Single-atom Catalysts Research Articles

Electron transfer mediated activation of periodate by contaminants to generate 1O2 by charge-confined single-atom catalyst.

The electron transfer process (ETP) is able to avoid the redox cycling of catalysts by capturing electrons from contaminants directly. However, the ETP usually leads to the formation of oligomers and the reduction of oxidants to anions. Herein, the charge-confined Fe single-atom catalyst (Fe/SCN) with Fe-N3S1 configuration was designed to achieve ETP-mediated contaminant activation of the oxidant by limiting the number of electrons gained by the oxidant to generate 1O2. The Fe/SCN-activate periodate (PI) system shows excellent contaminant degradation performance due to the combination of ETP and 1O2. Experiments and DFT calculations show that the Fe/SCN-PI* complex with strong oxidizing ability triggers the ETP, while the charge-confined effect allows the single-electronic activation of PI to generate 1O2. In the Fe/SCN + PI system, the 100% selectivity dechlorination of ETP and the ring-opening of 1O2 avoid the generation of oligomers and realize the transformation of large-molecule contaminants into small-molecule biodegradable products. Furthermore, the Fe/SCN + PI system shows excellent anti-interference ability and application potential. This work pioneers the generation of active species using ETP's electron to activate oxidants, which provides a perspective on the design of single-atom catalysts via the charge-confined effect.

Activating the Mn Single Atomic Center for an Efficient Actual Active Site of the Oxygen Reduction Reaction by Spin-State Regulation.

The ligand engineering for single-atom catalysts (SACs) is considered a cutting-edge strategy to tailor their electrocatalytic activity. However, the fundamental reasons underlying the reaction mechanism and the contemplation for which the actual active site for the catalytic reaction depends on the pyrrolic and pyridinic N ligand structure remain to be fully understood. Herein, we first reveal the relationship between the oxygen reduction reaction (ORR) activity and the N ligand structure for the manganese (Mn) single atomic site by the precisely regulated pyrrolic and pyridinic N4 coordination environment. Experimental and theoretical analyses reveal that the long Mn-N distance in Mn-pyrrolic N4 enables a high spin state of the Mn center, which is beneficial to reduce the adsorption strength of oxygen intermediates by the high filling state in antibond orbitals, thereby activating the Mn single atomic site to achieve a half-wave potential of 0.896 V vs RHE with outstanding stability in acidic media. This work provides a new fundamental insight into understanding the ORR catalytic origin of Mn SACs and the rational design strategy of SACs for various electrocatalytic reactions.

Unique Oxygen-Bridged Nickel Atomic Pairs Efficiently Boost Electrochemical Reduction of Carbon Dioxide.

Benefiting from the synergism between adjacent bimetallic atoms, in comparison with single atom catalysts, the dual atom catalysts have displayed great potential in electrocatalytic CO2 reduction reaction (CO2RR). However, the further modulation of the electronic structure of dual atom sites to enhance CO2RR performance still remains a challenge. Herein, an atomically dispersed oxygen-bridged Ni2N6O/NC catalyst with unique Ni-O-Ni sites is successfully synthesized through the microwave pyrolysis of the supported mixture containing the dinuclear nickel phthalocyanine and glucose on N-doped carbon nanosheets. Experiments and density functional theory calculation reveal that the Ni-O-Ni sites can adsorb H+ from the KHCO3 electrolyte to in situ-form the unique Ni-OH-Ni sites without Ni─Ni bonding interaction, which effectively lowers the energy barrier towards the formation of *COOH from CO2. As a result, the Ni2N6OH/NC catalyst exhibits a 99.4% of CO Faradaic efficiency with a 32.4 mA·cm-2 of CO partial current density at -0.7V versus RHE in H-cell, much superior to the Ni2N6/NC with a Ni-Ni bonding interaction prepared by a similar procedure to that for Ni2N6O/NC but replacing microwave pyrolysis by a traditional heating process.

Single-atom Barium Promoter Enormously Enhanced Non-noble Metal Catalyst for Ammonia Decomposition.

