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Article Cite This: J. Am. Chem. Soc. 2019, 141, 10729−10735

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Ordered Nanostructure Enhances Electrocatalytic Performance by Directional Micro-Electric Field Qing-Xia Chen,†,∥ Ying-Huan Liu,‡,∥ Xiao-Zhuo Qi,§ Jian-Wei Liu,*,† Hui-Jun Jiang,*,‡ Jin-Long Wang,† Zhen He,† Xi-Feng Ren,§ Zhong-Huai Hou,‡ and Shu-Hong Yu*,†

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†

Division of Nanomaterials & Chemistry, Hefei National Laboratory for Physical Sciences at the Microscale, CAS Center for Excellence in Nanoscience, Hefei Science Center of CAS, Collaborative Innovation Center of Suzhou Nano Science and Technology, Department of Chemistry, University of Science and Technology of China, Hefei 230026, China ‡ Department of Chemical Physics & Hefei National Laboratory for Physical Sciences at Microscales, iChEM, University of Science and Technology of China, Hefei 230026, China § Synergetic Innovation Center of Quantum Information & Quantum Physics, Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei 230026, China S Supporting Information *

ABSTRACT: Designing high-efficiency catalyst is at the heart of a transition to future renewable energy systems. Great achievements have been made to optimize thermodynamics to reduce energetic barriers of the catalytic reactions. However, little attention has been paid to design catalysts to improve kinetics to enrich the local concentration of reactant molecules surrounding electrocatalysts. Here, we find that welldesigned nanocatalysts with periodic structures can optimize kinetics to accelerate masstransport from bulk electrolyte to the catalyst surface, leading to the enhanced catalytic performance. This achievement stems from regulation of the surface reactant flux due to the gradient of the microelectric field directing uniformly to the nearest catalyst on ordered pattern, so that all of the reactant molecules are utilized sufficiently for reactions, enabling the boost of the electrocatalytic performance. This novel concept is further confirmed in various catalytic systems and nanoassemblies, such as nanoparticles, nanorods, and nanoflakes.

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INTRODUCTION The ever-growing global energy crisis is posing great urgency on the exploitation of clean and renewable energy resources. Developing highly efficient electrode materials in fuel cells is one of the most promising and practical approaches to address this problem.1−3 To date, strategies to enhance the electrocatalytic performances mainly include coordination number engineering,1,4 electronic coupling,5−8 strain engineering,9 and collective effect.10−12 However, these methods are mostly focused on the thermodynamic of electrocatalysts by reducing the energetic barrier of corresponding catalytic reactions, and little attention has been paid to modulate the kinetics which directly determines the local concentration of reactant molecules surrounding electrocatalysts. Recently, Sargent et al. demonstrated a gold nanotip catalyst to concentrate reagent around catalyst, giving rise to the enhanced electrochemical CO2 reduction performance,13 which strongly indicates that optimization of the kinetic is one of the most promising pathways for future catalyst design.14 Herein, we report the effect of ordered nanostructures in modulating catalytic kinetics. Compared with disordered counterparts, the well-designed ordered catalysts can regulate the surface flux of the reactant so that all of the reactant molecules are utilized sufficiently for reactions, thus enabling a © 2019 American Chemical Society

boost of the electrocatalytic performances. Detailed analyses show that such regulation results from the gradient of the microelectric field (MEF) formed by ordered catalyst pattern which directs uniformly to the nearest catalyst. The generality of the kinetic modulation in ordered nanocatalysts is further confirmed by both methanol oxidation reaction (MOR) and formic acid oxidation reaction (FAOR) on different catalysts including zero-dimensional (0D) nanoparticles (Pt NP), onedimensional (1D) nanowires or nanotubes (PtTe NWs, PtPdTe NWs, PtAuTe NWs, and PtPdRuTe NTs), and twodimensional (2D) nanoflakes (Pt NFs). Thus, regulation of the surface reactant flux (RSF) is a versatile strategy, which opens avenues in energy conversion field and offers a new idea to optimize catalytic performance.

