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Letter Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Highly Selective Reduction of Carbon Dioxide to Methane on Novel Mesoporous Rh Catalysts Hamidreza Arandiyan,*,▼,† Kenya Kani,‡,§,∥,▼ Yuan Wang,⊥,#,▼ Bo Jiang,∥ Jeonghun Kim,§ Masahiro Yoshino,□ Mehran Rezaei,○ Alan E. Rowan,§ Hongxing Dai,*,△ and Yusuke Yamauchi*,‡,§,▽ †

Laboratory of Advanced Catalysis for Sustainability, School of Chemistry, The University of Sydney, Sydney 2006, Australia College of Chemistry and Molecular Engineering, Qingdao University of Science and Technology, Qingdao 266042, China § Australian Institute for Bioengineering and Nanotechnology (AIBN) and School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia ∥ International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan ⊥ Particles and Catalysis Research Group, School of Chemical Engineering, The University of New South Wales, Sydney, New South Wales 2052, Australia # Fritz-Haber-Institut der Max-Planck-Gesellschaft, Department of Inorganic Chemistry, Faradayweg 4-6, 14195 Berlin, Germany □ Yoshino Denka Kogyo, Inc., Yoshikawa, Saitama 342-0008, Japan ○ Catalyst and Advanced Materials Research Laboratory, Chemical Engineering Department, University of Kashan, Kashan 87317-51167, Iran △ Beijing Key Laboratory for Green Catalysis and Separation, Department of Chemistry and Chemical Engineering, College of Environmental and Energy Engineering, Beijing University of Technology, Beijing 100124, China ▽ Department of Plant & Environmental New Resources, Kyung Hee University, 1732 Deogyeong-daero, Giheung-gu, Yongin-si, Gyeonggi-do 446-701, South Korea

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‡

S Supporting Information *

ABSTRACT: Mesoporous metals with high surface area hold promise for a variety of catalytic applications, especially for the reduction of CO2 to value-added products. This study has used a novel mesoporous rhodium (Rh) nanoparticles, which were recently developed via a simple wet chemical reduction approach (Nat. Commun. 2017, 8, 15581) as catalyst for CO2 methanation. Highly efficient performance and selectivity for methane formation are achieved due to their controllable crystallinity, high porosity, high surface energy, and large number of atomic steps distributions. The mesoporous Rh nanoparticles, possessing the largest surface area (69 m2 g−1), exhibit a substantially higher reaction rate (5.28 × 10−5 molCO2 gRh−1 s−1) than the nonporous Rh nanoparticles (1.28 × 10−5 molCO2 gRh−1 s−1). Our results indicate the extensive use of mesoporous metals in heterogeneous catalysis processes. KEYWORDS: CO2 reduction, mesoporous materials, rhodium, nanocatalysts, atomic steps or the last several decades, “global warming” has been considered as one of the most serious environmental issues in the world and researchers have attributed the main factor to greenhouse gases (mostly CO2). Additionally, along with the dramatic growth in science and technology, energyshortage derived from lack of fossil fuels has been arising as another significant issue in our society. Under this situation, conversion of carbon dioxide into chemicals is regarded as an alternative strategy which can replace the conventional energy source and at the same time to decrease the emission levels of CO2 in the atmosphere. Although various chemicals can be

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© XXXX American Chemical Society

produced from CO2 reduction such as CO, HCOOH, H2C2O4, CH3OH, CH4, CH2CH2, and CH3CH2OH in the presence of heterogeneous catalysts,1−4 the study on catalytic methanation of CO2 at low temperature is challenging. According to the formula CO2 + 4H2 → CH4 + 2H2O (ΔH298 K = −164.7 kJ mol−1), converting CO2 to CH4 is Received: April 28, 2018 Accepted: July 12, 2018

