Single Atomic Site Catalysts Research Articles

Precise Modulation of the Coordination Environment of Single Cu Site Catalysts to Regulate the Peroxymonosulfate Activation Pathway for Water Remediation.

Single atom site catalysts (SACs) with atomically dispersed active sites can be expected to be potential ideal catalysts for accurately modulating the persulfate activation pathway during the water remediation process because of their well-defined structure and the maximum metallic atom utilization. In this paper, a series of Cu SACs with different coordination environments were synthesized to elaborately regulate the peroxymonosulfate activation pathway in AOPs to clarify active species generation and transformation in water remediation. The degradation rate constants (kobs) of Cu-N2, Cu-N3, and Cu-N4 were 0.028, 0.021, and 0.015 min-1, respectively. Cu-N2 SACs exhibited a noticeable enhanced performance for bisphenol A (BPA) removal from water compared to that of the Cu-Nx SACs (x = 3, 4), accompanied by peroxymonosulfate (PMS) activation pathway variation. As shown by experimental and theoretical results, the PMS activation pathway was transformed from ROS to electron transfer with nitrogen coordination numbers decreasing from 4 to 2, which can be ascribed to the uneven charge distribution of Cu sites as well as upshifts in the d-band center, and thereby optimized electron transfer for PMS activation. Furthermore, the increasing nitrogen vacancies of single Cu site catalysts can also result in more unoccupied 3d orbitals of Cu atoms in SACs, thereby improving the intermediates' (PMS and BPA) adsorption-desorption process and BPA removal performance. These findings provided a beneficial approach for the coordination number regulation of SACs in water remediation.

General Design Concept of High-Performance Single-Atom-Site Catalysts for H2O2 Electrosynthesis.

Hydrogen peroxide (H2O2) as a green oxidizing agent is widely used in various fields. Electrosynthesis of H2O2 has gradually become a hotspot due to its convenient and environment-friendly features. Single-atom-site catalysts (SASCs) with uniform active sites are the ideal catalysts for the in-depth study of the reaction mechanism and structure-performance relationship. In this review, the outstanding achievements of SASCs in the electrosynthesis of H2O2 through 2e- oxygen reduction reaction (ORR) and 2e- water oxygen reaction (WOR) in recent years, are summarized. First, the elementary steps of the two pathways and the roles of key intermediates (*OOH and *OH) in the reactions are systematically discussed. Next, the influence of the size effect, electronic structure regulation, the support/interfacial effect, the optimization of coordination microenvironments, and the SASCs-derived catalysts applied in 2e- ORR are systematically analyzed. Besides, the developments of SASCs in 2e- WOR are also overviewed. Finally, the research progress of H2O2 electrosynthesis on SASCs is concluded, and an outlook on the rational design of SASCs is presented in conjunction with the design strategies and characterization techniques.

Atomically Dispersed ZnN4 Sites Anchored on P-Functionalized Carbon with Hierarchically Ordered Porous Structures for Boosted Electroreduction of CO2.

Tuning the coordination structures of metal sites is intensively studied to improve the performances of single-atom site catalysts (SASC). However, the pore structure of SASC, which is highly related to the accessibility of active sites, has received little attention. In this work, single-atom ZnN4 sites embedded in P-functionalized carbon with hollow-wall and 3D ordered macroporous structure (denoted as H-3DOM-ZnN4 /P-C) are constructed. The creation of hollow walls in ordered macroporous structures can largely increase the external surface area to expose more active sites. The introduction of adjacent P atoms can optimize the electronic structure of ZnN4 sites through long-rang regulation to enhance the intrinsic activity and selectivity. In the electrochemical CO2 reduction reaction, H-3DOM-ZnN4 /P-C exhibits high CO Faradaic efficiency over 90% in a wide potential window (500mV) and a large turnover frequency up to 7.8×104 h-1 at -1.0V versus reversible hydrogen electrode, much higher than its counterparts without the hierarchically ordered structure or P-functionalization.