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EXPERIMENTAL SECTION

Chemicals. Na2TeO3 was purchased from Maya Reagent Co. Ltd. Poly(vinylpyrrolidone) (PVP, molecular weight = 300 k), H2PtCl6, hydrazine hydrate (N2H4, 85% w/w%), aqueous ammonia solution (NH3·H2O, 25−28% w/w%), absolute ethanol, ethylene glycol (EG), acetone, benzoic acid, benzyl alcohol, N,N-dimethylformamide (DMF), trichloromethane (CHCl3), perchloric acid (HClO4), and Received: April 3, 2019 Published: June 3, 2019 10729

DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735

Article

Journal of the American Chemical Society

Electrochemical Measurements. IM6ex electrochemical workstation (Zahner, Germany) combined with three-electrode configuration was applied to carry out all of the electrochemical measurements. Platinum foil (1 cm × 1 cm) electrode was used as the counter electrode and Ag/AgCl (3.5 M) was used as the reference one. Detachable glassy carbon electrode (5 mm diameter, 0.196 cm2) was polished to a mirror finish and thoroughly cleaned before used to deposit the catalyst assembly. Cyclic voltammetry (CV) and MOR curves were carried out in 0.5 M HClO4 and 0.5 M HClO4 + 1.0 M CH3OH degassed by bubbling argon for 30 min at the potential from −0.2 to +1.05 V at room temperature, respectively. The measurement of FAOR was similar to the procedure of MOR, just conducted in 0.5 M HClO4 + 1.0 M HCOOH solution. Kinetic Model. We present a kinetic model to illustrate the regulation result from the MEF. The model is based on the following reaction-diffusion equations for a position r on the surface

methanol (CH3OH) were commercially available from Shanghai Chemical Reagent Co. Ltd. Palladium chloride (PdCl2), anhydrous ruthenium trichloride (RuCl3), potassium chloroplatinate (K2PtCl6), potassium chloropalladate (K2PdCl6), platinum acetylacetonate (Pt(acac)2), and palladium acetylacetonate (Pd(acac)2) was obtained from J&K chemical Ltd. All of the water used was Millipore Milli-Q water (resistivity = 18.2 MΩ). All chemicals are of analytical grade and were used as received without further purification. Preparation of Pt NTs and Other Pt-Based Nanostructures. Ultrathin and uniform Pt NTs were prepared with Te NWs serving as sacrificial template described by our group previously.15 Highly uniform Te NWs with a diameter of about 7 nm were synthesized with a simple hydrothermal method at 180 °C. After 0.05 mmol assynthesized Te NWs were collected with sufficient acetone and redispersed in EG, 0.1 mmol of H2PtCl6 dissolved in EG was added. After being sufficiently mixed by stirring vigorously for 10 min, the final solution was shaken at a rotation rate of 260 rpm by an Innova 40 Benchtop Incubator Shaker for 13 h at 50 °C. Finally, the products were washed several times with deionized water for further characterizations and measurements. The preparation procedures for other Pt-based nanostructures are detailed in the Supporting Information and Table S1. Assembly of Pt NTs and Other Pt-Based Nanoblocks. The assembly of Pt NTs and other Pt-based nanoblocks were realized with a modified Langmuir−Blodgett (LB) technique described previously.16 Moderate Pt NTs DMF dispersion was mixed with CHCl3 in equal volume fully. Before dropping onto the gas−liquid interface, the assembly ink must be homogeneous and monodispersed enough. At 30 min after spreading the mixture on the interface with a syringe, the mixture surface layer was compressed with two paralleled barriers at a compression rate of 20 cm2 min−1. Then the compression was stopped immediately as the first wrinkle at interface just appeared. After the compression, the assembly system was left to stand for another 20 min until CHCl3 volatilized completely. Before exposing to electrochemical measurement, the assembly was deposited onto a polished detachable glassy carbon electrode. Other Pt-based nanoblocks were assembled in a similar way with a modification of the ratio between DMF and CHCl3 additions. Preparation and Quantification of Ordered and Disordered Catalysts. After adding dropwise given Pt NTs dispersion on the air−water interface, we transferred the ordered monolayer with substrates for quantification and electrochemical measurements. Using glass substrates with different sizes to remove the membrane on different positions of the interface for inductively coupled plasma mass spectrometry (ICP-MS) test, we obtained the standard curve between the catalyst mass and substrate area. Based on the standard curve, we got the mass (m mol) of deposited ordered Pt NTs on the detachable glassy carbon electrode with an area of 0.196 cm2. After quantification of the ordered catalyst, we prepared Pt NTs dispersion with appropriate concentration and dropped the constant moles (m mol) of Pt NTs onto the detachable glassy carbon electrode for preparation of disordered catalyst. In this case, the deposited Pt NTs for electrochemical measurements in ordered and disordered assemblies were controlled to the same mass. Sample Characterizations. Morphology and size of the nanoblocks were determined by transmission electron microscopy (TEM) images carried out with a Hitachi H7650 TEM operating at 120 kV. High-resolution transmission electron microscope (HRTEM) observations were conducted on JEOL-2010F with an acceleration voltage of 200 kV. The transmittance measurement and UV−vis spectra were recorded on UV−2501PC/2550 at room temperature (Shimadzu Corporation, Japan). The Pt and other element contents of catalysts were measured by ICP-MS (ThermoScientific PlasmaQuad 3). The small-angle X-ray diffraction (SAXRD) patterns were obtained on a Philips X’Pert Pro Super X-ray diffractometer equipped with graphite-monochromatized Cu Kα radiation. The polarized optical transmission spectra were carried out with an incident white light from a stabilized tungsten-halogen source by rotating the sample stage.

