A metal-organic framework/polymer derived catalyst containing single-atom nickel species for electrocatalysis

Modulating the Structure and Composition of Single-Atom Electrocatalysts for CO2 reduction

Electrochemical CO2 reduction reaction (eCO2 RR) is a promising strategy to achieve carbon cycling by converting CO2 into value-added products under mild reaction conditions. Recently, single-atom catalysts (SACs) have shown enormous potential in eCO2 RR due to their high utilization of metal atoms and flexible coordination structures. In this work, the recent progress in SACs for eCO2 RR is outlined, with detailed discussions on the interaction between active sites and CO2 , especially the adsorption/activation behavior of CO2 and the effects of the electronic structure of SACs on eCO2 RR. Three perspectives form the starting point: 1) Important factors of SACs for eCO2 RR; 2) Typical SACs for eCO2 RR; 3) eCO2 RR toward valuable products. First, how different modification strategies can change the electronic structure of SACs to improve catalytic performance is discussed; Second, SACs with diverse supports and how supports assist active sites to undergo catalytic reaction are introduced; Finally, according to various valuable products from eCO2 RR, the reaction mechanism and measures which can be taken to improve the selectivity of eCO2 RR are discussed. Hopefully, this work can provide a comprehensive understanding of SACs for eCO2 RR and spark innovative design and modification ideas to develop highly efficient SACs for CO2 conversion to various valuable fuels/chemicals.

Guided Synthesis of a Mo/Zn Dual Single-Atom Nanozyme with Synergistic Effect and Peroxidase-like Activity

We present a facile route towards a dual single-atom nanozyme composed of Zn and Mo, which utilizes the non-covalent nano-assembly of polyoxometalates, supramolecular coordination complexes as the metal-atom precursor, and a macroscopic amphiphilic aerogel as the supporting substrate. The dual single-atoms of Zn and Mo have a high content (1.5 and 7.3 wt%, respectively) and exhibit a synergistic effect and a peroxidase-like activity. The Zn/Mo site was identified as the main active center by X-ray absorption fine structure spectroscopy and density functional theory calculation. The detection of versatile analytes, including intracellular H₂ O₂ , glucose in serum, cholesterol, and ascorbic acid in commercial beverages was achieved. The nanozyme has an outstanding stability and maintained its performance after one year's storage. This study develops a new peroxidase-like nanozyme and provides a robust synthetic strategy for single-atom catalysts by utilizing an aerogel as a facile substrate that is capable of stabilizing various metal atoms.

Potential Applications of Nickel-Based Metal-Organic Frameworks and their Derivatives

Metal-Organic Frameworks (MOFs), a novel class of porous extended crystalline structures, are favored in different fields of heterogeneous catalysis, CO₂ separation and conversion, and energy storage (supercapacitors) due to their convenience of synthesis, structural tailor-ability, tunable pore size, high porosity, large specific surface area, devisable structures, and adjustable compositions. Nickel (Ni) is a ubiquitous element extensively applied in various fields of catalysis and energy storage due to its low cost, high abundance, thermal and chemical stability, and environmentally benign nature. Ni-based MOFs and their derivatives provide us with the opportunity to modify different properties of the Ni center to improve their potential as heterogeneous catalysts or energy storage materials. The recent achievements of Ni-MOFs and their derivatives as catalysts, membrane materials for CO₂ separation and conversion, electrode materials and their respective performance have been discussed in this review.

Synthetic strategies for MOF-based single-atom catalysts for photo- and electro-catalytic CO2 reduction

The excessive CO₂ emission has resulted in climate changes, which has threatened human existence. Photocatalytic and electrocatalytic CO₂ reduction, driven by wind electricity and solar energy, are feasible ways of tackling carbon dioxide emission, as both energies are clean and renewable. Single-atom catalyst (SAC) is a candidate owing to excellent electrocatalytic and photocatalytic performance. Methods for preparing an SAC by using metal-organic frameworks (MOFs) as support or precursors are summarized. Also, applications in energy conversion are exhibited. However, the real challenge is to improve the selectivity of catalytic reactions to yield higher value products, which is to be discussed.

Copper(II) Frameworks with Varied Active Site Distribution for Modulating Selectivity of Carbon Dioxide Electroreduction

Metal-organic frameworks (MOFs) can be utilized as electrocatalysts for CO₂ reduction reaction (CO₂RR) due to their well dispersed metal centers. However, the influence of metal node distribution on electrochemical CO₂RR was rarely explored. Here, three Cu-MOFs with different copper(II) site distribution were employed for CO₂ electroreduction. The Cu-MOFs [Cu(L)SO₄]·H₂O (Cu1), [Cu(L)₂(H₂O)₂](CH₃COO)₂·H₂O (Cu2), and [Cu(L)₂(H₂O)₂](ClO₄)₂ (Cu3) were achieved by using the same ligand 1,3,5-tris(1-imidazolyl)benzene (L) but different Cu(II) salts. The results show that the Faraday efficiency of CO (FE_CO) for Cu1 is 4 times that of the FE_H2, while the FE_CO of Cu2 is twice that of the FE_H2. As for Cu3, there is not much difference between FE_CO and FE_H2. Such difference may arise from the distinct electrochemical active surface area and charge transfer kinetics caused by different copper site distribution. Furthermore, the different framework structures also affect the activity of the copper sites, which was supported by the theoretically calculated Gibbs free energy and electron density, contributing to the selectivity of CO₂RR. This study provides a strategy for modulating the selectivity of CO₂RR by tuning the distribution of the active centers in MOFs.

