Ultrathin CoOOH Oxides Nanosheets Realizing Efficient Photocatalytic

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Ultrathin CoOOH Oxides Nanosheets Realizing Efficient Photocatalytic Hydrogen Evolution Shi He, Yuanyuan Huang, Junheng Huang, Wei Liu, Tao Yao, Shan Jiang, Fumin Tang, Jinkun Liu, Fengchun Hu, Zhiyun Pan, and Qinghua Liu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09442 • Publication Date (Web): 05 Nov 2015 Downloaded from http://pubs.acs.org on November 12, 2015

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The Journal of Physical Chemistry

Ultrathin CoOOH Oxides Nanosheets Realizing Efficient Photocatalytic Hydrogen Evolution Shi He†, Yuanyuan Huang†, Junheng Huang, Wei Liu, Tao Yao*, Shan Jiang, Fumin Tang, Jinkun Liu, Fengchun Hu, Zhiyun Pan, and Qinghua Liu* National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, People’s Republic of China †

These authors contributed equally to this work. *Email: [email protected]; [email protected] Abstract Producing H2 by means of direct photocatalytic water splitting using suspension system is highly desired in efficiently transforming solar energy to chemical energy. Here, using an ultrathin β-CoOOH nanosheet as photocatalyst suspended in aqueous Na2SO3 solution, we realize highly efficient and stable photocatalytic hydrogen evolution under visible light irradiation. The as-prepared ultrathin β-CoOOH nanosheets suspension can directly photocatalyze hydrogen evolution in a high rate of 1200 µmol/g/h and large quantum efficiencies of 10.7% at 380 nm, 6.9% at 420 nm, and 2.3% at 450 nm. X-ray photoelectron and X-ray absorption measurements reveal that the excellent hydrogen evolution activity of the β-CoOOH nanosheet is attributed to the surface low-coordinated Co catalytic site, which results in a strong hybridization of Co 3d states with the S p states of SO32+, and facilitates the electron transfer to reduce H+. The results may be helpful for designing and understanding two-dimensional oxyhydroxide-based photocatalyst for hydrogen production.

Keywords: Solar energy conversion; Suspension photocatalyst; β-CoOOH nanosheets; Surface low-coordinated catalytic site

1

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1. Introduction Transforming solar energy into chemical energy in the form of hydrogen represents a prospective solution for addressing both the energy crisis and the environmental contamination.1 To this end, the most attractive strategies to realize such technology is through direct photocatalytic water splitting using suspension system to produce hydrogen under light irradiation.2 Over the past several decades, considerable efforts have been paid to construct hydrogen evolution photocatalytic suspension systems based on the metal-ligand molecular photosensitizers such as [Ru(bpy)3]2+, Pt terpyridyl acetylide,

xanthene

dyes,

and

other

metal

complexes.3-5

Although

these

homogeneous-based photocatalysis systems are shown prominent hydrogen evolution performance, they quickly lose functionality due to the easy decomposition of the molecular sensitizers.6 Owing to abundant light absorption, relatively high stability, and good photocatalytic activity,2,7 semiconductor photocatalyst is a potential alternative way in converting sunlight into hydrogen applications.7-9 For a long time, the semiconducting photocatalysts for hydrogen evolution have been mostly focused on the p-type semiconductors such as sulfides and phosphides.10-12 Typically, using Zn0.8Cd0.2S as a photocatalyst, high hydrogen evolution rate of 1824 µmol/g/h quantum efficiency of 23.4% at 420 nm in aqueous Na2S/Na2SO3 solution have been achieved.13,14 Further, N-doped graphene/CdS nanocomposite has been synthesized to improve the efficiency, and a high hydrogen yield of about 1200 µmol/g/h under visible light irradiation has been realized.15 However, the main drawback of these p-type semiconductor materials is their easy photocorrosion. In this respect, transition-metal oxides (TMOs) are stable, abundant and nontoxic, and thus are served as potential candidates for hydrogen evolution semiconductor photocatalysts.7 Particularly, cobalt-based oxides have been widely regarded as excellent catalytic activity for electrochemical reactions.16 For instance, Co-phosphate compound has been found efficiently catalyzing water splitting reaction and self-healing in neutral and weakly basic medium.17 It was revealed that the catalytic active component is a cobalt oxyhydroxide

