomposites.     

Interface-Induced Electrocatalytic Enhancement of CO2-to-Formate Conversion on Heterostructured Bismuth-Based Catalysts

Electrochemical CO₂ reduction reaction (CO₂RR) is a promising approach to convert CO₂ to carbon-neutral fuels using external electric powers. Here, the Bi₂S₃-Bi₂O₃ nanosheets possessing substantial interface being exposed between the connection of Bi₂S₃ and Bi₂O₃ are prepared and subsequently demonstrate to improve CO₂RR performance. The electrocatalyst shows formate Faradaic efficiency (FE) of over 90% in a wide potential window. A high partial current density of about 200 mA cm^?2 at ?1.1 V and an ultralow onset potential with formate FE of 90% are achieved in a flow cell. The excellent electrocatalytic activity is attributed to the fast-interfacial charge transfer induced by the electronic interaction at the interface, the increased number of active sites, and the improved CO₂ adsorption ability. These collectively contribute to the faster reaction kinetics and improved selectivity and consequently, guarantee the superb CO₂RR performance. This study provides an appealing strategy for the rational design of electrocatalysts to enhance catalytic performance by improving the charge transfer ability through constructing a functional heterostructure, which enables interface engineering toward more efficient CO₂RR.     

Catalytic oxidation of cyclohexane by size-selected palladium clusters pinned on graphite

We report the catalytic oxidation of cyclohexane to CO and CO₂ over size-selected palladium clusters (Pd _N clusters, N = 10–120) supported on graphite as a function of cluster size. The stability of the pinned clusters (nanoparticles) under reaction conditions is investigated by scanning tunnelling microscopy measurement both before and after reaction. Temperature-programmed reaction experiments at 800 Torr show that the turnover rates (per surface Pd atom) for both CO and CO₂ increase significantly as cluster size decreases and correlate with the number of Pd perimeter atoms at the graphite interface. Under oxygen-rich conditions, the activity of the clusters increases by a factor of 3 while the product ratio CO:CO₂ rises by an order of magnitude.     

Fabrication of Au25(SG)18–ZIF‐8 Nanocomposites: A Facile Strategy to Position Au25(SG)18 Nanoclusters Inside and Outside ZIF‐8

Multifunctional composite materials are currently highly desired for sustainable energy applications. A general strategy to integrate atomically precise Au₂₅(SG)₁₈ with ZIF‐8 (Zn(MeIm)₂, MeIm = 2‐methylimidazole), is developed via the typical Zn‐carboxylate type of linkage. Au₂₅(SG)₁₈ are uniformly encapsulated into a ZIF‐8 framework (Au₂₅(SG)₁₈@ZIF‐8) by coordination‐assisted self‐assembly. In contrast, Au₂₅(SG)₁₈ integrated by simple impregnation is oriented along the outer surface of ZIF‐8 (Au₂₅(SG)₁₈/ZIF‐8). The porous structure and thermal stability of these nanocomposites are characterized by N₂ adsorption–desorption isothermal analysis and thermal gravimetric analysis. The distribution of Au₂₅(SG)₁₈ in the two nanocomposites is confirmed by electron microscopy, and the accessibility of Au₂₅(SG)₁₈ is evaluated by the 4‐nitrophenol reduction reaction. The as‐prepared nanocomposites retain the high porosity and thermal stability of the ZIF‐8 matrix, while also exhibiting the desired catalytic and optical properties derived from the integrated Au₂₅(SG)₁₈ nanoclusters (NCs). Au₂₅(SG)₁₈@ZIF‐8 with isolated Au₂₅ sites is a promising heterogenous catalyst with size selectivity imparted by the ZIF‐8 matrix. The structural distinction between Au₂₅(SG)₁₈@ZIF‐8 and Au₂₅(SG)₁₈/ZIF‐8 determines their different emission features, and provides a new strategy to adjust the optical behavior of Au₂₅(SG)₁₈ for applications in bioimaging and biotherapy.     

