Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient

Jan 28, 2016 - Gao, Sheng, Zhuang, Fang, Gu, Jiang, and Yan. 2014 136 (19), pp 7077–7084. Abstract: Electrochemical water splitting is a clean techn...
0 downloads 0 Views 3MB Size
Download PDF
Subscriber access provided by George Washington University Libraries

Letter

Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation Tingting Sun, Lianbin Xu, Yushan Yan, Anvar A. Zakhidov, Ray H. Baughman, and Jianfeng Chen ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.5b02571 • Publication Date (Web): 28 Jan 2016 Downloaded from http://pubs.acs.org on January 30, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Ordered Mesoporous Nickel Sphere Arrays for Highly Efficient Electrocatalytic Water Oxidation Tingting Sun,† Lianbin Xu,*,† Yushan Yan,‡ Anvar A. Zakhidov,§,║ Ray H. Baughman,§ and Jianfeng Chen† †

State Key Laboratory of Organic-Inorganic Composites, Beijing University of Chemical Technology, Beijing 100029, China ‡ Department of Chemical and Biomolecular Engineering, University of Delaware, Newark, Delaware 19716, United States § The Alan G. MacDiarmid NanoTech Institute, University of Texas at Dallas, Richardson, Texas 75083, United States ║ Energy Efficiency Center, National University of Science and Technology, MISiS, Moscow 119049, Russia KEYWORDS: ordered mesoporous Ni spheres, templating, electrocatalyst, oxygen evolution reaction, durability ABSTRACT: We report the preparation and use of the three-dimensionally ordered mesoporous Ni sphere arrays (3D-OMNiSA) as a highly effective OER catalyst in alkaline electrolyte. The 3D-OMNiSA is fabricated through lyotropic liquid crystal templating within a polymer inverse opal. The prepared 3D-OMNiSA catalyst exhibits a low overpotential of 254 mV at 10 mA cm−2, and a small Tafel slope of 39 mV decade-1, better than the commercial precious RuO2 catalyst. The mass activity (166.5 A g−1) and turnover frequency (0.0281 s−1) of 3D-OMNiSA is about 4.3 and 2.2 times that of RuO2, respectively. Additionally, this 3DOMNiSA catalyst shows a high durability under harsh water oxidation cycling test. The outstanding OER performance of the 3DOMNiSA could be attributed to the large surface area, efficient mass and charge transport, and high structural stability arising from the unique 3D hierarchical porous structure of the 3D-OMNiSA consisting of ordered close-packed mesoporous spheres.

To meet rapidly increasing global energy demand, considerable interest has been stimulated in efficient energy conversion and storage systems.1-3 As the efficiency-limiting process for many key renewable-energy technologies, such as water splitting devices, metal–air batteries, and fuel cells, oxygen evolution reaction (OER) during electrocatalytic water oxidation has been intensely researched in recent years.4-6 Compared to the reduction half-reaction, the OER is kinetically sluggish and imposes serious overpotential requirement.7,8 Hence, an optimal electrode involving effective electrocatalyst is essential to expedite the reaction and reduce the large overpotential, thereby improving energy conversion efficiency.9,10 So far, RuO2 and IrO2 are identified as the most active and durable OER electrocatalysts in both acidic and alkaline solutions,11,12 but their widespread use is greatly hindered by their high cost and element scarcity. Therefore, extensive efforts have been devoted to developing OER electrocatalysts based on the nonprecious transition metals.13-16 Among these electrocatalysts, Ni metal and Ni-based alloys are of particular interest due to their earth-abundance, low cost, environmental benignity, relatively high catalytic activity and good corrosion resistance in alkaline water oxidation.17-20 To achieve better catalytic performances of the Ni-based electrocatalysts, various strategies have been developed. Two of the most common ones include nanostructuring the catalysts to increase the catalytically active surface areas21 and making porous structures of the catalysts to enhance mass transport and improve electrical and mechanical properties.22 Mesoporous metals are of special interest in electrocatalysis because of their combination of large specific surface area,