As a well-established topic, single-atom catalyst has drawn growing interest for its high utilization of metal. However, researchers prefer to develop various active metals with single-atom form, the intrinsic roles of single-atom promoters are usually underrated, which are significant in boosting reaction activity. In this work, Ba single atoms were in situ prepared in the Co-Ba/Y2O3 catalyst with crystallized BaCO3 as the precursor under the ammonia decomposition reaction condition. The optimized Co-Ba/Y2O3 catalyst achieves extremely high H2 production rate of 138.3 mmolH2·gcat-1·min-1 at very low temperature (500 °C, GHSV = 840,000 mL·g-1·h-1) and Co-Ba/Y2O3 exhibits excellent durability during the 350 h test, which realizes the highest activity among all non-noble catalysts, and reaches or even exceeds numerous reported Ru-based catalysts. Both Y2O3 and Co demonstrate positive interactions with Ba, which significantly facilitates the dispersion of Ba species at high temperatures (≥ 600 °C). Ba single atoms significantly enhance the charge density of Co and form additionally active Co-O-Ba-Y2O3 interfacial sites, which alleviates hydrogen poisoning and decreases the reaction barrier of the N-H bond activation of *NH. The exploration of atomically dispersed promoters is groundbreaking in heterogeneous catalysis, which opens up a whole new domain of catalytic material.

Band gap effect of TiO2 on supported Ru single-atom catalysts for CO2 methanation by DFT calculations

The influence of TiO2 band gap on structure and reactivity of the supported single ruthenium (Ru1) atom was studied by density functional theory calculations, utilizing Ru1/2L-TiO2 and Ru1/3L-TiO2 as model catalysts for CO2 methanation. The supports have band gaps of 2.39 eV and 1.48 eV, respectively. The band gap plays a significant role in electronic metal-support interactions (EMSIs) and the position of the d-band center of the Ru1 on the TiO2. The Ru1/3L-TiO2, the Ru1 catalyst supported on the 3L-TiO2 with a narrower band gap, shows enhanced EMSIs and a d-band center that is positioned farther from Fermi level, leading to lower charge density on the Ru1 and weaker adsorption of H2, CO2, and CO compared to the Ru1/2L-TiO2. CO2 methanation followed CO pathway, with the hydrogenation of CO* to HCO* identified as the rate-determining step on the Ru1/nL-TiO2. The Ru1 catalyst supported on TiO2 with a narrower band gap is more favorable kinetically and thermodynamically for CO2 methanation, despite the band gap not altering the reaction pathway. Enhanced hydrogen mobility and a pronounced promotional effect of hydrogen on CO adsorption, due to the narrower band gap support, are key factors facilitating the easier hydrogenation of CO* on the Ru1/3L-TiO2.

Modulating the Local Coordination Environment of M‐Nx Single‐Atom Site for Enhanced Electrocatalytic Oxygen Reduction

AbstractEfficient, durable, and economical oxygen reduction catalysts are key for practical applications such as fuel cells and metal–air batteries. Single atom catalysts (SACs) have attracted sustained and widespread attention owing to their unique electronic properties and exceptional atomic utilization, positioning them as promising electrocatalysts in energy conversion and storage. However, the symmetric charge distribution of the metal site in the symmetric M‐N4 configuration of SACs is not conducive to electron transfer and transport in electrocatalytic reactions, resulting in a low adsorption energy for oxygen reduction reaction (ORR) related species (*OH, *O, and *OOH), which severely limits the intrinsic activity of the electrocatalysts. To overcome this limitation and improve the activity and durability, heteroatom doping can effectively modulate the local coordination environment (LCE) of the metal atom, including the coordinating atoms, coordination shells and coordination number. These modifications have significantly improved the performance of carbon supported SACs with M‐N4 configuration in the ORR. Based on this, a thorough summary of the major progress made in recent years in adjusting the LCE of SACs through doping with heteroatoms is provided and a perspective on the future development is offered here.

Tuning proton affinity on Co-N-C atomic interface to disentangle activity-selectivity trade-off in acidic oxygen reduction to H2O2.

In oxygen reduction reaction to H2O2via two-electron pathway (2e- ORR), adsorption strength of oxygen-containing intermediates determines both catalytic activity and selectivity. However, it also causes activity-selectivity trade-off. Herein, we propose a novel strategy through modulating the interaction between protons and *OOH intermediates to break the activity-selectivity trade-off for highly active and selective 2e- ORR. Taking the typical cobalt-nitrogen-carbon single-atom catalyst as an example, boron heteroatoms doped into second coordination sphere of CoN4 (Co1-NBC) increase proton affinity on catalyst surface, facilitating proton attack on the former oxygen of *OOH and thereby promoting H2O2 formation. As a result, Co1-NBC simultaneously achieves prominent 2e- ORR activity and selectivity in acid with onset potential of 0.724 V vs. RHE and H2O2 selectivity of 94%, surpassing most reported catalysts. Furthermore, Co1-NBC exhibits a record-high H2O2 productivity of 202.7 mg cm-2 h-1 and a remarkable stability of 60 h at 200 mA cm-2 in flow cell. This work provides new insights into resolving activity-selectivity trade-off in electrocatalysis.

