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Based on experimental and computational evidence, phthalocyanine (Pc) compounds in the form of quaternary-bound metal-nitrogen (N) atoms are the most effective catalysts for oxygen reduction reaction (ORR). However, the heat treatment process used in their synthesis may compromise the ideal structure, causing the agglomeration of transition metals. To overcome this issue, a novel method is developed for synthesizing iron (Fe) single-atom catalysts with ideal structures supported by thermally exfoliated graphene oxide (GO). This is achieved through a short heat treatment of only 2.5 min involving FePc and N, N-dimethylformamide in the presence of GO. According to the synthesis mechanism revealed by this study, carbon monoxide acts as a strong linker between the single Fe atoms and graphene. It facilitates the formation of a structure containing oxygen species between FeN4 and graphene, which provides high activity and stability for the ORR. These catalysts possess an enormous number of active sites and exhibit enhanced activity toward the alkaline ORR. They demonstrate excellent performance when applied to real electrochemical devices, such as zinc-air batteries and anion exchange membrane fuel cells. It is expected that the instantaneous heat treatment method developed in this study will aid in the development of high-performing single-atom catalysts.

RESUMEN

Precise configurations of isolated metal atoms in nitrogen-doped carbon materials with 2D single or multilayers and 3D nanoarchitectures are gaining attention owing to their good stability and activity at high current densities. Atomic metal-Nx moieties, which utilize maximum atoms to attain high intrinsic activity and novel electronic architecture of support materials, facilitate strong interaction between the central metal atom and support matrix. However, resource consumption is considerably high due to the inferior atomic utilization of active sites. Therefore, energy-efficient electrochemical processes are needed to develop advanced isolated single-atom architecture, which would provide high atom-utilization and good durability. Herein, the concepts of atomically dispersed metal sites in single-atom and alloy architectures and their electronic features associated with structural evolution are discussed. Opportunities and challenges associated with the use of isolated single-atoms in 2D materials are discussed based on their unique electronic defects, low-valence central metals, mechanical flexibility, and maximum access to metal sites. This insightful revisit into the engineering of single-atom and alloy architectures would provide a profound understanding of electronic modulations and regulation of geometric characteristics, and unravels potential directions for electrochemical energy conversion, charge storage, and sensing processes.

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Developing cost-effective Pt-based electrocatalysts for the hydrogen evolution reaction (HER) is highly urgent. Herein, we report novel electrocatalysts with individually dispersed Pt active sites and tunable Pt-Ni interaction decorated on carbon-wrapped nanotube frameworks (Pt/Ni-DA). Pt/Ni-DA exhibits superior HER performance at low Pt concentrations with an ultralow overpotential of 18 mV at 10 mA cm-2 and an ultrahigh mass activity of 2.13 A mgPt-1 at an overpotential of 50 mV, which is about four times higher than that of commercial Pt/C. X-ray absorption fine structure (XAFS) confirms the extension of Pt from the Ni surface to the Ni bulk phase. Mechanistic research and density functional theory (DFT) calculations collectively reveal that the dispersibility and distribution of Pt atoms in Ni regulate the electronic configuration of Pt sites, optimizing the binding energy of reaction intermediates and facilitating electron transfer during the HER process. This work highlights the importance of the electronic structure alternation through the accommodation effect toward enhanced catalytic performance in HER.

RESUMEN

It is highly desired to achieve controllable product selectivity in CO2 hydrogenation. Herein, we report light-induced switching of reaction pathways of CO2 hydrogenation towards CH3 OH production over actomically dispersed Co decorated Pt@UiO-66-NH2 . CO, being the main product in the reverse water gas shift (RWGS) pathway under thermocatalysis condition, is switched to CH3 OH via the formate pathway with the assistance of light irradiation. Impressively, the space-time yield of CH3 OH in photo-assisted thermocatalysis (1916.3 µmol gcat -1 h-1 ) is about 7.8 times higher than that without light at 240 °C and 1.5 MPa. Mechanism investigation indicates that upon light irradiation, excited UiO-66-NH2 can transfer electrons to Pt nanoparticles and Co sites, which can efficiently catalyze the critical elementary steps (i.e., CO2 -to-*HCOO conversion), thus suppressing the RWGS pathway to achieve a high CH3 OH selectivity.

