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1.
J Am Chem Soc ; 2020 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-32433880

RESUMO

Fluorides have been widely applied in pharmaceutical, medicinal, and materials science as well as in fine chemical manufacturing. The performance of fluorides, however, can be markedly affected by the water content. One previous study (Maiti, A.; et al. Phys. Chem. Chem. Phys. 2008, 10, 5050) suggested that anhydrous 1,3-dimethylimidazolium fluoride ([DMIm]F) was unstable since the fluoride undergoes a self-decomposition reaction. Herein we first show quantum-chemical calculation evidence that although gas-phase [DMIm]F is unstable, the bulk phase of anhydrous [DMIm]F is quite stable. We then demonstrate the successful synthesis of the anhydrous [DMIm]F compound via the reaction between 1,3-dimethylimidazolium iodide and silver fluoride. Importantly, we find that anhydrous [DMIm]F possesses a high dissolution capability toward 1,3,5-triamino-2,4,6-trinitrobenzene (TATB), although it is known that TATB is hardly dissolved in many common organic solvents. Our Born-Oppenheimer molecular dynamics (BOMD) simulations further show that the high dissolving ability of anhydrous [DMIm]F toward TATB can be attributed to the chemical reaction between the F- anion and the TATB molecules, which disrupts the strong hydrogen-bonding interaction among the TATB molecules. Alternatively, water molecules in hydrous [DMIm]F tend to form a hydration layer around the F- anion, thereby preventing F- from reacting with the TATB molecule. This result explains why TATB is barely dissolved in hydrous [DMIm]F.

2.
J Phys Chem Lett ; : 3481-3487, 2020 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-32298119

RESUMO

Single-atom catalysis has recently emerged as a promising approach for catalyzing the carbon dioxide reduction reaction (CO2RR). In this study, we present a principle for designing active single-atom catalysts (SACs) for CO2RR. We systematically examine totally 24 transition metals supported by a graphitic carbon nitride (g-CN) monolayer and find that their catalytic activities are highly correlated with the adsorption free energies of two intermediate species (OH and OCH). We then identify two important intrinsic descriptors, namely, the number of electrons in the outmost d-shell and the enthalpy of vaporization of the transition metal. Test calculations on transition metals supported by a C2N monolayer indicate that both descriptors are quite universal for SACs of CO2RR. Based on these results, we show that Ni@g-CN, Cu@g-CN, and Co@C2N are promising SACs for CO2RR. This study offers an effective principle for designing highly active SACs for CO2RR on the basis of intrinsic properties of transition metals.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32167638

RESUMO

Full quantum mechanical (FQM) calculation of the excited state of aggregation-induced-emission (AIE) materials is highly sought but still a challenging task. Herein, we employed the recently developed electrostatically embedded generalized molecular fractionation (EE-GMF) method, a method based on the systematic fragmentation approach, to predict, for the first time, the spectra of a prototype AIE fluorophore: di(p-methoxylphenyl)dibenzofulvene (FTPE). Compared to the single molecular or QM/MM calculations, the EE-GMF method shows significantly improved accuracy, nearly reproducing the experimental optical spectra of FTPE in both condensed phases. Importantly, we show that the conventional restriction of the intramolecular rotation mechanism cannot fully account for AIE, whereas the two-body intermolecular quantum mechanical interaction plays a crucial role in AIE.

4.
Artigo em Inglês | MEDLINE | ID: mdl-32126760

RESUMO

Electrocatalysts with high activities toward multiple electrode reactions are scarce and therefore highly sought. Here, we investigate the electrocatalytic performance of the two-dimensional (2D) Pt5Se4 monolayer toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Our density functional theory calculations show that the Pt5Se4 monolayer can serve as a low-Pt-loading trifunctional electrocatalyst with good kinetic and thermal stabilities. Specifically, the HER performance of the Pt5Se4 basal plane is predicted to be superior to that of 2D layered Pd or Pt dichalcogenides. Even considering the solvent effect, the catalytic OER performance of the Pt5Se4 monolayer is predicted to be comparable to the prevalent OER catalyst-IrO2, while the catalytic ORR performance of the Pt5Se4 monolayer is even higher than the predominating Pt(111) surface. Overall, the Pt5Se4 monolayer can be a promising trifunctional catalyst that exhibits high activities toward all hydrogen and oxygen electrode reactions.