periodic pore structure and high electrical conductivity.23 Specifically, mesoporous Ni is promising for use as a highly active electrode material in alkaline water electrolysis, since it could provide large surface area for high exposure of catalytically active sites and uniform mesopores for ion diffusion.24 Compared with previously reported bulk mesoporous Ni powders, mesoporous Ni spheres are expected to more effectively enhance electrolyte accessibility because of their high surfaceto-volume ratio.25,26 The organization of monodispersed mesoporous Ni spheres into a three-dimensionally (3D) ordered close-packed array structure would offer the important advantage of ready integration into electrochemical applications. The 3D ordered mesporous Ni spheres arrays (3D-OMNiSA) contain hierarchically interconnected macropores (the voids between the close-packed spheres) and mesopores. The mesopores can improve electrocatalytic performance by providing high electrochemically active surface areas and the macropores can enable efficient transport of reactants and products (e.g., OH− and O2 in the case of OER) to the catalytic sites in the mesopores.27,28 In addition, the high packing density of microspheres enables formation of a compact electrode combining exceptional electrical conductivity and mechanical properties, thereby avoiding use of extra catalyst supports and conductive additives.29 However, due to the difficulty in obtaining highly uniform and monodisperse mesoporous metal spheres, it remains challenging to fabricate 3D ordered mesoporous metal sphere arrays through traditional colloidal crystal self-assembly methods. In this work, we first synthesize 3D ordered mesoporous Ni sphere arrays (3D-OMNiSA) by using a poly(methyl meth-

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

acrylate) (PMMA) inverse opal molded from silica opal (colloidal crystal) as a hard template and the lyotropic liquid crystals (LLC) of the nonionic surfactant Brij 58 (C16H33(OCH2CH2)20OH) as the meso-structural template, removing the necessity of using hard-to-obtain uniform mesoporous Ni spheres. The electrocatalytic OER properties of the prepared 3D-OMNiSA are investigated in an alkaline electrolyte. Scheme 1 briefly describes the fabrication procedure of 3DOMNiSA. Opal consisting of 3D ordered silica spheres was used as the initial template to synthesize PMMA inverse opal by chemical polymerization of methyl methacrylate (MMA) monomer inside the opal and then removal of the opal template using a dilute HF solution. After that, a high concentration aqueous precursor solution containing nonionic surfactant (Brij 58, C16H33(OCH2CH2)20OH) and Ni source (NiCl2·6H2O) was infiltrated into the pores of the PMMA inverse opal. The surfactant molecules self-assembled to form the LLC, thereby filling the void space of the PMMA inverse opal with LLC containing Ni2+ ions. Subsequent chemical reduction of Ni2+ ions by dimethylamine borane (DMAB) to deposit Ni and then removal of the templates (PMMA inverse opal and Brij 58) produced the 3D periodic mesoporous Ni spheres (for more details, see the Supporting Information).

Page 2 of 6

range of 3–5 nm, which is similar to those of several other independently prepared batches of 3D-OMNiSA samples (Figure S2), indicating a good reproducibility of the material synthesis. The average diameter of Ni particles is about 4 nm, which is much smaller than that of the Ni nanoparticles (NPs) (~10 nm, Figure S3) used for comparative studies of catalytic performance.

Scheme 1. Schematic of the Preparation of the 3D Ordered Mesoporous Ni Sphere Arrays (3D-OMNiSA) Figure 1. SEM images of (a) PMMA inverse opal and (b) 3DOMNiSA. Inset: at a higher magnification. (c) TEM image of 3DOMNiSA. (d) Higher magnification TEM image of one of the mesoporous Ni spheres.

A scanning electron microscopy (SEM) image of the PMMA inverse opal (Figure 1a) reveals a uniform macroporous structure, wherein the size of the macropores is around 290 nm, very similar to that of the original silica spheres (Figure S1). Since the macropores in the PMMA inverse opal are interconnected, the PMMA inverse opal allows the precursor solution to diffuse through the porous network and fill the pores in the PMMA inverse opal. Figure 1b shows the SEM images of the 3D-OMNiSA. The 3D-OMNiSA inherits the spherical shape and ordered close-packed facecentered cubic (fcc) structure of the original silica opal architecture. The diameter of the mesoporous Ni spheres is observed to be ~290 nm, which well matches the macropore size of the PMMA inverse opal, indicating that the LLC densely fills the pores in the PMMA inverse opal and the Ni spheres do not contract during removal of the PMMA template. Further insight into the structural characterizations of the 3DOMNiSA was gained using transmission electron microscopy (TEM). Figure 1c shows a typical TEM image of the mesoporous Ni spheres. The higher magnification TEM image of one of the spheres (Figure 1d) provides clear indication of a welldefined mesoporous structure. The mesopore size is in the