Catalyst Activation of Peroxymonosulfate for Reactive Species Generation and Organic Pollutant Degradation: A Mini Review

This review focuses on the application and mechanisms of peroxymonosulfate (PMS) in advanced oxidation processes (AOPs). It clarifies the significance of PMS in degrading organic pollutants, highlighting its high efficiency in treating persistent contaminants, such as antibiotics. The review details the roles and mechanisms of various catalysts, including single-atom catalysts, metal oxides, non-metal oxides and their composites, as well as metal-organic frameworks (MOFs), in activating PMS. It emphasizes the influence of catalyst surface active sites on both radical and nonradical activation pathways. Key factors affecting PMS activation efficiency, such as PMS concentration, pH value, coexisting ions, and temperature, are examined to underline the importance of optimizing these parameters for effective reaction conditions. By synthesizing existing research, the review not only illustrates the extensive application potential of PMS in AOPs but also identifies future research challenges and directions. This provides a theoretical foundation and technical support for developing efficient, economical, and sustainable water treatment technologies.

Investigation of a Single Atom Iron Catalyst for the Electrocatalytic Reduction of Nitric Oxide to Hydroxylamine: A DFT Study.

Hydroxylamine, as an important reducing agent, disinfectant, foaming agent, and biocide, plays a role in both human life and industrial production. However, its synthesis is confronted with challenges, such as high pollution and large consumption. Here, we propose a coordination tailoring strategy to design 47 graphene-supported single iron atom catalysts (SACs), namely, Fe@CxZy (Z = B, N, O, P, and S), for the reduction of nitric oxide to hydroxylamine. Using density functional theory calculations, we demonstrated the great impact of the coordination environment on the stability, catalytic selectivity, and activity of the Fe site. We identified that the experimentally available Fe@N4 possesses an ultralow theoretical limiting potential of -0.32 V compared to that of other catalysts. A comprehensive investigation of the electronic properties elucidates the underlying active origin and reaction mechanism of the nitric oxide reduction reaction to hydroxylamine on Fe@N4. These results not only explain the catalytic origin of synthesized SACs for the NH2OH production but also offer theoretical guidance for further optimizing high-performance catalysts.

Unique electron-feeding mechanism in CoN3O for enhanced acidic oxygen reduction

Co-centered single-atom catalysts (SACs) have emerged as an increasingly promising non-platinum group candidate for acidic oxygen reduction reaction (ORR) due to their balanced activity and stability. However, the intrinsic ORR activity of present Co-centered SACs remains far below the commercial Pt/C. Herein, a CoN3O-structured SAC is successfully fabricated by a gas-phase strategy and achieves a peak power density of 492.6 mW cm−2 under the 1.0 bar H2/air condition, demonstrating its excellent application potential in practical fuel cells. Unique electron-feeding mechanism is revealed to account for the remarkably enhanced ORR activity inner CoN3O SAC. It is indicated that the electron interaction inner active site governed by both electronegativity in σ bond and d-p back-feeding in π bond reaches balance at CoN3O, thus optimized adsorption of oxygen-containing intermediates. Our work provides multiple insights into the orbital scale laws for higher-performance PGM-free ORR catalysts.

Selenic Acid Etching Assisted Atomic Engineering for Designing Metal-Semimetal Dual Single-Atom Catalysts for Enhanced CO2 Electroreduction.

Single-atom catalysts are promising for electrocatalytic CO2 conversion but face challenges in controllable syntheses. Herein, a facile selenic acid etching-assisted strategy has been developed to fabricate a hybrid metal-semimetal dual single-atom catalyst for electrocatalytic CO2 reduction. This strategy enables the simultaneous generation of monodisperse active sites and hierarchical morphologies with hollow nanostructures. The as-obtained catalyst with Fe-Se dual single-atom sites supported by porous nitrogen-doped carbon (FeSe-NC) shows exceptional catalytic activity and CO selectivity, delivering a Faradaic efficiency (FE) of >97% with industrially comparable jCO, superior to the Fe single-atom catalyst. Moreover, the FeSe-NC-based rechargeable Zn-CO2 battery delivers a high power density (2.01 mW cm-2) and outstanding FECO (>90%), as well as excellent cycling stability. Experimental results together with theoretical calculations reveal that the etching-induced defects and the Se-modulated Fe centers with asymmetrical polarized charge distributions synergistically facilitate the key intermediate *CO desorption and thus accelerate the CO2-to-CO conversion.

The Reaction Mechanism and Rates at Ru Single-Atom Catalysts for Hydrogenation of Biomass BHMF to Produce BHMTHF for Renewable Polymers.