Synergistic Optimization of Morphology and Vacancies on Diatomic Rhodium Catalysts Dispersed on Carbon Nitride for Efficient Photocatalytic Reduction of CO2

AbstractDiatomic site catalysts (DAC) have better performance with higher metal content and more flexible active sites compared with single atomic site catalysts (SAC). Herein, the authors for the first time achieved Rh2 DAC on loose porous g‐C3N4 hollow nanospheres with N‐vacancies and applied to photocatalytic CO2 reduction reaction, overcoming the current limitations of the low electron–hole recombination rate and prolong the lifetime of the photogenerated carrier. The high specific surface area of hollow nanosphere facilitates the uniform dispersion and anchoring of Rh2 diatomic pairs, while the N‐vacancies induce a stable 3N/Rh‐Rh/1N2C coordination between the carrier and Rh2 diatomic pairs. The local charges on the support framework with N vacancies tend to be transferred to Rh2 diatomic site by 3N/Rh‐Rh/1N2C bridge, which made the charge enriched Rh2 diatomic site become the active center of reaction, enhance charge separation efficiency of Rh2/HCNS‐Nv. Compared with Rh1 SAC, further Density Functional Theory (DFT) calculation confirms that Rh2 DAC can effectively stabilize rate‐limiting intermediates CHO*, and well weaken the C─O bond strength in CH3O* species, promote the generation and separation of CH4, resulting in high CO2 reduction efficiency and CH4 electron selectivity of up to 91.65%.

Ultrasound-Driven Defect Engineering in TiO2-x Nanotubes─Toward Highly Efficient Platinum Single Atom-Enhanced Photocatalytic Water Splitting.

Single-atom catalysts (SACs) have demonstrated superior catalytic activity and selectivity compared to nanoparticle catalysts due to their high reactivity and atom efficiency. However, stabilizing SACs within hosting substrates and their controllable loading preventing single atom clustering remain the key challenges in this field. Moreover, the direct comparison of (co-) catalytic effect of single atoms vs nanoparticles is still highly challenging. Here, we present a novel ultrasound-driven strategy for stabilizing Pt single-atomic sites over highly ordered TiO2 nanotubes. This controllable low-temperature defect engineering enables entrapment of platinum single atoms and controlling their content through the reaction time of consequent chemical impregnation. The novel methodology enables achieving nearly 50 times higher normalized hydrogen evolution compared to pristine titania nanotubes. Moreover, the developed procedure allows the decoration of titania also with ultrasmall nanoparticles through a longer impregnation time of the substrate in a very dilute hexachloroplatinic acid solution. The comparison shows a 10 times higher normalized hydrogen production of platinum single atoms compared to nanoparticles. The mechanistic study shows that the novel approach creates homogeneously distributed defects, such as oxygen vacancies and Ti3+ species, which effectively trap and stabilize Pt2+ and Pt4+ single atoms. The optimized platinum single-atom photocatalyst shows excellent performance of photocatalytic water splitting and hydrogen evolution under one sun solar-simulated light, with TOF values being one order of magnitude higher compared to those of traditional thermal reduction-based methods. The single-atom engineering based on the creation of ultrasound-triggered chemical traps provides a pathway for controllable assembling stable and highly active single-atomic site catalysts on metal oxide support layers.

Two-Dimensional Covalent Framework Derived Nonprecious Transition Metal Single-Atomic-Site Electrocatalyst toward High-Efficiency Oxygen Reduction

Designing an active, stable, and nonprecious metal catalyst substitute for Pt in the oxygen reduction reaction (ORR) is highly demanded for energy-efficient and cost-effective prototype devices. Single-atomic-site catalysts (SASCs) have been widely concerning because of their maximum atomic utilization and precise structural regulation. Despite being challenging, the controllable synthesis of SASCs is crucial for optimizing ORR activity. Here, we demonstrate an ultrathin organometallic framework template-assisted pyrolysis strategy to synthesize SASCs with a unique two-dimensional (2D) architecture. Electrochemical measurements revealed that Fe-SASCs displayed an excellent ORR activity in an alkaline media, having a half-wave potential and a diffusion-limited current density comparable to those of commercial Pt/C. Remarkably, the durability and methanol tolerance of Fe-SASCs were even superior to those of Pt/C. Furthermore, Fe-SASCs displayed a maximum power density of 142 mW cm-2 with a current density of 235 mA cm-2 as a cathode catalyst in a zinc-air battery, showing its great potential for practical applications.