Heterogeneous Single-Atom Catalysts for Electrochemical CO2 Reduction Reaction

The electrochemical CO₂ reduction reaction (CO₂RR) is of great importance to tackle the rising CO₂ concentration in the atmosphere. The CO₂RR can be driven by renewable energy sources, producing precious chemicals and fuels, with the implementation of this process largely relying on the development of low-cost and efficient electrocatalysts. Recently, a range of heterogeneous and potentially low-cost single-atom catalysts (SACs) containing non-precious metals coordinated to earth-abundant elements have emerged as promising candidates for the CO₂RR. Unfortunately, the real catalytically active centers and the key factors that govern the catalytic performance of these SACs remain ambiguous. Here, this ambiguity is addressed by developing a fundamental understanding of the CO₂RR-to-CO process on SACs, as CO accounts for the major product from CO₂RR on SACs. The reaction mechanism, the rate-determining steps, and the key factors that control the activity and selectivity are analyzed from both experimental and theoretical studies. Then, the synthesis, characterization, and the CO₂RR performance of SACs are discussed. Finally, the challenges and future pathways are highlighted in the hope of guiding the design of the SACs to promote and understand the CO₂RR on SACs.     

Geometric and Electronic Structural Engineering of Isolated Ni Single Atoms for a Highly Efficient CO2 Electroreduction

Tuning the coordination environment and geometric structures of single atom catalysts is an effective approach for regulating the reaction mechanism and maximize the catalytic efficiency of single-atom centers. Here, a template-based synthesis strategy is proposed for the synthesis of high-density NiN_x sites anchored on the surface of hierarchically porous nitrogen-doped carbon nanofibers (Ni-HPNCFs) with different coordination environments. First-principles calculations and advanced characterization techniques demonstrate that the single Ni atom is strongly coordinated with both pyrrolic and pyridinic N dopants, and that the predominant sites are stabilized by NiN₃ sites. This dual engineering strategy increases the number of active sites and utilization efficiency of each single atom as well as boosts the intrinsic activity of each active site on a single-atom scale. Notably, the Ni-HPNCF catalyst achieves a high CO Faradaic efficiency (FE_CO) of 97% at a potential of −0.7 V, a high CO partial current density (j_CO) of 49.6 mA cm⁻² (−1.0 V), and a remarkable turnover frequency of 24 900 h⁻¹ (−1.0 V) for CO₂ reduction reactions (CO₂RR). Density functional theory calculations show that compared to pyridinic-type NiN_x, the pyrrolic-type NiN₃ moieties display a superior CO₂RR activity over hydrogen evolution reactions, resulting in their superior catalytic activity and selectivity.     

Two distinct fluorescent quantum clusters of gold starting from metallic nanoparticles by pH-dependent ligand etching

Two fluorescent quantum clusters of gold, namely Au₂₅ and Au₈, have been synthesized from mercaptosuccinic acid-protected gold nanoparticles of 4–5 nm core diameter by etching with excess glutathione. While etching at pH ∼3 yielded Au₂₅, that at pH 7–8 yielded Au₈. This is the first report of the synthesis of two quantum clusters starting from a single precursor. This simple method makes it possible to synthesize well-defined clusters in gram quantities. Since these clusters are highly fluorescent and are highly biocompatible due to their low metallic content, they can be used for diagnostic applications. Electronic Supplementary Material  Supplementary material is available for this article at and is accessible for authorized users. This article is published with open access at Springerlink.com     

Integrated 3D Open Network of Interconnected Bismuthene Arrays for Energy-Efficient and Electrosynthesis-Assisted Electrocatalytic CO2 Reduction

Electrocatalytic CO₂ reduction reaction (CO₂RR) toward formate production can be operated under mild conditions with high energy conversion efficiency while migrating the greenhouse effect. Herein, an integrated 3D open network of interconnected bismuthene arrays (3D Bi-ene-A/CM) is fabricated via in situ electrochemically topotactic transformation from BiOCOOH nanosheet arrays supported on the copper mesh. The resulted 3D Bi-ene-A/CM consists of 2D atomically thin metallic bismuthene (Bi-ene) in the form of an integrated array superstructure with a 3D interconnected and open network, which harvests the multiple structural advantages of both metallenes and self-supported electrodes for electrocatalysis. Such distinctive superstructure affords the maximized quantity and availability of the active sites with high intrinsic activity and superior charge and mass transfer capability, endowing the catalyst with good CO₂RR performance for stable formate production with high Faradaic efficiency (≈90%) and current density (>300 mA cm^?2). Theoretical calculation verifies the superior intermediate stabilization of the dominant Bi plane during CO₂RR. Moreover, by further coupling anodic methanol oxidation reaction, an exotic electrolytic system enables highly energy-efficient and value-added pair-electrosynthesis for concurrent formate production at both electrodes, achieving substantially improved electrochemical and economic efficiency and revealing the feasibility for practical implementation.     