The nitrogen adsorption-desorption isotherm of the 3DOMNiSA is shown in Figure S4. The isotherm can be classified as type IV, typical for mesoporous materials according to the IUPAC classification.30 The Brunauer–Emmett–Teller (BET) surface area and total pore volume of the 3D-OMNiSA are 108 m2 g-1 and 0.24 cm3 g−1, respectively. The pore size distribution of the 3D-OMNiSA shown in the inset of Figure S4 was calculated by the Barrett–Joyner–Halenda (BJH) method applying the desorption branch of the isotherm. The average pore diameter is 3.9 nm, and the mesopore size distribution is in a narrow range of 3–5 nm, implying substantial homogeneity of the mesopores for the Ni spheres. The BJH derived pore size distribution is consistent with the TEM observation. Inductively coupled plasma-atomic emission spectrometry (ICP) analysis demonstrated that the 3D-OMNiSA and Ni NPs contain ~6 wt% boron, which originated from the DMAB reducing agent used to produce Ni. In the wide-angle XRD patterns of the Ni samples (Figure S5a), both show a broad peak at around 2θ = 45° and a weak hump ranging from 70° to 90°, indicating that the incorporation of the B phase in 3D-OMNiSA and Ni NPs results in an amorphous-like state.31,32 The observed other two small peaks centered at 33.7° and 59.8° match the (101) and (110) reflections of Ni(OH)2 (JCPDS card, No. 38-715), respectively, suggesting that the surface Ni was partially oxidized to Ni(OH)2, consistent with the previous reports for metallic Ni-based materials.33,34 A small-angle XRD (SAXRD) pattern of the 3D-OMNiSA is shown in Figure S5b, which exhibits a peak at around 2θ =

ACS Paragon Plus Environment

Page 3 of 6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

1.3° (d-spacing ~6.7 nm), indicative of the formation of ordered mesostructure in the 3D-OMNiSA. The electrocatalytic OER activities for the samples were investigated in O2-saturated 0.1 M KOH solution using a standard three-electrode system. Figure 2a shows the iR-corrected linear sweep voltammetry (LSV) curves of the different catalysts. The bare GC electrode exhibits negligible catalytic activity, while the oxygen-evolving current recorded on the 3DOMNiSA is much higher than that of the other catalysts. The 3D-OMNiSA exhibits an early onset potential of ~1.42 V vs. reversible hydrogen electrode (RHE), lower than that of the Ni NPs (~1.50 V), commercial Pt/C (~1.60 V), and the highly active RuO2 catalyst (~1.48 V), featuring much better catalytic performance of the 3D-OMNiSA.

Figure 2. (a) LSV curves for the OER on a bare glassy carbon (GC) electrode and modified GC electrodes comprising 3DOMNiSA, RuO2, Ni NPs, and Pt/C in an O2-saturated 0.1 M KOH solution (1600 rpm, scan rate: 5 mV s−1). (b) Tafel plots derived from (a) (error bars show standard deviations for five independent tests). (c) Nyquist plots of 3D-OMNiSA, RuO2, and Ni NPs, and Pt/C recorded at 1.70 V vs. RHE. Inset: the corresponding equivalent circuit used to fit the EIS data. (d) Theoretically calculated versus measured O2 production catalyzed by 3D-OMNiSA at different current densities in 0.1 M KOH. (e) Retention percentage of the catalytic current for 3D-OMNiSA, RuO2, Ni NPs, and Pt/C at the overpotential of 0.40 V vs. RHE. (f) LSVs of 3DOMNiSA initially and after every 100 CV sweeps between 0.10 and 1.90 V vs. RHE. All LSV and CV curves are iR-corrected.