2


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(CoOOH) layer that was formed on the catalyst surface during the operation.18,19 However, the bulk oxyhydroxide materials hardly show photocatalytic activity, perhaps because of their unsuitable band structures for hydrogen evolution reaction.20,21 Nanostructured materials, particularly two-dimensional (2D) nanostructures have been exploited to effectively modulate the electron transportation and reduce the barriers of water redox reactions.22-27 Taking the typical atomically-thin MoS2 nanosheet as an example, the 2D confinement effect and the exposed surface significantly reduce the catalytic overpotential by over 100 mV and enhance the catalytic current by several times in comparison with that of the bulk counterpart.28,29 Therefore, the 2D nanostructuring might be an effective strategy to improve the electronic properties of the oxyhydroxides and to bring about good photocatalytic hydrogen evolution activity. In this work, we report an ultrathin β-CoOOH oxide nanosheet photocatalyst, the suspension of which exhibits efficient photocatalytic hydrogen evolution activity in aqueous Na2SO3 solution under visible light irradiation. The space group of β-CoOOH is P-3M and bulk β-CoOOH possesses a layered structure along the c-axial direction. The atomically thin β-CoOOH nanosheets exfoliated from bulk β-CoOOH can effectively photocatalyze the water reduction in aqueous Na2SO3 solution with high hydrogen production rate of 1200 µmol/g/h and large quantum efficiencies of 10.7% at 380 nm and 6.9% at 420 nm. Moreover, the β-CoOOH nanosheets showed excellent stability during the photocatalytic hydrogen evolution reaction of six runs for 24 hours irradiation. X-ray absorption and X-ray photoelectron spectroscopy characterizations reveal the existence of low-coordinated surface Co catalytic sites that could promote the electron transfer to the surface to reduce H+. These results provide some hints for developing efficient and stable TMO photocatalysts based on the 2D oxyhydroxide nanostructures.

2. Experimental Section Synthesis of materials. Firstly, bulk β-CoOOH material was produced by a hydrothermal method followed by the oxidation. Specially, 0.05 M CoCl2 solutions with 3



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deionized water/ethylene glycol solvent were heated at 130 °C for 10 h in a Teflon-lined stainless steel autoclave, and the product was oxidized by added NaClO at 50 °C to obtain bulk β-CoOOH. Then, bulk β-CoOOH was ultrasonicated in deionized water under the frequency of 35 kHz for 2h. After ultrasonic treating, 16 mg β-CoOOH nanosheets were obtained and kept in aqueous solutions for photocatalytic reaction. Structural characterization. X-ray diffraction (XRD) patterns were recorded by using a Philips X’Pert Pro Super diffractometer with Cu Kα radiation (λ = 1.54178 Å). Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) were performed by using a JEOL-2010 TEM with an acceleration voltage of 200 kV. X-ray photoelectron spectra (XPS) were acquired on Thermo ESCALAB 250 with Al Kα (hν = 1486.6 eV) as the excitation source. The binding energies obtained in the XPS spectral analysis were corrected for specimen charging by referencing C 1s to 284.8 eV. X-ray absorption near-edge spectroscopy (XANES) measurements at Co K-edge were carried out in transmission mode beamline BL14W1 of the Shanghai Synchrotron Radiation Facility (SSRF) and U7C of National Synchrotron Radiation Laboratory (NSRL). The storage rings of SSRF and NSRL were operated at 3.5 and 0.8 GeV, respectively. Performance measurement. Photocatalytic hydrogen reactions were performed in a top-irradiation-type photoreactor (Pyrex glass) connected to a closed gas circulation system, and used a 300 W Xe-lamp (PLS-SXE 300, Beijing perfectlight Co. Ltd, China) as irradiation sources. 100 ml aqueous solution containing 8 mg β-CoOOH nanosheets as photocatalysts and 0.5 M Na2SO3 as sacrificial reagents was used for the photocatalytic measurement. The photocatalytic H2 evolution rate was measured by gas chromatography (GC7900, TCD detector, 5A molecular sieve columns and Ar carrier). The temperatures of the detector and column were maintained at 130 ºC and 60 ºC, respectively. The quantum efficiency (QE) calculated by the following equation was measured using a 300 W Xe lamp with a band-pass filter (FWHM=15 nm), and the average intensity of each irradiation wavelength was determined by an optical power meter. QE =