Quantitative Analysis of Multiple Proteins of Different Invasive Tumor Cell Lines at the Same Single‐Cell Level

Tumor cell invasion is pivotal to the development, metastasis, and prognosis of tumors. It is reported that the invasive ability of tumor cells is mainly dependent on the expression levels of membrane type‐1 matrix metalloproteinase (MT1‐MMP) and integrin α_Vβ₃ proteins on cell membranes. To precisely distinguish between tumor cells with different invasive abilities, it is important to establish a highly sensitive and precise quantification method to differentiate the expression levels of MT1‐MMP and integrin α_Vβ₃ in the same single tumor cell at the same time. Herein, two functional peptides to construct red‐emissive Au₂₆ clusters and green‐emissive Ag₁₂ clusters are reported. Moreover, the Au₂₆ clusters and Ag₁₂ clusters have the ability to specifically target MT1‐MMP and integrin α_Vβ₃, respectively, in the same single cell at the same time. By utilizing the fluorescent properties and metallic compositions of metal clusters, the MT1‐MMP and integrin α_Vβ₃ levels of the more invasive SiHa cells or the less invasive HeLa cells are simultaneously and quantitatively differentiated via laser ablation inductively coupled plasma mass spectrometry. This method of quantitatively detecting multiple invasive proteins on the same cell is of great value for accurately diagnosing aggressive tumors and monitoring the invasiveness of these tumors.     

Quantum-chemical modeling of interaction between gold nanoclusters and thiols

Ab initio calculations are used to model small Au _n nanoclusters and Au _m SH clusters. The results for the Au₆, Au₈, and Au₂₀ clusters demonstrate that the substitution of a SH group for a Au atom gives a stable cluster of the same geometry if the Au atom has an acute bond angle and a negative effective charge. The example of the Au₁₀ cluster suggests that SH substitution for Au has a stabilizing effect. The modeling results are discussed with application to self-organizing thiol monolayers on gold clusters.     

Promoting Electrocatalytic CO2 Reduction to CH4 by Copper Porphyrin with Donor–Acceptor Structures

Molecular catalysts have been receiving increasingly attention in the electrochemical CO₂ reduction reaction (CO₂RR) with attractive features such as precise catalytic sites and tunable ligands. However, the insufficient activity and low selectivity of deep reduction products restrain the utilization of molecular catalysts in CO₂RR. Herein, a donor–acceptor modified Cu porphyrin (CuTAPP) is developed, in which amino groups are linked to donate electrons toward the central CuN₄ site to enhance the CO₂RR activity. The CuTAPP catalyst exhibited an excellent CO₂-to-CH₄ electroreduction performance, including a high CH₄ partial current density of 290.5 mA cm⁻² and a corresponding Faradaic efficiency of 54.8% at –1.63 V versus reversible hydrogen electrode in flow cells. Density functional theory calculations indicated that CuTAPP presented a much lower energy gap in the pathway of producing *CHO than Cu porphyrin without amino group modification. This work suggests a useful strategy of introducing designed donor–acceptor structures into molecular catalysts for enhancing electrochemical CO₂ conversion toward deep reduction products.     

Confinement Catalysis with 2D Materials for Energy Conversion

The unique electronic and structural properties of 2D materials have triggered wide research interest in catalysis. The lattice of 2D materials and the interface between 2D covers and other substrates provide intriguing confinement environments for active sites, which has stimulated a rising area of “confinement catalysis with 2D materials.” Fundamental understanding of confinement catalysis with 2D materials will favor the rational design of high‐performance 2D nanocatalysts. Confinement catalysis with 2D materials has found extensive applications in energy‐related reaction processes, especially in the conversion of small energy‐related molecules such as O₂, CH₄, CO, CO₂, H₂O, and CH₃OH. Two representative strategies, i.e., 2D lattice‐confined single atoms and 2D cover‐confined metals, have been applied to construct 2D confinement catalytic systems with superior catalytic activity and stability. Herein, the recent advances in the design, applications, and structure–performance analysis of two 2D confinement catalytic systems are summarized. The different routes for tuning the electronic states of 2D confinement catalysts are highlighted and perspectives on confinement catalysis with 2D materials toward energy conversion and utilization in the future are provided.     

