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[1] Li Zhijun, Dong Xiuli, Zhang Mingyang, LengLeipeng, Chen Wenxing, Horton J. Hugh, Wang Jun, Li Zhijun, Wu Wei. SelectiveHydrogenation on a Highly Active Single-Atom Catalyst of Palladium Dispersed onCeria Nanorods by Defect Engineering [J]. ACS applied materials &interfaces, 2020, 10.1021/acsami.0c17009.
Single-atom catalysis representsa new frontier that integrates the merits of homogeneous and heterogeneouscatalysis to afford exceptional atom efficiency, activity, and selectivity fora range of catalytic systems. Herein we describe a simple defect engineeringstrategy to construct an atomically dispersed palladium catalyst (Pddelta+, 0< delta < 2) by anchoring the palladium atoms on oxygen vacancies createdin CeO2 nanorods. This was confirmed by spherical aberration correctionelectron microscopy and extended X-ray absorption fine structure measurement.The as-prepared catalyst showed exceptional catalytic performance in thehydrogenation of styrene (99% conversion, TOF of 2410 h-1), cinnamaldehyde (99%conversion, 99% selectivity, TOF of 968 h-1), as well as oxidation oftriethoxysilane (99% conversion, 79 selectivity, TOF of 10 000 h-1). Thissingle-atom palladium catalyst can be reused at least five times withnegligible activity decay. The palladium atoms retained their dispersion on thesupport at the atomic level after thermal stability testing in Ar at 773 K.Most importantly, this synthetic method can be scaled up while maintainingcatalytic performance. We anticipate that this method will expedite access tosingle-atom catalysts with high activity and excellent resistance to sintering,significantly impacting the performance of this class of catalysts.
[2] Tang Panjuan, Paganelli Stefano, Carraro Francesco, Blanco Matias,Ricco Raffaele, Marega Carla, Badocco Denis, Pastore Paolo, Doonan ChristianJ., Agnoli Stefano. Postsynthetic Metalated Mofs as Atomically Dispersed Catalystsfor Hydroformylation Reactions [J]. ACS applied materials & interfaces,2020, 12(49): 54798-805. 10.1021/acsami.0c17073.
A manganese-based metal-organicframework with dipyrazole ligands has been metalated with atomically dispersedRh and Co species and used as a catalyst for the hydroformylation of styrene.The Rh-based materials exhibited excellent conversion at 80 °C with completechemoselectivity, high selectivity for the branched aldehyde, highrecyclability, and negligible metal leaching.
[3] Van Velthoven N., Wang Y. H., Van Hees H., Henrion M., Bugaev A.L., Gracy G., Amro K., Soldatov A. V., Alauzun J. G., Mutin P. H., De Vos D. E.Heterogeneous Single-Site Catalysts for C-H Activation Reactions: Pd(Ii)-LoadedS,O-Functionalized Metal Oxide-Bisphosphonates [J]. Acs Applied Materials &Interfaces, 2020, 12(42): 47457-66. 10.1021/acsami.0c12325.
Heterogeneous single-sitecatalysts contain spatially isolated, well-defined active sites. This allowsnot only their easy recovery by solid-liquid separation but also the detailedactive site design similar to homogeneous catalysts. Here, heterogeneous Pd(II)single-site catalysts were assembled, based on mesoporous metaloxide-bisphosphonate materials as supports. This new family of hybrid organic-inorganicmaterials with tunable porosity was further functionalized with thioetherligands containing S,O-binding sites that enhance the activity of Pd(II) forC-H activation reactions. The structures of the resulting Pd(II) single-sitecatalysts were carefully analyzed via solid-state NMR spectroscopy, via textureanalysis by N-2 physisorption, infrared spectroscopy, and transmission electronmicroscopy. Furthermore, the immediate environment of the isolated Pd(II)active sites was studied with X-ray absorption spectroscopy. A clearrelationship between the thioether ligand surface density and catalyst activitycould be established. Significantly higher yields were obtained using highlyporous metal oxide-bisphosphonate materials as supports compared to materialswith lower porosities, such as conventional metal oxides, indicating that thehigh surface area facilitates the presence of isolated, well-accessibleS,O-supported Pd(II) active sites. A wide scope of model substrates, includingindustrially relevant arenes, can be converted with high yields by the optimalheterogeneous Pd catalyst.
[4] Wang S. Y., Shi L., Bai X. W., Li Q., Ling C. Y., Wang J. L. HighlyEfficient Photo-/Electrocatalytic Reduction of Nitrogen into Ammonia by Dual-Metal Sites [J]. Acs Central Science, 2020, 6(10): 1762-71.10.1021/acscentsci.0c00552.
The photo-/electrocatal)rtnitrogen reduction reaction. (NRR) is an up and coming method for sustainableNH3 Production, however, its Practical application is impeded by poor Faradaicefficiency originating fromthe competing hydrogen evolution reaction (HER) andthe inert N equivalent to N triple bond activation. In this work, we put fortha method to boost NRR through construction of donor-acceptor couples ofdual-metal sites. The synergistic effect of dual active sites can potentiallybreak the metal-based activity benchmark toward efficient NRR. Bysystematically evaluating the stability, activity, and selectivity of 28heteronuclear dual-atom catalysts (DACs) of M1M2/g-C3N4 candidates, FeMo/g-C3N4is screened out as an effective electrocatalyst for NRR with a particularly lowlimiting potential of -0.23 V for NRR and a rather high potential of -0.79 Vfor HER. Meanwhile, TiMo/g-C3N4, NiMo/g-C3N4, and MoW/g-C3N4 with suitable bandedge positions and visible light absorption can be applied to NRR asphotocatalysts. The excellent catalytic activity is attributed to the tunablecomposition of metal dimers, which play an important role in modulating thebinding strength of the target intermediates. This work may pave a new way forthe rational design of heteronuclear DACs with high activity and stability forNRR which may also apply to other reactions.
[5] Zhang J. C., Yang H. B., Liu B. Coordination Engineering ofSingle-Atom Catalysts for the Oxygen Reduction Reaction: A Review [J]. AdvancedEnergy Materials, 2020, Artn 2002473
10.1002/Aenm.202002473.
Future renewable energy suppliesand a sustainable environment rely on many important catalytic processes.Single-atom catalysts (SACs) are attractive because of their maximum atomutilization efficiency, tunable electronic structures, and outstanding catalyticperformance. Of particular note, transition-metal SACs exhibit excellentcatalytic activity and selectivity for the oxygen reduction reaction (ORR)-animportant half reaction in fuel cells and metal-air batteries as well as forportable hydrogen peroxide (H2O2) production. Although considerable effortshave been made on the synthesis of SACs for ORR, the regulation of thecoordination environments of SACs and thus the electronic structures still posea big challenge. In this review, strategies for manipulating the coordinationenvironments of SACs are classified into three categories, including regulationof the center metal atoms, manipulation of the surrounding environmentconnecting to the center metal atom, and modification of the geometric configurationof the support. Finally, some issues regarding the future development of SACsfor ORR are raised and possible solutions are proposed.
[6] Gong X. F., Zhu J. B., Li J. Z., Gao R., Zhou Q. Y., Zhang Z., DouH. Z., Zhao L., Sui X. L., Cai J. J., Zhang Y. L., Liu B., Hu Y. F., Yu A. P.,Sun S. H., Wang Z. B., Chen Z. W. Self-Templated Hierarchically Porous CarbonNanorods Embedded with Atomic Fe-N-4 Active Sites as Efficient Oxygen ReductionElectrocatalysts in Zn-Air Batteries [J]. Advanced Functional Materials, 2020,Artn 2008085
10.1002/Adfm.202008085.
Iron-nitrogen-carbon materialsare being intensively studied as the most promising substitutes for Pt-basedelectrocatalysts for the oxygen reduction reaction (ORR). A rational design ofthe morphology and porous structure can promote the accessibility of the activesite and the reactants/products transportation, accelerating the reactionkinetics. Herein, 1D porous iron/nitrogen-doped carbon nanorods (Fe/N-CNRs)with a hierarchically micro/mesoporous structure are prepared by pyrolyzing thein situ polymerized pyrrole on the surface of Fe-MIL-88B-derived 1D Fe2O3nanorods (MIL: Material Institut Lavoisier). The Fe2O3 nanorods not onlypartially dissolve to generate Fe3+ for initiating polymerization but serve astemplates to form the 1D structure during polymerization. Furthermore, thepyrrole coated Fe2O3 nanorod architecture prevents the porous structure fromcollapsing and protects Fe from aggregation to yield atomic Fe-N-4 moietiesduring carbonization. The obtained Fe/N-CNRs display exceptional ORR activities(E-1/2 = 0.90 V) and satisfactory long-term durabilities, exceeding those forPt/C. Furthermore, the unprecedented Fe/N-CNRs catalytic performance isdemonstrated with Zn-air batteries, including a superior maximum power density(181.8 mW cm(-2)), specific capacity (998.67 W h kg(-1)), and long-termdurability over 100 h. The prominent performance stems from the unique 1Dstructure, hierarchical pore system, high surface area, and homogeneously dispersedsingle-atom Fe-N-4 moieties.