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DOI: 10.1021/acsami.8b06977 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces Scheme 1. Schematic Illustration for Preparation of Mesoporous Rh Nanoparticles

reduction process as an efficient catalyst for CO2 conversion to generate energy-rich CH4. The research demonstrates that introduction of (PEO(10500)-b-PMMA(18000)) as a template can cause the subsequent generation of mesoporous structure, thus significantly increase the total available surface area of the meso-Rh catalysts and enhance the number of available sites for reaction and the collision frequency between the reactants and the surface. The synthesis of meso-Rh was carried out according to our previous report.17 The typical preparation procedures are as follows: 5 mg of poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO(10500)-b-PMMA(18000), which is purchased from Polymer Source Inc. was fully dispersed into 0.6 mL of N,NDMF and 0.4 mL of distilled water and 1.1 mL of Na3RhCl6 aqueous solution (40 mM) were taken to the as-prepared DMF solution, achieving a transparent solution with lightbrown color. Here, Rh precursors presented in the state of aqua complex ([Rh(H2O)xCl6‑x](3‑x)‑) and formed composites with PEO(10500)-b-PMMA(18000) micelles by hydrogen bonding between [Rh(H2O)xCl6−x](3−x)‑ and PEO units of micelles.17 Finally, 1 mL of 100 mM ascorbic acid was added into the above solution to reduce Rh precursors on micelles. The color of the solution varied from light brown to black after keeping in a hot water bath at 70 °C for 12 h. Then centrifugation at 14 000 rpm was conducted for 20 min to collect the solids. Five consecutive washing and centrifugation cycles was applied to remove the residual PEO(10500)-b-PMMA(18000) in the samples. After which, these samples were taken for characterization (Scheme 1). For comparison, nonporous Rh nanoparticles (denoted as “NP-Rh”) was also prepared using the same method in the absence of block polymer. The mesostructure of the meso-Rh catalyst was investigated by low and high-magnification SEM, TEM and high-angle annular dark-field scanning TEM (HAADF-STEM). As illustrated in Figure 1, the meso-Rh sample showed that the nanoparticles were very uniform in size and shape. By measuring 200 nanoparticles on SEM image, the average

exothermic. To date, conventional catalysts for CO2 reduction include metals and transition metal complexes, for instance, Ni/Al2O3, Pd/Al2O3, and Pt/Al2O3 or their combination with Rh or Ir.1,5 Due to its attractiveness as a low-cost metal, the catalytic conversion using Ni-based materials as catalysts have been fully studied. However, Ni-supported catalysts suffer an inevitable disadvantage of being readily deactivated, through the coke formation arising from the complete dissociation of CO2. The main advantage of noble metals is their ability to activate both the C−O and H−H bonds and loading on matrix such as Al2O3 enables noble metals to disperse well to make the most use of this advantage in a wide range of operating temperatures. In fact, these materials have shown high activity, but their commercial utilization is hampered by the relatively high volatility of oxides and sintering with ease above 500 °C.6,7 In addition to these catalysts, various metal nanostructures have been prepared by distinct synthesis strategies.8 Among them, templating methods, involving a hard- or a softtemplate, is the most frequently used strategy to synthesize mesoporous materials.9 It has been reported that mesoporous materials possess high accessibility for guest species from outside, and abundant catalytically active sites derived from high surface area.10−12 For instance, Sun et al. discovered a three-dimensional ordered mesoporous Ni sphere arrays which acted as a successful oxygen evolution reaction catalyst in alkaline electrolyte.13 However, to the best of our knowledge, while a variety of Rh nanoarchitectures have been reported,14−16 mesoporous Rh nanoparticles (denoted as “meso-Rh”) had never been explored until our recently report,17 because their desirable surface chemistry attributes to high surface energy of Rh metal in comparison with other noble metals.18 As it is mentioned in our previous paper17 the chemical reduction of self-assembled polymeric micelles not only can produce size-controlled meso-Rh, but also can stabilize them against serious aggregation without additional stabilizers. In this study, we employ meso-Rh based on a wet chemical B

DOI: 10.1021/acsami.8b06977 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Figure 2. (a, b) HRTEM images of meso-Rh, (c) TEM image of single nanoparticle, and (d) SAED pattern from the TEM image in panel c.