5.
Chem Commun (Camb) ; 56(20): 2995-2998, 2020 Mar 10.
Artigo em Inglês | MEDLINE | ID: mdl-32043505

RESUMO

A new atomic structure of chiral thiolate-protected gold nanocluster Au22(SR)17- is predicted on the basis of the new ligand-binding strategy, namely, redistributing the Au-S "staple" motifs on the well-known Au10 core from previously laboratory-determined Au21(SR)15 crystal structure. Density functional theory calculations show that this structure is very likely the realistic structure for the synthesized Au22(SR)17-.

6.
J Am Chem Soc ; 142(12): 5574-5582, 2020 Mar 25.
Artigo em Inglês | MEDLINE | ID: mdl-32091211

RESUMO

Aqueous-phase processing of methylglyoxal (MG) has been suggested to play a key role in the formation of secondary organic aerosols and catalyze particle growth in the atmosphere. However, the details of these processes remain speculative owing to the lack of a complete description of the physicochemical behavior of MG on atmospheric aerosols. Here, the solvation and hydrolysis of MG at the air/liquid water interface is studied via classical and first-principles molecular dynamics simulations combined with free-energy methods. Our results reveal that the polarity of the water solvent catalyzed the trans-to-cis isomerization of MG at the air/liquid water interface relative to the gas phase. Despite the presence of a hydrophobic group, MG often solvates with both the ketone and methyl groups parallel to the water interface. Analysis of the instantaneous water surface reveals that when MG is in the trans state, the methyl group repels interfacial water to maintain the planarity of the molecule, indicating that lateral and temporal inhomogeneities of interfacial environments are important for fully characterizing the solvation of MG. The counterintuitive behavior of the hydrophobic group is ascribed to a tendency to maximize the number of hydrogen bonds between MG and interfacial water while minimizing the torsional free energy. This drives MG hydration, and our simulations indicate that the formation of MG diol is catalyzed at the air/liquid water interface compared to the gas phase and occurs through nucleophilic attack of water on the carbonyl carbon.

7.
Langmuir ; 36(7): 1691-1698, 2020 Feb 25.
Artigo em Inglês | MEDLINE | ID: mdl-32008324

RESUMO

Ice recrystallization (IR) is ubiquitous, playing an important role in many areas of science, such as cryobiology, food science, and atmospheric physics. However, controllable ice recrystallization remains a challenging task largely due to an incomplete understanding of the physical mechanism associated with ice recrystallization. Herein, we explore the molecular mechanism underlying the controlling of ice recrystallization by using different small amphiphilic molecules (surfactants) through joint experimental measurements and molecular dynamics simulation. Our experiment shows that in nonionic/zwitterionic surfactant solutions, the mean size of the recrystallized ice grains increases monotonically with the concentration of surfactants, whereas in the ionic surfactant solutions, the mean size of the recrystallized ice grains tends to increase first and then decrease with increasing the concentration, yielding a peak typically at ∼5 µM. Further sequential ice affinity purification experiments and molecular dynamics simulations show that the surfactants actually do not bind to ice directly. Rather, the different spatial distributions of counter ions and molecular surfactants in the interfacial regions (ice-water interface and water-air interface) and bulk region can markedly affect the mean size of the recrystallized ice grain.

8.
Nature ; 578(7795): 392-396, 2020 02.
Artigo em Inglês | MEDLINE | ID: mdl-32025037

RESUMO

Extensive efforts have been made to harvest energy from water in the form of raindrops1-6, river and ocean waves7,8, tides9 and others10-17. However, achieving a high density of electrical power generation is challenging. Traditional hydraulic power generation mainly uses electromagnetic generators that are heavy, bulky, and become inefficient with low water supply. An alternative, the water-droplet/solid-based triboelectric nanogenerator, has so far generated peak power densities of less than one watt per square metre, owing to the limitations imposed by interfacial effects-as seen in characterizations of the charge generation and transfer that occur at solid-liquid1-4 or liquid-liquid5,18 interfaces. Here we develop a device to harvest energy from impinging water droplets by using an architecture that comprises a polytetrafluoroethylene film on an indium tin oxide substrate plus an aluminium electrode. We show that spreading of an impinged water droplet on the device bridges the originally disconnected components into a closed-loop electrical system, transforming the conventional interfacial effect into a bulk effect, and so enhancing the instantaneous power density by several orders of magnitude over equivalent devices that are limited by interfacial effects.