The cyclic voltammogram (CV) of the 3D-OMNiSA (Figure S6) shows a pair of redox peaks between 1.1 and 1.4 V vs. RHE, corresponding to the Ni(OH)2/NiOOH transformation.35,36 The overpotential (η) required to deliver a current density of 10.0 mA cm−2 (a metric relevant to solar fuel synthesis)37 for the 3D-OMNiSA is merely 254 mV, which is much smaller than that of the RuO2 (~371 mV), Ni NPs (~404

mV), and commercial Pt/C (~554 mV). This excellent OER activity of 3D-OMNiSA is not only better than that of most of the high-activity Ni-based electrocatalysts, such as ultrasmall NiO nanoparticles,38 amorphous Fe6Ni10Ox,39 and 3D Ni-Co hydroxide nanotube arrays,40 and of the best reported Co3O4based catalysts, such as Au/mesoporous Co3O4,41 and Co3O4carbon porous nanowire arrays,42 but also superior to that of some reported noble metal catalysts,43,44 confirming the outstanding catalytic behavior of the 3D-OMNiSA. In addition, the catalytic kinetics for oxygen evolution was probed by Tafel plots (Figure 2b) derived from the LSV results. The 3DOMNiSA shows a Tafel slope of ~39 mV decade−1, which is much smaller than those of the other studied catalysts, even the RuO2 (~76 mV decade−1) (Table 1). This Tafel slope of 39 mV decade−1 is also smaller than or comparable to those reported for the other highly active OER catalysts in the literature (Table S2), demonstrating the outstanding OER kinetics of the 3D-OMNiSA. The electrochemical impedance spectroscopy (EIS) technique was applied to further examine the electrode kinetics under OER operating conditions. The Nyquist plots (Figure 2c) reveal that the 3D-OMNiSA has much lower charge transfer resistance Rct (the diameter of the semicircle) than that of RuO2, Ni NPs and Pt/C, indicating the higher charge transport efficiency of the 3D-OMNiSA. Figure 2d compares the amounts of O2 experimentally measured and theoretically calculated, and the good match of the experimental and theoretical values indicates that the Faradaic efficiency (FE) during OER is close to 100% for the 3D-OMNiSA in different current densities (Figure S8 gives an optical image showing the formation of O2 bubbles during the FE test). At a η of 0.35 V, the 3D-OMNiSA catalyst exhibits the highest mass activity of 166.5 A g−1, which is ~4.3 and 5.7 times that of RuO2 and Ni NPs, respectively (Table 1). This mass activity (166.5 A g−1) also outperforms that of the reported high-performance αNi(OH)245 (150.1 A g−1) and perovskite SrNb0.1Co0.7Fe0.2O3- δ46 (~93.2 A g−1) catalysts. Based on the BET surface area (Figure S4 and S9), the 3D-OMNiSA gives a specific activity of 0.16 mA cm−2 at η = 0.35 V, slightly lower than that of RuO2 (0.24 mA cm−2), but higher than that of Ni NPs (0.06 mA cm−2). The turnover frequency (TOF, defined as the number of O2 molecules evolved per second per metal site) was employed to evaluate the intrinsic activities of catalysts.45 The TOF of the 3D-OMNiSA was calculated to be ~0.0281 s−1 at a η of 0.35 V by assuming that every metal atom is catalytically active. This value is ~2.2, 6.4, and 5.0 times as high as that of the RuO2, Ni NPs, and Pt/C catalysts, respectively (Table 1). The outstanding OER activity of the 3D-OMNiSA may be related to its unique 3D hierarchical porous structure. First, the ordered mesopores with high BET surface area provide more catalytically active sites for the HER.47 Second, the 3D ordered interconnected macropores and mesopores can facilitate the access of reactants (e.g., OH−) to the active sites, as well as promote the release and diffusion of product molecules (e.g., O2), leading to the improved utilization efficiency of the active areas.42,48 Third, the hierarchical porous channels can favor fast ion and electron transport through the whole electrode matrix, and thus increase conductivity, giving rise to the enhanced electrochemical kinetics.49 Durability is also of great significance for the practical utilization of an electrocatalyst. The chronoamperomograms (Figure 2e and Figure S10) reveal the high stability of the 3D-