[7] Zhang T. J., Chen Z. Y., Walsh A. G., Li Y., Zhang P. Single-AtomCatalysts Supported by Crystalline Porous Materials: Views from the Inside [J].Advanced Materials, 2020, 32(44): 10.1002/adma.202002910.
Single-atom catalysts (SACs) haverecently emerged as an exciting system in heterogeneous catalysis showingoutstanding performance in many catalytic reactions. Single-atom catalyticsites alone are not stable and thus require stabilization from substrates. Crystallineporous materials such as zeolites and metal-organic frameworks (MOFs) areexcellent substrates for SACs, offering high stability with the potential tofurther enhance their performance due to synergistic effects. This reviewfeatures recent work on the structure, electronic, and catalytic properties ofzeolite and MOF-protected SACs, offering atomic-scale views from the"inside" thanks to the subatomic resolution of synchrotron X-rayabsorption spectroscopy (XAS). The extended X-ray absorption fine structure andassociated methods will be shown to be powerful tools in identifying thesingle-atom site and can provide details into the coordination environment andbonding disorder of SACs. The X-ray absorption near-edge structure will bedemonstrated as a valuable method in probing the electronic properties of SACsby analyzing the white line intensity, absorption edge shift, and pre-/postedgefeatures. Emphasis is also placed on in situ/operando XAS usingstate-of-the-art equipment, which can unveil the changes in structure andproperties of SACs during the dynamic catalytic processes in a highly sensitiveand time-resolved manner.
[8] Zhao Shiyong, Zhang Lianji, Johannessen Bernt, Saunders Martin, LiuChang, Yang Shi‐Ze, Jiang SanPing. Designed Iron Single Atom Catalysts for Highly Efficient Oxygen ReductionReaction in Alkaline and Acid Media [J]. Adv Mater Interfaces, 2020, 2001788.10.1002/admi.202001788.
Single atom catalysts (SACs) haveattracted much attentions due to their advantages of high catalysis efficiencyand excellent selectivity. However, for industrial applications, synthesis ofSACs in large and practical quantities is very important. The challenge is todevelop synthesis methods with controllability and scalability. Herein, a well-characterizedand scalable method is demonstrated to synthesize atomically dispersed ironatoms coordinated with nitrogen on graphene, SAFe @ NG, with high atomicloading (approximate to 4.6 wt%) through a one-pot pyrolysis process. Themethod is scalable for the fabrication of Fe SACs with high quantities. TheFe-N-G catalyst exhibits high intrinsic oxygen reduction reaction (ORR)performance, reaching half potential of 0.876 and 0.702 V in alkaline andacidic solutions, respectively, with excellent microstructure stability.Furthermore, the density functional theory (DFT) simulation confirms that theFe atoms in coordination with four nitrogen atoms, FeN4, in graphene is theactive center for the 4-electron ORR process. This work demonstrates anefficient design pathway for single atom catalysts as highly active and stableelectrocatalysts for high-performance ORR applications.
[9] de Almeida L. D., Wang H., Junge K., Cui X., Beller M. RecentAdvances in Catalytic Hydrosilylations: Developments Beyond TraditionalPlatinumcatalysts [J]. Angew Chem Int Ed Engl, 2020, 10.1002/anie.202008729.
Hydrosilylation reactions, whichallow the addition of Si-H to C=C/C identical withC bonds, are typicallycatalyzed by homogeneous noble metal catalysts (Pt, Rh, Ir, and Ru). Althoughexcellent activity and selectivity can be obtained, the price, purification,and metal residues of these precious catalysts are problems in the siliconeindustry. Thus, a strong interest in more sustainable catalysts and for moreeconomic processes exists. In this respect, recently disclosed hydrosilylationsusing catalysts based on earth-abundant transition metals, for example, Fe, Co,Ni, and Mn, and heterogeneous catalysts (supported nanoparticles andsingle-atom sites) are noteworthy. This minireview describes the recentadvances in this field.
[10]Lou Xiong-Wen David. Atomically Dispersed Reactive Centers forElectrocatalytic Co2 Reduction and Water Splitting [J]. Angewandte Chemie(International ed in English), 2020, 10.1002/anie.202014112.
Developing electrocatalyticenergy conversion technologies for replacing the traditional energy source ishighly expected to resolve the fossil fuel exhaustion and related environmentalproblems. Exploring stable and high-efficiency electrocatalysts is of vitalimportance for the promotion of these technologies. Single-atom catalysts(SACs), with atomically distributed active sites on supports, perform asemerging materials in catalysis and present promising prospects for a widerange of applications. The rationally designed near-range coordinationenvironment, long-range electronic interaction and microenvironment of thecoordination sphere cast huge influence on the reaction mechanism and relatedcatalytic performance of SACs. In the current Review, some recent developmentsof atomically dispersed reactive centers for electrocatalytic CO 2 reductionand water splitting are well summarized. The catalytic mechanism and theunderlying structure-activity relationship are elaborated based on the recent progressesof various operando investigations. Finally, by highlighting the challenges andprospects for the development of single-atom catalysis, we hope to shed somelight on the future research of SACs for the electrocatalytic energyconversion.
[11]Xie Wenfu, Li Hao, Cui Guoqing, Li Jianbo, Song Yuke, Li Shijin,Zhang Xin, Lee Jin Yong, Shao Mingfei, Wei Min. Nisn Atomic Pair on IntegratedElectrode for Synergistic Electrocatalytic Co2 Reduction [J]. Angewandte Chemie(International ed in English), 2020, 10.1002/anie.202014655.
Electrochemical CO 2 reduction(CO 2 RR) to value-added chemicals offers an efficient way to mitigate globalwarming and energy supply issues. However, the development of highly efficientelectrocatalysts for CO 2 RR to boost reaction efficiency and guideunderstanding of catalytic mechanism remains a huge challenge. Herein, wedemonstrate a NiSn atomic pair electrocatalyst (NiSn-APC) on a hierarchicalintegrated electrode, which exhibits a synergistic effect in simultaneously promotingthe activity and selectivity of CO 2 RR to formate. The NiSn atomic pairconsist of adjacent Ni and Sn coordinated with four nitrogen atoms (N 4-Ni-Sn-N 4 ) respectively, which is confirmed by high-angle annular darkfield-scanning transmission electron microscopy (HAADF-STEM) and extended X-rayabsorption fine structure (EXAFS). Typically, the as-prepared NiSn-APC displaysan exceptional activity toward CO 2 RR to formate with a turnover frequency of4752 h -1 , a formate productivity of 36.7 mol h -1 g Sn -1 and an utilizationdegree of active sites (57.9%), which are superior to the previously reportedsingle-atomic catalysts (SACs). Moreover, both in situ attenuated totalreflection-infrared (ATR-IR) spectroscopy and density functional theory (DFT)calculation verify the electron redistribution of Sn imposed by adjacent Ni,which reduces the energy barrier of *OCHO intermediate and makes thispotential-determining step thermodynamically spontaneous. The NiSn synergisticcatalysis for CO 2 RR in this work provides a successful paradigm for rationaldesign and preparation of atomic pair electrocatalysts with largely enhancedperformance.
[12]Aguilar Nuria, Atilhan Mert, Aparicio Santiago. Single AtomTransition Metals on Mos2 Monolayer and Their Use as Catalysts for Co2Activation [J]. Applied Surface Science, 2020,534(10.1016/j.apsusc.2020.147611.
The properties of single metalatoms adsorbed on MoS2 monolayer surface as well as the behaviour of CO2molecules on these active sites are studied by using density functional theorymethods. Eleven different transition metals (Au, Co, Cr, Cu, Fe, Ir, Mn, Ni,Pd, Pt or Sn) were considered as well as the main adsorption sites on the surface.Reported results show adsorption on top of Mo atoms and hollow sites on thehexagonal ring centres leading to very large adsorption energies. Theadsorption is characterized by deep interaction wells and adsorbed metal tosurface charge transfer in most of the studied atoms. The low surface coverageupon single atom adsorption hinders in plane metal diffusion and thus onceatoms are adsorbed, they remain on top on each site as showed by Ab initiomolecular dynamics simulations. The behaviour of CO2 molecules on top of activesites formed by metal atoms adsorbed on the monolayer is characterized bystrong chemisorption, leading to large bending of gas molecules, thus showinghow CO2 molecules can react on these metal sites. This work reports for the firsttime a systematic evaluation of transition metal atoms adsorbed on MoS2monolayers, including their dynamic properties, as well as their properties asactive sites for CO2 reactions.