Reconstructing Oxygen‐Deficient Zirconia with Ruthenium Catalyst on Atomic‐Scale Interfaces toward Hydrogen Production

AbstractDownsizing a catalyst nanoparticle (NP) to a single atom (SA) has proven to be highly effective in increasing catalytic activity and decreasing the amount of catalyst required for various electrochemical reactions. However, insufficient stability of the single‐atom site catalysts (SACs) is still a significant challenge for their practical application. Here, SACs firmly bound to stable metal oxide NPs are proposed to dramatically increase the electrochemical activity and stability of SA‐based catalysts for hydrogen evolution reaction (HER). Starting from a Ru‐infiltrated, Zr‐based metal‐organic framework (MOF), the tetragonal zirconium oxide (ZrO2‐x) NPs‐embedded carbon matrix is fabricated as support through facile pyrolysis. Simultaneously, Ru SAs as active sites are well dispersed on the surface of ZrO2‐x NPs due to the generation of oxygen vacancies in the tetragonal ZrO2‐x. The Ru‐ZrO2‐x SAC exhibits a 4–5 times higher mass activity than commercial Pt and Ru catalysts and superior durability due to strong metal‐support interaction (SMSI) between Ru atoms and ZrO2‐x substrate.

Dual-Atomic-Site Catalysts for Molecular Oxygen Activation in Heterogeneous Thermo-/Electro-catalysis.

Efficient molecular oxygen activation (MOA) is the key to environmentally friendly catalytic oxidation reactions. In the last decade, single-atomic-site catalysts (SASCs) with nearly 100% atomic utilization and unique electronic structure have been widely investigated for MOA. However, the single active site makes the activation effect unsatisfactory and difficult to deal with complex catalytic reactions. Recently, dual-atomic-site catalysts (DASCs) have provided a new idea for the effective activation of molecular O2 due to more diverse active sites and synergetic interactions among adjacent atoms. In this review, we systematically summarized the recent research progress of DASCs for MOA in heterogeneous thermo- and electrocatalysis. Finally, we look forward to the challenges and application prospects in the construction of DASCs for MOA.

Dual‐Atomic‐Site Catalysts for Molecular Oxygen Activation in Heterogeneous Thermo‐/Electro‐catalysis

AbstractEfficient molecular oxygen activation (MOA) is the key to environmentally friendly catalytic oxidation reactions. In the last decade, single‐atomic‐site catalysts (SASCs) with nearly 100 % atomic utilization and unique electronic structure have been widely investigated for MOA. However, the single active site makes the activation effect unsatisfactory and difficult to deal with complex catalytic reactions. Recently, dual‐atomic‐site catalysts (DASCs) have provided a new idea for the effective activation of molecular oxygen (O2) due to more diverse active sites and synergetic interactions among adjacent atoms. In this review, we systematically summarized the recent research progress of DASCs for MOA in heterogeneous thermo‐ and electrocatalysis. Finally, we look forward to the challenges and application prospects in the construction of DASCs for MOA.

Two-Dimensional Fe-N-C Single-Atomic-Site Catalysts with Boosted Peroxidase-Like Activity for a Sensitive Immunoassay.

Single-atomic-site catalysts (SASCs) with peroxidase (POD)-like activities have been widely used in various sensing platforms, like the enzyme-linked immunosorbent assay (ELISA). Herein, a two-dimensional Fe-N-C-based SASC (2D Fe-SASC) is successfully synthesized with excellent POD-like activity (specific activity = 90.11 U/mg) and is used to design the ELISA for herbicide detection. The 2D structure of Fe-SASC enables the exposure of numerous single atomic active sites on the surface as well as boosts the POD-like activity, thereby enhancing the sensing performance. 2D Fe-SASC is assembled into competitive ELISA kit, which achieves an excellent detection performance for 2,4-dichlorophenoxyacetic acid (2,4-D). Fe-SASC has great potential in replacing high-cost natural enzymes and working on various advanced sensing platforms with high sensitivity for the detection of various target biomarkers.

Advanced dual-atom catalysts for efficient oxygen evolution reaction

This perspective discusses the latest exciting advancements in dual-atom catalysts (DACs) for the oxygen evolution reaction and battery devices, highlighting the fundamental principles for the intelligent design and application of DACs.

Single-atom site catalysis in Li-S batteries.

With their high theoretical energy density, Li-S batteries are regarded as the ideal battery system for next generation electrochemical energy storage. In the last 15 years, Li-S batteries have made outstanding academic progress. Recently, research studies have placed more emphasis on their practical application aspects, which puts forward strict requirements for the loading of S cathodes and the amount of electrolytes. To meet the above requirements, electrode catalysis design is of crucial significance. Among all the catalysts, single-atom site catalysts (SASCs) are considered to be ideal catalyst materials for the commercialization of Li-S batteries due to their high activity and highest utilization of catalytic sites. This perspective introduces the kinetic mechanism of S cathodes, the basic concept and synthesis strategy of SASCs, and then systematically summarizes the research progress of SASCs for S cathodes and, the related functional interlayers/separators in recent years. Finally, the opportunities and challenges of SASCs in Li-S batteries are summarized and prospected.