Realizing high selectivity for producing biodegradable 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) for renewable polymers from 5-hydroxymethylfurfural (HMF) biomass through ring hydrogenation on single-atom catalysts poses a considerable challenge due to the complexity of HMF functional groups and the difficulty of H2 dissociation. We developed a detailed reaction mechanism based on ab initio molecular dynamics (AIMD) and quantum mechanics (QM) to find that Ru single-atom catalysts can simultaneously dissociate H2 and perform the ring hydrogenation of biomass-derived 2,5-bis(hydroxymethyl)furan (BHMF) to produce biodegradable BHMTHF, with a free energy barrier of 0.82 eV. The unique property of Ru single-atom sites enables H2 to dissociate easily on a single active site of Ru to participate directly in the reaction without diffusion. Furthermore, our predicted reaction rate from microkinetic analysis indicates that ring hydrogenation and side-chain hydrogenolysis are much faster than ring-opening hydrogenation over the range of 300-550 K. The product BHMTHF dominates with a selectivity of 98.9% at 300 and 78.4% at 550 K (the second product is 5-methylfurfural (5-MFA)). This study underscores the unique effectiveness of Ru single atoms in ring hydrogenation reactions using H2 as the hydrogen source, offering insights for the design of single-atom catalysts for other biomass reactions.

Single nickel atoms anchored on porous N-doped nanocarbon with dual reaction sites for highly-efficient transfer hydrogenation of furfural to furfuryl alcohol

The non-precious metal single-atom catalysts (SACs) supported on carbon materials for the catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes (UAL) still suffer from the problems of harsh reaction conditions and low activity. In this work, nickel SACs anchored on porous N-doped nanocarbon (Ni1/NC900) with dual reaction sites were synthesized using the high internal-phase emulsion (HIPE) template method combined with impregnation. The Ni1/NC900 catalyst exhibited remarkable catalytic activity for the CTH of furfural (FF) to furfuryl alcohol (FFA), achieving >99.0 % conversion and selectivity at 100 °C for 60 min, with a turnover frequency (TOF) of 2908.1 h−1, surpassing other reported nickel-based catalysts by 1–3 orders of magnitude. The excellent catalytic performance of Ni1/NC900 was attributed to the high mass transfer efficiency (HMTE) of the support and the dual reaction sites of Ni–N4 and pyridinic N, where Ni–N4 as Lewis acidic site for adsorption of FF and isopropanol (i-PrOH), while the adjacent pyridinic N as Lewis basic site for the deprotonation of i-PrOH. The isotope labeling experiments revealed that the hydrogenation of FF was accomplished by proton transfer with i-PrOH, in agreement with the intermolecular hydride transfer mechanism. Furthermore, Ni1/NC900 demonstrated excellent stability and well general applicability, demonstrating its potential for industrial applications. This work provides a reference for the application of carbon-based non-precious metal SACs in the CTH reaction of UAL.

Computational screening and investigation of ligand effect on TM single atom catalyst for hydrogen evolution reaction

Here, we studied the stability, electronic characteristics, and HER catalytic performance of a transition metal single atom catalysts, both with and without the presence of chlorine ligand. The findings indicate that all catalysts, except for Au, Au-Cl, Ag, Ag-Cl, are thermodynamically stable. We found 3d transition metals are more stable than those in the 4d and 5d series. Ag-Cl, Sc, Ag, Fe-Cl, and Cr-Cl have the poorest electrochemical stability. We found a negative Pearson correlation between Fermi energy and formation energy for TM-Cl, which is opposite to the trend observed for bare TM catalysts. The higher HER activity of chlorine bonded system for the early 3d TM suggests that the downshifting of the d-band center facilitates the activity. We also observed a periodic trend in the d-band center for both TM and TM-Cl systems. Mn-Cl, Cr-Cl, Ti-Cl, Fe-Cl, V-Cl and Zn emerged as the superior catalysts in our study series.

An evaluate of ORR catalysts in fuel cell: Current Advances and Applications

Abstract. This thesis presents a comprehensive review of fuel cell technology, with a specific emphasis at the latest trends and programs of oxygen reduction response (ORR) catalysts. The examine starts offevolved with the aid of using evaluating the benefits and drawbacks of hydrogen fuel cells with different alternative power sources, which include sun power and secondary batteries, highlighting the ability of fuel cells to update traditional inner combustion engines because of their high power density and environmental benefits. The thesis then explores the essential running ideas of fuel cells and examines their operational mechanisms in numerous chemical environments. In the context of ORR catalysts, the assessment evaluates quite a number catalysts, which include precious metal catalysts, non-precious metal catalysts, and single-atom catalysts, that specialize in techniques to decorate their activity and stability. Finally, the thesis discusses the demanding situations and destiny possibilities for the industrial application of ORR catalysts in hydrogen fuel cells.