2 × the number of evolved H molecules × 100% the number of incident photons 4


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Figure 1. (a) Schematic representation of the synthetic route for the β-CoOOH nanosheets. (b) TEM and (c) HRTEM images for the β-CoOOH nanosheets.

3. Results and Discussion The β-CoOOH nanosheets were obtained by a two-step synthetic strategy (Figure 1a). First, β-CoOOH bulk was synthesized by a solvothermal reaction of Co ions precursor, followed by the oxidation in the presence of NaClO oxidant at 50 °C. Then, the ultrathin β-CoOOH nanosheets were obtained by the liquid sonicated exfoliation. To verify the successful formation of β-CoOOH nanosheets, the as-synthesized product was characterized by transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) as shown in Figure 1b,c. As shown by the TEM image in Fig. 1b, the nearly transparent feature suggested the ultrathin thickness of the as-obtained product, and the lateral size of these 2D nanosheets is up to about 0.5 µm. The thickness of the nanosheet can be estimated about 1.5 nm. The high-revolution TEM (HRTEM) images of the β-CoOOH nanosheets show distinct lattice fringes of 0.247 nm with 60° angles attributed to the (010) and (100) planes of β-CoOOH, respectively, suggesting the exposure of the (001) facets of the β-CoOOH matrix. All of above results illustrated the formation of clean and atomically-thin β-CoOOH nanosheets.

5



2nd run

1st run

3rd run

4th run

5th run

6th run

15 Nanosheet

4500

QE (%)

10

3000

U (mV)

b

a H2 yield (µmol/g)

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38 36 34 32 30 28 0

5

H2

2

4 6 8 Time (min)

10

1500 Bulk

0

4

8

12

16

20

24

0 350

400

450

500

550

wavelength (nm)

Time (h)

Figure 2. (a) Typical time course of hydrogen production from aqueous Na2SO3 solution under simulated sunlight irradiation. (b) QE curve of β-CoOOH nanosheet suspensions in aqueous solution. Inset is the GC result for the first four hours run.

The photocatalytic hydrogen evolution activity on the β-CoOOH nanosheets suspension in aqueous Na2SO3 under simulated sunlight irradiation is shown in Fig. 2a. Noticeably, the β-CoOOH nanosheets exhibited a high hydrogen evolution rate of 1200 µmol/h/g. After repeated runs for 24 hours irradiation, the hydrogen evolution rate showed no evident decrease and more than 230 µmol H2 was produced, indicating their high stability and photocatalytic activity throughout the testing cycles. In contrast, no appreciable hydrogen was observed when bulk β-CoOOH was used as the photocatalyst. Figure 2b shows the quantum efficiency (QE) of hydrogen evolution by the β-CoOOH nanosheet photocatalyst as a function of the wavelength of the incident light. Specifically, the amounts of evolved H2 at the typical wavelengths of 365, 380, 400, 420, 435, 450, 475, and 500 nm are 71.9, 71.8, 63.7, 52.6, 35.4, 18.7, 0.6, and 0 µmol, respectively. The numbers of incident photons are 8.03×1020, 8.36×1020, 8.8×1020, 9.24×1020, 9.57×1020, 9.9×1020, 1.04×1021, and 1.1×1021 at 365, 380, 400, 420, 435, 450, 475, and 500 nm, respectively. Dramatically, the quantum efficiency of the β-CoOOH nanosheets suspension is over ten percent (10.7%) at 380 nm. Moreover, the β-CoOOH nanosheet achieves 6.9% quantum efficiency at 420 nm and remains 2.3% quantum efficiency at 6