9.
J Am Chem Soc ; 142(5): 2150-2154, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31955571

RESUMO

The reaction between SO3 and water in the gas phase has always been of great interest, as it has important implications in atmospheric and environmental science. Compared to gas-phase water, however, heterogeneous hydration of SO3 on the surfaces of condensed phases of water/ice is relatively less explored. Here, we present a systematic study of the reactions between SO3 and three different phases of water, namely, water vapor, the surface of a liquid water droplet, and the {1 1 -2 0} plane of hexagonal ice (Ih). The computational results show that, contrary to the gas-phase water, the surface of a water droplet and the {1 1 -2 0} plane of Ih ice play distinctly different roles in the reaction, in which the HSO4-/H3O+ is formed within a few picoseconds. Moreover, the SO3 hydration exhibits multiple reaction pathways on the surface of a water droplet and the {1 1 -2 0} plane of Ih ice, including a newly observed chemical mechanism without the formation of water-loop structures. Considering temperature effects (winter vs summer), SO3/water vapor concentrations in the atmosphere, and the effective surface areas of water droplets in the atmosphere and ice on the ground, the reaction rates of SO3 with water in the gas phase, in aerosols, in clouds, and on snowpack are estimated and compared. Consistent with previous experimental studies, the loss rates of SO3 due to aerosols and clouds are less important compared to that due to water vapor. Surprisingly, the ice snowpack is shown to be an efficient sink for SO3 depletion, especially in the winter season.

10.
J Phys Chem Lett ; 11(2): 536-540, 2020 Jan 16.
Artigo em Inglês | MEDLINE | ID: mdl-31903767

RESUMO

A fundamental understanding of the structural growth of thiolate-protected gold nanoclusters not only benefits experimental synthesis but also will advance the methodology for structural predictions and for rational design of highly stable nanoclusters. Herein, we report numerous new structures (11 total) of thiolate-protected gold nanoclusters predicted from theoretical modulation of the double-helical cores of experimentally determined nanoclusters. Among these newly predicted structures, Au32(SR)22, Au40(SR)26, and Au48(SR)30 are obtained by adding a defective layer containing 4 gold atoms on a structural sequence of experimentally crystallized nanoclusters, namely, Au28(SR)20, Au36(SR)24, and Au44(SR)28. The generic growth pattern underlying this sequence of nanoclusters can be viewed as adding the highly stable tetrahedral Au4 unit on the double-helical cores. Likewise, the other eight newly predicted structures, including two groups of isomeric structures corresponding to the sequence of experimentally determined Au28(SR)20, Au36(SR)24, Au44(SR)28, and Au52(SR)32 nanoclusters, are successfully predicted. Density functional theory calculations show that these 11 newly predicted nanoclusters exhibit large highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and all-positive harmonic vibrational frequencies, suggesting their high chemical stabilities. Additional analyses on the structures and properties suggest that these newly predicted nanoclusters are very likely to be synthesized in the laboratory. Confirmation by experiments would validate the new strategy for structural prediction of thiolate-protected gold nanoclusters by taking advantage of a large structure database of crystallized ligand-protected gold nanoclusters with a variety of gold cores.

11.
Nature ; 577(7788): 60-63, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31894149

RESUMO

The formation and growth of water-ice layers on surfaces and of low-dimensional ice under confinement are frequent occurrences1-4. This is exemplified by the extensive reporting of two-dimensional (2D) ice on metals5-11, insulating surfaces12-16, graphite and graphene17,18 and under strong confinement14,19-22. Although structured water adlayers and 2D ice have been imaged, capturing the metastable or intermediate edge structures involved in the 2D ice growth, which could reveal the underlying growth mechanisms, is extremely challenging, owing to the fragility and short lifetime of those edge structures. Here we show that noncontact atomic-force microscopy with a CO-terminated tip (used previously to image interfacial water with minimal perturbation)12, enables real-space imaging of the edge structures of 2D bilayer hexagonal ice grown on a Au(111) surface. We find that armchair-type edges coexist with the zigzag edges usually observed in 2D hexagonal crystals, and freeze these samples during growth to identify the intermediate edge structures. Combined with simulations, these experiments enable us to reconstruct the growth processes that, in the case of the zigzag edge, involve the addition of water molecules to the existing edge and a collective bridging mechanism. Armchair edge growth, by contrast, involves local seeding and edge reconstruction and thus contrasts with conventional views regarding the growth of bilayer hexagonal ices and 2D hexagonal matter in general.