Transition metal atoms embedded graphyne as effective catalysts for nitrate electroreduction to ammonia: A theoretical study

Electrocatalytic nitrate reduction reaction (NO3RR) to ammonia has been proved to be a viable approach to dispose of nitrates pollution and simultaneously fabricate valuable ammonia at room temperature and pressure. It is essential to explore high-performance and selective electrocatalysts for NO3RR to overcome the sluggish kinetics. Herein, through adopting a four-step screening route based upon the calculation of density functional theory (DFT), we have performed a comprehensive investigation on the NO3RR catalytic activities for single-atom catalysts (SACs), taking transition metal atom embedded graphyne (TM-GY, TM = 3d ∼ 5d) as example. The computation results show that the electrochemical conversion of nitrate-to-ammonia can be realized on Cr-GY candidate with an extremely low limiting potential (-0.36 V) and high selectivity, which can be ascribed to the moderate adsorption strength between the intermediate species and Cr atom derived from its distinct electronic property. Our study not only reveals the NO3RR catalytic origin of TM-GY, but also provides a new route for the rational design of electrocatalysts for nitrate reduction to ammonia.

Cobalt single-site molecular Catalyst-mediated electrochemical Hydrodechlorination for detoxification of halogenated Antibiotics: Performance, reaction pathway and mechanism

Electrocatalytic hydrodehalogenation (ECHD) offers a promising approach for detoxification of the halogenated antibiotics via hydrogenolysis of the C-X bonds (X = F, Cl or Br). Herein we demonstrated that the commercially-available cobalt phthalocyanine (CoPc) molecules with a high-loading of −[Co-N4]- moieties (Co wt%: 10.8 %) were exceptionally active for hydrogenolysis of the C-Cl bonds in florfenicol (FLO). It afforded an impressive mass activity of 6.2 gFLO h−1 g-1Co, a low Co leaching of 0.34 μg/L and a strong tolerance to interference from impurities in water, significantly surpassing reported Co/Fe/Ni-based particle and single-site counterparts. Mechanistic studies revealed that the ECHD on CoPc underwent a direct electron transfer manner rather than the atomic hydrogen (H*)-mediated indirect way, and the ECHD efficacy was affected by both the electron and proton transfer kinetics. The single-atom Co, with its d orbitals constituting the lowest unoccupied molecular orbitals of CoPc, served as the primary active site. It facilitated both electron and proton transfer, as well as the cleavage of the C-Cl bond but not the C-F bond. In a continuous-flow cell, the CoPc/C-driven ECHD reduced the antibacterial activity of a FLO-contaminated natural lake water sample by 90.8 % with an energy consumption of 0.19 kwh g-1FLO. This study highlighted great promise of the single-atom metal-bearing molecular catalyst toward the sustainable detoxification of halogenated antibiotics-contaminated water.

The Relationship between Electronic Behavior of Single Atom Catalysts and CO2 Reduction to Oxygenates

The Relationship between Electronic Behavior of Single Atom Catalysts and CO2 Reduction to Oxygenates

Single atom catalysts for oxygen evolution reaction in acidic media

Single atom catalysts for oxygen evolution reaction in acidic media

Dual active site pathways in cobalt-based bimetallic catalysts enhance oxygen evolution reaction activity: Density functional theory studies

Co single-atom catalysts show significant potential in enhancing oxygen evolution reaction (OER) efficiency, crucial for advancing renewable energy technologies. However, their performance is constrained by a single active site, making it challenging for traditional OER pathways to surpass theoretical overpotential limits. By focusing on dual active sites, this study systematically investigates the structural evolution and catalytic performance of Co based double atom catalysts using density functional theory. Co as the primary metal (M1), pairs with 15 different transition metals (M2) to create bimetallic catalysts. The formation energies, binding energies, and Gibbs free energy changes along four potential OER reaction pathways are calculated to assess the stability and activity of these catalysts. The results show enhanced catalytic performance along path II (H₂O → *OH → *2OH → *OOH → O₂) for Co-Ni, Co-Cu, Co-Pd, and Co-Pt catalysts. This improvement stems from synergistic interactions between metal atoms, bypassing high-energy barriers in traditional pathways. Notably, the d-band centers of Cu, Pd, and Pt near the Fermi level boost electron transfer. Co provides stable adsorption sites, optimizing the conversion of intermediates. This study advances understanding of the reaction mechanism and guides the development of more efficient catalysts.