Metal-Support Interactions of Single-Atom Catalysts for Biomedical Applications

The development of single-atom catalysts (SACs) has become a rapidly growing research field. It is a critical challenge to understand the interactions between the single-atom metal active sites and the support materials. Recently, original research reports of SACs in biomedical applications have emerged in the literature, yet this topic has seldom been reviewed. Here, this review focuses on the latest advances in single-atom catalysis for biomedical applications and highlights the keys for the design of SACs, such as understanding the interactions between metals and supports and classifying various enzyme-like activities. This review helps bridge the knowledge of multiple disciplines and provides prospects regarding the development of SACs for biomedicine.

Highly Sensitive and Stable Determination of As(III) under Near-Neutral Conditions: Benefit from the Synergetic Catalysis of Pt Single Atoms and Active S Atoms over Pt1/MoS2

Designing new catalysts with high activity and stability is crucial for the effective analysis of environmental pollutants under mild conditions. Here, we developed a superior catalyst of Pt single atoms anchored on MoS₂ (Pt₁/MoS₂) to catalyze the determination of As(III). A detection sensitivity of 3.31 μA ppb^-1 was obtained in acetate buffer solution at pH 6.0, which is the highest compared with those obtained by other Pt-based nanomaterials currently reported. Pt₁/MoS₂ exhibited excellent electrochemical stability during the detection process of As(III), even in the coexistence of Cu(II), Pb(II), and Hg(II). X-ray absorption fine structure spectroscopy and theoretical calculations revealed that Pt single atoms were stably fixed by four S atoms and activated the adjacent S atoms. Then, Pt and S atoms synergistically interacted with O and As atoms, respectively, and transferred some electrons to H₃AsO₃, which change the rate-determining step of H₃AsO₃ reduction and reduce reaction energy barriers, thereby promoting rapid and efficient accumulation for As(0). Compared with Pt nanoparticles, the weaker interaction between arsenic species and Pt₁/MoS₂ enabled the effortless regeneration and cyclic utilization of active centers, which is more favorable for the oxidation of As(0). This work provides inspiration for developing highly efficient sensing platforms from the perspective of atomic-level catalysis and affords references to explore the detection mechanism of such contaminants.

Carbon support tuned electrocatalytic activity of a single-site metal-organic framework toward the oxygen reduction reaction

Metal-organic frameworks (MOFs) possess fantastic features such as structural diversity, tunable accessible pores and atomically dispersed active sites, holding tremendous potential as highly versatile platforms for fabricating single-site catalysts. The electrocatalytic activity of single-site MOFs can be improved and tuned via several approaches; however, the exploitation of different carbon supports to modulate the nature of single active sites in MOFs for electrocatalysis has not been reported. Here, we find that the electrocatalytic activity of single-site MOFs toward the oxygen reduction reaction (ORR) can be tuned by using carbon nanomaterials, i.e., carbon nanotubes and graphene, as supports through MOF-support interactions in the manner of geometric and electronic effects. The introduction of MOF-support interactions not only greatly improves the electrocatalytic performance of MOFs toward the ORR in terms of onset and half-wave potentials and current density, but also alters the reaction pathway of the ORR. This finding provides a new horizon for the design and synthesis of single-site MOFs for electrocatalysis.

Tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural over a Ni3Fe intermetallic supported Pt single-atom site catalyst

Single-atom site catalysts (SACs) have been used in multitudinous reactions delivering ultrahigh atom utilization and enhanced performance, but it is challenging for one single atom site to catalyze an intricate tandem reaction needing different reactive sites. Herein, we report a robust SAC with dual reactive sites of isolated Pt single atoms and the Ni3Fe intermetallic support (Pt1/Ni3Fe IMC) for tandem catalyzing the hydrodeoxygenation of 5-hydroxymethylfurfural (5-HMF). It delivers a high catalytic performance with 99.0% 5-HMF conversion in 30 min and a 2, 5-dimethylfuran (DMF) yield of 98.1% in 90 min at a low reaction temperature of 160 °C, as well as good recyclability. These results place Pt1/Ni3Fe IMC among the most active catalysts for the 5-HMF hydrodeoxygenation reaction reported to date. Rational control experiments and first-principles calculations confirm that Pt1/Ni3Fe IMC can readily facilitate the hydrodeoxygenation reaction by a tandem mechanism, where the single Pt site accounts for C[double bond, length as m-dash]O group hydrogenation and the Ni3Fe interface promotes the C-OH bond cleavage. This interfacial tandem catalysis over the Pt single-atom site and Ni3Fe IMC support may develop new opportunities for the rational structural design of SACs applied in other heterogeneous tandem reactions.