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longer visible light wavelength of 450 nm, implying the high utilization ratio of photogenerated carriers. It is of note that a typical GC result is shown in the inset of Figure 2b to confirm the hydrogen evolution catalyzed by the β-CoOOH nanosheets. We have also tested the photocatalytic hydrogen evolution performances of β-CoOOH nanosheets in other sacrificial reagents of Na2S and triethanolamine solutions. The photocatalytic hydrogen evolution rate in Na2S solution reached to 6700 µmol/g/h in the first hour but degraded to about 2000 µmol/g/h in four hours’ operation. The photocatalytic hydrogen evolution performance in triethanolamine solution was stable, while the evolution rate of 300 µmol/g/h is quite low in four hours’ operation. These results clearly demonstrate that the β-CoOOH nanosheet in suspension mode is quite robust and efficient in reducing protons to hydrogen till visible-light of 450 nm.

b (003)

a

10

20

30

40

(104) (015)

(003)

(101) (012) (006)

(006)

Absorption (a.u.)

β-CoOOH nanosheet β-CoOOH bulk

Intensity (a.u)

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50

1.0

β−CoOOH nanosheet β−CoOOH bulk

0.8 0.6 0.4 0.2 0.0

60

400

70

2theta (degree)

500 600 Wave length (nm)

700

Figure 3. (a) XRD patterns and (b) UV–vis absorption spectra for bulk and nanosheet β-CoOOH.

To understand the origin of the photocatalytic hydrogen evolution activity, the atomic structure and optical property of the β-CoOOH nanosheets were investigated by X-ray diffraction (XRD) and UV-vis absorption spectroscopy. The XRD patterns in Figure 3a show that the only a strong (003) diffraction peak, along with the weak (006) for diffraction peak can be observable for the β-CoOOH nanosheet. These results reasonably indicate that the (001) orientation is highly preferred, which is in accordance with the HRTEM result in Figure 1c. Hence, the XRD and TEM results conclude that the β-CoOOH nanosheets are of ultrathin feature, where 2D quantum size effect may play an 7



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important in modulating the electronic structure of the nanosheet. Figure 3b presents the UV-vis absorption spectra for bulk and nanosheet β-CoOOH. It can be seen that a clear semiconductor absorption character is observed for the β-CoOOH nanosheet. Meanwhile, the absorption edge of the nanosheet is shifted to short wavelength compared with the bulk counterpart. And the bandgap was enlarged from 2.0 eV for the bulk to 2.4 eV for the nanosheet. The increased bandgap for the β-CoOOH nanosheet is possibly attributed to the 2D quantum size effect, which has been observed in other 2D nanostructures.30,31 Although the bandgap is somewhat enlarged, the β-CoOOH nanosheets can still effectively absorb visible lights till 500 nm. This indicate that the ultrathin β-CoOOH nanosheet photocatalyst satisfy an important prerequisite for efficiently converting abundant sunlight to hydrogen.

Figure 4. (a) XPS spectra and (b) Co K-edge XANES spectra for bulk and nanosheet β-CoOOH.

(c) Schematic of the photocatalytic hydrogen evolution process by the β-CoOOH nanosheet.

To further correlate the structure-activity relationship, the electronic structure characters of the β-CoOOH nanosheets were examined. Figure 4a shows the Co 2p X-ray photoelectron spectra (XPS) for the β-CoOOH bulk and nanosheet. One can find that an 8