[13]Feng Zhen, Tang Yanan, Ma Yaqiang, Li Yi, Dai Yawei, Ding Hai, SuGuang, Dai Xianqi. Theoretical Investigation of Co2 Electroreduction on N(B)-Doped Graphdiyne Mononlayer Supported Single Copper Atom [J]. AppliedSurface Science, 2021, 538(10.1016/j.apsusc.2020.148145.
Carbon dioxide electrochemicalreduction reaction (CO2RR) with proton-electron pair delineates an intriguingprospect for converting CO2 to useful chemicals. However, CO2RR is urgentlyrequired low-cost and high efficient electrocatalysts to overcome the sluggishreaction kinetic and ultralow selectivity. Here by means of firstprinciplecomputations, the geometric constructions, electronic structures, and CO2RRcatalytic performance of boron- and nitrogen-doped graphdiyne anchoring asingle Cu atom (Cu@N-doped GDY and Cu@B-doped GDY) were systematically investigated.These eight Cu@doped GDY complexes possess excellent stability. The adsorptionfree energies showed that the eight Cu@doped GDY could spontaneously captureCO2 molecules. The Cu@N-doped GDY monolayers exhibit a more efficient catalyticperformance for CO2 reduction compared to Cu@B-doped GDY because of thedifferences in adsorption energies and charge transfer. The calculationsfurther indicated that the Cu@Nb-doped GDY complex possesses excellentcatalytic character toward CO2RR with the same limiting potentials of -0.65 Vfor production of HCOOH, CO, OCH2, CH3OH, and CH4. Charge analysis indicatedthat the *OCHO and *COOH species gain more electrons from Cu@N-doped GDY thanfrom Cu@Bdoped GDY complexes due to different electronegativity of coordinatedelement. Our findings highlighted the electronegativity of coordinated elementsfor the design of atomic metal catalysts.
[14]Zhang Z. M., Yao X., Lang X. Y., Zhu Y. F., Gao W., Jiang Q. W-N-3Center Supported on Blue Phosphorus as a Promising Efficient Electrocatalystwith Ultra-Low Limiting Potential for Nitrogen Fixation [J]. Applied SurfaceScience, 2021, 536(10.1016/j.apsusc.2020.147706.
The nitrogen reduction reaction(NRR) becomes increasingly important while it is challenging processes inelectrochemistry for the challenge to find the high-efficiency andhigh-selectivity catalysts. Herein, we systematically screened the capacity ofa sequence of representative transition metal-N-3 (TM-N-3) centers supported onblue phosphorus (TM-N-3@beta-P) as NRR catalysts by using of density functionaltheory (DFT). Our results show that W-N-3 center supported on blue phosphorus(W-N-3@beta-P) exhibits an excellent catalytic performance with an ultra-lowlimiting potential of -0.02 V, while the competitive hydrogen evolutionreaction (HER) can be suppressed on this catalyst. This work thus predictsW-N-3@beta-P has potential applications for electrocatalytic NRR.
[15]Pei J. H., Zhao R. L., Mu X. Y., Wang J. Y., Liu C. L., Zhang X. D.Single-Atom Nanozymes for Biological Applications [J]. Biomaterials Science,2020, 8(23): 6428-41. 10.1039/d0bm01447h.
Nanozymes have been widely usedas highly active and stable arterial enzymes due to their controllableelectronic transfer and unique catalytic reaction route. However, thedevelopment of nanozymes is hindered by their ambiguous structure, insufficientactivity and inadequate substrate selectivity. In comparison, single-atomnanozymes (SAzymes) hold superior catalytic activity 10-100 times higher than conventionalnanozymes by maximizing the utilization of metal atom dispersion, and exhibitversatile catalytic selectivity through precisely adjusting the atom spatialconfiguration. In this review, we highlight several well-defined SAzymes, anddiscuss their accurate atom configuration, catalytic mechanisms, enzyme-likeactivity, and applications in cancer treatment, brain disease, and woundhealing. It is of great significance to understand the advantages andproperties of SAzymes for further medical development.
[16]Pagliaro M., Della Pina C., Mauriello F., Ciriminna R. Catalysiswith Silver: From Complexes and Nanoparticles to Morals and Single-AtomCatalysts [J]. Catalysts, 2020, 10(11): 10.3390/catal10111343.
Silver catalysis has a rich andversatile chemistry now expanding from processes mediated by silver complexesand silver nanoparticles to transformations catalyzed by silver metal organicalloys and single-atom catalysts. Focusing on selected recent advances, weidentify the key advantages offered by these highly selective heterogeneouscatalysts. We conclude by offering seven research and educational guidelinesaimed at further progressing the field of new generation silver-based catalyticmaterials.
[17]Li X. F., Hu Z., Li Q., Lei M., Fan J. J., Carabineiro S. A. C., LiuY., Lv K. L. Three in One: Atomically Dispersed Na Boosting the Photoreactivityof Carbon Nitride Towards No Oxidation [J]. Chemical Communications, 2020,56(91): 14195-8. 10.1039/d0cc05948j.
Single atomic Na (Na-SA) was successfullyanchored on the surface of carbon nitride nanosheets (CN-NSs) by simple directcalcination of the hydrothermally NaHCO3 pretreated dicyandiamide (DCDA)precursor. The introduction of Na-SA results in the electron transfer from Nato the complex N-2C, not only improving the light absorption and increasing theadsorption ability, but also stimulating the separation of charge carriers,which sharply improves the NO removal rate from 36.8% to 52.5%, and preventsthe production of toxic NO2 by-product. The excellent photo-stability makesNa-SA/NN-NSs a good candidate photocatalyst for air purification.
[18]Babucci M., Guntida A., Gates B. C. Atomically Dispersed Metals onWell-Defined Supports Including Zeolites and Metal-Organic Frameworks:Structure, Bonding, Reactivity, and Catalysis [J]. Chemical Reviews, 2020,120(21): 11956-85. 10.1021/acs.chemrev.0c00864.
When metals in supportedcatalysts are atomically dispersed, they are usually cationic and bondedchemically to supports. Investigations of noble metals in this class aregrowing rapidly, leading to discoveries of catalysts with new properties.Characterization of these materials is challenging because the metal atomsreside on surfaces that are typically nonuniform in composition and structure.We posit that understanding of structures and catalytic properties of thesematerials is emerging most strongly from investigations of structurally uniformcatalysts (metal atoms dispersed on crystalline supports) which can becharacterized incisively with atomic-resolution electron microscopy, X-rayabsorption spectroscopy, and infrared spectroscopy, bolstered by densityfunctional theory. We assess the literature of such catalysts supported onzeotype materials, metal-organic frameworks, and covalent organic frameworks.Assessing characterization, reactivity, and catalytic performance of catalystsfor oxidation, hydrogenation, the water-gas shift reaction, and others, weconsider metal-support interactions and ligand effects for variousmetal-support combinations, evaluating the degree of structural uniformity ofexemplary catalysts and summarizing structure-reactivity andstructure-catalytic property relationships.
[19]Gao C., Low J. X., Long R., Kong T. T., Zhu J. F., Xiong Y. J.Heterogeneous Single-Atom Photocatalysts: Fundamentals and Applications [J].Chemical Reviews, 2020, 120(21): 12175-216. 10.1021/acs.chemrev.9b00840.
Single-atom photocatalysts haveshown their compelling potential and arguably become the most active researchdirection in photocatalysis due to their fascinating strengths in enhancinglight-harvesting, charge transfer dynamics, and surface reactions of aphotocatalytic system. While numerous comprehensions about the single-atomphotocatalysts have recently been amassed, advanced characterization techniquesand vital theoretical studies are strengthening our understanding on thesefascinating materials, allowing us to forecast their working mechanisms andapplications in photocatalysis. In this review, we begin by describing thegeneral background and definition of the single-atom photocatalysts. A briefdiscussion of the metal-support interactions on the single-atom photocatalystsis then provided. Thereafter, the current available characterization techniquesfor single-atom photocatalysts are summarized. After having some fundamentalunderstanding on the single-atom photocatalysts, their advantages andapplications in photocatalysis are discussed. Finally, we end this review witha look into the remaining challenges and future perspectives of single-atomphotocatalysts. We anticipate that this review will provide some inspirationfor the future discovery of the single-atom photocatalysts, manifestlystimulating the development in this emerging research area.
[20]Hannagan R. T., Giannakakis G., Flytzani-Stephanopoulos M., Sykes E.C. H. Single-Atom Alloy Catalysis [J]. Chemical Reviews, 2020, 120(21):12044-88. 10.1021/acs.chemrev.0c00078.