with polycrystal (Figure 2d) and confirmed that the frameworks were highly crystallized in the meso-Rh sample. This result indicates that the synthesis approach facilitates the formation of a unique porous structure on the surface of the meso-Rh sample, giving rise to a large surface area and improved catalytic activity. For comparison purposes, we also synthesized NP-Rh via same method in the absence of block polymer (PEO(10500)-b-PMMA(18000)) (Figure S4). It shows that the block polymer method can generate both high-quality mesostructure and provided good resistance to sintering. It suggests that the (PEO(10500)-b-PMMA(18000)) had significant effects on the production of mesostructured skeletons of mesoRh sample. The typical electrochemical oxidation peaks of CO monolayer were observed on both meso-Rh and NP-Rh catalysts, and the peak current of meso-Rh was much higher than NP-Rh (Figure S5). According to these peaks, the electrochemical active surface area (ECSA) values were calculated to be 69 m2 g−1 and 8 m2 g−1, respectively, suggesting a much larger surface area for meso-Rh, which provides more active sites for better catalytic performance. The catalytic performance of Rh samples (meso-Rh and NPRh) in the selective CO2 reduction between 350 and 550 °C is presented in Figure 3. Notably, the CO2 conversion toward meso-Rh significantly surpasses that of NP-Rh sample in the whole range temperatures, with 98.9% conversion at 550 °C compared to NP-Rh with lower than 50% conversion at the same temperature (Figure 3a). It is noticed that NP-Rh and meso-Rh perform the completely different selectivity of the CO2 reduction reaction to achieve distinct products of CO and CH4. High selectivity of essentially 100% toward CO production is known to result over NP-Rh, whereas meso-Rh provides 100% selectivity toward CH4 production at 450 °C. It is reported by Behm et al.19 that the selectivity of CO/CO2 methanation is dependent on the particle size of Ru catalysts. Kwak et al.20 also found that the selectivity and activity of Pd/ Al2O3 for carbon dioxide reduction vary by a great extent from different configuration of active metals (Pd in this case) and metal clusters appear to possess high CH4 selectivity. Upon the increase of temperature, there is a small amount CH4 and CO generated by NP-Rh and meso-Rh, respectively (Figure 3c-d). These results indicate that large number of atomic steps meso-Rh sample not only dramatically influence its catalytic

Figure 1. (a) Low-magnification and (b) high-magnification SEM images, (c) TEM, (d) HAADF-STEM images, (e) SAXS profile (the observed d value indicates the pore-to-pore distance) and (f) wideangle XRD pattern of the as-prepared meso-Rh.

particles size was estimated to be about 93 nm (Figure S1). Moreover, we found that numerous pores (which size was approximately 10 nm) were formed throughout the nanoparticles, which can be found in the focused high-resolution SEM and TEM images (Figure 1b, c). The high-magnification SEM images of Rh mesostructured shows nanoparticles were interconnected (Figure S2). These mesoporous structures are further clarified by the contrast in HAADF-STEM image (Figure 1d). From the small-angle X-ray scattering (SAXS) profile, we obtained one peak at around 0.216 nm−1, indicating the pore-to-pore diameter is 29 nm (Figure 1e). It means the estimated wall thickness is 19 nm, by adopting the assumed pore diameter. The crystal structure was studied by wide-angle X-ray diffraction (XRD) and the patterns revealed five remarkable peaks of pure face-centered cubic ( fcc) Rh structure, which can be attributed to (111), (200), (220), (311), and (222), respectively, whose crystal planes are in accordance with JCPDS No. 05−0685 (Figure 1f). The average crystallite sizes (D) of all the Rh catalysts were estimated using the Debye−Scherrer equation and it was calculated to be about 4.8 nm. For further investigation on atomic state of meso-Rh sample, high-resolution TEM (HRTEM) and selected area electron diffraction (SAED) were taken into the discussion (Figure 2 and Figure S3). It was indicated that the surface was composed of countless pores and branched frameworks, which could generate a number of low-coordinated atoms (Figure 2a−c). Besides, at the edges of meso-Rh, we could see the atomic array clearly with a large amount of atomic steps, as highlighted by the arrows in Figure 2b. The lattice parameter was 0.2 nm, which is in accordance with pure fcc Rh (111) facet. Moreover, the multiple bright electron diffraction rings in the SAED patterns from Figure 2c showed the feature of fcc Rh structure C

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Figure 3. Catalytic performance toward CO2 reduction over NP-Rh and meso-Rh (a) CO2 conversion, (b) reaction rate, (c, d) selectivity of NP-Rh and meso-Rh, respectively.