∂C(r ) D = φ0(1 − C) − kdC − kC + D∇2 C − ∂t kBT

∂CCO2(r ) ∂t

∇[C(1 − C)∇(∂cV )]

(1)

= kC − kdCO2CCO2 + DCO2∇2 CCO2

(2)

In these equations, T is the temperature of the system and kB is the Boltzmann constant. D and DCO2 are the surface diffusion coefficients of CH3OH and the product CO2, respectively. C and CCO2 are the normalized surface concentrations of CH3OH and CO2, respectively. ϕ0, kd and k are rate constants of effective adsorption, desorption and MOR reaction, respectively. V is the effective potential for CH3OH in the MEF around NTs. The first term in eq 1, ϕ0(1 − C), denotes the effective adsorption of CH3OH from the solution to the surface, compacting CH3OH diffusion from the solution to the nearby electrode and adsorption of CH3OH to the electrode surface, i.e., ϕ0 ∝ c0, with c0 being the bulk concentration of CH3OH. The second term, kdC, is CH3OH desorption from the surface back into the solution. The equilibrium surface concentration without any reactions, Ceq, is determined by these pair of reversible processes as Ceq = ϕ0/(ϕ0 + kd). Considering the enhanced MEF, the third term, kC, is the oxidization reaction with the reaction rate constant k(U) = kη=0eλη(U), where λ is the barrierreducing coefficient and η(U) is the overpotential of the reaction. Besides the conventional diffusion term (the forth term, ∇2C) according to Fick’s law, it should be noticed that the NT-enhanced MEF will lead to the extra mass transfer of CH3OH (the last term, D ∇[C(1 − C)∇(∂cV )]) due to an effective potential V exerted by k T B

the MEF on the CH3OH molecules. Since the exact spatial distribution of V(r) is unknown, we consider this effective potential for a position r as a Gaussian interaction potential just like: V(r)= αCε*exp{−|r − ra|2/r02}. r0 is the character length of the potential, α is the interaction strength, ra is the location of the center of active area, ε = u0rs−0.7 is the intensity of the MEF at the active area, rs is a parameter determined by the size of catalyst, and u0 is the electrode potential, respectively.