Rational design of atomic site catalysts for electrochemical CO2 reduction.

Renewable-energy-powered electrochemical CO2 reduction (ECR) is a promising way of transforming CO2 to value-added products and achieving sustainable carbon recycling. By virtue of the extremely high exposure rate of active sites and excellent catalytic performance, atomic site catalysts (ASCs), including single-atomic site catalysts and diatomic site catalysts, have attracted considerable attention. In this feature article, we focus on the rational design strategies of ASCs developed in recent years for the ECR reaction. The influence of these strategies on the activity and selectivity of ASCs for ECR is further discussed in terms of electronic regulation, synergistic activation, microenvironmental regulation and tandem catalytic system construction. Finally, the challenges and future directions are indicated. We hope that this feature article will be helpful in the development of novel ASCs for ECR.

Regulating the charge densities of s-Block calcium single-atom site catalysts for efficient N2 activation and reduction

The s-block alkaline earth metal (AM) sites in single atom catalysts (SACs) present promising potential for catalyzing reactions but their application to the N2 electroreduction reaction (eNRR) has so far received little attention. Using first-principles calculations, we propose an effective strategy for regulating the d orbital-related electronic structures of s-block calcium (Ca) in a single-atom-based catalyst for driving the eNRR. In contrast to previous AM SAC studies that involve only s and p valence orbitals, we show that the d orbitals of a Ca atom can be effectively utilized for N2 activation and reduction. The filled Ca d orbital can perform Ca-to-N back-donation by interacting with an antibonding orbital of N2, thus weakening the NN bond. Changes in the local N coordination structure and number regulate the d orbital-related electronic structures of the Ca atom, resulting in moderately positive charge densities on Ca. As a result, the adsorption behavior of key intermediates, especially the *N-*NH, can be optimized, which greatly promotes N2 reduction to NH3. Utilization of a d orbital thus provides a new dimension for designing s-block metal catalysts for efficient catalysis of reactions.

Coupling Transition Metal Compound with Single-Atom Site for Water Splitting Electrocatalysis.

Single-atom site catalysts (SACs) provide an ideal platform to identify the active centers, explore the catalytic mechanism, and establish the structure-property relationships, and thus have attracted increasing interests for electrocatalytic energy conversion. Substantial endeavors have been devoted to the construction of carbon-supported SACs, and their progress have been comprehensively reviewed. Compared with carbon-supported SACs, transition metal compounds (TMCs)-supported SACs are still in their infancy in the field of electrocatalysis. However, they have also aroused ever-increasing attention for driving electrocatalytic water splitting, and emerged as an indispensable class of SACs in recent years, predominately owing to their inherently structural features, such as rich anchoring sites, surface defects, and lattice vacancy. Herein, in this review, we have systematically summarized the recent advances of a variety of TMC supported SACs toward electrocatalytic water splitting. The advanced characterization techniques and theoretical analyses for identifying and monitoring the atomic structure of SACs are firstly manifested. Subsequently, the anchoring and stabilization mechanisms for TMC supported SACs are also highlighted. Thereafter, the advances of TMC supported SACs for driving water electrolysis are systematically unraveled.

Band Structure Engineering of Single Pt Atoms on Fe-TiO2 for Enhanced Photocatalytic Performance.

Single atomic site catalysts display the maximal atom-utilization efficiency, unique structural properties, and remarkable enhancements on catalytic activity. Herein, single Pt atoms loaded Fe-TiO2 catalysts were prepared. Fe3+ doping leads to the formation of oxygen vacancies and improve the interaction between TiO2 and Pt. Single Pt atoms are thus anchored and effectively modify the local energy band structure of TiO2 . The optimized local band structures improve the intrinsic photoexcitation of Pt/Fe-TiO2 , promote the separation of photogenerated carriers, and extend the lifetime of photogenerated carriers. Meanwhile, the electrons transfer from the excited dyes to the conduction band edge of Pt/Fe-TiO2 is also facilitated due to the shift-down of the conduction band edge. Therefore, with the increase of the Pt content (till up to 0.6 wt%), the photocatalytic performance of Pt/ Fe-TiO2 with the confined single Pt atoms is significantly boosted in either the intrinsic or the sensitized photocatalytic process.