CO2 reduction, which derives from high porosity and large number of atomic steps, in conjunction with abundant lowcoordination atoms. The meso-Rh sample, possessing the largest ECSA (69 m2 g−1), exhibits a substantially higher reaction rate (5.28 × 10−5 molCO2 gRh−1 s−1) than the NP-Rh (1.28 × 10−5 molCO2 gRh−1 s−1). These results suggest the presence of a large number of atomic steps on the catalyst that assists the adsorption and activation of reactants and as such, is one of the most critical factors influencing the catalytic activity for the CO2 reduction reaction. The work will be of interest to energy-based catalysis researchers in general and contributes to understanding the structural influence of mesoporous materials. As there is enormous interest in heterogeneous catalysis, the unique mesoporous configuration together with its uniform pore sizes may be a powerful tool for fundamental and applied studies in the synthesis strategies.

activity, but also tune the selectivity toward CH4 other than generating CO like NP-Rh. The reaction rate at different reaction temperatures was normalized by the total catalyst molar weight of meso-Rh and NP-Rh, respectively. It is apparent from Figure 3b that the reaction rate for CO2 conversion at 450 °C increases by a factor of about 4, from 1.28 × 10−5 to 5.28 × 10−5 molCO2 gRh−1 s−1, when going from the NP-Rh to the meso-Rh catalyst, possessing the ECSA 8 and 69 m2 g−1, respectively. The increased reaction rate exhibited by the meso-Rh can be attributed to its elevated presence of atomic steps where the CO2 can adsorb at these sites and subsequently react with hydrogen to produce methane. This result is comparable with previously reported results, for examples reaction rate of 5 × 10−6 molCO2 gRu−1 s−1 for Ru/TiO2,19 2.5 × 10−6 molCO2 gPtCo−1 s−1 for PtCo/ BaZrO321 and 7.5 × 10−5 molCO2 gRu−1 s−1 for Ru/γ-TiO2.22 A comparison on CO2 reduction over numerous Rh and Ru based heterogeneous catalysts were summarized in Table S1. Obviously, the catalytic activity over meso-Rh catalyst was as good as that over precious metal catalysts, in which the former showed the high catalytic performance reported so far. In summary, we successfully fabricated mesoporous Rh nanoparticle catalysts with interconnected mesostructure by a wet chemical reduction process to convert CO2 directly to CH4 (closing the loop of carbon recycling). We found that the nature of the block polymer (PEO(10500)-b-PMMA(18000)) governed the formation of mesopores in the Rh nanoparticles. In this study, we detailed a design and preparation strategy for a mesoporous Rh catalyst, providing a highly active catalyst for

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EXPERIMENTAL SECTION

Characterization. The scanning electron microscope (SEM, HITACHI SU8000) was used to study the structure of the catalysts at the accelerating voltage of 10 kV. We also utilized JEOL JEM2100F for further investigation on structure by taking TEM, HRTEM, and HAADF-STEM images at the accelerating voltage of 200 kV. Wide-angle XRD patterns of the samples were recorded by a RIGAKU Smart lab diffractometer at the scanning rate of 2 deg min−1 with Cu Kα radiation (λ = 0.15406 nm, 40 kV, 30 mA) in the range from 20 to 90° (2θ). For the purpose of understanding pore-to-pore diameter, SAXS profiles were obtained by RIGAKU NANO-Viewer using Cu Kα radiation (40 kV, 30 mA) with a camera length of 700 nm. D