Assuntos
Gelo , Microscopia de Tunelamento , Cristalização
12.
Chemosphere ; 245: 125554, 2020 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-31874321

RESUMO

A recent quantitative measurement of rates of new particle formation (NPF) in urban Shanghai showed that the high rates of NPF can be largely attributed to the sulfuric acid (SA)-dimethylamine (DMA) nucleation due to relatively high DMA concentration in urban atmosphere (Yao et al., Science. 2018, 361, 278). In certain atmospheric conditions, the release of DMA is accompanied with the emission of high concentration of ammonia. As a result, the ammonia (A) may participate in SA-DMA-based NPF. However, the main sources of DMA and A can be different, thereby leading to different mechanism for the SA-DMA-A-based nucleation under different atmospheric conditions. Near industrial sources with relatively high DMA concentration of 108 molecules cm-3, the contribution of binary SA-DMA nucleation to cluster formation is 61% at 278 K, representing a dominant pathway for NPF. However, in the region not too close to major source of DMA emission, e.g., near agriculture farmland, the routes involving ternary SA-DMA-A nucleation make a 64% contribution at 278 K with DMA concentration of 107 molecules cm-3, showing that A has marked impact on the cluster formation. Under such a condition, we predict that coexisting DMA and A could be detected in the process of NPF. Moreover, at winter temperatures or at higher altitudes, our calculations suggest that the clustering of initial clusters likely involve ternary SA-DMA-A clusters rather than binary SA-DMA clusters. These new insights may be helpful to analyze and predict atmospheric-condition-dependent NFP in either urban or rural regions and/or in different season of the year.


Assuntos
Poluentes Atmosféricos/química , Atmosfera/química , Dimetilaminas/química , Modelos Químicos , Ácidos Sulfúricos/química , Amônia , China , Clima , Temperatura
13.
Nanoscale ; 12(2): 538-547, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31850430

RESUMO

The development of highly efficient metal or metal compound electrocatalysts under mild conditions has always been a challenging task for N2 reduction. Herein, we show that pristine two-dimensional (2D) MXenes are promising N2 electroreduction catalysts due in part to the availability of multiple active sites per unit area. We systematically explore a series of 3d, 4d and 5d-transition metal M2C (M = Sc, Ti, V, Cr, Mn, Fe, Zr, Nb, Mo, Ta and Hf) MXenes and compute their limiting potentials for the N2 reduction reaction (NRR). We find that 4d4-Mo2C gives rise to the lowest free-energy barrier (ΔG) of 0.46 eV, among the synthesized M2C MXenes as of today. More importantly, we find that two hypothetical MXenes, 3d5-Mn2C and 3d6-Fe2C, possess even lower ΔG of 0.28 and 0.23 eV, respectively, compared to the state-of-the-art 4d4-Mo2C, thereby likely being more efficient NRR catalysts. The N2 capture strength, a key parameter of the potential-limiting step, is found to be closely related to the d-electron arrangement on the occupied and empty spin-split d-orbitals. Hence, the excellent NRR performance of Mn2C and Fe2C can be attributed to the desirable half-filled 3d5 or 3d6 electron arrangements. The adsorption of N2 on Mn2C results in the donation of 1σ electrons to the empty spin-down 3d orbitals of Mn. The donated electrons weaken the N2 adsorption strength and lower the energy barrier of the potential-limiting step of hydrogenation. The insights obtained from this comprehensive study offer guidance to design new and efficient electrocatalysts for N2 fixation.

14.
Proc Natl Acad Sci U S A ; 116(50): 24966-24971, 2019 Dec 10.
Artigo em Inglês | MEDLINE | ID: mdl-31767772

RESUMO

Despite the high abundance in the atmosphere, alcohols in general and methanol in particular are believed to play a small role in atmospheric new particle formation (NPF) largely due to the weak binding abilities of alcohols with the major nucleation precursors, e.g., sulfuric acid (SA) and dimethylamine (DMA). Herein, we identify a catalytic reaction that was previously overlooked, namely, the reaction between methanol and SO3, catalyzed by SA, DMA, or water. We found that alcohols can have unexpected quenching effects on the NPF process, particularly in dry and highly polluted regions with high concentrations of alcohols. Specifically, the catalytic reaction between methanol and SO3 can convert methanol into a less-volatile species--methyl hydrogen sulfate (MHS). The latter was initially thought to be a good nucleation agent for NPF. However, our simulation results suggest that the formation of MHS consumes an appreciable amount of atmospheric SO3, disfavoring further reactions of SO3 with H2O. Indeed, we found that MHS formation can cause a reduction of SA concentration up to 87%, whereas the nucleation ability of MHS toward new particles is not as good as that of SA. Hence, a high abundance of methanol in the atmosphere can lower the particle nucleation rate by as much as two orders of magnitude. Such a quenching effect suggests that the recently identified catalytic reactions between alcohols and SO3 need to be considered in atmospheric modeling in order to predict SA concentration from SO2, while also account for their potentially negative effect on NPF.