ACS Paragon Plus Environment

ACS Catalysis

Page 4 of 6

Table 1. Comparison of OER Activity Data for Different Catalysts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

overpotential at 10 mA cm-2 ( mV vs. RHE )

Tafel slope (mV decade-1)

mass activity at η = 0.35 V (A g-1)

specific activity at η = 0.35 V (mA cm−2)a

TOF at η = 0.35 V (s-1)b

3D-OMNiSA

254

39

166.5

0.16

0.0281

45.5

RuO2

371

76

38.5

0.24

0.0128

124.2

Ni NPs

404

84

29.1

0.06

0.0044

209.4

catalyst

Rct at 1.70 V (Ω)

20 wt% Pt/C 554 129 9.2 0.0056 884.0 a b The data were calculated based on the BET surface area (see Figure S4 and S9). See experimental section in Supporting Information for the calculation method.

OMNiSA, which shows little performance attenuation (4.9%) in 10 h, in contrast to a much sharper activity loss of other studied catalysts. Further, negligible anodic current loss was observed for the 3D-OMNiSA after 1000 continuous potential cycles at an accelerated scanning rate of 100 mV s−1 (Figure 2f), confirming that the catalyst is also highly stable to withstand accelerated degradation testing. For comparison, similar accelerated CV measurements for other catalysts were also performed (Figures S11b-d), and all exhibit much poorer catalyst stability. The excellent durability could be attributed to the scarcely noticeable mechanical deformation and swelling of the 3D close-packed spherical materials, as revealed in Figure S12a and b, which show that the morphology and porous structure of the 3D-OMNiSA are well maintained. In sharp contrast, such continuous potential cycling causes significant migration, particle aggregation, and detachment of the nanoparticulate catalysts for RuO2, Ni NPs, and Pt/C, leading to the loss of the OER activities (Figures S12c-h). The superior longterm durability of the 3D-OMNiSA catalyst implies the great potential of implementing this new catalyst into a realistic oxygen evolution electrode.

Figure 3. (a) Ni 2p, and (b) O 1s XPS spectra of 3D-OMNiSA before and after chronoamperometric stability test.

The surface composition and chemical state of the 3DOMNiSA before and after the chronoamperometric stability test were determined by the X-ray photoelectron spectroscopy (XPS) analysis. The XPS spectra show the presence of Ni, O, and B elements on the surface of 3D-OMNiSA (Figure S13), in agreement with the XRD analysis. The XPS derived surface composition percentages (at. %) before and after the stability test are summarized in Table S1. Before electrolysis, the Ni:O atomic ratio is 21.82:32.62, indicating that the nickel-oxygen species are enriched on 3D-OMNiSA surface. After OER catalysis for 10 h, the Ni:O atomic ratio is observed to be 16.43:39.14, suggesting the thickness of surface oxide layer increased after the electrochemical oxidation. It needs to be mentioned that the possible existence of trace amount of Fe impurity in KOH electrolyte could also affect the OER per-

formance of the Ni-based catalysts,13,16 although no Fe peak is visible in the XPS spectra (Figure S13). The high-resolution Ni 2p spectra (Figure 3a) of 3D-OMNiSA show two main signals corresponding to Ni 2p3/2 (855.6) and Ni 2p1/2 (873.2 eV), respectively, and two intense shake-up satellite peaks (at ca. 861.2 and 879.7 eV), indicating that the oxidized Ni species are predominantly present in Ni2+ cations.50-52 The peak at 852.7 eV is assigned to Ni0 species.53 After OER, the peak for Ni0 disappeared, suggesting that the surface metallic Ni has been oxidized after water electrolysis. The high-resolution O 1s region of 3D-OMNiSA catalyst can be deconvoluted into three components, including Ni(OH)2, NiOOH and absorbed H2O (Figure 3b).51 The enhanced peak intensity at around 532.2 eV after stability test could be associated with the conversion of Ni(OH)2 to NiOOH on the 3D-OMNiSA surface in the OER. Noting that the XPS preferentially detects the surface chemical species, these results demonstrate the great possibility of forming a core-shell structure where an amorphous Ni core is coated by a hydrated Ni oxide shell.54 In summary, 3D ordered mesoporous Ni sphere arrays (3DOMNiSA) have been successfully synthesized by a two-step replication approach. The prepared 3D-OMNiSA catalyst shows higher OER activity, more favorable kinetics, and higher durability than Ni nanoparticles and the state-of-the-art RuO2 catalyst. The outstanding electrocatalytic OER performance of the 3D-OMNiSA may be attributed to its unique 3D hierarchical interconnected porous structure comprised of ordered close-packed mesoporous spheres, which contributes to the enlarged surface area, high structural stability, and improved mass/charge transport. The distinct features of the 3DOMNiSA render it a promising electrocatalyst for water oxidation. Also, it is expected that the present method could be readily extended to fabricate other metals (e.g. Co, Pt, and Pd) or alloys (e.g. Ni-Co, Ni-Fe, and Pt-Ni alloys) with similar ordered mesoporous spherical structures, which may be of technological importance in various areas, such as fuel cells, batteries, catalysis, adsorption, and magnetics.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website. Experimental details, calculation methods of mass activity, specific activity, and TOF, Figures S1–S13, and Tables S1–S2 (PDF)