DOI: 10.1021/acsami.8b06977 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces Electrochemical Active Surface Area (ECSA). The ECSA of meso-Rh and NP-Rh were determined by electrochemical oxidation of preadsorbed CO, so-called CO stripping, which is common way, especially for Rh samples. All electrochemical experiments were conducted by CHI 842B electrochemical analyzer (CHI Instrument, USA) with conventional three-electrode cell consisted with Pt wire counter electrode, glassy carbon electrode (GCE) as a working electrode, and Ag/AgCl (3 M NaCl) as reference electrode. The working electrode was prepared by polishing the surface of GCE with 1 μm diamond and 0.05 μm alumina in sequence. Then, 10 μg (5 μL) of the samples were deposited on the surface from 1 mL of the suspension consisting 2 mg of the samples and dried at room temperature, followed by the final coating with 5 μL of Nafion (0.05 wt %). Before carrying out CO stripping, this modified GCE was electrochemically activated by a potential cycling between −0.3 and 1.0 V (vs Ag/AgCl) in 0.5 M H2SO4 at the scan rate of 0.05 V s−1 for 20 cycles. CO was adsorbed on the GCE by using 30 mL min−1 CO gas flow for 20 min in the N2-purged 0.5 M H2SO4 solution, and this solution was purged by nitrogen gas for 20 min again to remove the extra carbon monoxide gas dissolved in the solution. After all pretreatment finished, cyclic voltammogram (CV) was collected in the range of 0−1.0 at 0.05 V s−1 scan rate. According to the results of this obtained CO oxidation peaks, we calculated ECSA of both mesoRh and NP-Rh by the following equation. ECSA[m 2/g] =

Q [AV] 100 V [V/s]Q 0[μC/cm 2]g[g]

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selectivity of CH4[%] =

[CO2 ]out

*E-mail: [email protected] (H.A.). *E-mail: [email protected] (H.D.). *E-mail: [email protected] (Y.Y.). ORCID

Hamidreza Arandiyan: 0000-0001-5633-3945 Jeonghun Kim: 0000-0001-6325-0507 Hongxing Dai: 0000-0003-1738-0348 Yusuke Yamauchi: 0000-0001-7854-927X Author Contributions ▼

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the Australian Research Council (ARC) Future Fellow (grant FT150100479), Discovery Project (grant DP170104853), Research Fellowship (grant no. L0915/U2403) from The University of Sydney, JSPS KAKENHI (grants 17H05393 and 17K19044), Strategic Core Technology Advancement Program from METI-Kanto, Industry-Academia Collaborative Development Project from Saitama Prefecture, and the research fund from the Suzuken Memorial Foundation. The authors sincerely thank New Innovative Technology (NIT) and Yoshino Denka Kogyo Inc. for valuable suggestions and instructions on materials preparation.

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REFERENCES

(1) Wang, Y.; Arandiyan, H.; Scott, J.; Bagheri, A.; Dai, H.; Amal, R. Recent Advances in Ordered Meso/Macroporous Metal Oxides for Heterogeneous Catalysis: a review. J. Mater. Chem. A 2017, 5, 8825− 8846. (2) Chen, J.; Arandiyan, H.; Gao, X.; Li, J. Recent Advances in Catalysts for Methane Combustion. Catal. Surv. Asia 2015, 19, 140− 171. (3) Wang, Y.; Arandiyan, H.; Tahini, H. A.; Scott, J.; Tan, X.; Dai, H.; Gale, J. D.; Rohl, A. L.; Smith, S. C.; Amal, R. The Controlled Disassembly of Mesostructured Perovskites as an Avenue to Fabricating High Performance Nanohybrid Catalysts. Nat. Commun. 2017, 8, 15553. (4) Diercks, C. S.; Liu, Y.; Cordova, K. E.; Yaghi, O. M. The Role of Reticular Chemistry in the Design of CO2 Reduction Catalysts. Nat. Mater. 2018, 17, 301−307. (5) Karelovic, A.; Ruiz, P. Improving the Hydrogenation Function of Pd/γ-Al2O3 Catalyst by Rh/γ-Al2O3 Addition in CO2 Methanation at Low Temperature. ACS Catal. 2013, 3, 2799−2812. (6) Arandiyan, H.; Chang, H.; Liu, C.; Peng, Y.; Li, J. DextroseAided Hydrothermal Preparation with Large Surface Area on 1D Single-Crystalline Perovskite La0.5Sr0.5CoO3 Nanowires Without Template: Highly Catalytic Activity for Methane Combustion. J. Mol. Catal. A: Chem. 2013, 378, 299−306. (7) Arandiyan, H.; Dai, H.; Deng, J.; Wang, Y.; Xie, S.; Li, J. DualTemplating Synthesis of Three-Dimensionally Ordered Macroporous La0.6Sr0.4MnO3-Supported Ag Nanoparticles: Controllable Alignments and Super Performance for the Catalytic Combustion of Methane. Chem. Commun. 2013, 49, 10748−10750. (8) Arandiyan, H.; Wang, Y.; Sun, H.; Rezaei, M.; Dai, H. Ordered Meso- and Macroporous Perovskite Oxide Catalysts for Emerging Applications. Chem. Commun. 2018, 54, 6484−6502.