Single-atom alloys (SAAs) play anincreasingly significant role in the field of single-site catalysis and aretypically composed of catalytically active elements atomically dispersed inmore inert and catalytically selective host metals. SAAs have been shown tocatalyze a range of industrially important reactions in electro-, photo-, andthermal catalysis studies. Due to the unique geometry of SAAs, the location ofthe transition state and the binding site of reaction intermediates are oftendecoupled, which can enable both facile dissociation of reactants and weakbinding of intermediates, two key factors for efficient and selectivecatalysis. Often, this results in deviations from transition metal scalingrelationships that limit conventional catalysts. SAAs also offer reducedsusceptibility to CO poisoning, cost savings from reduced precious metal usage,opportunities for bifunctional mechanisms via spillover, and higher resistanceto deactivation by coking that plagues many industrial catalysts. In thisreview, we begin by introducing SAAs and describe how model systems andnanoparticle catalysts can be prepared and characterized. We then review allavailable SAA literature on a per reaction basis before concluding with adescription of the general properties of this new class of heterogeneouscatalysts and presenting opportunities for future research and development.
[21]Ji S. F., Chen Y. J., Wang X. L., Zhang Z. D., Wang D. S., Li Y. D.Chemical Synthesis of Single Atomic Site Catalysts [J]. Chemical Reviews, 2020,120(21): 11900-55. 10.1021/acs.chemrev.9b00818.
Manipulating metal atoms in acontrollable way for the synthesis of materials with the desired structure andproperties is the holy grail of chemical synthesis. The recent emergence ofsingle atomic site catalysts (SASC) demonstrates that we are moving toward thisgoal. Owing to the maximum efficiency of atom-utilization and unique structuresand properties, SASC have attracted extensive research attention and interest.The prerequisite for the scientific research and practical applications of SASCis to fabricate highly reactive and stable metal single atoms on appropriatesupports. In this review, various synthetic strategies for the synthesis ofSASC are summarized with concrete examples highlighting the key issues of thesynthesis methods to stabilize single metal atoms on supports and to suppresstheir migration and agglomeration. Next, we discuss how synthesis conditionsaffect the structure and catalytic properties of SASC before ending this reviewby highlighting the prospects and challenges for the synthesis as well asfurther scientific researches and practical applications of SASC.
[22]Kaiser S. K., Chen Z. P., Akl D. F., Mitchell S., Perez-Ramirez J.Single-Atom Catalysts across the Periodic Table [J]. Chemical Reviews, 2020,120(21): 11703-809. 10.1021/acs.chemrev.0c00576.
Isolated atoms featuring uniquereactivity are at the heart of enzymatic and homogeneous catalysts. Incontrast, although the concept has long existed, single-atom heterogeneouscatalysts (SACs) have only recently gained prominence. Host materials havesimilar functions to ligands in homogeneous catalysts, determining thestability, local environment, and electronic properties of isolated atoms andthus providing a platform for tailoring heterogeneous catalysts for targetedapplications. Within just a decade, we have witnessed many examples of SACsboth disrupting diverse fields of heterogeneous catalysis with theirdistinctive reactivity and substantially enriching our understanding ofmolecular processes on surfaces. To date, the term SAC mostly refers to latetransition metal-based systems, but numerous examples exist in which isolatedatoms of other elements play key catalytic roles. This review provides acompositional encyclopedia of SACs, celebrating the 10th anniversary of the introductionof this term. By defining single-atom catalysis in the broadest sense, weexplore the full elemental diversity, joining different areas across the wholeperiodic table, and discussing historical milestones and recent developments.In particular, we examine the coordination structures and associated propertiesaccessed through distinct single-atom-host combinations and relate them totheir main applications in thermo-, electro-, and photocatalysis, revealingtrends in element-specific evolution, host design, and uses. Finally, wehighlight frontiers in the field, including multimetallic SACs, atom proximitycontrol, and possible applications for multistep and cascade reactions,identifying challenges, and propose directions for future development in thisflourishing field.
[23]Lang R., Du X. R., Huang Y. K., Jiang X. Z., Zhang Q., Guo Y. L.,Liu K. P., Qiao B. T., Wang A. Q., Zhang T. Single-Atom Catalysts Based on theMetal-Oxide Interaction [J]. Chemical Reviews, 2020, 120(21): 11986-2043. 10.1021/acs.chemrev.0c00797.
Metal atoms dispersed on theoxide supports constitute a large category of single-atom catalysts. In thisreview, oxide supported single-atom catalysts are discussed about theirsynthetic procedures, characterizations, and reaction mechanism inthermocatalysis, such as water-gas shift reaction, selectiveoxidation/hydrogenation, and coupling reactions. Some typical oxide materials,including ferric oxide, cerium oxide, titanium dioxide, aluminum oxide, and soon, are intentionally mentioned for the unique roles as supports in anchoringmetal atoms and taking part in the catalytic reactions. The interactionsbetween metal atoms and oxide supports are summarized to give a picture on howto stabilize the atomic metal centers, and rationally tune the geometricstructures and electronic states of single atoms. Furthermore, severaldirections in fabricating single-atom catalysts with improved performance areproposed on the basis of state-of-the-art understanding in metal-oxide interactions.
[24]Li J., Stephanopoulos M. F., Xia Y. N. Introduction: HeterogeneousSingle-Atom Catalysis [J]. Chemical Reviews, 2020, 120(21): 11699-702.10.1021/acs.chemrev.0c01097.
[25]Qin R. X., Liu K. L., Wu Q. Y., Zheng N. F. Surface CoordinationChemistry of Atomically Dispersed Metal Catalysts [J]. Chemical Reviews, 2020,120(21): 11810-99. 10.1021/acs.chemrev.0c00094.
Atomically dispersed metalcatalysts (ADCs), as an emerging class of heterogeneous catalysts, have beenwidely investigated during the past two decades. The atomic dispersion natureof the catalytic metal centers makes them an ideal system for bridginghomogeneous and heterogeneous metal catalysts. The recent rapid development ofnew synthetic strategies has led to the explosive growth of ADCs with a widespectrum of metal atoms dispersed on supports of different chemicalcompositions and natures. The availability of diverse ADCs creates a powerfulmaterials platform for investigating mechanisms of complicated heterogeneouscatalysis at the atomic levels. Considering most dispersed metal atoms on ADCsare coordinated by the donors from supports, this review will demonstrate howthe surface coordination chemistry plays an important role in determining thecatalytic performance of ADCs. This review will start from the link betweencoordination chemistry and heterogeneous catalysis. After the brief descriptionon the advantages and limitations of common structure characterization methodsin determining the coordination structure of ADCs, the surface coordinationchemistry of ADCs on different types of supports will be discussed. We willmainly illustrate how the local and vicinal coordination species on differentsupport systems act together with the dispersed catalytic metal center to determinethe catalytic activity, selectivity, and stability of ADCs. The dynamiccoordination structure change of ADCs in catalysis will be highlighted. At theend of the review, personal perspectives on the further development of thefield of ADCs will be provided.
[26]Wang Y. X., Su H. Y., He Y. H., Li L. G., Zhu S. Q., Shen H., Xie P.F., Fu X. B., Zhou G. Y., Feng C., Zhao D. K., Xiao F., Zhu X. J., Zeng Y. C.,Shao M. H., Chen S. W., Wu G., Zeng J., Wang C. Advanced Electrocatalysts withSingle-Metal-Atom Active Sites [J]. Chemical Reviews, 2020, 120(21): 12217-314.10.1021/acs.chemrev.0c00594.
Electrocatalysts with singlemetal atoms as active sites have received increasing attention owing to theirhigh atomic utilization efficiency and exotic catalytic activity andselectivity. This review aims to provide a comprehensive summary on the recentdevelopment of such single-atom electrocatalysts (SAECs) for variousenergy-conversion reactions. The discussion starts with an introduction of thedifferent types of SAECs, followed by an overview of the syntheticmethodologies to control the atomic dispersion of metal sites and atomicallyresolved characterization using state-of-the-art microscopic and spectroscopictechniques. In recognition of the extensive applications of SAECs, theelectrocatalytic studies are dissected in terms of various importantelectrochemical reactions, including hydrogen evolution reaction (HER), oxygenevolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxidereduction reaction (CO2RR), and nitrogen reduction reaction (NRR). Examples ofSAECs are deliberated in each case in terms of their catalytic performance,structure-property relationships, and catalytic enhancement mechanisms. Aperspective is provided at the end of each section about remaining challengesand opportunities for the development of SAECs for the targeted reaction.
[27]Wei Y. S., Zhang M., Zou R. Q., Xu Q. Metal-Organic Framework-BasedCatalysts with Single Metal Sites [J]. Chemical Reviews, 2020, 120(21):12089-174. 10.1021/acs.chemrev.9b00757.
Metal-organic frameworks (MOFs)are a class of distinctive porous crystalline materials constructed by metalions/clusters and organic linkers. Owing to their structural diversity,functional adjustability, and high surface area, different types of MOF-basedsingle metal sites are well exploited, including coordinately unsaturated metalsites from metal nodes and metallolinkers, as well as active metal speciesimmobilized to MOFs. Furthermore, controllable thermal transformation of MOFscan upgrade them to nanomaterials functionalized with active single-atomcatalysts (SACs). These unique features of MOFs and their derivatives enablethem to serve as a highly versatile platform for catalysis, which has actuallybeen becoming a rapidly developing interdisciplinary research area. In thisreview, we overview the recent developments of catalysis at single metal sitesin MOF-based materials with emphasis on their structures and applications forthermocatalysis, electrocatalysis, and photocatalysis. We also compare theresults and summarize the major insights gained from the works in this review,providing the challenges and prospects in this emerging field.
[28]Zhuo H. Y., Zhang X., Liang J. X., Yu Q., Xiao H., Li J. TheoreticalUnderstandings of Graphene-Based Metal Single-Atom Catalysts: Stability andCatalytic Performance [J]. Chemical Reviews, 2020, 120(21): 12315-41.10.1021/acs.chemrev.0c00818.
Research on heterogeneoussingle-atom catalysts (SACs) has become an emerging frontier in catalysisscience because of their advantages in high utilization of noble metals,precisely identified active sites, high selectivity, and tunable activity.Graphene, as a one-atom-thick two-dimensional carbon material with uniquestructural and electronic properties, has been reported to be a superb supportfor SACs. Herein, we provide an overview of recent progress in investigationsof graphene-based SACs. Among the large number of publications, we willselectively focus on the stability of metal single-atoms (SAs) anchored ondifferent sites of graphene support and the catalytic performances ofgraphene-based SACs for different chemical reactions, including thermocatalysisand electrocatalysis. We will summarize the fundamental understandings on theelectronic structures and their intrinsic connection with catalytic propertiesof graphene-based SACs, and also provide a brief perspective on the futuredesign of efficient SACs with graphene and graphene-like materials.
[29]Li G. W., Gu D. F., Cao R., Hong S., Liu Y. S., Liu Y. Z. HighlyCatalytically Active High-Spin Single-Atom Iron Catalyst Supported byCatechol-Containing Microporous 2d Polymer [J]. Chemistry Letters, 2020,49(10): 1240-4. 10.1246/cl.200416.
Traditionally, Fe-SACs areprepared through energy-intense processes, which often lead to the loss ofprecision in structural features from the starting substrates and impedingrational design. We herein described the synthesis of a uniquecatechol-containing porous polymer with designed features in the substratesmaintained, affording atomically dispersed iron catalyst (Fe-SAC) throughtreatment of ferrous chloride (FeCl2). An aberration-corrected scanningtransmission electron microscope (AC-STEM) and synchrotron X-ray absorptionspectroscopy (XAS) were employed to shed light on the local coordinationgeometry of the atomically dispersed iron catalyst. The resulting Fe-SACexhibits excellent catalytic performance in reduction of nitroaromatics withhighest molar K-app among all Fe based catalysts.
[30]Mahlberg D., Gross A. Vacancy Assisted Diffusion on Single-AtomSurface Alloys [J]. Chemphyschem, 2020, 10.1002/cphc.202000838.
Bimetallic surfaces can exhibitan improved catalytic activity through tailoring the concentration and/or thearrangement of the two metallic components. However, in order to becatalytically active, the active bimetallic surface structure has to be stableunder operating conditions. Typically, structural changes in metals occur viavacancy diffusion. Based on the first-principles determination of formationenergies and diffusion barriers we have performed kinetic Monte-Carlo (kMC)simulations to analyse the (meta-)stability of PtRu/Ru(0001), AgPd/Pd(111),PtAu/Au(111) and InCu/Cu(100) surface alloys. In a first step, here we considersingle-atom alloys together with one vacancy per simulation cell. We willpresent results of the time evolution of these structures and analyse them interms of the interaction between the constituents of the bimetallic surface.
[31]Cao P. K., Quan X., Zhao K., Chen S., Yu H. T., Su Y.High-Efficiency Electrocatalysis of Molecular Oxygen toward Hydroxyl RadicalsEnabled by an Atomically Dispersed Iron Catalyst [J]. Environmental Science& Technology, 2020, 54(19): 12662-72. 10.1021/acs.est.0c03614.
Fenton catalysis represents thepromising technology to produce super-active center dot OH for tackling severewater environment pollution issues, whereas it suffers from low atomicefficiency, poor pH adaptability, and catalyst non-reusability in a homogeneousor heterogeneous system. Here, single-atom iron catalysis is creativelyintroduced to drive electrochemical center dot OH evolution utilizingearth-abundant oxygen and water as raw materials. The atomically dispersed ironsettled by defective three-dimensional porous carbon (AD-Fe/3DPC) with uniqueC, Cl unsaturated coordination can efficiently tune the multi-electron oxygenreduction process, enabling O-2-to-center dot OH conversion. The mass activityin center dot OH production by AD-Fe/3DPC is almost two-orders of magnitudehigher as compared to that by nanoparticular iron oxide catalyst. Meanwhile,the AD-Fe/3DPC electro-Fenton system exhibits fast elimination of refractorytoxic pollutants, surpassing nanoparticular iron oxides in kinetic rate by 59times or homogeneous Fenton by 10 times under similar experimental conditions.Experimental and theoretical results demonstrate that the remarkable enhancedmass activity of AD-Fe/3DPC in catalyzing O-2 to center dot OH is contributedby the synergistic effects of the maximized catalysis of atomically dispersediron and the unique unsaturated coordination environment. The AD-Fe/3DPCcatalytic system is demonstrated to be pH-universal, long-term stable, and wellrecyclable, truly satisfying flexible, sustainable, and green application ofwastewater purification. This study gives a new sight into local coordinationmodulation of single-atom catalysts for selective electrocatalytic oxygenreduction.
[32]Xu H. X., Cheng D. J. First-Principles-Aided Thermodynamic Modelingof Transition-Metal Heterogeneous Catalysts: A Review [J]. Green Energy &Environment, 2020, 5(3): 286-302. 10.1016/j.gee.2020.07.006.
Over the past decade, thefirst-principles-aided thermodynamic models have become standard theoreticaltools in research on structural stability and evolution of transition-metalheterogeneous catalysts under reaction environment. Advances infirst-principles-aided thermodynamic models mean it is now possible to enablethe operando computational modeling, which provides a deep insight intomechanism behind structural stability and evolution, and paves the way forhigh-through screening for promising transition-metal heterogeneous catalysts.Here, we briefly review the framework and foundation of first-principles-aidedthermodynamic models and highlight its contribution to stability analysis oncatalysts and identification of reaction-induced structural evolution of catalystunder reaction environment. The present review is helpful for understanding theongoing developments of first-principles-aided thermodynamic models, which canbe employed to screen high-stability catalysts and predict their structuralreconstruction in future rational catalyst design. (C) 2020, Institute ofProcess Engineering, Chinese Academy of Sciences. Publishing services byElsevier B.V. on behalf of KeAi Communications Co., Ltd.
[33]Banu A. A., Karazhanov S. Z., Kumar K. V., Jose S. P. Platinum DopedIron Carbide for the Hydrogen Evolution Reaction: The Effects of ChargeTransfer and Magnetic Moment by First-Principles Approach [J]. InternationalJournal of Hydrogen Energy, 2020, 45(56): 31825-40.10.1016/j.ijhydene.2020.08.163.
In this work, the catalyticactivity towards hydrogen evolution reaction (HER) was studied for hydrogenadsorption on Pt doped Fe2C (001) surface configuration (Pt/Fe2C) and comparedwith pure Pt (001). The adsorption of H on the pristine Fe2C, Pt doped Fe2C,and pure Pt in (001) slab was computed. The best and promising HER activity(Delta G(H*) = -0.02 eV) is obtained at the hollow site adsorption of Pt/Fe2C(Fe13Pt3C8) compared to the experimental value of pure Pt (Delta G(H*) = -0.09eV) suggesting the possibility of the H-2 formation on the surface ofFe13Pt3C8. The structural stabilities of Fe2C and Pt/Fe2C were investigated bythe formation energy analysis. Also, it is observed that to enhance the HERmechanism, the modification of the d-electron structure of Pt atoms isessential which can be achieved by the increased Pt doping. The Bader chargeanalysis demonstrated the charge transfer between the substrate and theadsorbed H atoms. The density of states (DOS) of pure Fe2C and optimal Pt/Fe2Cwere calculated which revealed the magnetic and metallic nature of thesematerials. In addition, the adsorption and resulted activation of H-2 werefacilitated by the elongation of H-H bond length in Fe13Pt3C8 This worksupports the HER over single atom catalysts (SACs) with lower Pt loading butwith high catalytic activity and the maximum atom utilization of SACs. (C) 2020Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rightsreserved.
[34]Liang Z., Liu C., Chen M. W., Luo M. M., Qi X. P., Peera S. G.,Liang T. X. Theoretical Screening of Di-Metal Atom (M = Fe, Co, Ni, Cu, Zn)Electrocatalysts for Ammonia Synthesis [J]. International Journal of HydrogenEnergy, 2020, 45(56): 31881-91. 10.1016/j.ijhydene.2020.08.208.
Electrochemical N-2 reductionreaction (NRR) has received much attention in recent times. Aiming for,discovering potential electrocatalysts with superior activity, stability andselectivity, a series of 3 d transition metal dimers were studied by density functionaltheory (DFT) calculations. The investigation reveals that most of the metaldimers have admirable stability, and partial density of states (PDOS) confirmsthat the unoccupied and occupied d orbitals of metal atoms are the key foreffective activation of N-2. Especially, two metal dimers bonded tonitrogen-doped graphene, FeFe and CoCo, can selectively adsorb and activate N-2for efficient conversion. Their limiting potentials are -0.44 and -0.45 V,which are superior than to most of the catalysts and they can well suppress thehydrogen evolution reaction (HER). Moreover, the desorption free energy of NH3is 0.54 and 0.57 eV respectively for FeFe and CoCo, guarantees the gooddurability of the catalysts. (C) 2020 Hydrogen Energy Publications LLC. Publishedby Elsevier Ltd. All rights reserved.
[35]Shao Q. J., Xu L., Guo D. C., Su Y., Chen J. Atomic Level Design ofSingle Iron Atom Embedded Mesoporous Hollow Carbon Spheres as Multi-EffectNanoreactors for Advanced Lithium-Sulfur Batteries [J]. Journal of MaterialsChemistry A, 2020, 8(45): 23772-83. 10.1039/d0ta07010f.
The practical application oflithium-sulfur (Li-S) batteries is still facing the challenges of lithiumpolysulfide (LiPS) shuttling and uncontrollable Li2S growth due to the solublenature and sluggish conversion kinetics of LiPSs. Herein, we propose auniversal strategy to synthesize monodisperse iron atom embedded nitrogen-dopedmesoporous hollow carbon spheres (Fe-N/MHCS) as multi-effect nanoreactors forsulfur at the atomic level. Using a combination of experimental and theoreticalmethods, the Fe-N-4 center is found to be an efficient electrocatalyst topropel the reversible conversion between LiPSs and Li2S, inhibit the LiPSshuttling and mediate the deposition of Li2S. As a result, S@Fe-N/MHCS exhibitssignificantly improved rate properties and cycling stability (only 0.0187%capacity fade in 1000 cycles at 1C) without using conductive carbon. Even at apractical high sulfur loading (5.4 mg cm(-2)) and low E/S ratio (8.0 mL mg(-1)),the areal capacity reaches 6.4 mA h cm(-2) and 81.7% of it is retained after100 cycles. Furthermore, a S@Fe-N/MHCS pouch cell is also assembled showingexceptional cycling stability with a high capacity retention of 77.1% after 200cycles. Therefore, this work provides valuable insights into the fundamentalunderstanding of the catalysis mechanism for practical Li-S batteries with highspecific energy and prolonged lifespan.
[36]Tian R. B., Wang S. Y., Hu X. F., Zheng J. G., Ji P., Lin J., ZhangJ., Xu M. J., Bao J., Zuo S. W., Zhang H., Zhang W., Wang J. L., Yu L. D. NovelApproaches for Highly Selective, Room-Temperature Gas Sensors Based onAtomically Dispersed Non-Precious Metals [J]. Journal of Materials Chemistry A,2020, 8(45): 23784-94. 10.1039/d0ta05775d.
Atomically dispersed (AD)materials have incredible catalytic ability and offer atom economy with 100%metal utilization during catalytic reactions. Herein, we report the firstattempt to synthesize AD FeNC materials for use as highly selective,room-temperature gas sensors. Aberration-corrected high-angle annulardark-field scanning transmission electron microscopy (AC-HAADF-STEM), extendedX-ray absorption fine structure (EXAFS) spectroscopy, and Mossbauerspectroscopy characterization methods confirm the existence of atomicallydispersed Fe with an FeN4 coordination. We demonstrate a room temperature,sensitive, and selective NO2 gas sensor technology using this platform,offering significant advantages over existing technology. Density functionaltheory (DFT) calculations verify that electrons are transferred to NO2 fromFeN4 during NO2 adsorption. Both DFT calculations and experiments also revealthat the barrier for NO2 decomposition by AD FeNC is 0.73 eV, which issignificantly lower than previously reported barriers (2.60-3.54 eV) in othermaterials. Such unique catalytic properties combined with a high surfaceaffinity for NO2 molecules enable AD FeNC gas sensors to have excellentselective NO2 detection at room temperature. The method proposed here caninspire the use of AD materials to detect other gases and catalyze similarnovel developments in the gas sensor industry.
[37]Niu X. Y., Zhu Q., Jiang S. L., Zhang Q. Photoexcited ElectronDynamics of Nitrogen Fixation Catalyzed by Ruthenium Single-Atom Catalysts [J].Journal of Physical Chemistry Letters, 2020, 11(22): 9579-86.10.1021/acs.jpclett.0c02833.
It is still a grand challenge toexploit efficient catalysts to achieve sustainable photocatalytic N-2 reductionunder ambient conditions. Here, we developed a ruthenium-based single-atomcatalyst anchored on defect-rich TiO2 nanotubes (denoted Ru-SAs/Def-TNs) as amodel system for N-2 fixation. The constructed Ru-SAs/Def-TNs exhibited acatalytic efficiency of 125.2 mu mol g(-1) h(-1), roughly 6 and 13 times higherthan those of the supported Ru nanoparticles and DefTNs, respectively. Throughultrafast transient absorption and photoluminescence spectroscopy, we revealedthe relationship between catalytic activity and photoexcited electron dynamicsin such a model SA catalytic system. The unique ligand-to-metal charge-transferstate formed in Ru-SAs/Def-TNs was found to be responsible for its highcatalytic activity because it can greatly promote the transfer ofphotoelectrons from Def-TNs to the Ru-SAs center and the subsequent capture byRu-SAs. This work sheds light on the origin of the high performance of SAcatalysts from the perspective of photoexcited electron dynamics and henceenriches the mechanistic understanding of SA catalysis.
[38]Zhang Z. H., Ke X. X., Zhang B., Deng J. G., Liu Y. X., Liu W. W.,Dai H. X., Chen F. R., Sui M. L. Facet-Dependent Cobalt Ion Distribution on theCo3o4 Nanocatalyst Surface [J]. Journal of Physical Chemistry Letters, 2020,11(22): 9913-9. 10.1021/acs.jpclett.0c02901.
Co3O4 is an important catalystwidely used for CO oxidation or electrochemical water oxidation near roomtemperature and was also recently used as support for single-atom catalysts(SACs). Co3O4 with a spinel structure hosts dual oxidation states of Co2+ andCo3+ in the lattice, leading to the complexity of its surface structure as theexposure of Co2+ and Co3+ has a significant impact on the performance of thecatalysts. Although it is acknowledged that different facets exhibit variedcatalytic activities and different abilities in hosting single atoms to provideactive centers in SACs, the Co3O4 surface structure remains underinvestigated.In this study, major facets of {111}, {110}, and {100} were studied down tosubangstrom scale using advanced electron microscopy. We noticed that eachfacet has its own most stable surface configuration. The distribution of Co2+and Co3+ on each facet was quantified, revealing a facet-dependent distributionof Co2+ and Co3+. Co3+ was found to be preferentially exposed on {100} and{110} as well as surface steps. Surface reconstruction was revealed, where asubangstrom scale shift of Co2+ was confirmed on facets of {111} and {100} dueto polarity compensation and oxygen deficiency on the surface. This work notonly improves our fundamental understanding of the Co3O4 surface structure butalso may promote the design of Co3O4-based catalysts with tunable activity andstability.
[39]Yang Y. C., Yang Y. W., Pei Z. X., Wu K. H., Tan C. H., Wang H. Z., WeiL., Mahmood A., Yan C., Dong J. C., Zhao S. L., Chen Y. Recent Progress ofCarbon-Supported Single-Atom Catalysts for Energy Conversion and Storage [J].Matter, 2020, 3(5): 1442-76. 10.1016/j.matt.2020.07.032.
Single-atom catalysts (SACs) havethe advantages of both homogeneous and heterogeneous catalysts, which showpromising application potentials in many renewable energy-conversiontechnologies and critical industrial processes. In particular, carbon-supportedSACs (CS-SACs) are of great interest because of their maximal atom utilization(similar to 100%), unique physicochemical structure, and beneficial synergisticeffects between active catalytic sites and carbon substrates. In this review,we offer a critical overview of the unique advantages of CS-SACs related totheir material designs, catalytic activities, and potential application areas.The state-of-the-art design and synthesis of CS-SACs are described under theframework of bottom-up and top-down approaches. We also comprehensivelysummarize recent advances in developing CS-SACs for important electrochemicalreactions, i.e., oxygen reduction reaction, hydrogen evolution reaction, oxygenevolution reaction, CO2 reduction reaction, nitrogen reduction reaction,serving as bi-/multi-functional electrocatalysts, and usages in super.capacitors and batteries. Lastly, the critical challenges and futureopportunities in this emerging field are highlighted.
[40]Gu Y., Xi B. J., Wei R. C., Fu Q., Qain Y. T., Xiong S. L. SpongeAssembled by Graphene Nanocages with Double Active Sites to Accelerate AlkalineHer Kinetics [J]. Nano Letters, 2020, 20(11): 8375-83.10.1021/acs.nanolett.0c03565.
Elaborate design of novel hybridstructures for hydrogen-evolution electrocatalysts is a crucial strategy forsynergistically accelerating the reaction kinetics of water splitting. Herein,we prepare a three-dimensional (3D) sponge assembled by graphene nanocages(SGNCs) in which Ni nanoparticles and Ni single atoms coexist via a facileone-pot selft-emplating and self-catalytic strategy. Driven by simultaneousatomization and agglomeration under higher temperature, dual active sites ofsingle atoms and nanoparticles are formed on graphene nanocages. Benefitingfrom the unique 3D porous structure and dual active sites, the SGNCs exhibitexcellent hydrogen evolution reaction (HER) performance, which affords thecurrent density of 10 mA cm(-2). at a low overpotential of 27 mV. Theoreticalcalculations reveal that the interaction between single atoms and nanoparticlespromotes HER kinetics. The controlled engineering strategy of non-noblemetal-based hybrid materials provides prospects for innovative electrocatalystdevelopment.
[41]Liu X. K., Ao C. C., Shen X. Y., Wang L., Wang S. C., Cao L. L.,Zhang W., Dong J. J., Bao J., Ding T., Zhang L. D., Yao T. Dynamic SurfaceReconstruction of Single-Atom Bimetallic Alloy under Operando ElectrochemicalConditions [J]. Nano Letters, 2020, 20(11): 8319-25.10.1021/acs.nanolett.0c03475.
The atomic-level understanding ofthe dynamic evolution of the surface structure of bimetallic nanoparticlesunder industrially relevant operando conditions provides a key guide forimproving their catalytic performance. Here, we exploit operando X-ray absorptionfine structure spectroscopy to determine the dynamic surface reconstruction ofCu/Au bimetallic alloy where single-atom Cu was embedded on the Aunanoparticle, under electrocatalytic conditions. We identify the migration ofisolated Cu atoms from the vertex position of the Au nanoparticle to the stable(100) plane of the Au first atom layer, when the reduction potential isapplied. Density functional theory calculations reveal that the surface atommigration would significantly modulate the Au electronic structure, thusserving as the real active site for the catalytic performance. These findingsdemonstrate the real structural change under electrochemical conditions andprovide guidance for the rational design of high-activity bimetallic nanocatalysts.
[42]Luo X. M., Gong C. H., Dong X. Y., Zhang L., Zang S. Q. Evolution ofAll-Carboxylate-Protected Superatomic Ag Clusters Confined in Ti-Organic Cages[J]. Nano Res, 2020, 10.1007/s12274-020-3227-5.
In this study, the size of thetitanium organic cage was controlled to achieve the restricted growth from asingle Ag(I) atom (Ag@Ti-5) to rare all-carboxylate-protected superatomic Agcluster (Ag-6@Ti-6). The classical octahedral Ag-6(4+) cluster with twodelocalized electrons (2e) has been encapsulated in a Ti-6 organic cage, whichshows high stability in air and dimethyformamide (DMF). Furthermore, larger 2enested double-tetrahedra Ag clusters (Ag-8(6+) and Ag-9(7+)) protected using atetrahedral hollow metalloligand framework (Ag-8@Ti-4 and Ag-9@Ti-4) wereobtained. Electrospray ionization mass spectrometry (ESI-MS) and densityfunctional theory (DFT) calculations confirmed that there are two delocalizedelectrons on these small Ag clusters. This study provides a new form ofprotection for superatomic Ag clusters and provides a feasible strategy for thedevelopment of stable Ag clusters.
[43]Xue Q., Xie Y., Wu S. S., Wu T. S., Soo Y. L., Day S., Tang C. C.,Man H. W., Yuen S. T., Wong K. Y., Wang Y., Lo B. T. W., Tsang S. C. E. ARational Study on the Geometric and Electronic Properties of Single-AtomCatalysts for Enhanced Catalytic Performance [J]. Nanoscale, 2020, 12(45):23206-12. 10.1039/d0nr06006b.
We investigate the geometric andelectronic properties of single-atom catalysts (SACs) within metal-organicframeworks (MOFs) with respect to electrocatalytic CO2 reduction as a modelreaction. A series of mid-to-late 3d transition metals have been immobilisedwithin the microporous cavity of UiO-66-NH2. By employing Rietveld refinementof new-generation synchrotron diffraction, we not only identified thecrystallographic and atomic parameters of the SACs that are stabilised with arobust MMIDLINE HORIZONTAL ELLIPSISN(MOF) bonding of ca. 2.0 angstrom, but alsoelucidated the end-on coordination geometry with CO2. A volcano trend in theFEs of CO has been observed. In particular, the confinement effect within therigid MOF can greatly facilitate redox hopping between the Cu SACs, renderinghigh FEs of CH4 and C2H4 at a current density of -100 mA cm(-2). Although onlydemonstrated in selected SACs within UiO-66-NH2, this study sheds light on therational engineering of molecular interactions(s) with SACs for the sustainableprovision of fine chemicals.
[44]Yang Q. H., Xu W. W., Gong S., Zheng G. K., Tian Z. Q., Wen Y. J.,Peng L. M., Zhang L. J., Lu Z. Y., Chen L. Atomically Dispersed Lewis AcidSites Boost 2-Electron Oxygen Reduction Activity of Carbon-Based Catalysts [J].Nature Communications, 2020, 11(1): 10.1038/s41467-020-19309-4.
Elucidating thestructure-property relationship is crucial for the design of advancedelectrocatalysts towards the production of hydrogen peroxide (H2O2). In thiswork, we theoretically and experimentally discovered that atomically dispersedLewis acid sites (octahedral M-O species, M=aluminum (Al), gallium (Ga))regulate the electronic structure of adjacent carbon catalyst sites. Densityfunctional theory calculation predicts that the octahedral M-O with strongLewis acidity regulates the electronic distribution of the adjacent carbon siteand thus optimizes the adsorption and desorption strength of reactionintermediate (*OOH). Experimentally, the optimal catalyst (oxygen-rich carbonwith atomically dispersed Al, denoted as O-C(Al)) with the strongest Lewisacidity exhibited excellent onset potential (0.822 and 0.526V versus reversiblehydrogen electrode at 0.1mAcm(-2) H2O2 current in alkaline and neutral media,respectively) and high H2O2 selectivity over a wide voltage range. This studyprovides a highly efficient and low-cost electrocatalyst for electrochemicalH2O2 production. H2O2 production via oxygen reduction offers a renewableapproach to obtain an often-used oxidant. Here, authors show the incorporationof Lewis acid sites into carbon-based materials to improve H2O2electrosynthesis.
[45]Xu Z. W., Song R. F., Wang M. Y., Zhang X. Z., Liu G. W., Qiao G. J.Single Atom-Doped Arsenene as Electrocatalyst for Reducing Nitrogen to Ammonia:A Dft Study [J]. Physical Chemistry Chemical Physics, 2020, 22(45): 26223-30. 10.1039/d0cp04315j.
Due to the wide application ofNH3 in the energy and chemical industry, the rational design of a highlyefficient and low-cost electrocatalyst for nitrogen fixation at moderateconditions is highly desirable to meet the increasing demand for sustainableenergy production in the modern society. Herein, we have systematically studiedthe catalytic performance of transition metal (TM) atom (i.e., V, Cr, Fe, Co,Cu, Ru, Pd, Ag, Pt, Au)-doped arsenene nanosheet, a new two-dimensional (2D) nanomaterialin VA group, as a heterogeneous catalyst for nitrogen reduction reaction (NRR).By density functional theory (DFT) calculation and systematic theoreticalscreening, our study predicts that the systems of V-, Fe-, Co- and Ru-dopedarsenene have promising potentials as NRR electrocatalysts with high-loading TMand highly stable adsorption of N-2 molecule. Particularly, the V-doped systemexhibits two feasible configurations for N-2 adsorption and an ultralowoverpotential (0.10 V) via the enzymatic pathway, which is very competitiveamong similar reported electrocatalysts. This theoretical study not onlyextends the electrocatalyst family for nitrogen fixation, but also furtherdeepens our physical insights into catalytic improvement, which can be expectedto guide the rational design of novel NRR catalysts.