15.
J Am Chem Soc ; 141(49): 19312-19320, 2019 Dec 11.
Artigo em Inglês | MEDLINE | ID: mdl-31722172

RESUMO

A source of missing sulfate production associated with high-level fine-particle pollution in the megacities of China is believed to stem from the oxidation of a notable fraction of sulfur dioxide (SO2) by nitrogen dioxide (NO2) in aqueous aerosol environments, suggesting that an unknown reaction pathway exists for aqueous sulfur oxidation. At weakly acidic aerosols, the dissolved SO2 mainly exists in the form of HSO3-, whereas at neutral aerosols, SO32- becomes the main form. Herein, by using both ab initio molecular metadynamics simulations and high-level quantum mechanical calculations, we show a hitherto unreported chemical mechanism for the formation of sulfate through the reaction between HSO3-/SO32- anions at the surface/in the interior of a water nanodroplet and gas-phase NO2 molecules. For weakly acidic aerosols, contrary to the conventional high-barrier electron-transfer pathway in the gas phase, HSO3- at the water nanodroplet surface can transfer an electron to NO2 with a low free-energy barrier of 4.7 kcal/mol through a water bridge. For neutral aerosols, the electron-transfer pathway between SO32- in the interior of the water nanodroplet and NO2 needs to overcome a lower free-energy barrier of 3.6 kcal/mol to form SO3-, with the assistance of the hydrogen-bonding network of water molecules. This new reaction pathway for the sulfate formation from HSO3-/SO32- via water nanodroplets and gaseous NO2 provides a new perspective on the growth of haze particles from pre-existing aqueous aerosols and suggests that new control strategies are needed to address haze pollution.

16.
Nanoscale ; 11(42): 19806-19813, 2019 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-31621752

RESUMO

Two new two-dimensional (2D) layered materials, namely, MgX2Se4 (X = Al, Ga) monolayers, are predicted to possess novel electronic properties. Ab initio electronic structure calculations show that both MgAl2Se4 and MgGa2Se4 monolayers are direct-gap semiconductors with bandgaps of 3.14 eV and 2.34 eV, respectively. The bandgap of both 2D materials is very sensitive to the in-plane biaxial strain, while the strain induced bandgap changes allow the tuning of optical absorption from the violet to green-light region. Also importantly, the in-plane electron mobility of both 2D materials is predicted to be as high as ∼0.7-1.0 × 103 cm2 V-1 s-1, notably higher than that of the MoS2 sheet (∼200 cm2 V-1 s-1), while it is comparable to that of black phosphorene (∼1000 cm2 V-1 s-1), suggesting their potential application in n-type field-effect transistors. Moreover, suitable bandgap and band-edge alignment make the monolayer MgX2Se4 a potential photocatalyst for water splitting. Lastly, we show that MgX2Se4 possesses a lower monolayer cleavage energy than that of graphite, indicating easy exfoliation of MgX2Se4 layers from their bulk.

17.
Proc Natl Acad Sci U S A ; 116(34): 16723-16728, 2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31375634

RESUMO

Water-solid interfaces play important roles in a wide range of fields, including atmospheric science, geochemistry, electrochemistry, and food science. Herein, we report simulation evidence of 2-dimensional (2D) ice formation on various surfaces and the dependence of the 2D crystalline structure on the hydrophobicity and morphology of the underlying surface. Contrary to the prevailing view that nanoscale confinement is necessary for the 2D liquid-to-bilayer ice transition, we find that the liquid-to-bilayer hexagonal ice (BHI) transition can occur either on a model smooth surface or on model fcc-crystal surfaces with indices of (100), (110), and (111) near room temperature. We identify a critical parameter that characterizes the water-surface interaction, above which the BHI can form on the surface. This critical parameter increases as the temperature increases. Even at temperatures above the freezing temperature of bulk ice (I h ), we find that BHI can also form on a superhydrophilic surface due to the strong water-surface interaction. The tendency toward the formation of BHI without confinement reflects a proper water-surface interaction that can compensate for the entropy loss during the freezing transition. Furthermore, phase diagrams of 2D ice formation are described on the plane of the adsorption energy versus the fcc lattice constant (E ads-a fcc), where 4 monolayer square-like ices are also identified on the fcc model surfaces with distinct water-surface interactions.