AUTHOR INFORMATION Corresponding Author

ACS Paragon Plus Environment

Page 5 of 6

ACS Catalysis

*E-mail: [email protected] (L.X.).

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (51172014), National 973 Program of China (2009CB219903), Open Project of the State Key Laboratory of Organic-Inorganic Composites (oic-201601003), and Ministry of Education and Science of the Russian Federation in the framework of Increase Competitiveness Program of NUST “MISiS” (К2-2015-014).

ABBREVIATIONS 3D-OMNiSA, ordered mesoporous nickel sphere arrays; RHE, reversible hydrogen electrode; OER, oxygen evolution reaction.

REFERENCES (1) Mai, L. Q.; Tian, X. C.; Xu, X.; Chang, L.; Xu, L. Chem. Rev. 2014, 114, 11828–11862. (2) Duan, J. J.; Chen, S.; Jaroniec, M.; Qiao, S. Z. ACS Catal. 2015, 5, 5207–5234. (3) Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Chem. Soc. Rev. 2015, 44, 2060–2086. (4) Friebel, D.; Louie, M. W.; Bajdich, M.; Sanwald, K. E.; Cai, Y.; Wise, A. M.; Cheng, M.-J.; Sokaras, D.; Weng, T.-C.; AlonsoMori, R.; Davis, R. C.; Bargar, J. R.; Nørskov, J. K.; Nilsson, A.; Bell, A. T. J. Am. Chem. Soc. 2015, 137, 1305–1313. (5) Takeguchi, T.; Yamanaka, T.; Takahashi, H.; Watanabe, H.; Kuroki, T.; Nakanishi, H.; Orikasa, Y.; Uchimoto, Y.; Takano, H.; Ohguri, N.; Matsuda, M.; Murota, T.; Uosaki, K.; Ueda, W. J. Am. Chem. Soc. 2013, 135, 11125–11130. (6) Ma, T. Y.; Ran, J. R.; Dai, S.; Jaroniec, M.; Qiao. S. Z. Angew. Chem. Int. Ed. 2015, 54, 4646–4650. (7) Katsounaros, I.; Cherevko, S.; Zeradjanin, A. R.; Mayrhofer, K. J. J. Angew. Chem. Int. Ed. 2014, 53, 102–121. (8) Trotochaud, L.; Ranney, J. K.; Williams, K. N.; Boettcher, S. W. J. Am. Chem. Soc. 2012, 134, 17253–17261. (9) Chen, S.; Duan, J. J.; Bian, P. J.; Tang, Y. H.; Zheng, R. K.; Qiao, S. Z. Adv. Energy Mater. 2015, 5, 1500936. (10) Chen, S.; Duan, J. J.; Jaroniec, M.; Qiao, S. Z. Adv. Mater. 2014, 26, 2925–2930. (11) Paoli, E. A.; Masini, F.; Frydendal, R.; Deiana, D.; Schlaup, C.; Malizia, M.; Hansen, T. W.; Horch, S.; Stephens, I. E. L.; Chorkendorff, I. Chem. Sci. 2015, 6, 190–196. (12) Antolini, E. ACS Catal. 2014, 4, 1426–1440. (13) Burke, M. S.; Kast, M. G.; Trotochaud, L.; Smith, A. M.; Boettcher, S. W. J. Am. Chem. Soc. 2015, 137, 3638–3648. (14) Landon, J.; Demeter, E.; Đnoğlu, N.; Keturakis, C.; Wachs, I. E.; Vasić, R.; Frenkel, A. I.; Kitchin, J. R. ACS Catal. 2012, 2, 1793– 1801. (15) Burke, M. S.; Zou, S. H.; Enman, L. J.; Kellon, J. E.; Gabor, C. A.; Pledger, E.; Boettcher, S. W. J. Phys. Chem. Lett. 2015, 6, 3737–3742. (16) Trotochaud, L.; Young, S. L.; Ranney, J. K.; Boettcher, S. W. J. Am. Chem. Soc. 2014, 136, 6744–6753. (17) Ledendecker, M.; Clavel, G.; Antonietti, M.; Shalom, M. Adv. Funct. Mater. 2015, 25, 393–399. (18) Wang, J.; Zhong, H. X.; Qin, Y. L.; Zhang, X. B. Angew. Chem. Int. Ed. 2013, 52, 5248–5253. (19) Chen, S.; Duan, J. J.; Ran, J. R.; Jaroniec, M.; Qiao, S. Z. Energy Environ. Sci. 2013, 6, 3693–3699. (20) Qiu, Y.; Xin, L.; Li, W. Z. Langmuir 2014, 30, 7893–7901. (21) Xu, K.; Chen, P. Z.; Li, X. L.; Tong, Y.; Ding, H.; Wu, X. J.; Chu, W. S.; Peng, Z. M.; Wu, C. Z.; Xie, Y. J. Am. Chem. Soc. 2015, 137, 4119–4125. (22) Lu, X. Y.; Zhao, C. Nat. Commun. 2015, 6, 6616.