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[CH4]out 100[%] + [CH4]out + [CO]out (3)

where [CO2]in and [CO2]out are the inlet and outlet flow rate normalized by peak area of CO2, respectively; [N2]in and [N2]out are the inlet and outlet flow rate normalized by peak area of N2, respectively; [CH4]out and [CO]out are the flow rate normalized by peak area of CH4 and CO outlets, respectively.

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AUTHOR INFORMATION

Corresponding Authors

Here, Q is the integrated peak area, V is the scan rate, Q0 is the assumed charge density for electrochemical oxidation of monolayer CO adsorbed on Rh catalysts (442 μC cm−2),23 and g is the mass of Rh loaded on GCE. Catalytic Activity Measurements. The activity of the samples for CO2 methanation was measured in a fixed-bed quartz tubular microreactor (i.d. = 6.0 mm) at ambient pressure. Before the activity test, the sample (10 mg) was activated in gas flow of H2 (25 mL/min) and N2 (13 mL/min) at 450 °C for 2 h and followed by purging with 30 mL/min N2 during the cooling down process to 150 °C (Figure S6). After the catalyst pretreatment, the reaction gas with a total flow rate of 40 mL/min (5% CO2:20% H2:75% N2) flew into the reactor. The gas hourly space velocity (GHSV) in this condition is calculated as ca. 48 000 mL g−1 h−1. The CO2 conversion was measured over an elevated temperature range of 150−550 °C with a gas chromatograph (GC, Young Lin 6100) equipped with a helium ionization detector (HID) and a Carboxen-1010 PLOT column. The conversion of CO2 and selectivity of CH4 were calculated using the following formulas: conversion of CO2 [%] [CO2]in /[N2]in − [CO2]out /[N2]out = 100[%] [CO2]out /[N2]in

catalyst, CO stripping measurement, and catalytic activity evaluation (PDF)

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b06977. Catalyst characterization procedures, electrochemical active surface area, particle size distribution, HRSEM images of meso-Rh catalyst, HRTEM images of meso-Rh E