[46]Chen Z., Zhang G., Du L., Zheng Y., Sun L., Sun S. NanostructuredCobalt-Based Electrocatalysts for Co2 Reduction: Recent Progress, Challenges,and Perspectives [J]. Small, 2020, e2004158. 10.1002/smll.202004158.
CO2 reduction reaction (CO2 RR)provides a promising strategy for sustainable carbon fixation by converting CO2into value-added fuels and chemicals. In recent years, considerable efforts arefocused on the development of transition-metal (TM)-based catalysts for theselectively electrochemical CO2 reduction reaction (ECO2 RR). Co-basedcatalysts emerge as one of the most promising electrocatalysts with highFaradaic efficiency, current density, and low overpotential, exhibiting excellentcatalytic performance toward ECO2 RR for CO and HCOOH productions that areeconomically viable. The intrinsic contribution of Co and the synergisticeffects in Co-hybrid catalysts play essential roles for future commercialproductions by ECO2 RR. This review summarizes the rational design of Co-basedcatalysts for ECO2 RR, including molecular, single-metal-site, andoxide-derived catalysts, along with the nanostructure engineering techniques tohighlight the distribution of the ECO2 RR products by Co-based catalysts. Thedensity functional theory (DFT) simulations and advanced in situcharacterizations contribute to interpreting the synergies between Co and othermaterials for the enhanced product selectivity and catalytic activity.Challenges and outlook concerning the catalyst design and reaction mechanism,including the upgrading of reaction systems of Co-based catalysts for ECO2 RR,are also discussed.
[47]Zhang M. D., Si D. H., Yi J. D., Zhao S. S., Huang Y. B., Cao R.Conductive Phthalocyanine-Based Covalent Organic Framework for Highly EfficientElectroreduction of Carbon Dioxide [J]. Small, 2020, e2005254.10.1002/smll.202005254.
The electroreduction of CO2 tovalue-added chemicals such as CO is a promising approach to realizecarbon-neutral energy cycle, but still remains big challenge including lowcurrent density. Covalent organic frameworks (COFs) with abundant accessibleactive single-sites can offer a bridge between homogeneous and heterogeneouselectrocatalysis, but the low electrical conductivity limits their applicationfor CO2 electroreduction reaction (CO2 RR). Here, a 2D conductiveNi-phthalocyanine-based COF, named NiPc-COF, is synthesized by condensation of2,3,9,10,16,17,23,24-octa-aminophthalocyaninato Ni(II) and tert-butylpyrene-tetraonefor highly efficient CO2 RR. Due to its highly intrinsic conductivity andaccessible active sites, the robust conductive 2D NiPc-COF nanosheets exhibitvery high CO selectivity (>93%) in a wide range of the applied potentials of-0.6 to -1.1 V versus the reversible hydrogen electrode (RHE) and large partialcurrent density of 35 mA cm(-2) at -1.1 V versus RHE in aqueous solution thatsurpasses all the conventional COF electrocatalysts. The robust NiPc-COF thatis bridged by covalent pyrazine linkage can maintain its CO2 RR activity for 10h. This work presents the implementation of the conductive COF nanosheets forCO2 RR and provides a strategy to enhance energy conversion efficiency inelectrocatalysis.
[48]Zhang Z., Hao J., Lu Y., Xu Y., Li L., Shi W. Ink-Assisted SyntheticStrategy for Stable and Advanced Composite Electrocatalysts with Single FeSites [J]. Small, 2020, e2006113. 10.1002/smll.202006113.
The oxygen evolution reaction iscritical to the efficiency of many energy technologies that store renewableelectricity in chemical form. However, the rational design of high-performanceand stable catalysts to drive this reaction remains a formidable challenge.Here, a facile ink-assisted strategy to construct a series of stable and advancedcomposite electrocatalysts with single Fe sites for permitting seriouslyimproved performance characteristics is reported. As revealed by a suit ofcharacterization techniques and theoretical methods, the improvedelectrocatalytic performance and stability can be attributed to the uniquecoordination states of Fe in the form of distorted FeO4 C and the interfacialeffect in the composite system that optimize and stabilize single Fe sites inchanging to better configurations for intermediates adsorption. The findingsprovide a novel strategy to in-depth understanding of practical guidelines forthe electrocatalyst design for energy conversion devices.
[49]Ding Shichao, Lyu Zhaoyuan, Zhong Hong, Liu Dong, Sarnello Erik,Fang Lingzhe, Xu Mingjie, Engelhard Mark H., Tian Hangyu, Li Tao, Pan Xiaoqing,Beckman Scott P., Feng Shuo, Du Dan, Li Jin-Cheng, Shao Minhua, Lin Yuehe. AnIon-Imprinting Derived Strategy to Synthesize Single-Atom Iron Electrocatalystsfor Oxygen Reduction [J]. Small (Weinheim an der Bergstrasse, Germany), 2020,e2004454-e. 10.1002/smll.202004454.
Carbon-based single-atomcatalysts (CSACs) have recently received extensive attention in catalysisresearch. However, the preparation process of CSACs involves a high-temperaturetreatment, during which metal atoms are mobile and aggregated intonanoparticles, detrimental to the catalytic performance. Herein, anion-imprinting derived strategy is proposed to synthesize CSACs, in whichisolated metal-nitrogen-carbon (Me-N4 -Cx ) moiety covalently binds oxygenatoms in Si-based molecular sieve frameworks. Such a feature makes Me-N4 -Cxmoiety well protected/confined during the heat treatment, resulting in thefinal material enriched with single-atom metal active sites. As a proof ofconcept, a single-atom Fe-N-C catalyst is synthesized by using thision-imprinting derived strategy. Experimental results and theoreticalcalculations demonstrate high concentration of single FeN4 active sitesdistributed in this catalyst, resulting in an outstanding oxygen reductionreaction (ORR) performance with a half-wave potential of 0.908V in alkalinemedia.
[50]Ao C. C., Zhao W., Ruan S. S., Qian S. Y., Liu Y., Wang L., Zhang L.D. Theoretical Investigations of Electrochemical Co2 Reduction by TransitionMetals Anchored on Cnts [J]. Sustainable Energy & Fuels, 2020, 4(12):6156-64. 10.1039/d0se01127d.
Transition metals supported onnitrogen doped carbon materials are a class of promising electrochemicalcatalysts toward electrochemical CO2 reduction reactions (CO2RR) that haveexhibited excellent catalytic performance. Herein, M-N-4 (M = Fe, Co and Ni)coordination structures embedded in carbon nanotubes (CNTs) were constructed toexplore detailed mechanisms as electrocatalysts for CO2RR via densityfunctional theory (DFT) calculations. Nitrogen atoms of coordination structuresrather than only single transition metal atoms were demonstrated to beeffective active sites toward CO2RR. For two possible pathways of the firststep, forming *COOH or *OCHO, according to the catalytic activity of nitrogenatoms to the H atom, *COOH generation was facilitated in terms of kinetics over*OCHO in three systems. Meantime, it is suggested that the products ofelectrochemical CO2RR on the three catalysts are heavily dependent on theinteraction of CO and the catalysts. Ni-N-4/CNT exhibits a considerableselectivity to CO due to the weak interaction of CO and the substrates with alimiting potential of 1.79 V. On the contrary, CO prefers to remain onFe-N-4/CNT due to the strong binding energy of CO adsorbed on Fe-N-4/CNT. Thenthe CO of the Fe-N-4/CNT system undergoes further hydrogenation to produceCH3OH and CH4 at the same limiting potential of 0.68 V, indicating that thereis no distinct selectivity in forming CH3OH and CH4. Nevertheless, the limitingpotentials of CO, CH3OH and CH4 on Co-N-4/CNT are totally different, 0.43 V,0.56 V and 0.87 V, respectively. In particular, CO2RR to CO on Co-N-4/CNT hasthe lowest potential limit. Thus, Co-N-4/CNT has a considerable potential asthe catalyst for electrochemical CO2RR. In addition, the catalysts of Ni singleatoms, unsaturated coordination with nitrogen atoms, edge-anchored on CNTs wereinvestigated for their activity for the CO2RR. Our comprehensive understandingof M-N-4/CNT materials may be instructive and meaningful to design advancedcatalysts from nonprecious metals for electrochemical CO2RR.
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