(23) Linares, N.; Silvestre-Albero, A. M.; Serrano, E.; SilvestreAlbero, J.; García-Martínez, J. Chem. Soc. Rev. 2014, 43, 7681–7717. (24) Nelson, P. A.; Elliott, J. M.; Attard, G. S.; Owen, J. R. Chem. Mater. 2002, 14, 524–529. (25) Sun, Z. K.; Liu, Y.; Li, B.; Wei, J.; Wang, M. H.; Yue, Q.; Deng, Y. H.; Kaliaguine, S.; Zhao, D. Y. ACS Nano 2013, 7, 8706– 8714. (26) Li, Y. Q.; Bastakoti, B. P.; Malgras, V.; Li, C. L.; Tang, J.; Kim, J. H.; Yamauchi, Y. Angew. Chem. Int. Ed. 2015, 54, 11073– 11077. (27) Kim, O.-H.; Cho, Y.-H.; Kang, S. H.; Park, H.-Y.; Kim, M.; Lim, J. W.; Chung, D. Y.; Lee, M. J.; Choe, H.; Sung, Y.-E. Nat. Commun. 2013, 4, 2473. (28) Yuan, Z. Y.; Su, B. L. J. Mater. Chem. 2006, 16, 663–677. (29) Zhang, C. W.; Xu, L. B.; Shan, N. N.; Sun, T. T.; Chen, J. F.; Yan, Y. S. ACS Catal. 2014, 4, 1926–1930. (30) Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603–619. (31) Saito, T.; Sato, E.; Matsuoka, M.; Iwakura, C. J. Appl. Electrochem. 1998, 28, 559–563. (32) Tan, Y. Y.; Sun, D. B.; Yu, H. Y.; Yang, B.; Gong, Y.; Yan, S.; Chen, Z. J.; Cai, Q.; Wu, Z. H. CrystEngComm 2014, 16, 9657– 9668. (33) Sciortino, L.; Giannici, F.; Martorana, A.; Ruggirello, A. M.; Liveri, V. T.; Portale, G.; Casaletto, M. P.; Longo, A. J. Phys. Chem. C 2011, 115, 6360–6366. (34) Jiang, H.; Guo, Y.; Wang, T.; Zhu, P.-L.; Yu, S. H.; Yu, Y.; Fu, X.- Z.; Sun, R.; Wong, C.-P. RSC Adv. 2015, 5, 12931–12936. (35) Hu, C.-C.; Wu, Y.-R. Mater. Chem. Phys. 2003, 82, 588–596. (36) Batchellor, A. S.; Boettcher, S. W. ACS Catal. 2015, 5, 6680– 6689. (37) McCrory, C. C. L.; Jung, S.; Peters, J. C.; Jaramillo, T. F. J. Am. Chem. Soc. 2013, 135, 16977–16987. (38) Fominykh, K.; Feckl, J. M.; Sicklinger, J.; Döblinger, M.; Böcklein, S.; Ziegler, J.; Peter, L.; Rathousky, J.; Scheidt, E.-W.; Bein, T.; Fattakhova-Rohlfing, D. Adv. Funct. Mater. 