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RESULTS AND DISCUSSION Ordering Characterizations and Electrocatalytic Performance of the Structured Catalyst. Given that Pt is one of the most classical electrocatalysts in fuel cells,17−19 we selected ultrathin Pt NTs (Figure S1) as the model catalyst to investigate the ordering-function relationship in electrocatalytic reactions. As shown in Figure 1a, the schematic diagram describes the preparation procedures for ordered and disordered catalysts. Ordered Pt NT catalyst was obtained by aligning Pt NTs using LB technique. Some given mass of Pt NTs were deposited onto the glass substrates for quantification, from which we obtained the standard curve (Figure 1b) 10730

DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735

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Figure 1. (a) Schematic diagram of the preparation and quantification procedures of ordered and disordered Pt NTs catalysts. (b) Mass quantification results of ordered and disordered Pt NTs deposited on glass substrates with various areas. (c) Mass quantification results of ordered and disordered Pt NTs deposited on detached glassy carbon electrodes for 8 times.

Figure 2. (a) Typical TEM image of the large-area assembly of Pt NT monolayer. (b) The circular color map coding (upper) and the angular space correlation alignment intensity distributions of the disordered (middle) and ordered (lower) Pt NT catalysts. (c) Orientational parameter S determined from Image-J software. (d) SAXRD pattern of Pt NT three layers on silicon wafer with the incident X-ray vertical and parallel to the orientation of the Pt NTs. Inset: Schematic illustration of the source of the peaks in SAXRD pattern. (e) The polarization dependence of transmission intensity on rotation angle (γ) of sample stage in polar coordinates. Dots: experimental data; line: fitting curve. (f) Histograms of ipeak forward of Pt catalysts for MOR. Error bars correspond to the standard deviations taken over at least three measurements.

between Pt NTs mass and substrate area. In this case, the ordered Pt NT catalyst transferred to detached glassy carbon electrode (inset in Figures 1a and S2) could be determined. After quantification, the disordered counterpart was prepared by dropping traditionally to the electrode. Multiple quantitative experimental results of ordered and disordered Pt NT catalysts in Figure 1c ensured that the catalysts deposited by our and traditional methods are of the same mass. TEM image in Figure 2a shows the uniform Pt NTs were well arranged in a periodic alignment. Quantification of this ordering is determined by statistical analysis with Image-J software of both ordered and disordered Pt NTs using the orientational parameter S (0 ≤ S ≤ 1) (details in the Supporting Information).20,21 The upper image in Figure 2b is the circular color map coding, where the angle is defined as the intersection angle between a NT and the horizontal line. Positive and negative angles represent the intersections in different directions. The middle/lower image is the angular space correlation alignment intensity distributions of the disordered/ordered Pt NT catalyst, respectively. The color changing from multicolored to uniform blue indicates the angular alignment intensity distribution of Pt NTs shifting from S = 0.15 (no ordering) to S = 0.88 (excellent ordering; Figure 2c). In addition to these microscopic local-ordering characterizations, the long-range ordering is further evidenced by SAXRD and polarized light transmission spectrum.16,22 As displayed in Figure 2d, the peaks of 2θ = 0.62°, 0.89°, and 1.15° in SAXRD pattern illustrate the periodic arrangement of Pt NTs (schematic illustrations in Figure S3), which is consistent with the observation in TEM results. As we know, the polarization of the incident light determines the mode of excited surface plasmon which is related to the periodic structures.23 The transmission spectra of the Pt NT monolayer

were recorded by a spectrograph through a fiber shown in Figures 2e and S4. When the sample rotated from γ = 0° to 360°, the intensity of the transmittance changes as a sine function of rotation angle, manifesting the long-range structural ordering. Insights into the Diffusion Control of the Catalytic Reaction. It is very impressive that the ordered Pt NT monolayer delivers the elevated MOR mass activity of ca. 1349.4 mA mg−1, which is approximately 1.8- and 2.8-fold higher than that of disordered one (743.6 mA mg−1) and Pt/C (486.5 mA mg−1), respectively, as shown in Figure 2f and Table S2. The MOR performances standardized by electrochemically accessible surface area are detailed in Figure S5, which exhibits a larger activity for ordered Pt NTs compared with disordered one. Also the chronoamperogram measurements in Figure S5e display the superiority for ordered monolayer than disordered counterpart. Besides, we studied the effect of different rotating speeds on the performances for ordered and disordered catalysts. As the Figure S6 shows, when the electrode was rotating during the measurement, the corresponding improvement can also be obtained. Given the negligible surface area increase in Figure S7, it is then very interesting to explore the underlying more important mechanism of the ordering-enhanced catalytic performance. In general, a catalytic reaction may be controlled by the thermodynamic or the kinetic. Considering that, the ordered and disordered Pt NTs are of the same material and the energetic barrier of the catalytic reaction can be hardly affected by their arrangement, implying that the ordering-enhanced catalytic performance may result from the kinetic.13,24 For a kinetic-controlled reaction, the dependence of peak current of the forward scan (ipeak forward) on the reactant concentration (c), scan rate (v) and angular velocity of the 10731

DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735

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Journal of the American Chemical Society rotating disk (w) should follow the Randle-Sevcik equation25 and Levich equation,26 which is ipeak forward ∝ c, v1/2 and w1/2, respectively. Clearly, the ipeak forward increases almost linearly accompanied by the concentration of CH3OH changing from 0.16 to 7.2 M (Figure 3a), indicating that MOR is kinetic-

Figure 4. (a) Electron density of CH3OH molecule. (b) Schematic of the kinetic model for MOR near ordered Pt NTs on electrode surface. (c) Reaction rates with different reaction constants k. (d) Reaction rates of MOR with different effective adsorption rates ϕ0 of CH3OH to the electrode surface. (e) Reaction rates of MOR with different configurations of Pt NTs. All rates are dimensionless.

rate (Figure 4d) and the ordering-enhanced MOR catalytic performance (Figure 4e) are in good accordance with experimental results, indicating that the kinetic model captures the main physics of the ordering-enhanced catalytic performance. To dive deep into the underlying mechanism of the ordering-enhanced catalytic performance, potentials of the CH3OH molecules induced by the MEF around ordered and disordered Pt NTs are given in Figure 5a,b. Overtly, the potential in ordered NTs pattern consists of many wellarranged valleys with the same periodical ordering as that of NTs as shown in Figure 5c. More interestingly, peaks of the potential locate between two adjacent NTs while the position of each NT is coincident with a potential valley. For disordered NTs, such local valleys induced by individual NT cannot be observed but merge into a few much larger potential wells (Figure 5d). As a result, there are no potential valleys corresponding to each NT anymore, i.e., many NTs or NTs segments locate at peaks of the potential or halfway up the peaks. Therefore, the CH3OH flux will be quite different for ordered and disordered NTs. For a CH3OH molecule adsorbed on the area other than NTs in ordered pattern, the potential is very high and the molecule will be driven by the potential gradient to a nearby potential valley. As aforementioned, each potential valley lies an NT. Therefore, each NT can receive nearly equal amount of molecules for catalysis and each CH3OH molecule can be utilized adequately by NTs. Nevertheless, for disordered NTs, many NTs do not locate at the potential valley, thus CH3OH molecules will pass over these NTs. In other words, few NTs at the valley will be oversupplied with the reactant which, just the other way, is always lacked on other NTs. To verify such a picture, the distribution of CH3OH concentration on NTs during the catalytic process is plotted in Figure 5e. For ordered NTs, the distribution is a very narrow Gaussian-like one, whereas for disordered NTs, the distribution broadens with a lower mean and a long tail where the CH3OH concentration on most of NTs is very low. In summary, local MEF formed by ordered NTs can render optimal extra reactant flux to each NT, so that all reactant molecules can be utilized utmostly for the catalytic reaction.