Regulating Cu atom orbital state on self-built photogate catalyst for improving HCOOH selectivity of CO2 reduction

While single atom site catalysts receive tremendous attention for CO2 reduction, the understanding of orbital coupling interaction between metal-atom and CO2 molecular remains challenging and rare toward CO2 activation and selectivity of reduction products. Herein, binuclear-site Zn/Cu-porphyrin covalent organic framework (ZnCu-COF) photogate catalyst was synthesized, with characterizations of intraskeletal photogate molecular device (PMD). The ZnCu-COF showed the HCOOH selectivity of 89.1%, which was superior than Zn-COF and Cu-COF counterparts. The in-depth experimental and theoretical analyses reveal that Cu atom centers can enrich the electrons of Zn photocenters via directional and stepwise electron diffusion, which remarkably affects the orbital energy of Cu-3d, further deciding the electron state re-distribution of Cu-3d (dxy, dyz, dzx, dz2, and dx2−y2) orbitals. By a strong orbital coupling strength between Cu-3dz2 and C-2pz, Cu atom centers promote CO2 activation and nucleophilic reaction of the unsaturated carbon of *COOH intermediate, which clearly accounts for the different HCOOH and CO selectivity in COFs. This work opens critical perspective to the rational engineering, catalytic mechanism, and application of PMD-derived atomic-site catalysts.

Microalgae-derived single-atom oxygen reduction catalysts for zinc-air batteries

The need to fight against global warming has motivated the development of new technologies for green production of various chemicals and materials. Microalgae can convert CO2 into valuable biofuels, thus playing important roles in carbon neutrality. However, appropriately utilization of microalgae biomass remains an important issue to address. Here we demonstrate that the microalgae biomass with abundant membrane-bound biomolecules and singly isolated metal atoms can be upgraded into single-atom site catalysts (SACs) with high oxygen reduction reaction (ORR) activity. Through hydrothermal and pyrolysis treatment of microalgae, Fe–N4 structured SACs (malg-SACs) are obtained, as confirmed by near edge X-ray absorption fine structure (NEXAFS), X-ray absorption near-edge structure (XANES), and extended X-ray absorption fine structure (EXAFS). Under optimal conditions, the malg-SAC exhibits a remarkable ORR activity (E1/2 = 0.875 V vs. RHE), outstanding long-term stability, and good resistance to CO and CH3OH poisoning. When assembled in a primary zinc-air battery, the full device reaches a maximum power density of 220.7 mW cm−2 with negligible voltage decay over the 6 h test, far outperforming the commercial Pt/C (112.1 mW cm−2). Our work reports a sustainable pathway to convert CO2-capture biomass into high-performance SACs, simultaneously addressing environmental and energy issues.

The superiority and perspectives in single-atom site and multi-atom site catalysts for energy conversion

Atomically dispersed metal catalysts have been a research hotspot in the field of nanocatalysis due to their unique advantages in recent years. The isolated single or few atoms can be anchored on supports via chemical bonding or space confinement to maximize atom utilization efficiency, reducing the use of metal resources while displaying distinguished catalytic performance. This perspective presents the latest advances in single-atom site catalysts (SACs) and multi-atom site catalysts (MACs), highlights their superiority, and discusses the current limitations as well as the outlooks facing their future development.

Comprehensive Review for an Efficient Charge Transfer in Single Atomic Site Catalyst/Organic Polymers toward Photocatalytic CO2 Reduction

AbstractSingle atomic site catalyst/organic polymers hybrid photocatalyst has been demonstrated as a potential material for photocatalytic CO2 reduction that can solve both environmental and energy issues simultaneously. The charge migration and transfer between organic polymers and single atomic site catalysts are attributed to the high performance of the hybrid material. In this review, two typical charge transfers between the single atomic site catalyst and organic polymer‐based semiconductor, namely intermolecular electron transfer and intramolecular electron transfer, are discussed. Typical single‐atomic site catalysts, organic polymers, and methods are first reviewed for the fabrication of hybrid systems. Why intramolecular electron transfer between the single atomic site catalyst and organic polymers exhibits higher photocatalytic activity than intermolecular electron transfer is also discussed. Finally, the critical challenges in fabricating these hybrid photocatalysts toward an efficient photocatalytic CO2 reduction are highlighted, and propose solutions to these challenges.