2014, 24, 3123– 3129. (39) Kuai, L.; Geng, J.; Chen, C. Y.; Kan, E. J.; Liu, Y. D.; Wang, Q.; Geng, B. Y. Angew. Chem. Int. Ed. 2014, 53, 7547–7551. (40) Zhao, Z. L.; Wu, H. X.; He, H. L.; Xu, X. L.; Jin, Y. D. Adv. Funct. Mater. 2014, 24, 4698–4705. (41) Lu, X. Y.; Ng, Y. H.; Zhao, C. ChemSusChem 2014, 7, 82–86. (42) Ma, T. Y.; Dai, S.; Jaroniec, M.; Qiao, S. Z. J. Am. Chem. Soc. 2014, 136, 13925–13931. (43) Ortel, E.; Reier, T.; Strasser, P.; Kraehnert, R. Chem. Mater. 2011, 23, 3201–3209. (44) Lee, Y.; Suntivich, J.; May, K. J.; Perry, E. E.; Shao-Horn, Y. J. Phys. Chem. Lett. 2012, 3, 399–404. (45) Gao, M. R.; Sheng, W. C.; Zhuang, Z. B.; Fang, Q. R.; Gu, S.; Jiang, J.; Yan, Y. S. J. Am. Chem. Soc. 2014, 136, 7077–7084. (46) Zhu, Y. L.; Zhou, W.; Chen, Z.-G.; Chen, Y. B.; Su, C.; Tadé, M. O.; Shao, Z. P. Angew. Chem. Int. Ed. 2015, 54, 3897–3901. (47) Sun, T. T.; Zhang, C. W.; Chen, J. F.; Yan, Y. S.; Zakhidov, A. A.; Baughman, R. H.; Xu, L. B. J. Mater. Chem. A 2015, 3, 11367–11375. (48) Ma, T. Y.; Dai, S.; Jaroniec, M.; Qiao, S. Z. Angew. Chem. Int. Ed. 2014, 53, 7281–7285. (49) Xiao, J. W.; Yang, S. X.; Wan, L.; Xiao, F.; Wang, S. J. Power Sources 2014, 245, 1027–1034. (50) Yu, X. X.; Sun, Z. J.; Yan, Z. P.; Xiang, B.; Liu, X.; Du, P. W. J. Mater. Chem. A 2014, 2, 20823–20831. (51) Ratcliff, E. L.; Meyer, J.; Steirer, K. X.; Garcia, A.; Berry, J. J.; Ginley, D. S.; Olson, D. C.; Kahn, A.; Armstrong, N. R. Chem. Mater. 2011, 23, 4988–5000. (52) Biesinger, M. C.; Payne, B. P.; Lau, L. W. M.; Gerson, A.; Smart, R. S. C. Surf. Interface Anal. 2009, 41, 324–332. (53) Jeon, T.-Y.; Watanabe, M.; Miyatake, K. ACS Appl. Mater. Interfaces 2014, 6, 18445–18449. (54) Prieto, P.; Nistor, V.; Nouneh, K.; Oyama, M.; Abd-Lefdil, M.; Díaz, R. Appl. Surf. Sci. 2012, 258, 8807– 8813.

ACS Paragon Plus Environment

ACS Catalysis

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

TOC Graphic

ACS Paragon Plus Environment

Page 6 of 6