Figure 3. Current density of MOR at 0.65 V dependence on (a) concentration of CH3OH, (b) rooting of scan rate, and (c) rooting of rotating speed. Dots: experimental data; line: fitting curves. R is the correlation coefficient. (d) Histograms of ipeak forward of Pt NTs with different electrolyte additives. The Pt mass loading was 20.4 μg cm−2.

controlled in a wide concentration range of CH3OH. Similarly, ipeak forward is also linearly dependent on both v1/2 (Figure 3b) and w1/2 (Figure 3c), respectively, which demonstrates again the kinetic-controlled catalytic reaction.26 Furthermore, for a kinetic-controlled reaction, ions that can interact with the reactant will also influence the reaction dramatically.13,27 In Figure 3d, the ipeak forward of MOR with and without trace amounts of fluoride (NaF and KF) in the electrolyte are compared. Obviously, adding ions does change the reaction rate as expected (Figure S8),28−30 further validating that the catalytic reaction is kinetic-controlled. Microelectric Field Induced Reactant-Flux Regulation. To illustrate how ordered structure of Pt NT catalysts affects the kinetic catalytic reaction, we established a reactiondiffusion kinetic model based on the free energy density function of the adsorbed chemical species on the electrode surface with assumptions of local equilibrium and linear dependence of the diffusion flux on the corresponding driving force. With density functional theory calculation, the electron density of CH3OH molecule is shown in Figure 4a. The red region is the partial negative region while the blue region is the partial positive region. Obviously, CH3OH is a polar molecule which can be actuated by the MEF (Figure S9). During the whole catalytic process (Figure 4b), CH3OH adsorbs onto the electrode from the solution, diffuses on the surface and is oxidized on the NTs. The numerical simulation setup is shown in Figure S10. As CH3OH can be polarized in MEF, it will be attracted to the surface of the NTs on account of the MEF induced by NTs,13 resulting in extra mass transfer other than normal diffusion. As shown in Figure 4c, when the reaction rate constant k is larger than 1000, the rate dependence on k for ordered and disordered NTs are curved, indicating the MOR reaction is controlled by kinetics. With parameters given in Table S3, the simulated linear dependence of reaction rate on the effective adsorption 10732

DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735

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Figure 5. (a and b) Effective potential of CH3OH in MEF induced by ordered (a) and disordered (b) Pt NTs, where red arrows denote the gradient of the potential and dark orange strips indicate the position of Pt NTs. Inset: the overview of the potential. (c and d) The sectional potential on Pt NTs in ordered (c) and disordered (d) configurations, where red dashed arrows show the mass-transfer direction of CH3OH. (e) The distributions of CH3OH concentration on ordered and disordered Pt NTs during the MOR catalytic process. CNTs is the normalized surface concentrations of CH3OH on Pt NTs and PCNTs denotes the distribution of CH3OH concentration on Pt NTs. (f) The rates of MOR on ordered and disordered Pt NTs with the variation of molecule-field interaction strength α. All values are dimensionless.

Figure 6. TEM images of ordered PtTe NWs (a), PtPdTe NWs (b), PtAuTe NWs (c), PtPdRuTe NWs (d), Pt NPs (e), and Pt NFs (f) catalysts. (g) MOR performance comparations between ordered and disordered other Pt-based assemblies in 0.5 M HClO4 + 1.0 M CH3OH solution at a sweep rate of 50 mV s−1. (h) FAOR performance of Pt NTs in 0.5 M HClO4 + 1.0 M HCOOH solution at a sweep rate of 50 mV s−1. Error bars correspond to the standard deviations taken over at least three measurements.

confirmed in other catalytic systems (such as FAOR) as displayed in Figure 6h (Figure S25 and Table S6). It was found that ordered Pt NTs exhibited more outstanding FAOR mass activity (Figure S26) compared with disordered Pt NTs because strongly directional MEF distribution could help to facilitate formic acid molecules captured onto the surface of ordered Pt NTs.