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Metal- and nitrogen-doped nanocarbons (M-N-Cs) are promising alternatives to precious metals for catalyzing electrochemical energy conversion processes. However, M-N-Cs synthesized by high-temperature pyrolysis frequently suffer from compositional heterogeneity with the simultaneous presence of atomically dispersed M-Nx sites and crystalline metal nanoparticles (NPs), which hinders the identification of active sites and rational optimization in performance. Herein, a universal and efficient strategy is reported to obtain both precious- and nonprecious-metal-based M-N-Cs (M = Pt, Fe, Co, Ni, Mn, Cu, Zn) with exclusive atomic dispersion by making use of ammonium iodide as the etchant to remove excessive metal aggregates at high temperature. Taking Pt-N-C as a proof-of-concept demonstration, the complete removal of Pt NPs in Pt-N-C enables clarification on the contributions of the atomic Pt-Nx moieties and Pt NPs to the catalytic activity toward the hydrogen evolution reaction. Combined electrochemical measurements and theoretical calculations identify that the atomic Pt-Nx moieties by themselves possess negligible activity, but they can significantly boost the activity of the Pt NPs via the synergistic effect.

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Triethylamine (TEA) is a widely used volatile organic chemical, which is harmful and can cause headache, dizziness, and respiratory discomfort. Developing an efficient sensor to detect trace amounts of TEA is significant for industrial and healthcare monitoring. In this work, SnO2 with a three-dimensional ordered macroporous structure (3DOM) was prepared through a polymethylmethacrylate sphere template route. The TEA sensing performance of the 3DOM SnO2 was enhanced through Pt loading. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy images and X-ray absorption fine-structure analysis indicate that Pt on the 3DOM 0.20% Pt/SnO2 surface mainly exists in the state of atomic dispersion, which results in more active sites, higher Hall mobility and active oxygen contents, and lower response energy barriers. The 0.20% Pt/SnO2 sensor has a low operating temperature of 80 °C and a low limit of detection (0.32 ppb). Because of the uniform adsorption of TEA on the atomically dispersed Pt, the 3DOM Pt/SnO2 sensor exhibits high selectivity.

RESUMEN

Direct conversion of methane into value-added chemicals, such as methanol under mild conditions, is a promising route for industrial applications. In this work, atomically dispersed Rh on TiO2 suspended in an aqueous solution was used for the oxidation of methane to methanol. Promoted by copper cations (as co-catalyst) in solution, the catalysts exhibited high activity and selectivity for the production of methanol using molecular oxygen with the presence of carbon monoxide at 150 °C with a reaction pressure of 31 bar. Millimole level yields of methanol were reached with the selectivity higher than 99 % using the Rh/TiO2 catalysts with the promotion of the copper cation. CO was the reductive agent to generate H2 from H2 O, which led to the formation of H2 O2 through the reaction of H2 and O2 . Atomically dispersed Rh activated the C-H bond in CH4 and catalyzed the oxidation using H2 O2 . Copper cations maintained the low-valence state of Rh. Moreover, copper acted as a scavenger for suppressing the overoxidation, thus leading to the high selectivity of methanol.

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Electrocatalytic reduction of CO2 (CO2 RR) to value-added chemicals is of great significance for CO2 utilization, however the CO2 RR process involving multi-electron and proton transfer is greatly limited by poor selectivity and low yield. Herein, We have developed an atomically dispersed monovalent zinc catalyst anchored on nitrogenated carbon nanosheets (Zn/NC NSs). Benefiting from the unique coordination environment and atomic dispersion, the Zn/NC NSs exhibit a superior CO2 RR performance, featuring a high current density up to 50 mA cm-2 with an outstanding CO Faradaic efficiency of ≈95 %. The center ZnI atom coordinated with three N atoms and one N atom that bridges over two adjacent graphitic edges (Zn-N3+1 ) is identified as the catalytically active site. Experimental results reveal that the twisted Zn-N3+1 structure accelerates CO2 activation and protonation in the rate-determining step of *CO2 to *COOH, while theoretical calculations elucidate that atomically dispersed Zn-N3+1 moieties decrease the potential barriers for intermediate COOH* formation, promoting the proton-coupled CO2 RR kinetics and boosting the overall catalytic performance.

RESUMEN

We considered the effect of coverage of the surface of In2O3 films with rhodium on the sensitivity of their electrophysical properties to ozone (1 ppm). The surface coverage with rhodium varied in the range of 0-0.1 ML. The In2O3 films deposited by spray pyrolysis had a thickness of 40-50 nm. The sensor response to ozone depends on the degree of rhodium coverage. This dependence has a pronounced maximum at a coverage of ~0.01 ML of Rh. An explanation is given for this effect. It is concluded that the observed changes are associated with the transition from the atomically dispersed state of rhodium to a 3D cluster state.

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Single-atom catalysts (SACs) with metal-nitrogen (M-N) sites are one of the most promising electrocatalysts for electrochemical carbon dioxide reduction (ECO2R). However, challenges in simultaneously enhancing the activity and selectivity greatly limit the efficiency of ECO2R due to the improper interaction of reactants/intermediates on these catalytic sites. Herein, we report a carbon-based nickel (Ni) cluster catalyst containing both single-atom and cluster sites (NiNx-T, T = 500-800) through a ligand-mediated method and realize a highly active and selective electrocatalytic CO2R process. The catalytic performance can be regulated by the dispersion of Ni-N species via controlling the pyrolysis condition. Benefitting from the synergistic effect of pyrrolic-nitrogen coordinated Ni single-atom and cluster sites, NiNx-600 exhibits a satisfying catalytic performance, including a high partial current density of 61.85 mA cm-2 and a high turnover frequency (TOF) of 7,291 h-1 at -1.2 V vs. RHE, and almost 100% selectivity toward carbon monoxide (CO) production, as well as good stability under 10 h of continuous electrolysis. This work discloses the significant role of regulating the coordination environment of the transition metal sites and the synergistic effect between the isolated single-site and cluster site in enhancing the ECO2R performance.

RESUMEN

When metal nanoparticles on supports are made smaller and smaller-to the limit of atomic dispersion-they become cationic and take on new catalytic properties that are only recently being discovered. The synthesis of these materials is reviewed, including their structure characterization-especially by atomic-resolution electron microscopy and X-ray absorption and infrared spectroscopies-and relationships between structure and catalyst performance, for reactions including hydrogenations, oxidations, and the water gas shift. Structure determination is challenging because of the intrinsic nonuniformity of the support surfaces-and therefore the structures on them-but fundamental understanding has advanced rapidly, benefiting from nearly uniform catalysts consisting of metals on well-defined-crystalline-supports and their characterization by spectroscopy and microscopy. Recent advances in atomic-resolution electron microscopy have spurred the field, providing stunning images and deep insights into structure. The iridium catalysts have typically been made from organoiridium precursors, opening the way to understanding and control of the metal-support bonding and ligands on the metal, including catalytic reaction intermediates. Platinum catalysts are usually made with less precision, from salt precursors, but they catalyze a wider array of reactions than the iridium, typically being stable at higher temperatures and seemingly offering rich prospect for discovery of new catalysts.

RESUMEN

As an important industrial chemical, formaldehyde is used in various fields but is harmful to health. Developing a convenient detection device for formaldehyde is significant. Based on atomically dispersed Au on In2O3 nanosheets, a formaldehyde sensor was fabricated in this work. The highly dispersed Au obtained by the ultraviolet (UV) light-assisted reduction method helps improve the sensing performance. A meager loading amount (0.01 wt %) of Au on In2O3 nanosheets exhibits high sensitivity toward ppb-level formaldehyde. Au acts as an electron sink and promotes the oxidation of formaldehyde. Atomically dispersed Au on In2O3 nanosheets decreases the activation energy and increases the number of active sites, which result in a highly efficient conversion of formaldehyde and a marked resistance change of the fabricated sensors. The selective adsorption and oxidation of formaldehyde on single atom Au's uniform sites establish excellent selectivity. Besides, the sensor exhibits short response/recovery time and excellent stability, with promising applications in formaldehyde detection.

Asunto(s)

RESUMEN

Utilizing Zn as a "fencing" agent has enabled the pyrolytic synthesis of atomically dispersed metal-nitrogen-carbon (AD-MNC) materials for broad electrocatalysis such as fuel cells, metal-air batteries, and water electrolyzers. Yet the Zn residue troubles the precise identification of the responsible sites in active service. Herein we developed a simple aerosil-assisted method for preparing AD-MNC materials to cautiously avoid the introduction of Zn. The combined analysis of extended X-ray absorption fine structure (EXAFS) and aberration-corrected high-resolution transition electron microscopy verified the atomic dispersion of Fe species in the as-made Fe-NC sample with a well-defined structure of Fe-N4. Besides, the EXAFS studies indicated the formation of oxygenated Fe-N4 moieties (O-Fe-N4) after the removal of aerosil nanoparticles. Therefore, the immobilization of Fe atoms in the carbon substrate was attributed to the heavily doping N and rich oxygen dangling species at the aerosil surface. Electrochemical measurements revealed that the as-made Fe-NC material furnished with O-Fe-N4 moieties exhibited excellent oxygen reduction reaction (ORR) performance, characterized by individually indicating ∼22 mV higher half-wave potentials, with respect to commercial Pt/C catalyst. Density functional theory (DFT) computations suggested that the dangling oxygen ligand on the Fe-N4 moiety could significantly boost the cleavage of OOH* and the reductive release of *OH intermediates, leading to the enhancement of overall ORR performance.

RESUMEN

M-N-C catalysts have attracted considerable attention in the fields of energy storage and conversion as well as catalysis over the past decades. However, the current synthetic strategies for fabricating M-N-C catalysts via high-temperature pyrolysis unavoidably lead to a structural heterogeneity with the presence of a mixture of species including atomically dispersed M-Nx moieties and inorganic metal-containing particles, which not only decreases the atomic utilization but also clouds the accurate understanding of the nature of the catalytically active sites. Herein, we first report a straightforward and cost-effective preparation strategy for fabricating a Cu-N-C catalyst with atomically dispersed and coordinately unsaturated Cu-N2 moieties on hierarchically N-doped porous carbon (Cu1/NC-800) without formation of any metal-containing phases. Cu1/NC-800 exhibits outstanding catalytic performance for Glaser-Hay coupling of terminal alkynes under mild and sustainable conditions, which surpass those of the state-of-the-art catalysts. A broad set of (un)symmetrical aryl-aryl, aryl-alkyl, and alkyl-alkyl 1,3-diynes were selectively synthesized in high yields with good tolerance of various functional groups. More importantly, the Cu1/NC-800 could be easily reused with good maintenance of the activity and atomic dispersion of Cu in the structure. Experimental results and theoretical calculations reveal that the low N coordination number of single-atom Cu sites in Cu-N2 exhibit a preferential adsorption to terminal alkyne; meanwhile, the adjacent pyridinic N sites on the carbon matrix facilitate the deprotonation of the adsorbed alkyne to generate the key intermediate Cuδ-acetylide species, thus synergistically boosting the reaction. Therefore, this work not only provides an alternative facile synthetic strategy for fabricating atomically dispersed M-N-C catalysts but also represents a significant advance for accessing (un)symmetrical 1,3-diynes from Glaser-Hay coupling.

RESUMEN

Atomically dispersed metal-nitrogen sites-anchored carbon materials have been developed as effective catalysts for CO2 electroreduction (CO2ER), but they still suffer from the imprecisely control of type and coordination number of N atoms bonded with central metal. Herein, we develop a family of single metal atom bonded by N atoms anchored on carbons (SAs-M-N-C, M = Fe, Co, Ni, Cu) for CO2ER, which composed of accurate pyrrole-type M-N4 structures with isolated metal atom coordinated by four pyrrolic N atoms. Benefitting from atomically coordinated environment and specific selectivity of M-N4 centers, SAs-Ni-N-C exhibits superior CO2ER performance with onset potential of - 0.3 V, CO Faradaic efficiency (F.E.) of 98.5% at - 0.7 V, along with low Tafel slope of 115 mV dec-1 and superior stability of 50 h, exceeding all the previously reported M-N-C electrocatalysts for CO2-to-CO conversion. Experimental results manifest that the different intrinsic activities of M-N4 structures in SAs-M-N-C result in the corresponding sequence of Ni > Fe > Cu > Co for CO2ER performance. An integrated Zn-CO2 battery with Zn foil and SAs-Ni-N-C is constructed to simultaneously achieve CO2-to-CO conversion and electric energy output, which delivers a peak power density of 1.4 mW cm-2 and maximum CO F.E. of 93.3%.