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additional shake-up shoulder at the higher energy side was observed for the XPS spectrum of nanosheet, in comparison with that of bulk counterpart. This suggests that the electron population of Co ion is changed, and partial electrons of t2g states were transferred to eg states, leaving some empty states in the t2g orbitals.32 Furthermore, the X-ray absorption near-edge spectra (XANES) for the samples are measured, and their results are shown in Fig. 4b. It can be seen that the absorption edge of β-CoOOH nanosheet is shifted by about 2–3 eV to the low energy side, implying the decrease of valence state for Co ions.33 This indicates the reduction of Co-O coordination, which might critical to the structural stability for the ultrathin nanosheet where the Co ions are almost at the surface. Hence, the Co ions on the nanosheet surface are coordination unsaturated, in accord with that observed for the Co3O4 nanosheets.34 Therefore, the above results indicate that 2D effect of the nanosheet changes the local coordination environment of Co ions and thus results in a modified electronic structure of the β-CoOOH nanosheet. In the process of hydrogen evolution by a photocatalyst, the photons are first absorbed and converted to photocarriers by the semiconductors; and then the photocarriers are transferred to the surface and separated at the active sites to reduce or oxidize water.2 According to the XPS and XANES results, the distribution of Co 3d states for the β-CoOOH nanosheet gets more delocalized, as confirmed by the partial transfer of t2g electrons to eg states. This variation of electronic structure strengthens the hybridizations of catalytic sites low-coordinated Co 3d orbitals and the p orbitals of hole scavenger. Especially in the presence of sacrificial agent SO32− that serves as the hole scavenger, the oxidation of SO32− can be kinetically facile by a two-electron transfer process on the low-coordinated Co ions (Figure 4c). This process enables an effective separation of the electron–hole pairs and carriers transportation. On the other hand, owing to the strong hybridization of Co ions and the adsorbed H2O molecules, the electrons at the eg states of Co ions could easily transfer to the surface to participate the reduction of H+ (Figure 4c).30 Furthermore, because of the partially empty Co t2g states, the conductivity of the nanosheet material is enhanced and the electron transfer in the 9



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material is facilitated. Hence, for the β-CoOOH nanosheet, their modified atomic and electronic structures are quite beneficial for the HER catalytic reaction, leading to a much accelerated hydrogen evolution reaction rate.

4. Conclusion In summary, an ultrathin β-CoOOH nanosheet suspension was obtained to realize efficient photocatalytic hydrogen evolution in aqueous Na2SO3 solution with high hydrogen production rate of 1200 µmol/g/h, large quantum efficiencies of 2–11% in the light range of 350–450 nm, and robust stability. Optical property characterization reveals that the β-CoOOH nanosheets could effectively utilize the visible light till 500 nm. X-ray absorption

spectroscopy

and

X-ray

photoelectron

spectroscopy

measurements

demonstrate that the low-coordinated surface Co ion strengthens the hybridization of Co 3d states and S p states of the SO32− hole scavenger. This strong electron state hybridization facilitates the hole transfer between Co ions and SO32- and the electron transfer between the surface catalytic sites and H+ ions, thus evidently enhancing photocatalytic

hydrogen

evolution

activity.

We

believe

that

this

kind

of

oxyhydroxide-based nanosheet materials would be promising photocatalyst for hydrogen production.

Acknowledgements This work was supported by the National Basic Research Program of China (2012CB825800), the National Natural Science Foundation of China (Grants No. 21533007, 11135008, U1332111, U1532265, 11435012, 11305174, 11321503, and 11422547), and the Fundamental Research Funds for the Central Universities (WK2310000050).

References (1) Gratzel, M. Photoelectrochemical Cells. Nature 2001, 414, 338-344. (2) Chen, X. B.; Shen, S. H.; Guo, L. J.; Mao, S. S. Semiconductor-Based 10


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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


Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503-6570. (3) Du, P. W.; Knowles, K.; Eisenberg, R. A Homogeneous System for the Photogeneration of Hydrogen from Water Based on a Platinum(Ii) Terpyridyl Acetylide Chromophore and a Molecular Cobalt Catalyst. J. Am. Chem. Soc. 2008, 130, 12576-12577. (4) Lazarides, T.; McCormick, T.; Du, P. W.; Luo, G. G.; Lindley, B.; Eisenberg, R. Making Hydrogen from Water Using a Homogeneous System without Noble Metals. J. Am. Chem. Soc. 2009, 131, 9192-9194. (5) McCormick, T. M.; Calitree, B. D.; Orchard, A.; Kraut, N. D.; Bright, F. V.; Detty, M. R.; Eisenberg, R. Reductive Side of Water Splitting in Artificial Photosynthesis: New Homogeneous Photosystems of Great Activity and Mechanistic Insight. J. Am. Chem. Soc. 2010, 132, 15480-15483. (6) Thoi, V. S.; Sun, Y. J.; Long, J. R.; Chang, C. J. Complexes of Earth-Abundant Metals for Catalytic Electrochemical Hydrogen Generation under Aqueous Conditions. Chem. Soc. Rev. 2013, 42, 2388-2400. (7) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q. X.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446-6473. (8) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37-38. (9) Kim, T. W.; Choi, K. S. Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting. Science 2014, 343, 990-994. (10) Yi, Z. G.; Ye, J. H.; Kikugawa, N.; Kako, T.; Ouyang, S. X.; Stuart-Williams, H.; Yang, H.; Cao, J. Y.; Luo, W. J.; Li, Z. S. et al. An Orthophosphate Semiconductor with Photooxidation Properties under Visible-Light Irradiation. Nature Mater. 2010, 9, 559-564. (11) Ha, E.; Lee, L. Y. S.; Wang, J. C.; Li, F. H.; Wong, K. Y.; Tsang, S. C. E. Significant Enhancement in Photocatalytic Reduction of Water to Hydrogen by Au/Cu2ZnSnS4 Nanostructure. Adv. Mater. 2014, 26, 3496-3500. 11



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

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(12) Khaselev, O.; Turner, J. A. A Monolithic Photovoltaic-Photoelectrochemical Device for Hydrogen Production Via Water Splitting. Science 1998, 280, 425-427. (13) Zhang, J.; Yu, J. G.; Jaroniec, M.; Gong, J. R. Noble Metal-Free Reduced Graphene Oxide-ZnxCd1-xS Nanocomposite with Enhanced Solar Photocatalytic H2 Production Performance. Nano Lett. 2012, 12, 4584-4589. (14) Li, Q.; Guo, B. D.; Yu, J. G.; Ran, J. R.; Zhang, B. H.; Yan, H. J.; Gong, J. R. Highly Efficient Visible-Light-Driven Photocatalytic Hydrogen Production of CdS-Cluster-Decorated Graphene Nanosheets. J. Am. Chem. Soc. 2011, 133, 10878-10884. (15) Jia, L.; Wang, D. H.; Huang, Y. X.; Xu, A. W.; Yu, H. Q. Highly Durable N-Doped

Graphene/CdS

Nanocomposites

with

Enhanced

Photocatalytic

Hydrogen Evolution from Water under Visible Light Irradiation. J. Phys. Chem. C 2011, 115, 11466-11473. (16) Smith, R. D. L.; Prevot, M. S.; Fagan, R. D.; Zhang, Z. P.; Sedach, P. A.; Siu, M. K. J.; Trudel, S.; Berlinguette, C. P. Photochemical Route for Accessing Amorphous Metal Oxide Materials for Water Oxidation Catalysis. Science 2013, 340, 60-63. (17) Kanan, M. W.; Nocera, D. G. In Situ Formation of an Oxygen-Evolving Catalyst in Neutral Water Containing Phosphate and Co2+. Science 2008, 321, 1072-1075. (18) Surendranath, Y.; Kanan, M. W.; Nocera, D. G. Mechanistic Studies of the Oxygen Evolution Reaction by a Cobalt-Phosphate Catalyst at Neutral pH. J. Am. Chem. Soc. 2010, 132, 16501-16509. (19) Surendranath, Y.; Lutterman, D. A.; Liu, Y.; Nocera, D. G. Nucleation, Growth, and Repair of a Cobalt-Based Oxygen Evolving Catalyst. J. Am. Chem. Soc. 2012, 134, 6326-6336. (20) Song, F.; Hu, X. L. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nature Commun. 2014, 5, 4477. (21) Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; 12