With the mechanism above, it can be predicted that since the interaction strength α between CH3OH molecules and the MEF may be fluctuated with ions added, the enhanced performance can always be observed for varying α, which is validated by the dependence of the reaction rate on α for both ordered and disordered NTs (Figure 5f and S11). Effect of ordering on catalytic performance could also be anticipated by the kinetic model. In Figure S11c, the ratio between reaction rates on ordered and disordered NTs increases monotonically as the ordering of NTs arrangement increases. Generality of the Function-Ordering Strategy. As a general and versatile method, this ordered structures inducedcatalytic properties improvement strategy reported here can be extended to many other kinds of nanosized building blocks with different components and dimensionalities, such as nanoparticles, nanowires, and nanoflakes. Figure 6a−f shows representative TEM images of ordered multicomponent monolayers, such as PtTe NWs, PtPdTe NWs, PtAuTe NWs, PtPdRuTe NTs, Pt nanoparticles (NPs), and Pt nanoflakes (NFs) (details of morphological and orientational characterizations in Figures S12−17 and Table S1). As expected, all of the ordered counterparts exhibited raised current densities for MOR (Figures 6g and S18−22), which convincingly demonstrates that the RSF tactic could also be applicable for both 0D and 2D catalysts (Figures S23−24 and Tables S4−5). Moreover, this novel strategy was further

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CONCLUSION A robust RSF design strategy via strongly directional MEF distribution to improve the electrocatalytic performances was proposed. Using ordered Pt NT monolayer and MOR as model catalyst and model reaction, respectively, we obtained nearly twice the MOR performance enhancement by lining up disordered catalysts under the same condition. Actually, surface areas of ordered NT monolayer is little larger than that of the disordered NT film (just 5.0%) which slightly affects the performance but is insufficient to account for the nearly doubled improvement. Simulation calculations unveil that the MEF distributing uniaxially targeting to Pt NTs on ordered monolayer gathers CH3OH molecules much more efficiently, which vastly optimizes the kinetic process. In addition, this concept that employing periodic nanostructured catalysts to optimize kinetics for enhanced electrocatalytic performance can be extended to other catalytic system (FAOR) or utilizing other kinds of nanosized building blocks with different components and dimensionalities as nano10733

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structured catalysts. It should be emphasized here that designing ordered structures to improve the kinetics for elevated electrocatalytic performance shows a superposition effect, which means that based on the traditional thermodynamic design to reduce energetic barriers of the catalytic reactions, the electrocatalytic performance can be further improved by this ordering-function strategy. With such a contrivable platform, we believe that in-depth exploitation of ordering would bring about a leap forward in electrocatalyst engineering.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/jacs.9b03617.

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Article

Experimental procedures; supplementary notes of determination of orientational parameter; kinetic simulations; morphological and structural characterizations and electrocatalytic performances (PDF)

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Corresponding Authors

*[email protected] *[email protected] *[email protected] ORCID

Qing-Xia Chen: 0000-0001-7063-8446 Ying-Huan Liu: 0000-0002-4770-190X Xiao-Zhuo Qi: 0000-0002-5872-5253 Jian-Wei Liu: 0000-0001-9237-1025 Hui-Jun Jiang: 0000-0001-7243-5431 Jin-Long Wang: 0000-0002-6211-8472 Zhen He: 0000-0001-8565-9717 Xi-Feng Ren: 0000-0001-6559-8101 Zhong-Huai Hou: 0000-0003-1241-7041 Shu-Hong Yu: 0000-0003-3732-1011 Author Contributions ∥

Q.-X.C. and Y.-H.L. contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We acknowledge the funding support from the National Natural Science Foundation of China (Grants 21761132008, 21431006, 51471157, 21771168, 21790350, and 21833007), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant 21521001), Key Research Program of Frontier Sciences, CAS (Grant QYZDJ-SSW-SLH036), the National Basic Research Program of China (Grants 2014CB931800 and 2013CB931800), the Ministry of Science and Technology of China (Grant 2018YFA0208702), the Users with Excellence and Scientific Research Grant of Hefei Science Center of CAS (2015HSC-UE007), and the Fundamental Research Funds for the Central Universities (WK2100000005), and the Joint Funds from Hefei National Synchrotron Radiation Laboratory (UN2018LHJJ). We acknowledge fruitful discussion with Prof. Min-Rui Gao. This work was partially carried out at the USTC Center for Micro and Nanoscale Research and Fabrication. 10734

DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735

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DOI: 10.1021/jacs.9b03617 J. Am. Chem. Soc. 2019, 141, 10729−10735