RESUMEN

Immobilizing metal atoms by multiple nitrogen atoms has triggered exceptional catalytic activity toward many critical electrochemical reactions due to their merits of highly unsaturated coordination and strong metal-substrate interaction. Herein, atomically dispersed Fe-NC material with precise sulfur modification to Fe periphery (termed as Fe-NSC) was synthesized, X-ray absorption near edge structure analysis confirmed the central Fe atom being stabilized in a specific configuration of Fe(N3)(N-C-S). By enabling precisely localized S doping, the electronic structure of Fe-N4 moiety could be mediated, leading to the beneficial adjustment of absorption/desorption properties of reactant/intermediate on Fe center. Density functional theory simulation suggested that more negative charge density would be localized over Fe-N4 moiety after S doping, allowing weakened binding capability to *OH intermediates and faster charge transfer from Fe center to O species. Electrochemical measurements revealed that the Fe-NSC sample exhibited significantly enhanced oxygen reduction reaction performance compared to the S-free Fe-NC material (termed as Fe-NC), showing an excellent onset potential of 1.09 V and half-wave potential of 0.92 V in 0.1 M KOH. Our work may enlighten relevant studies regarding to accessing improvement on the catalytic performance of atomically dispersed M-NC materials by managing precisely tuned local environments of M-Nx moiety.

RESUMEN

Interface engineering of two-dimensional (2D) transition-metal composites for activating plane and edge sites is a significant yet step challenging in boosting their performance for hydrogen evolution reaction (HER). Herein, two-dimensional (2D) MoO3 with petal-shaped nanosheets confining Pd nanoparticles (Pd@MoO3 heterostructure) was prepared via an efficient solvothermal and subsequently hydrogen reduction processes. The atomically dispersed Pd-substituted sites in the interface of Pd nanoparticles and 2D MoO3 lattices significantly play an important role in enhancing the electrocatalytic and photocatalytic performances of the Pd@MoO3 heterostructure. As a result, the Pd@MoO3 heterostructure exhibits a high HER catalytic activity with an overpotential (η) of 71 mV to achieve a current density of 10 mA cm-2 and an extremely low Tafel slope of 42.8 mV dec-1 in 0.5 M H2SO4 solution. Furthermore, the photoresponse of the Pd@MoO3 heterostructure is about 3 times higher than that of the MoO3 nanosheets. This work highlighted a strategy of interface engineering for highly efficient cost-effective catalyst for hydrogen evolution by electric and solar energy conversion.

RESUMEN

Herein, we present an approach to create a hybrid between single-atom-dispersed silver and a carbon nitride polymer. Silver tricyanomethanide (AgTCM) is used as a reactive comonomer during templated carbon nitride synthesis to introduce both negative charges and silver atoms/ions to the system. The successful introduction of the extra electron density under the formation of a delocalized joint electronic system is proven by photoluminescence measurements, X-ray photoelectron spectroscopy investigations, and measurements of surface ζ-potential. At the same time, the principal structure of the carbon nitride network is not disturbed, as shown by solid-state nuclear magnetic resonance spectroscopy and electrochemical impedance spectroscopy analysis. The synthesis also results in an improvement of the visible light absorption and the development of higher surface area in the final products. The atom-dispersed AgTCM-doped carbon nitride shows an enhanced performance in the selective hydrogenation of alkynes in comparison with the performance of other conventional Ag-based materials prepared by spray deposition and impregnation-reduction methods, here exemplified with 1-hexyne.