18.
Nanoscale ; 11(41): 19422-19428, 2019 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-31393509

RESUMO

In metal-free carbon-fullerene-based or defective graphene-based electrocatalysts, pentagon rings are known to play a key role in boosting catalytic activities for the oxygen reduction reaction (ORR). However, the fundamental chemical mechanism underlying the remarkable catalytic effect of the pentagon rings towards the ORR is still not fully understood. Herein, we perform a comprehensive computational study of the catalytic activities of various carbon fullerenes and fullerene fragment species, all containing pentagon rings, by using the density functional theory (DFT) and computational hydrogen electrode (CHE) methods. We find that more active sites on carbon are associated with more neighbouring pentagon rings and stronger adsorption of the key intermediates of O*, OH* and OOH* for the ORR. Importantly, two C60-based fragments, namely, C60-frag1 and C60-frag2l, show a very high activity towards the ORR, as both yield overpotentials as low as 0.389 and 0.407 V, and entail suitable adsorption free energy of OH* and OOH* species. These desirable chemical properties of fullerene fragments can be attributed to the high-energy HOMO orbitals, induced by the low-symmetry fullerene-fragment structures. Both the number of neighbouring pentagon rings and the degree of overall symmetry of the fragment appear to be the two important factors that can be adjusted for the design of optimal metal-free carbon electrocatalysts towards high ORR activities.

19.
ACS Nano ; 13(10): 11853-11862, 2019 Oct 22.
Artigo em Inglês | MEDLINE | ID: mdl-31461618

RESUMO

Single-atom catalysts (SACs) have emerged as one of the most promising alternatives to noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). While SACs can offer notable benefits in terms of lowering overall catalyst cost, there is still room for improvement regarding catalyst activity. To this end, we designed and successfully fabricated an ORR electrocatalyst in which atomic clusters are embedded in an atomically dispersed Fe-N-C matrix (FeAC@FeSA-N-C), as shown by comprehensive measurements using aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption spectroscopy (XAS). The half-wave potential of FeAC@FeSA-N-C is 0.912 V (versus reversible hydrogen electrode (RHE)), exceeding that of commercial Pt/C (0.897 V), FeSA-N-C (0.844 V), as well as the half-wave potentials of most reported non-platinum-group metal catalysts. The ORR activity of the designed catalyst stems from single-atom active centers but is markedly enhanced by the presence of Fe nanoclusters, as confirmed by both experimental measurements and theoretical calculations.

20.
Nanoscale ; 11(25): 12210-12219, 2019 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-31204748

RESUMO

Atomically thin two-dimensional (2D) materials have received intense research interest due to their novel properties and promising applications in nanodevices. By using density functional theory (DFT) calculations, we investigate catalytic activities of several newly predicted two-dimensional (2D) triphosphides GeP3, SnP3 and InP3 monolayers for hydrogen evolution reaction (HER). The calculation results show that GeP3 and SnP3 monolayers are active catalysts for HER with suitable free energy of hydrogen adsorption in the basal plane. In particular, the Gibbs free energy of hydrogen adsorption (ΔGH*) of GeP3 is 0.024 eV, a value even more favorable compared to the precious-group-metal (PGM) catalyst Pt. Moreover, the 2D GeP3 and SnP3 are intrinsically compatible with the graphene substrate so that the HER performance can be improved via building a hybrid multilayer with graphene sheet. The charge transfer from GeP3 or SnP3 to graphene, estimated to be 0.1278e or 0.2157e, can significantly enhance the electric conductivity and promote the electrocatalytic activity. Although the electronic band structure of GeP3 and SnP3 can be tuned by external strain, we find that the HER performance of GeP3 and SnP3 monolayer is actually insensitive to the external strain, a feature desirable for the catalytic application. The desirable properties for HER with nearly zero Gibbs free energy render 2D GeP3 and SnP3 promising candidates for future application in electrocatalysis.

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