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Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M. Trends in Activity for the Water Electrolyser Reactions on 3d M(Ni,Co,Fe,Mn) Hydr(Oxy)Oxide Catalysts. Nature Mater. 2012, 11, 550-557. (22) Geim, A. K. Graphene: Status and Prospects. Science 2009, 324, 1530-1534. (23) Schwierz, F. Graphene Transistors. Nature Nanotechnol. 2010, 5, 487-496. (24) Cheng, W. R.; He, J. F.; Yao, T.; Sun, Z. H.; Jiang, Y.; Liu, Q. H.; Jiang, S.; Hu, F. C.; Xie, Z.; He, B. et al. Half-Unit-Cell Alpha-Fe2O3 Semiconductor Nanosheets with Intrinsic and Robust Ferromagnetism. J. Am. Chem. Soc. 2014, 136, 10393-10398. (25) Sun, Y.; Sun, Z.; Gao, S.; Cheng, H.; Liu, Q.; Piao, J.; Yao, T.; Wu, C.; Hu, S.; Wei, S. et al. Fabrication of Flexible and Freestanding Zinc Chalcogenide Single Layers. Nature Commun. 2012, 3, 1057. (26) Sun, Y. F.; Liu, Q. H.; Gao, S.; Cheng, H.; Lei, F. C.; Sun, Z. H.; Jiang, Y.; Su, H. B.; Wei, S. Q.; Xie, Y. Pits Confined in Ultrathin Cerium(IV) Oxide for Studying Catalytic Centers in Carbon Monoxide Oxidation. Nature Commun. 2013, 4, 2899. (27) Cai, L.; He, J. F.; Liu, Q. H.; Yao, T.; Chen, L.; Yan, W. S.; Hu, F. C.; Jiang, Y.; Zhao, Y. D.; Hu, T. D. et al. Vacancy-Induced Ferromagnetism of MoS2 Nanosheets. J. Am. Chem. Soc. 2015, 137, 2622-2627. (28) Lukowski, M. A.; Daniel, A. S.; Meng, F.; Forticaux, A.; Li, L. S.; Jin, S. Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets. J. Am. Chem. Soc. 2013, 135, 10274-10277. (29) Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M. W.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222-6227. (30) Butler, S. Z.; Hollen, S. M.; Cao, L. Y.; Cui, Y.; Gupta, J. A.; Gutierrez, H. R.; Heinz, T. F.; Hong, S. S.; Huang, J. X.; Ismach, A. F. et al. Progress, Challenges, and Opportunities in Two-Dimensional Materials Beyond Graphene. ACS Nano 2013, 7, 2898-2926. 13



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(31) Li, H.; Wu, J. M. T.; Yin, Z. Y.; Zhang, H. Preparation and Applications of Mechanically Exfoliated Single-Layer and Multi Layer MoS2 and WSe2 Nanosheets. Acc. Chem. Res. 2014, 47, 1067-1075. (32) Suntivich, J.; May, K. J.; Gasteiger, H. A.; Goodenough, J. B.; Shao-Horn, Y. A Perovskite Oxide Optimized for Oxygen Evolution Catalysis from Molecular Orbital Principles. Science 2011, 334, 1383-1385. (33) Sun, Z. H.; Yan, W. S.; Yao, T.; Liu, Q.; Xie, Y.; Wei, S. Q. XAFS in Dilute Magnetic Semiconductors. Dalton Transactions 2013, 42, 13779-13801. (34) Sun, Y. F.; Gao, S.; Lei, F. C.; Liu, J. W.; Liang, L.; Xie, Y. Atomically-Thin Non-Layered Cobalt Oxide Porous Sheets for Highly Efficient Oxygen-Evolving Electrocatalysts. Chem. Sci. 2014, 5, 3976-3982.

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Ultrathin CoOOH Oxides Nanosheets Realizing Efficient Photocatalytic

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