Enhancement of photocatalytic activity and stability of Ag2CO3 by formation of AgBr/Ag2CO3 heterojunction in mordenite zeolite

Two serious problems for semiconductor photocatalysts are their poor photocatalytic activity and low stability. In this work, Ag₂CO₃ nanoparticles incorporated in mordenite zeolite (MOR) by a facile precipitation method. Silver bromide (AgBr) with different weight percentage (20%, 40% and 50%) was coupled into Ag₂CO₃-MOR composite and producing a series of novel AgBr/Ag₂CO₃-MOR nanocomposites. The effects of AgBr on the Ag₂CO₃–MOR catalyst for the photocatalytic degradation of methyl blue (MB) under visible light irradiation have been investigated. The structure, composition and optical properties of nanocomposites were investigated by UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The prepared AgBr/Ag₂CO₃-MOR photocatalyst with the optimal content of AgBr (50 wt%) indicated higher photocatalytic activity than that of the Ag₂CO₃-MOR and Ag₂CO₃ for degradation of methylene blue (MB) under visible light irradiation. For studying of stability of nanocomposites, Fe⁺³ ions, as a cheap and available cocatalyst, was inserted into mordenite matrix (Fe³⁺/MOR) by impregnation method. The hybrid material (AgBr/Ag₂CO₃) was synthesized in the Fe³⁺/MOR matrix by precipitation method. The cycle experiments on the AgBr/Ag₂CO₃-Fe/MOR nanocomposite indicated that cocatalyst, not only to improve photocatalytic activity, but also enhance photoinduced stability of photosensitive silver compounds in all cycles with respect to MOR. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of silver compounds by Fe³⁺ cocatalyst was proposed. The mordenite support played an important role in decreases of recombination of photogenerated electrons-holes and increases of MB absorption. The Fe cocatalyst reduced photocorrosion of silver compounds.     

Metal‐Free Carbon Materials for CO2 Electrochemical Reduction

The rapid increase of the CO₂ concentration in the Earth's atmosphere has resulted in numerous environmental issues, such as global warming, ocean acidification, melting of the polar ice, rising sea level, and extinction of species. To search for suitable and capable catalytic systems for CO₂ conversion, electrochemical reduction of CO₂ (CO₂RR) holds great promise. Emerging heterogeneous carbon materials have been considered as promising metal‐free electrocatalysts for the CO₂RR, owing to their abundant natural resources, tailorable porous structures, resistance to acids and bases, high‐temperature stability, and environmental friendliness. They exhibit remarkable CO₂RR properties, including catalytic activity, long durability, and high selectivity. Here, various carbon materials (e.g., carbon fibers, carbon nanotubes, graphene, diamond, nanoporous carbon, and graphene dots) with heteroatom doping (e.g., N, S, and B) that can be used as metal‐free catalysts for the CO₂RR are highlighted. Recent advances regarding the identification of active sites for the CO₂RR and the pathway of reduction of CO₂ to the final product are comprehensively reviewed. Additionally, the emerging challenges and some perspectives on the development of heteroatom‐doped carbon materials as metal‐free electrocatalysts for the CO₂RR are included.     

Synergistic Catalysis over Iron‐Nitrogen Sites Anchored with Cobalt Phthalocyanine for Efficient CO2 Electroreduction

Simultaneously achieving high Faradaic efficiency, current density, and stability at low overpotentials is essential for industrial applications of electrochemical CO₂ reduction reaction (CO₂RR). However, great challenges still remain in this catalytic process. Herein, a synergistic catalysis strategy is presented to improve CO₂RR performance by anchoring Fe‐N sites with cobalt phthalocyanine (denoted as CoPc©Fe‐N‐C). The potential window of CO Faradaic efficiency above 90% is significantly broadened from 0.18 V over Fe‐N‐C alone to 0.71 V over CoPc©Fe‐N‐C while the onset potential of CO₂RR over both catalysts is as low as ?0.13 V versus reversible hydrogen electrode. What is more, the maximum CO current density is increased ten times with significantly enhanced stability. Density functional theory calculations suggest that anchored cobalt phthalocyanine promotes the CO desorption and suppresses the competitive hydrogen evolution reaction over Fe‐N sites, while the *COOH formation remains almost unchanged, thus demonstrating unprecedented synergistic effect toward CO₂RR.