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ACS Applied Materials & Interfaces (9) Malgras, V.; Ji, Q.; Kamachi, Y.; Mori, T.; Shieh, F.-K.; Wu, K. C.-W.; Ariga, K.; Yamauchi, Y. Templated Synthesis for Nanoarchitectured Porous Materials. Bull. Chem. Soc. Jpn. 2015, 88, 1171− 1200. (10) Malgras, V.; Ataee-Esfahani, H.; Wang, H.; Jiang, B.; Li, C.; Wu, K. C.-W.; Kim, J. H.; Yamauchi, Y. Nanoarchitectures for Mesoporous Metals. Adv. Mater. 2016, 28, 993−1010. (11) Jiang, B.; Li, C.; Qian, H.; Hossain, M. S. A.; Malgras, V.; Yamauchi, Y. Layer-by-Layer Motif Architectures: Programmed Electrochemical Syntheses of Multilayer Mesoporous Metallic Films with Uniformly Sized Pores. Angew. Chem., Int. Ed. 2017, 56, 7836− 7841. (12) Jiang, B.; Li, C.; Tang, J.; Takei, T.; Kim, J. H.; Ide, Y.; Henzie, J.; Tominaka, S.; Yamauchi, Y. Tunable-Sized Polymeric Micelles and Their Assembly for the Preparation of Large Mesoporous Platinum Nanoparticles. Angew. Chem., Int. Ed. 2016, 55, 10037−10041. (13) Sun, T.; Xu, L.; Yan, Y.; Zakhidov, A. A.; Baughman, R. H.; Chen, J. Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation. ACS Catal. 2016, 6, 1446− 1450. (14) Yu, N.-F.; Tian, N.; Zhou, Z.-Y.; Huang, L.; Xiao, J.; Wen, Y.H.; Sun, S.-G. Electrochemical Synthesis of Tetrahexahedral Rhodium Nanocrystals with Extraordinarily High Surface Energy and High Electrocatalytic Activity. Angew. Chem., Int. Ed. 2014, 53, 5097−5101. (15) Duan, H.; Yan, N.; Yu, R.; Chang, C.-R.; Zhou, G.; Hu, H.-S.; Rong, H.; Niu, Z.; Mao, J.; Asakura, H.; Tanaka, T.; Dyson, P. J.; Li, J.; Li, Y. Ultrathin Rhodium Nanosheets. Nat. Commun. 2014, 5, 3093. (16) Zhao, L.; Xu, C.; Su, H.; Liang, J.; Lin, S.; Gu, L.; Wang, X.; Chen, M.; Zheng, N. Single-Crystalline Rhodium Nanosheets with Atomic Thickness. Adv. Sci. 2015, 2, 1500100. (17) Jiang, B.; Li, C.; Dag, Ö .; Abe, H.; Takei, T.; Imai, T.; Hossain, M. S. A.; Islam, M. T.; Wood, K.; Henzie, J.; Yamauchi, Y. Mesoporous Metallic Rhodium Nanoparticles. Nat. Commun. 2017, 8, 15581. (18) Wen, Y.-N.; Zhang, J.-M. Surface Energy Calculation of the fcc Metals by Using the MAEAM. Solid State Commun. 2007, 144, 163− 167. (19) Abdel-Mageed, A. M.; Widmann, D.; Olesen, S. E.; Chorkendorff, I.; Biskupek, J.; Behm, R. J. Selective CO Methanation on Ru/TiO2 Catalysts: Role and Influence of Metal-Support Interactions. ACS Catal. 2015, 5, 6753−6763. (20) Kwak, J. H.; Kovarik, L.; Szanyi, J. Heterogeneous Catalysis on Atomically Dispersed Supported Metals: CO2 Reduction on Multifunctional Pd Catalysts. ACS Catal. 2013, 3, 2094−2100. (21) Shin, H. H.; Lu, L.; Yang, Z.; Kiely, C. J.; McIntosh, S. Cobalt Catalysts Decorated with Platinum Atoms Supported on Barium Zirconate Provide Enhanced Activity and Selectivity for CO 2 Methanation. ACS Catal. 2016, 6, 2811−2818. (22) Xu, J.; Su, X.; Duan, H.; Hou, B.; Lin, Q.; Liu, X.; Pan, X.; Pei, G.; Geng, H.; Huang, Y.; Zhang, T. Influence of Pretreatment Temperature on Catalytic Performance of Rutile TiO2-Supported Ruthenium Catalyst in CO2 Methanation. J. Catal. 2016, 333, 227− 237. (23) Calderón-Cárdenas, A.; Ortiz-Restrepo, J. E.; MancillaValencia, N. D.; Torres-Rodriguez, G. A.; Lima, F. H. B.; BolañosRivera, A.; Gonzalez, E. R.; Lizcano-Valbuena, W. H. CO and Ethanol Electro-Oxidation on Pt-Rh/C. J. Braz. Chem. Soc. 2014, 25, 1391− 1398.

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DOI: 10.1021/acsami.8b06977 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX